Physiology Box

Physiology is the study of living things – their structure, organization, and biochemistry. This unit gives students an opportunity to discover the fundamental characteristics of living things and explore some ...

Physiology is the study of living things – their structure, organization, and biochemistry. This unit gives students an opportunity to discover the fundamental characteristics of living things and explore some basic cell biology. Students begin with several activities culminating in the creation of a list of characteristics that all living things have in common – the characteristics of life list. From here, students learn to test for signs of life by growing microbes on agar plates, conducting biochemical tests, visualizing cells, and experimenting with photosynthesis and respiration. Finally, students learn about the organization plants and animals through dissection and the raising of plants and fish in the classroom. Throughout the unit, students return to the characteristics of life list, refining and revising their list as they learn new concepts. A planning guide for a voyage with the Marine Science Institute is included as a way for students to learn about the many forms of life in the San Francisco Bay.

1. Is it alive?

Summary
What does it mean to be alive? Is a cactus alive? Is a seed alive? Is the air we breathe alive? What are the necessary characteristics? To hook students into the question, they are introduced to “glue monsters” (sometimes known as “scooting glue”) and the class discusses whether the “monsters” are alive or not. Next, students are given cards with the names of various objects and asked to sort them into categories: alive, once was alive, never alive, and not sure. Finally, students create a list defining the characteristics of life – a set of characteristics that all living things share. The list is initially developed in pairs, then in larger groups of 4, and ultimately as a whole class. The final list is turned into a poster that can be referenced and modified throughout the remainder of the unit as students learn more about what it takes to be alive.

Objectives
Can begin to discuss the necessary characteristics of life.
Can begin to categorize objects as alive or not alive.
Can recognize that movement does not necessarily mean something is alive.

Vocabulary
Alive
Characteristic
Cell
Metabolism
Evolve
Adapt
Homeostasis
Organic molecule
Organism

AttachmentSize
alive_sorting_cards.doc71.5 KB
1is_it_alive.doc67.5 KB

1. Is it alive? - Logistics

Time
10-15 min glue monsters demo
30-40 min alive or not alive card sorting and discussion
30-45 min create characteristics of life lists

Grouping
The card sorting activity and initial creation of a list of the characteristics of life is done in pairs. These pairs will eventually merge in groups of 4 to compare, discuss, and revise their lists. The remainder of the discussion takes place as an entire class.

Materials
For the “glue monsters” demo, the teacher needs:

  • 1 overhead projector
  • 1 tube of Duco® cement glue (according to Flinn Scientific, this is the only brand of glue that works reliably)
  • 1 clear Petri dish
  • water
  • ground pepper or pencil shavings

For the card sorting activity, each pair of students needs:

  • copy of the sorting cards on cardstock paper, cut out and placed in an envelope

For developing a characteristics of life list, each class needs:

  • butcher paper or flip chart paper
  • markers

Setting
Classroom

1. Is it alive? - Background

Teacher Background
Many middle school students believe that the defining characteristic of living things is that they move. When they see the “glue monsters” wiggle in the Petri dish, most will immediately assume they are alive. What is going on? Duco® cement is polymer mixed in a water soluble solvent. When the cement is exposed to air as it drops into the dish, a thin, solid polymer skin quickly forms around the liquid, solvent-polymer mixture. When the bead of cement is immersed in water, the solvent diffuses through the skin, causing the bead to shrink and the skin to rupture on one side of the bead. The solvent squirts out of the hole and the surface tension of the water on that side of the bead suddenly falls. Since the surface tension is now uneven, the bead will move away from the hole, towards the area with greater surface tension. The hole quickly repairs itself but the skin then bursts in another location. Thus, the bead appears to wiggle and twist as the surface tension changes depending on where the skin bursts.

Another way to demonstrate surface tension propulsion is to place a paper boat in a tub of water. Take a toothpick dipped in concentrated dish soap (which will lower the surface tension of water) and touch it to the water near the back of the boat. The boat with rush away from the toothpick.

As to the card sorting activity, students will struggle over many of the items. Do not expect students to correctly categorize items, even after a group discussion. The goal is to get students thinking and debating about the characteristics all living things share, not to get the “right” answer. Their classifications will also give you a good sense of their current state of understanding and sophistication. Keep a list of the items students disagree on or misclassified. Revisit these items at the end of the unit when students have mastered the major concepts. Keep in mind that there are some items that even scientists disagree on, such as viruses and prions. Some of the items (dirt and air) are mixtures in which some parts are alive and some are not. In addition, how you classify a part of a multicellular organism (like a single leaf, blood, or pollen) depends on your point of view. These ambiguous items provide opportunities to discuss the characteristics of life with your students.

Defining the characteristics of life is difficult and not completely clear cut. Although you will find different lists at different sources, most scientists agree that the following characteristics are shared by all living things:

  1. Living things are made of cells. The basic unit of life is the cell. All living things are composed of one or more cells.
  2. Living things grow larger over time.
  3. Living things reproduce. Each individual, given the right circumstances, has the potential to produce a new individual that resembles its parent.
  4. Living things respond to the environment. Sometimes this response takes the form of motion such as an animal running away from danger or a plant orienting towards the sun. Sometimes this response is more subtle such as closing certain membrane channels in response to changing salt concentrations.
  5. Living things metabolize, that is, they take in raw materials and convert them into energy and wastes. For instance, animals convert glucose and oxygen into energy and waste products (water and carbon dioxide) through the process of respiration.
  6. Living things evolve. Over many generations the traits of the species will change by natural selection to better fit the current environmental conditions. In other words, living things adapt to their environment. A basic assumption of evolution is heredity, the passing of traits from parent to offspring through genes. Thus it is also accurate to say that all living things inherit traits from their parents through some type of genetic material.

In addition to these 6, some lists included 2 additional characterisitics:

  1. Living things maintain homeostasis. That means that living things can maintain their internal environment relative to changes in the external environment. A good example is how our bodies maintain a constant body temperature – sweating to cool our bodies down and shivering to warm our bodies up when necessary.
  2. Living things are made of organic molecules. Organic molecules include proteins, lipids, carbohydrates (starches and sugars), and nucleic acids (like DNA and RNA).

The goal of these activities is not to force students to memorize the list above. Many are new, difficult concepts (like cells, metabolism, and organic molecules) that will develop over the course of the unit. Students should experience the process of creating the list themselves and revising it periodically as they learn new things. For instance, in the preliminary list, the items: “need nutrients”, “make wastes” and “need energy” may appear separately. After students learn about photosynthesis and respiration as metabolic processes, these 3 items can be combined under the umbrella of “living things metabolize”.

Student Prerequisites

none

1. Is it alive? - Getting Ready

Getting Ready
Glue monsters demo:

  1. Place a Petri dish half full of water on the overhead projector.
  2. Set aside a small dish of pencil shavings or black pepper.
  3. Try the demo yourself first, rehearsing the “release” of the “monsters” into the dish and their “feeding” with pepper or pencil shavings.
  4. Optional: wrap the tube of glue in paper or keep it in a brown paper bag so that students cannot tell what the “monsters” really are.


Alive or not alive card sorting:

  1. Copy sorting cards onto cardstock paper.
  2. Cut the cards apart.
  3. Place cards in an envelope.
  4. Optional: include some extra blank cards for students to add their own items to the set.


Characteristics of life list:

  1. Set out butcher paper or flip chart paper and markers.

1. Is it alive? - Lesson Plan

Lesson Plan
Glue monsters demo:

  1. Fill a Petri dish half full with water.
  2. Place the Petri dish on an overhead projector.
  3. Fabricate some story about small, blob-like monsters that live in the local watershed. Add a drop of Duco® glue to the water in the dish.
  4. To “feed” the “monster”, sprinkle a small amount of the pencil shavings or pepper near the “monster”. It should move towards the shavings or pepper and “eat” them.
  5. Add additional drops of glue and watch “monsters” interacting with one another.
  6. When the “monsters” slow down, turn off the projector and ask the students for their observations. What did they see? What happened when “food” was added? How did the monsters interact with each other? Most importantly, were they alive and how could you tell?
  7. After students reported their initial observations, do the demonstration again, this time very obviously showing students that it was a trick – the “monsters” were just drops of glue in water and the “food” was pencil shavings. Briefly explain the chemistry behind the demonstration.
  8. Discuss what characteristics they used to initially decide that the “monsters” were alive. Students will generally point out how they “moved on their own”. Ask students whether all living things “move on their own” and look for counterexamples like plants.

Alive or not alive card sorting:

  1. Describe the card sorting activity to the students. Working with a partner, they should divide the items on the cards into 4 categories: alive, never alive, once was alive, and not sure.
  2. Divide the students into pairs, distribute the sorting cards, and allow students to get started.
  3. Circulate around the room helping students that have questions. If an item is unfamiliar, describe what the item is without necessarily giving away whether it is alive or not.
  4. If groups finish early, you may ask them to come up with their own cards and add them to the set.
  5. When most groups are done, pull the class together to discuss their conclusions. Begin the discussion by creating a master list on the board. Have students name the items within each category that were easy to classify. Then discuss the more difficult items one by one. Don’t tell students the “right” answer. Allow them to make mistakes. In your discussion, repeatedly ask students to explain:
    • what criteria they used to make their decisions
    • what all the living things have in common
  6. You may wish to keep a list of those items that were miscategorized and those that had disagreements. Revisit this activity at the end of the unit as a way to review.


Characteristics of life list:

  1. Give each pair of students the task of creating a list of characteristics that they believe all living things have in common. Students should make sure that each criteria applies to all the living things from the card sorting activity. It is important that both students agree on every item. Both students should make their own copy of the list on a separate sheet of paper. Allow students around 15 minutes to discuss the problem and come up with their list.
  2. When each pair has a list, rearrange students into groups of 4. The original pairs should be split apart into different groups. In these new groups, the goal is to come up with a consensus list, one that each person in the group agrees with. Do not allow voting. Allow students around 10 minutes to come to consensus.
  3. Have each group read their list to the whole class. As they read out their lists, write down the characteristics on the board putting tally marks next to those reported by multiple groups.
  4. Moderate a discussion to come up with a consensus list for the whole class. Have different groups explain the reasoning behind criteria that there is disagreement about. When everyone (including you as the teacher) is comfortable with the consensus list, create a class poster with all the characteristics of life listed. This poster will be revisited and revised over the course of the next few weeks as students become more sophisticated and learn new concepts.

1. Is it alive? - Assessment

Assessment
Play the game “5 Alive”. On a piece of paper, the person who is “it” should write the name of any item that they know for sure is alive or not. The rest of the group gets to ask 5 yes or no questions to figure out if the mystery item is alive.

Going Further

  1. Many of the other activities in this box extend upon this first lesson.
    • The Life Trap activity demonstrates that living things can be microscopic, grow and reproduce.
    • The Testing for Life activity introduces the idea that all living things are made of the same organic molecules and has students test for proteins, starches and sugars.
    • The Seeing Cells activity introduces students to the idea that all living things are made of cells.
    • The Cell Energy activity brings up the concept of cell metabolism.
    • The Life on Mars project asks students to design 3 experiments to determine whether there is anything living in a sample of “Martian soil”.
  2. A great resource for additional lessons on the characteristics of life is the Life in the Universe curriculum, published by the SETI Institute.
  3. Another resource is the Searching for Life curriculum from NASA.

1. Is it alive? - Sources and Standards

Sources
I discovered the “glue monster” or “scooting glue” demo from Flinn Scientific (click on “Glue Monsters” to download the pdf file). Kitchen chemistry also provides a write up for the same activity with a better description of the chemistry behind the demo. For a quicktime movie of a paper boat “fleeing” from a dish soap coated toothpick, see the University of Iowa Physics and Astronomy Lecture Demonstrations.

To learn more about the characteristics of life, see the following sites:


Standards

Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.

2. Life Traps

Summary
Life trapsLife trapsAs part of recognizing the characteristics of life that all organisms share, students grow microbes on nutrient agar plates. Students swipe surfaces with a sterile Q tip swab and seed plates resulting in a wide range of colorful and prolific bacteria and fungi colonies. Other plates may be simply opened to the air to catch life floating in the air. Through these experiences, students learn that all living things, even those so small and invisible as to be floating in the air, grow and reproduce when provided with the proper nutrients and water. Teachable moments abound since the “dirtiest places”, like the toilet rim, often result in the least bacterial growth while presumably “clean” places, like the surface of your skin, have the most. A fun extension of this activity (see the Going Further section) is to start a sourdough culture from wild yeast in the air and make sourdough bread.

Objectives
Can grow microbes on nutrient agar plates.
Can make observations and keep track of data over several days.
Can identify the typical growth patterns of bacteria versus fungi.
Can begin to recognize the diversity of microbrial life in the local environment.
Can explain that all living things will grow and reproduce when provided with the proper nutrients and environmental conditions.

Vocabulary
Agar
Nutrients
Microbe
Bacteria
Fungi
Yeast
Colony

AttachmentSize
2life_trap.doc62 KB

2. Life Traps - Logistics

Time
30 min to introduce the activity and seed the plates
5-10 min to make observations every other day over the next 2 weeks

Grouping
Individual or in pairs.

Materials
For approximately 50 plates you need:

  • 50 sterile disposable plastic 15 mm x 100 mm Petri dishes (can be purchased from Ward’s Natural Science, item number 18 V 7101, approximately $4 for a package of 20 dishes)
  • 15 g agar agar powder (a gelatin substitute made from red seaweed, available at most Asian grocery stores and health food stores, ideally purchase the unsweetened variety but pre-sweetened is OK as long as you ensure that you subtract out the weight of the sugar when measuring out 15 g of agar agar)
  • 2 beef bouillon cubes
  • 1 liter distilled water
  • stove and large pot for preparing nutrient agar and steam sterilizing the Q tips (better yet, if you have a pressure cooker, you will be far more assured of initially sterile conditions in your agar plates)
  • 50 Q tips
  • paper towels
  • permanent markers for labeling plates
  • masking tape
  • bleach

Setting
Classroom

2. Life Traps - Background

Teacher Background
When living things are provided with the proper nutrients, water, and environmental factors (temperature, humidity, etc.) they will grow and reproduce, often explosively and in surprising ways. To kids, microbes are abstract, invisible germs that mysteriously spread disease, but otherwise have little relevance to their daily lives. However, microbes in the form of bacteria, fungi and viruses are prolific and exist all around us and even inside us. Of the 100 trillion cells found within your skin, only 10 trillion of these (a measly 10%) are human cells! The rest are primarily bacteria living on the surface of your skin, around your eyes, mouth, reproductive organs, and digestive tract, comprising between 500-1,000 different species. Since bacterial cells are generally much smaller than human cells, a great many more bacteria fit into the borders of the human body than human cells.

Nutrient agar plates are a classic tool for culturing microbes in the laboratory. The agar plate provides all the basic organic molecules - water, carbohydrates, fats, and proteins - and will support the growth of many bacteria and fungi species, though by no means will all microbes find the appropriate nutrient and environmental conditions to grow on an agar plate. It is important for students to recognize that many organisms that arrive on the plate will not have the right conditions to grow, thus, an empty plate does not necessarily mean no life exists there – only that this method could not detect life.

Luckily, pathogenic bacteria find it difficult to grow on nutrient agar so it is reasonably safe to use in schools. However, do NOT open the dishes once they have been seeded. High levels of mold and bacterial spores can be released. When you are finished with the experiment, disinfect the plates before disposal.

It is difficult to positively identify specific species from so rough a measure, however, it is possible to determine certain things about the colonies that grow. Bacteria tend to form low-growing buttons or streaks that are glistening and smooth. On the other hand, fungi tend to form fuzzy, irregular patches or fern-like, thread-like patterns. Different varieties can be distinguished by their color and texture. Colonies that were collected on a Q-tip swab from a hard surface will begin their growth where the Q-tip touched the agar. Colonies from the air that landed on the agar while the lid was open will begin as a dot located on part of the plate not touched by the Q tip swab. Each dot represents a single spore that landed on the plate.

Student Prerequisites

None

2. Life Traps - Getting Ready

Getting Ready
To prepare agar plates:

  1. Thoroughly wash your hands with soap and water.
  2. Set the pot (or pressure cooker) on the stove.
  3. In the pot, mix together 1 liter of distilled water, 15 g of agar agar, and 2 beef bouillon cubes.
  4. Heat to boiling, stirring occasionally to fully dissolve the agar agar and bouillon.
  5. If using a regular pot, simmer on medium-low for at least 30 minutes to get as sterilize as possible. (It is impossible to completely sterilize a solution simply by boiling but it’s good enough for a rough classroom experiment such as this one – 25% of the plates I made were contaminated, but that also means more microbes for the students to observe). To ensure a sterile starting solution, use a pressure cooker and cook for 15-20 minutes at 15 psi.
  6. While the nutrient agar is boiling, clean your work surface with warm water, soap, and perhaps even an antiseptic cleaning solution.
  7. Open the packages of Petri dishes and line them up on your work surface. Keep the lids on!
  8. When the nutrient agar has finished cooking, open the lid of each Petri dish as little as possible while carefully pouring 15-20 ml of the solution into the dish – each dish should end up between a third to a half full. If possible, hold the lid directly above the dish while pouring to prevent air-borne particles from settling onto the surface of the agar. Replace the lid immediately. This homemade nutrient agar will contain flecks of protein and fat from the beef bouillon, it will not disturb the experiment but students should carefully note the location of these flecks so that they are not mistaken with microbe colonies.
  9. Once the nutrient agar has solidified (10-15 minutes) it will turn cloudy and opaque as opposed to translucent. At that time, turn the plates upside-down to prevent condensation from pooling on the surface of the agar.
  10. Store them stacked upside-down in the refrigerator in their original plastic sleeves until ready to use.


To sterilize Q-tips:

  1. Wrap 10 Q-tips in a paper towel. Make several packets of Q-tips, enough for 1 Q-tip per agar plate.
  2. Set a pot (or pressure cooker) on the stove with water and a steamer basket in place.
  3. Place the Q-tip packets into the steamer basket and boil the water.
  4. Steam the Q tips for at least 30 minutes. If using a pressure cooker, cook for 15-20 minutes at 15 psi.
  5. When the Q-tip packets finish steaming, place them into a new ziplock bag and seal them until ready to be used. While the exterior of the paper towels will be contaminated, the Q-tips inside should be relatively sterile.

2. Life Traps - Lesson Plan

Fish tank microbes: Fish tank microbes collected by Woody, 6th grader, February 2006.Fish tank microbes: Fish tank microbes collected by Woody, 6th grader, February 2006. Air-borne microbes: Air-borne microbes collected by Irene Salter from her classroom with a 30 minute exposure.Air-borne microbes: Air-borne microbes collected by Irene Salter from her classroom with a 30 minute exposure.

Lesson Plan
Introducing the activity and seeding plates:

  1. Introduce the agar plates to your students. Discuss what ingredients you used (water, agar, and beef bouillon) and the reason for including each.
  2. Ask the students to guess what they think might happen if a microbe found its way onto the agar plate.
  3. Have students brainstorm about microbes they know already or have heard about – many of these will be disease related.
  4. Discuss places where students believe microbes will be found. If nobody brings up the air, ask students whether they think microbes are found in the air. If nobody brings up their bodies, ask students whether they think microbes are found on or inside their bodies.
  5. Describe the procedures that must be used to safely trap life in the Petri dishes:
    • Hands must be thoroughly washed with water and soap.
    • Plates can be seeded by taking a dry, sterile Q-tip and rubbing it on a test surface or dipping it into a test liquid, and then very gently rubbing it on the surface of the agar. Do not gouge the surface of the agar. In order to tell the difference between microbes that were intentionally placed on the agar with the Q-tip and ones that fell into the plate from the air, the Q-tip should be swiped across the agar in a distinctive pattern – a zig-zag, your initials, a smiley face, etc.
    • Plates can also be seeded by leaving them open to the air for 20 minutes in a specific location.
    • Agar plates should be opened only as long as necessary to seed the plates.
    • Once plates have been seeded and sealed, they should not be opened again.
    • Do not collect microbes from other teachers’ classrooms.
    • Do not collect microbes from other people’s bodies – you can collect from your own body or hair.
    • Do not collect microbes from urine or feces.
  6. Have students wash their hands thoroughly with warm water and soap.
  7. Each student should be given an agar plate and around 6 inches of masking tape.
  8. Break off two 1.5 inch pieces of masking tape and use them to seal the plate shut on opposite sides. One side will make a hinge while the other side can be opened temporarily to seed the plate, then sealed again. With a permanent marker, label one side L for left and the other side R for right.
  9. The remaining 3 inches of tape can be stuck to the bottom of the plate and labeled with the student’s name and source of his or her sample.
  10. Students can now get a Q-tip (if they want one) and seed their plates.
  11. When students return, in their lab notebooks they should make their first observation, being sure to note the following information:
  12. A detailed description of how the sample was collected. Be as specific as possible. Which button on the telephone was rubbed, or was it the mouthpiece? How hard did you rub the Q-tip on the surface? Exactly where was the plate left open to the air and for how long? Was there a window open nearby? What else was nearby?
  13. A drawing of the exact pattern drawn by the Q-tip on the surface of the agar.
  14. A detailed labeled drawing of the agar plate oriented so left and right is correctly positioned. Any flecks of protein or fat droplets should be labeled and carefully described.
  15. The Petri dishes should be stacked on a countertop upside-down until the next time students make their next observation.

Further observations and discussions:

  1. Every other day, create a new labeled drawing of the agar plate. Try to draw any colonies as accurately as possible – the correct size, shape, and place on the plate.
  2. Use a hand lens to examine any new growth. Measure the diameter of any colonies. Note their color and texture.
  3. Describe any changes since the previous observation
  4. Once students start seeing colonies, tell your students how to distinguish between bacteria and fungal colonies. Tell them how to tell different microbes apart by their color and texture. Explain how to determine whether a colony was intentionally seeded by a Q tip or fell from the air.
  5. Discuss the different forms of life that appeared in this experiment. Specifically talk about how we know that these creatures are alive – they grow, they reproduce, they need nutrients and water, etc. Mention the possibility of things that grow yet aren’t alive such as crystals, magic egg creatures that expand to many times its original size in water, inflatable plastic toys, etc. Discuss how these growing things are different from living things and how one could tell the difference between them.
  6. There are many directions to take this discussion from here:
    • Was it surprising to find microbes in the air? Using plates seeded from the air, calculate the number of microbes that landed per minute that the plate was open.
    • Compare the number of microbes trapped in different locations. What may have caused more microbes to grow in some places compared to others?
    • Do these life traps capture all the microbes in a given place? What factors might prevent a microbe from growing in these life traps? How would you modify the experiment to look for different microbes that didn’t grow in this experiment?
    • How could a life trap be used to look for life on other planets such as Mars or Venus?
    • When your investigations are over, the teacher should disinfect then dispose of the plates. One option is to prepare a bucket filled with one part bleach to 9 parts water. Submerge the plates in the bleach water to kill the cultures before disposing of them in the regular trash.

2. Life Traps - Assessments

Assessment

  1. Collect students’ lab notebooks with their observations and conclusions.
  2. Revisit the characteristics of life list from the Is It Alive? activity. Revise the criteria as necessary.

Going Further

  1. Test the effects of various antiseptics. After growth has taken place, add a piece of filter paper soaked in an antiseptic cleaning agent (Lysol®, bleach, 409, rubbing alcohol, Neosporin®) to the plate. Be very careful when opening the agar plates. Wear a dust mask and stay in a well ventilated area since the high concentrations of spores can cause lung distress.
  2. Make new life traps and test the effect of different environmental factors. For example, with similarly seeded plates, place one at room temperature, one in a warm place like near the water heater, and one in the refrigerator. Or investigate the effect of sunlight versus darkness.
  3. Make new life traps and compare the effectiveness of various manipulations thought to disinfect surfaces. Compare plates seeded with unwashed versus washed hands. Compare a table top before and after cleaning.
  4. Trap wild yeast from the air and use it to make sourdough bread! A mixture of water and flour provides the nutrient base for the yeast to establish itself. There are hundreds of recipes and different ways to create a sourdough culture. Before store bought yeast, sourdough cultures were the primary means of leavening bread. Since each culture has a slightly different population of yeast, every culture will produce its own distinctive flavor. Starting a sourdough culture is very simple to do and extremely fun. The Exploratorium website provides one way to start a culture using a lump of dough. Other sourdough starters use a more liquid culture with a consistency more similar to pancake batter than bread dough. For instance, the How Things Work website describes the procedure for creating a wild yeast starter with this more liquid consistency. I started my own sourdough starter using a procedure found in the cookbook, The Cheeseboard Collective Works, published by my all time favorite Berkeley bakery and cheese shop, The Cheeseboard.

2. Life Traps - Sources

Sources
The inspiration for this lesson was Mission 11 from the Life in the Universe curriculum, published by the SETI Institute. The recipe for the nutrient agar came from Biology F.A.Q. at Flinn Scientific. Sterilization tips were found at Science-Projects.com and Wikipedia. Finally, many teaching tips were discovered from Leslie Hathaway’s Bacteria Gathering lesson plan.

Statistics on bacteria in the human body were taken from Wikipedia.

Standards
Grade 6
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
e. Communicate the steps and results from an investigation in written reports and oral presentations.

3. Testing for Life's Molecules

Summary
All known life is made out of a small group of chemical compounds called organic molecules. Common organic molecules include proteins, glucose, starch, lipids, and nucleic acids. This lesson plan asks students to conduct tests for proteins, glucose, and starch. At the beginning of the activity, they choose 3 items to test: one known to be “never alive”, one known to be “once was alive”, and one mystery item. In addition, each station includes a positive control. By the end of the experiment, students should be familiar with some of the major organic molecules and should recognize that living things, and substances derived from them, are made of organic molecules. In addition, this is a chance to bring in topic surrounding nutrition, health, and digestion. Since our bodies are made up of organic molecules, we need each of these molecules as nutrients in our food.

Objectives

Can define and give examples of organic molecules.
Can recognize that living things are mode of organic molecules.
Can test for the presence of protein, glucose and starch.
Can interpret the results of an experiment.

Vocabulary
Organic molecule
Protein
Biuret solution
Carbohydrates
Glucose
Simple sugar
Benedict’s solution
Starch
Iodine
Lipids

AttachmentSize
3testing_life.doc63 KB
life_test_directions.doc34 KB
life_test_handout.doc40 KB

3. Testing for Life - Logistics

Time
10-20 min introduction (depending on how deeply you want to talk about the biochemistry)
35-50 min to conduct tests (10-15 min per station)
20-30 min to discuss results

Grouping
Teams of 3 students

Materials
General materials for students and test stations:

  • Copy of the lab handout for each student
  • Copy of test station directions at each test station
  • Biuret solution (see Sources section for ordering information)
  • Benedict’s solution (see Sources)
  • Iodine tincture
  • 3 beakers or cups for every group of students
  • 4 test tubes for every group of students
  • 1 test tube rack for every group of students
  • Permanent markers and labeling tape for the beakers and test tubes
  • 30-45 eye droppers
  • 6-9 trays or bins to keep the materials for each test station
  • 6-9 small 100 ml beakers or squeeze bottles to contain test reagents
  • Optional: 6-9 large squeeze bottles of water (500 ml disposable plastic water bottles are fine) for rinsing test tubes at test stations rather than going to a sink
  • 6-9 large beakers or cups to dump waste materials
  • hot plate or source of boiling water
  • 2-3 insulated containers such as a thermos or Styrofoam cup for creating a hot water bath
  • Optional: 2-3 thermometers to monitor the temperature in the hot water bath
  • disposable latex gloves


A variety of solutions to test:

  • cornstarch (mixed with water)
  • milk
  • glucose solution or glucose tablets (see Sources)
  • chicken broth
  • wheat flour (mixed with water)
  • orange juice
  • water
  • rubbing alcohol
  • diluted dish soap
  • vinegar
  • fish tank water or pond water
  • unsweetened powdered lemonade (mixed with water)
  • other substances that give interesting results include: honey (diluted in water), egg whites, potato juice, onion juice, table sugar (dissolved in water), salt water, lemon-line soda, hair conditioner, Cool Whip (mixed with water)… Be sure to choose solutions that are light in color so that you can see color changes that occur as the result of testing.

Setting
Classroom

3. Testing for Life - Background

Teacher Background
All living things (at least on Earth) are composed of organic molecules. All organic molecules include carbon-hydrogen bonds. The major classes of organic molecules are:

  • Carbohydrates (including glucose and starch)
  • Proteins
  • Lipids
  • Nucleic acids

GlucoseGlucoseCarbohydrates are particularly important for energy storage in living things. Sugars and starches are common examples of carbohydrates. Carbohydrates are can be found as simple sugars or monosaccharides such as glucose, a ring of 6 carbons with attached hydrogens and oxygens (C6H12O6). Other simple sugars include fructose (a common sugar found in fruit) and galactose. These simple sugars may be joined together in pairs. For instance, sucrose (table sugar) is a combination of glucose and fructose. Similarly lactose (the sugar found in milk) is a combination of glucose and galactose. Finally, simple sugars may be assembled into long chains called polysaccharides. Starch is a familiar example of a polysaccharide that is found in many foods including potatoes, flour, and corn. It is made from a long chain of glucose molecules.

Starch: chemical name amyloseStarch: chemical name amyloseTwo tests for carbohydrates are provided: a simple iodine test for starch and a Benedict’s test for glucose. Iodine is a yellow-brown solution that will react with starch to make a blue-black color. Benedict’s solution is a clear blue solution that will react with glucose to make a green, yellow, or red color depending on how much sugar is present. Test tubes must be kept in a 40-50 degrees Celsius water bath for 5 minutes in order for the color to change. An alternative test for glucose is described in the Sources section. Expect to spend some time explaining why starch does not test positive for glucose even though it is made of a long chain of glucose molecules and vice versa.

Protein: structure of hemoglobinProtein: structure of hemoglobinProteins are important for many processes within living things. They contribute to the overall structure of a cell such as muscle cells, to binding to specific molecules such as the protein hemoglobin that binds to oxygen, and to catalyzing chemical reactions in the cell through proteins known as enzymes. Proteins are composed of building blocks known as amino acids. There are 20 total amino acids. Proteins are long chains of amino acids. The length of the chain and the precise sequence of the amino acids in the chain determines what the protein can do.

Amino acid assembly into proteinsAmino acid assembly into proteinsThe Biuret test is a simple test for the presence of proteins. Biuret solution is a blue solution that will react with proteins to make a pink-purple color.

Lipids are a very diverse group of organic molecules. Their defining feature is that a large part of the molecule is hydrophobic, literally “water-fearing”. Most also have a water-loving or hydrophilic end as well. This property allows lipids in water to assemble into membranes or spheres with the hydrophilic ends facing outward and the hydrophobic ends facing in. Most of the membranes in cells are comprised of lipids. The lipids found in membranes are called phospholipids since their small hydrophilic head is linked to a long hydrophobic tail by a phosphate group.

Basic lipid structureBasic lipid structure Lipid organizationLipid organization

Finally, nucleic acids are the building blocks of DNA. For more on DNA structure, see the background section of DNA models.

A common organizing principle for all organic molecules is that they are composed of building blocks assembled into a long chains. For instance, proteins are long chains of amino acids. Polysaccharides like starch that are long chains of simple sugars. DNA is a long chain of nucleic acids. Many lipids have a tail that is a long chain of carbon and hydrogen atoms.

In my classroom, I set up this activity so that students rotate among several testing stations. They carry 3 cups with test solutions and a rack of test tubes with them. Students will empty and rinse their test tubes after each station. The reagents, eyedroppers, and positive controls, are found at each station.

Student Prerequisites
Some exposure to chemistry is useful, particularly if students are familiar with the idea of molecules, polymers, and pH testing with color-change indicators.

3. Testing for Life - Getting Ready

Getting Ready

  1. Order materials.
  2. Set up testing stations. It is recommended that the activity be arranged so that no more than 6 students (2 groups) share any given station. Thus, you may need to set up 2 of each type of testing station and position them strategically about the room.
  3. The protein station needs – gloves, Biuret solution, 2-4 eye droppers, milk, protein test station directions
  4. The starch station needs – iodine tincture, 2-4 eyedroppers, cornstarch solution, starch test station directions
  5. The glucose station needs – gloves, Benedict’s solution, 2-4 eyedroppers, glucose solution, glucose test station directions, hot water bath, access to boiling water
  6. Set up test tube racks with 4 test tubes per rack
  7. Set out test solutions and beakers
  8. Set out eyedroppers
  9. Set out labeling tape and permanent markers

3. Testing for Life - Lesson Plan

Lesson Plan

  1. Begin class with a discussion of food and the food groups. Each of the major organic molecules can be correlated to different classes of foods (protein = meat and beans group, simple sugars (glucose and fructose) = sweets and fruit groups, complex carbohydrates (starch) = grains group, lipids = fats group). Allow this discussion to lead into the idea that all food items are made up of building block organic molecules. Food items were all once alive. Therefore, all living things are made up of these same building blocks that our food is made of.
  2. Go into as much detail as necessary for your students on the biochemistry of organic molecules. You may want to describe the relationship between glucose and starch at this time.
  3. Pass out the student lab handouts. Describe the activity to your students. Each student will test solutions at 3 different stations. They should choose one solution from each of the following categories: “never alive”, “once was alive” and a mystery solution. They will be testing for protein, starch and glucose. In addition to the 3 solutions you will carry around with you, there will also be a 4th solution at each test station. This is one that is guaranteed to cause a color change so that you know what a color change looks like.
  4. Show students any special procedures, such as how to prepare the hot water bath. Answer any questions.
  5. Allow students 5 minutes to gather their materials and then 10-15 minutes at each test station. Help groups that are having difficulty.
  6. When all testing is complete and teams have cleaned up, create a master table on the board like the one below to collect all the teams results for all the different tests.
      Protein test Starch test Glucose test Alive?
    Chicken broth        
    Wheat flour        
    Orange juice        
    Water        
    Rubbing alcohol        
    Dish soap        
    Vinegar        
    Fish tank water (pond water)        
    Unsweetened powdered lemonade        
  7. Discuss the results paying close attention to how to correctly draw conclusions regarding whether a item was once alive or not.
  8. Bring things back to the idea of food. Discuss what protein, starch, and glucose are for, why our bodies need them, and where we get those nutrients from. Discuss how other creatures such as plants, bacteria, and fungi obtain these nutrients.

3. Testing for Life - Assessment

Assessment

  1. Collect student notebooks with data tables and conclusion questions.
  2. Revisit the characteristics of life list from the Is It Alive? activity. Revise the criteria as necessary.
  3. Have students propose a method for testing for life on another planet. For instance, how could you equip a Mars rover with the tools necessary for testing for organic molecules. What tests would you include and why?

Going Further

  1. Conduct tests for lipids. The simplest lipid test involves placing a drop of the test substance on a piece of brown paper bag from a grocery store. If the test substance contains lipids, the paper bag near the spot will become translucent and allow light to shine through. The greater the lipid content, the larger the translucent spot will be. If there are no lipids, the substance will evaporate and the paper bag will remain opaque. Interesting substances to try include cooking oil, whole milk, salad dressing, hand moisturizer, etc.
  2. Test “Martian” soils for signs of life. See Life on Mars Project.

3. Testing for Life - Sources

Sources
All the materials needed for this lab may be purchased from Flinn Scientific or other science supply companies.

  • Protein test - Biuret solution (Flinn Scientific catalog #B0050, $4 for 100 ml) an alternative test for protein uses Ninhydrin solution (Flinn Scientific catalog #N0039, $9.50 for 100 ml)
  • Glucose test - Benedict’s solution (Flinn Scientific catalog #B0171, $3.50 for 100 ml qualitative solution and #B0172, $5 for 100 ml quantitative solution) an alternative test for glucose that does not require the hot water bath is to use glucose test strips that can be purchased from the pharmacy for diabetic urine testing (approximately $15-20 for a bottle of 100 strips, double your supply by cutting each strip lengthwise)
  • Starch test – iodine tincture (purchase from your local pharmacy or Flinn Scientific catalog #I0009, $5 for 100 ml)
  • Positive control for glucose test – either use glucose solution (Flinn Scientific catalog #G0024, $7.75 for 100 ml) or dissolve glucose tablets for diabetics in water (purchase from your local pharmacy)

Unfortunately, the common tests for nucleic acids, such as the Dische test, are highly toxic (the Dische test solution is dissolved in 2M sulfuric acid) and is not ideal for use in a middle school classroom.

Testing for organic molecules is a common activity in biochemistry classes. The following are some of the resources available:

Standards
Grade 8
Chemistry of Living Systems (Life Sciences)
6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:
a. Students know that carbon, because of its ability to combine in many ways with itself and other elements, has a central role in the chemistry of living organisms.
b. Students know that living organisms are made of molecules consisting largely of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.       
c. Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

Grades 9-12 Biology
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
b. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings.
h. Students know most macromolecules (polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors.

Grades 9-12 Chemistry
Organic Chemistry and Biochemistry
10. The bonding characteristics of carbon allow the formation of many different organic molecules of varied sizes, shapes, and chemical properties and provide the biochemical basis of life. As a basis for understanding this concept:
a. Students know large molecules (polymers), such as proteins, nucleic acids, and starch, are formed by repetitive combinations of simple subunits.
b. Students know the bonding characteristics of carbon that result in the formation of a large variety of structures ranging from simple hydrocarbons to complex polymers and biological molecules.
c. Students know amino acids are the building blocks of proteins.

4. Seeing Cells

Summary
The invisibly small world of the cell comes to life as students look at plant and animal cells through a microscope. Students create wet-mount slides of onion skin, elodea leaf, and human cheek cells. They learn some of the gross differences between plant and animal cells (cell walls are present in plant but not in animal cells), and even some of the differences between different plant cells (chloroplasts are found in the leaves but not in the roots). It is suggested that this lesson take place after students learn the parts of a cell and their functions. Resources for good cell diagrams are provided in the Sources section. This lesson may be used in conjunction with the Pond Water activity for students to get a sense of the diversity of microscopic life, both single celled and multi-celled.

Objectives
Can name and describe the function of certain plant and animal cell organelles.
Can identify whether a cell viewed through a microscope if plant or animal.
Can draw and label a picture of plant and animal cells.
Can recognize that all living things are made of cells.
Can begin to recognize the huge variations in cell size, shape, structure, and function.
Can operate a compound light microscope.
Can make simple wet-mount slides.

Vocabulary
Cell
Organelle
Cell membrane
Cell wall
Cytoplasm or cytosol
Nucleus
Chloroplast
Microscope
Objective lens
Eyepiece
Focus
Stage
Elodea
Methylene blue

AttachmentSize
4seeing_cells.doc57.5 KB
cell_images.doc1.64 MB
cells_lab_handout.doc41.5 KB
cell_quiz.doc316.5 KB

4. Seeing Cells - Logistics

Time
45-75 min introduce the parts of a cell and their functions
Optional: 10-15 min discuss microscope parts and usage
5-10 min demonstrate proper procedures for making slides
45-90 min make slides, look at cells, create diagrams, and answer questions
10-15 min discussion and review

Grouping
Teams of 2.

Materials

  • A copy of plant and animal cell coloring diagrams (see Sources for several ways to obtain cell coloring diagrams)
  • A copy of the Seeing Cells lab handout for each student
  • Transparency or photocopies of the Cell Images page for the final discussion
  • Overhead projector
  • Assortment of colorful transparency markers
  • Colored pencils
  • 1 compound light microsope for every 2 students
  • 3 glass or plastic slides for every 2 students
  • 3 glass or plastic cover slips for every 2 students
  • Iodine
  • Methylene blue (0.25% solution, available from aquarium stores for the treatment of fungal infections in fish or at science supply companies such as Carolina Biological catalog # 87-5911, $9 for 25 ml).
  • Tap water
  • Eye droppers
  • Half of a red onion chopped into 1 cm x 1 cm or smaller pieces
  • Several Elodea plants (available from aquarium stores)
  • Flat toothpicks
  • Optional: images of other kinds of cells (For best collection of images of cells, see the Cells Alive website and particularly the cells image gallery)

Setting
Classroom

4. Seeing Cells - Background

Animal cell: Image created by Mariana Ruiz VillarrealAnimal cell: Image created by Mariana Ruiz Villarreal Plant cell: Image created by Mariana Ruiz VillarrealPlant cell: Image created by Mariana Ruiz Villarreal Bacterial cell: Image created by Mariana Ruiz VillarrealBacterial cell: Image created by Mariana Ruiz Villarreal

Teacher Background
Students often have difficulty conceptualizing that cells are the basic building block of all living things. Thus, it is essential for them to have experience making slides of familiar living things – onions, plants and their own cheek cells – and viewing them under a microscope to see that cells really do make up all living things.

Multicellular creatures such as plants and animals have different levels of organization, from organic molecules to organelles to cells to tissues to organs to organ systems to a whole organism. Cells are the smallest unit that can fulfill all the necessary characteristics of life – it can metabolize, grow, reproduce, maintain homeostasis, evolve, respond to its environment and so on. Its organelles (parts of a cell, each has a specific job similar to the organs in the human body) participate in fulfilling these various functions.

Important organelles in eukaryotes such as plants and animals (prokaryotes such as bacteria have much simpler cells):

  • Cell membrane – the cell’s skin that protects the cell from changing environmental conditions and from invaders as well as letting selected molecules in and out of the cell
  • Cell wall – a feature of plants cells that functions like stiff lattice-like wall which helps plant cells maintain their structure and shape
  • Nucleus – the cell’s control center that contains the DNA
  • Cytoplasm – a jelly-like liquid that fills the interior of a cell and surrounds and supports all the organelles
  • Chloroplast – a feature of plant cells that allows plants to do photosynthesis and make their own glucose from sunlight, water and carbon dioxide
  • Mitochondria – the cell’s power plant that turns glucose into energy that the cell can use to run its organelles
  • Ribosome – tiny organelles that function as little protein factories (see Protein Factory activity)
  • Golgi complex – a complex series of interconnected membranes that functions like a post office - it processes, sorts, and labels proteins, making the proteins more effective at their various jobs and helping them to end up in the right place
  • Endoplasmic reticulum – a system of membrane-enclosed canals and passageways used to quickly transport proteins within the cell
  • Vacuole – a prominent feature of certain plant cells, though animal cells also have vacuoles as well, that is used as a storage container for nutrients or other materials
  • Lysosome – a cell’s garbage and recycling center for digesting wastes and recycling the building blocks for other purposes
  • Centriole – a feature of animal cells important for coordinating cell division

Using a light microscope only the largest features of a cell can be observed (the first 5 organelles on the list above). Greater magnification is required to visualize other cell parts. Still students can discover how all living things are similar in that they are made of cells but also discover the great diversity in cells themselves.

Student Prerequisites

Experience with light microscopes is helpful. A basic understanding of the parts of a cell is essential to the completion of this activity.

4. Seeing Cells - Getting Ready

Getting Ready

  1. Make copies of cell coloring diagrams. Make one copy on a transparency so that you have one to color in along with your students.
  2. Make copies of Seeing Cells Lab handouts.
  3. Make transparency of the Cell Images and any other images of cells you found.
  4. Set up microscopes.
  5. Set out stations for students to make slides. Each station should include glass slides, cover slips, iodine, methylene blue, tap water, eye droppers, several pieces of red onion, one Elodea stem, and clean toothpicks.

4. Seeing Cells - Lesson Plan

Lesson Plan

  1. Ask students to free associate what comes to mind when you write the word “cell”. In addition to biological cells, they may come up with prison cells, cell phones, a terrorist cell and more. In all these uses, a “cell” is a single functioning unit or compartment that is part of a larger whole. That too is what a cell is in biological terms, the building block upon which all living things are built.
  2. Show students pictures of cells. Have students tell you what they see and notice. Emphasize both the diversity of different cell shapes and sizes and also how all cells share certain features.
  3. Give students the cell coloring diagrams. Lead your students in coloring the diagrams and describe the job of each cell part as you go. You may want to have students write the job of each part of the cell beside the name of the part.
  4. Now that students have learned a little bit about cells, they will now get a chance to look at some real cells through a microscope. If students have not used a microscope before, go over the parts of a microscope and how to properly use it.
  5. Demonstrate how to make each type of slide (see the directions on the Seeing Cells student handout, one of the attachments at the bottom of the main summary page).
  6. Answer any questions then let students begin work on the lab in groups of two. By the end of the activity, students should have 2 labeled drawings of each type of cell, one at 40x and one at 400x.
  7. Assist students with making slides, using the microscopes, and bringing cells into focus. The human cheek cells are often difficult to find and get into focus since they are much smaller and more disperse than the onion and Elodea cells. Many will need help locating these cells on the slide.
  8. When all student have completed the drawings, review what they saw using the Cell Images transparency.
  9. Point out the cell parts that can be seen through a light microscope (cell membrane, cell wall, cytoplasm, nucleus, and chloroplasts).
  10. Discuss why it is that other cell parts could not be readily observed (they are too small or need special dyes to be able to see them).
  11. Discuss the differences between plant and animal cells (plants have cell walls and chloroplasts) as well as the difference between the elodea and onion skin cells (only leaf cells have chloroplasts).

4. Seeing Cells - Assessment

Assessment

  1. Have students turn in their labeled diagrams and conclusion questions.
  2. Provide an unlabelled cell diagram for them to correctly label and describe the function of each part.
  3. Assign a cell quiz. Use the one attached to this lesson, use the one at Shannan Muskopf’s Biology Corner website, or create your own.

Going Further

  1. Build a model of a cell in any of a hundred different ways. Use the Slimy Cells activity. Make shoebox cells. Turn your classroom into a cell. Be creative.
  2. Ask students to draw an analogy between cells and a city, a factory, a school, a fantasy kingdom or science fiction evil empire. Show your students Shannan Muskopf’s analogy of a city that makes widgets then invite your students to come up with their own analogy.
  3. Observe microscopic organisms found in pond water in the Pond Water activity. Some of the creatures you find, like diatoms, are single celled creatures. Of the multicellular creatures, you can observe single cells at work in many of them, particularly the algae.

4. Seeing Cells - Sources

Sources
Blank cell coloring diagrams can be found at:

The best resource for this lesson is the fabulous Biology Corner website of Shannan Muskopf. In Biology 1 and 1A, Chapter 3, she provides:

  • a fantastic overview of how to use a microscope including a lab, worksheet and quiz
  • a cheek cell lab
  • plant and animal cell coloring diagrams
  • a “cell city” extension activity
  • a webquest using the Cells Alive website
  • a cell crossword puzzle
  • a cell quiz

Thank you thank you thank you! Check out all the other fantastic labs, projects, field trips and assessments at Biology Corner.

Standards
Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
a. Students know cells function similarly in all living organisms.
b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls.
c. Students know the nucleus is the repository for genetic information in plant and animal cells.
d. Students know that mitochondria liberate energy for the work that cells do and that chloroplasts capture sunlight energy for photosynthesis.
e. Students know cells divide to increase their numbers through a process of mitosis, which results in two daughter cells with identical sets of chromosomes.
f. Students know that as multicellular organisms develop, their cells differentiate.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Grades 9-12 Biology
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
c. Students know how prokaryotic cells, eukaryotic cells (including those from plants and animals), and viruses differ in complexity and general structure.
e. Students know the role of the endoplasmic reticulum and Golgi apparatus in the secretion of proteins.
f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.
g. Students know the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.
j. * Students know how eukaryotic cells are given shape and internal organization by a cytoskeleton or cell wall or both.

5. Slimy cells

Summary
To solidify students’ conceptualization of cells, students build a model of a cell in a ziplock bag using polyvinyl alcohol slime as cytoplasm. So far, students’ experience with cells has been 2 dimensional – diagrams and microscopic slides. The 3 dimensional nature of cells comes to life as students use everyday objects to represent the many parts of a cell. In addition, students can use this activity to develop a sense of scale, calculating how big a human would be if the ziplock bag cell model were really the size of a cheek cell.

Objectives
Can build a three dimensional scale model of a cell.
Can name and describe the function of certain plant and animal cell organelles.
Can draw and label a picture of plant and animal cells.
Can recognize that all living things are made of cells.
Can use proportions and ratios to calculate the size of a person made of ziplock bag sized cells.
Can begin to use the metric system of measurement.

Vocabulary
Polyvinyl alcohol (PVA)
Borax
Polymer
Cell
Organelle
Cell membrane
Cell wall
Cytoplasm or cytosol
Nucleus
DNA
Chloroplast
Mitochondria
Ribosome
Golgi apparatus
Endoplasmic reticulum
Vacuole
Lysosome
Scientific notation
Metric system

AttachmentSize
5slimy_cells.doc67 KB
cell_model-handout.doc44 KB

5. Slimy cells - Logistics

Time
20-25 min introduction and make PVA slime
30-45 min assemble cell models
10-15 min create cell model keys
20 min discuss the metric system of measurement and use ratios to calculate the relative size of a person made of ziplock bag sized cells

Grouping
Individual

Materials
Each student needs a copy of the Slimy Cell Models handout.

For enough PVA slime for a class of 30 students:

  • 240 g PVA (order from Flinn Scientific catalog # P0154, $19 for 500 g)
  • 75 g Borax (Sodium Tetraborate Decahydrate (Na2B4O7*10H2O), marketed as a “laundry booster” and found in most grocery stores and pharmacies among the laundry detergents for around $10 for a lifetime supply, 76 oz box)
  • water
  • several colors of food coloring
  • 30 ziplock sandwich bags
  • 9-12 empty water bottles with pop-top lids
  • 3-4 empty two liter soda bottles
  • 8-10 100 ml graduated cylinders
  • 8-10 50 ml beakers with gradations on the side
  • 3-4 trays or plastic bins for placing materials for making slime
  • large pot and stove (PVA requires heat to fully dissolve in water)

For cell walls, gather as many pint-sized strawberry baskets as you can – two baskets, one inverted over the other, readily enclose a filled ziplock bag, demonstrate the structural support provided by the cell wall, and illustrate the permeability of the cell wall.

For organelles, assemble a wide assortment of small, inexpensive items that students can select from. It is best to avoid food items like beans and candy since they will decompose and grow mold inside slime, creating a disgusting mess. An alternative is for students to bring objects from home for their models. Some items you may want to consider include:

  • large confetti
  • pony beads
  • pom-pom balls
  • wooden beads
  • Styrofoam peanuts
  • paper clips
  • tin foil
  • saran wrap
  • bubble wrap
  • aquarium gravel
  • plastic drinking straws
  • aquarium tubing
  • yarn
  • ribbon
  • Christmas tinsel
  • plastic Easter eggs

Setting
Classroom 

5. Slimy cells - Background

Teacher Background
Making models of cells is a fun, meaningful activity for students to help them visualize the 3 dimensional nature of cells. See the background section of the Seeing Cells activity for a description of cell parts and their functions. This puts a slightly different twist on the standard shoebox cell model by using PVA slime to suspend the various organelles much like a real cell's cytoplasm does. It is also much less messy than the often-used jello cell models since everything stays contained within a ziplock bag (and is not sticky if spilled on the floor - though avoid getting slime on carpet).

The PVA slime recipe used in this activity is:

  • 180 ml 4% PVA solution
  • 30-35 ml 5% Borax solution

This makes a wonderful, viscous, oozing slime that is wet to the touch but holds together well even if removed from the ziplock bag. Polyvinyl alcohol exists in water as a long polymer of (C2H4O)n units. Each chain is up to 2,000 units long. When Borax is combined with the PVA solution, the PVA chains crosslink, forming a highly viscous gel. Since the crosslinks are weak, they continually break and reform as the slime is handled.

PVA slime is quite safe to touch and handle, although you don't want to eat any since the Borax is toxic in large doses. It is easy to clean up with soap and water. Unadulterated slime can be stored for several weeks in a ziplock bag.

I also use this activity to introduce students to the metric system of measurement and the use of ratios to see the relative size of things. Although students realize that cells are tiny, especially after looking through the microscope at them, it is often hard for them to imagine just how tiny cells really are. By going through all the steps of calculating how big a human would be if one of their ziplock bag cell models was really a cell, they are better able to recognize just how tiny a cell is.

For your reference, below is a table showing standard versus scientific notation as well as the common metric prefixes for each.

Standard notation Scientific notation Common prefix Common symbol Example
1000 1 x 103 kilo- k kilometer (km)
100 1 x 102      
10 1 x 101      
1 1 x 100 none none meter (m)
0.1 1 x 10-1 deci- d decimeter (dm)
0.01 1 x 10-2 centi- c centimeter (cm)
0.001 1 x 10-3 milli- m millimeter (mm)
0.0001 1 x 10-4      
0.00001 1 x 10-5      
0.000001 1 x 10-6 micro- u micrometer (um)
0.0000001 1 x 10-7      
0.00000001 1 x 10-8      
0.000000001 1 x 10-9 nano- n nanometer (nm)
0.0000000001 1 x 10-10      

A human cheek cell is approximately 58 micrometers (um) or 0.000058 meters (m) wide. A typical seventh grader is approximately 1.6 meters (m) tall. A standard ziplock sandwich bag is approximately 16 centimeters (cm) or 0.16 meters (m) wide. Thus you can set up a proportion to figure out how big a human being would be (x) if the ziplock bag represented a cheek cell:
__x__ = __0.16 m__
1.6 m     0.000058 m
Solving for x you get 4414 meters or 4.4 kilometers. Thus, a human made of cells as big as a ziplock bag would be 4.4 kilometers tall (over 2.7 miles)! Just imagine how many slimy cell models it would take to fill a statue over 4 kilometers tall (around 10 trillion, that's 1 x 1013). A blood cell takes around 30 seconds to circulate around the human body - in our enlarged model, that's comparable to a ziplock bag blood cell completing a 3 mile round-trip journey in 30 seconds, at 360 miles an hour!

Student Prerequisites
Students need a good background in cell structure, parts of a cell, and their functions before undertaking this activity. It is helpful if students have experience with ratios and proportions in math class and if they have had some exposure to the metric system of measurement though not required.

5. Slimy cells - Getting Ready

Getting Ready

  1. Make copies of the Slimy Cell Models handout (or make a single transparency copy for the teacher).
  2. Set out assorted materials for the cell parts in a sort of buffet line.
  3. Set out graduated cylinders, 50 ml beakers, ziplock bags,

To make PVA solution:

  1. Bring 5.76 liters of water to a boil in a very large pot.
  2. Measure out 240 g PVA.
  3. Mix PVA into boiling water. Simmer on medium-low heat, stirring regularly, for 10-15 minutes or until all PVA has been dissolved.
  4. Allow PVA solution time to cool slightly in the pot.
  5. Pour into 3 or 4 two liter bottles.

To make Borax solution:

  1. In a large container, combine 1.5 liters of water with 75 g Borax.
  2. Stir until fully dissolved.
  3. Distribute the Borax solution among 9-12 pop-top water bottles.
  4. Add 3-4 drops of food coloring to each of the bottles. I made my stock solutions the standard red, yellow and blue so that my students could mix the colors themselves to achieve other colors of the rainbow.

5. Slimy cells - Lesson Plan

Lesson Plan

  1. Begin class with a review of the parts of the cell.
  2. Describe the activity to students – they will be making 3 dimensional cell models. A ziplock bag will represent the cell membrane. Slime will represent the cytoplasm. If they wish to make a plant cell, strawberry baskets will represent the cell walls. Students can choose the rest of the “parts” to make up all the organelles.
  3. Discuss as much of the chemistry behind the making of slime as you wish.
  4. Pass out the slime making materials and lead students through the creation of slime.
    • First, each student will need a ziplock bag.
    • Using the graduated cylinders, measure out 180 ml PVA and add that to the bag.
    • Using the small beakers, measure out 30-35 ml colored Borax – mix and match colors as you wish to get the final color you want – and add that to the bag.
    • Zip the bag closed and gently massage the contents until the colored Borax is evenly distributed throughout the PVA and the slime coalesces.
    • The slime may now be touched and/or carefully taken out of the bag.
  5. Pass out the handout and describe the assignment – in addition to adding organelles to the cell, students should create a key describing what was to represent each part of the cell and why that object was chosen. (Is it similar in size? shape? function? design?)
  6. Answer any questions. Have students set up the key on a piece of paper before they go to the cell parts “buffet” (or else some may never get around to creating a key at all or understanding the purpose of the activity).
  7. Once students have their key outlined and decided whether to make an animal or plant cell, allow them to browse the cell parts “buffet” and add objects to their cell. Make sure that they record what they chose for each organelle and why on their key.
  8. When all the cells are complete, go through each part of the cell and survey what different students chose to represent that part and why. This helps reinforce the vocabulary and the functions of each organelle.
  9. Ask students how many times larger this ziplock bag cell is compared to the cheek cells they observed under the microscope. (Almost 3,000 times larger!)
  10. To show students how this is calculated, present and describe the metric system of measurement.
    • A ziplock bag is around 16 centimeters wide. A centimeter is one hundreth of a meter (0.01 meters). This a ziplock bag is 0.16 meters wide.
    • A cheek cell is 58 micrometers wide. A micrometer is one millionth of a meter (0.000001 meters). Thus, the cheek cell is 0.000058 meters wide.
    • To see how much larger a ziplock bag is compared to a cheek cell, divide the size of a ziplock bag (in meters) by the size of a cheek cell (in meters): 0.16 m/0.000058 m = 2,759
  11. Since all living things are made of cells, how tall would a person made of ziplock bag sized cells be? A typical middle school student is around 1.6 meters tall. To calculate this, you need to set up a ratio:
    __x__ = __0.16 m__
    1.6 m    0.000058 m
    Solving this ratio, you find that x is 4414 meters (4.4 kilometers or 2.7 miles)! Thus a person made of ziplock bag sized cells would be 2.7 miles tall! See some of the other fun facts in the teacher background.

5. Slimy cells - Assessment

Assessment

  1. Collect the ziplock bag cells and the keys. They can be displayed around the room for some time although students tend to like to take the models home and play with them.
  2. Provide other example conversion and ratio problems for students to solve.
  3. Revisit the characteristics of life list from the Is It Alive? activity. Revise the criteria as necessary to include that all living things are made of cells.

5. Slimy cells - Standards

Standards
Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
a. Students know cells function similarly in all living organisms.
b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls.
c. Students know the nucleus is the repository for genetic information in plant and animal cells.
d. Students know that mitochondria liberate energy for the work that cells do and that chloroplasts capture sunlight energy for photosynthesis.
e. Students know cells divide to increase their numbers through a process of mitosis, which results in two daughter cells with identical sets of chromosomes.
f. Students know that as multicellular organisms develop, their cells differentiate.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
d. Construct scale models, maps, and appropriately labeled diagrams to communicate scientific knowledge (e.g., motion of Earth's plates and cell structure).

Grades 9-12 Biology
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
a. Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.
c. Students know how prokaryotic cells, eukaryotic cells (including those from plants and animals), and viruses differ in complexity and general structure.
e. Students know the role of the endoplasmic reticulum and Golgi apparatus in the secretion of proteins.
f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.
g. Students know the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.
j. * Students know how eukaryotic cells are given shape and internal organization by a cytoskeleton or cell wall or both.

6. Cell Energy (photosynthesis and respiration)

Summary
Here you will find a toolbox full of inquiry investigations on photosynthesis and respiration. Rather than the detailed lesson plans provided elsewhere at My Science Box, each experiment only contains a short background, materials, procedure, and going further section. It is up to you to decide which of the many experiments you wish to try with your students and how to sequence them. You will find everything from descriptions for how to extract chlorophyll, discover that plants “breathe”, recreate the experiments of Priestly and Ingenhousz, detect carbon dioxide production, and measure the rate of yeast respiration. None of these experiments require expensive equipment such as metabolism chambers or oxygen meters although those are great tools if you can afford them.

Briefly, photosynthesis occurs in the chloroplasts of plants as a means of turning solar energy into chemical energy in the form of glucose, the primary food/energy source of cells. Through a series of biochemical reactions, sunlight energy transforms carbon dioxide and water into glucose and oxygen.

6CO2 + 6H2O + light → C6H12O6 + 6O2

Respiration releases the chemical energy stored in glucose and turns it into energy that can be used by the cell in the form of ATP (adenosine 5’triphosphate). ATP may be considered the standard currency of the cell, much as the dollar is the standard currency in American society. Nearly all cellular processes depend on ATP as their energy source. The chemical equation for respiration using glucose is the mirror image of the chemical equation for photosynthesis.

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

Objectives
Can recognize that all living things metabolize and thus require nutrients, take advantage of chemical reactions to release energy, and produce wastes.
Can describe the general process of photosynthesis and respiration.
Can recognize the reciprocal relationship between photosynthesis and respiration.
Can explain the jobs of chloroplasts and mitochondria and their importance to cells.
Can design, conduct, and interpret experiments on plants and animals related to photosynthesis and respiration.

Vocabulary
Metabolism
Chemical reaction
Energy
Photosynthesis
Respiration
Chloroplast
Chlorophyll
Mitochondria
Carbon dioxide
Oxygen
Glucose
Bromthymol blue
Carbonic acid
Elodea
Yeast

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6. Cell Energy - Plant Pigments

Chlorophyll extractionChlorophyll extractionSummary
Chlorophyll is the pigment in plants that captures sunlight energy and uses it to drive photosynthesis. While chlorophyll does give plants their characteristic green color, chlorophyll actually comes in many colors and subtypes ranging from green to yellow to orange to red. In this experiment, students use paper chromatography to separate the many pigments from one another. First the pigments are extracted from the plants by simply crushing the plant cells open on the filter paper with the edge of a penny. When the filter paper is then immersed in rubbing alcohol, the pigments are carried upwards through capillary action. The smallest pigments travel more quickly and thus separate from the larger pigments that remain closer to the origin line.

Chlorophyll is an amazing chemical that is the essential ingredient in photosynthesis, the process through which plants capture light from the sun to create glucose. When photons of light hit chlorophyll, the electrons in the central magnesium atom donate an electron to a series of chemical reactions – the electron transport chain – that produce ATP, the cells primary unit of energy currency. The chlorophyll gets this electron back by taking one from water, resulting in the release of oxygen gas as a byproduct.

Chlorophyll comes in two main forms: chlorophyll a and chlorophyll b. Each has a slightly different chemical structure and therefore absorbs light of different wavelengths. In this paper chromatography experiment, chlorophyll a will appear as a bright yellow-green band while chlorophyll b will appear as a dull green band. In addition, there are many other accessory pigments in plants that absorb light and help transfer photons to the chlorophyll. These include carotene (an orange band) and xanthophyll (a yellow band). A final pigment that may be detected is anthocyanin (a red-brown band) that acts as a type of sunscreen for plants, protecting the plant from UV damage.

For more information on paper chromatography and its use in chlorophyll extraction, a fabulous scientific description may be found on the Science Buddies website. Also see this photosynthesis lesson plan by Sara Swisher, Barb Wilson, and Jean Wilson. Finally, Cheryl Massengale has a great write up for chlorophyll extraction including a table illustrating how to calculate the Rf value for each band and use that as a quantitative means of identifying the various pigments.

Materials

  • Filter paper cut into 9 cm x 2 cm strips (coffee filters work but not as well)
  • Pennies
  • Beaker or cup no more than 9 cm tall
  • Small stick - bamboo skewer, pencil, plastic stirrer, drinking straw, etc.
  • Rubbing alcohol
  • Tape
  • Ruler
  • Assorted fresh plant leaves – spinach, lettuce, or leaves collected from around the neighborhood (unusually colored leaves such as white, purple, red, and yellow are particularly interesting)

Procedure

  1. Use a pencil to draw a line across the filter paper strip, 2 cm from one end.
  2. Place the leaf you want to test on top of the filter paper strip, remembering where the line is.
  3. Using the edge of a penny, trace the penny across the leaf right on top of where you drew the line. Push down hard enough to leave a green smear on the paper on top of the original pencil mark.
  4. Repeat 2 more times with fresh sections of leaf to make the smear darker. Try to keep the smear as close to the original pencil line as possible.
  5. Fill the cup or beaker to a depth of 1 cm with rubbing alcohol.
  6. Carefully lower the filter paper strip, green smear end in first, into the beaker until the bottom just touches the alcohol. Make sure that the green smear does not actually touch the alcohol, only the tip of the paper should actually be in contact with the alcohol.
  7. Lay the stick across the mouth of the beaker like a bridge from one edge to the other.
  8. Tape the filter paper strip to the stick so that the paper is held in place just touching the alcohol but not touching the sides of the beaker.
  9. Wait. The alcohol should gradually move up the paper, bringing many of the pigments along with it.
  10. Remove the stick and paper when the alcohol has almost reached the stick. The actual length of time will depend on the type of paper you use.
  11. Mark how far up the paper the alcohol traveled with a pencil.
  12. Determine how many bands of pigment you have, what color they are, and measure how far each band traveled from the origin line. Some of the pigments will fade and disappear over time. It may help to trace around each band in pencil while they are still clear so that the strip can still be analyzed if and when the bands fade.
  13. Calculate an Rf value for each band (Rf value = distance that band traveled divided by distance the alcohol front traveled).
  14. Identify the pigments based on their colors or by their Rf value. The Rf values allow you to compare one pigment band to another from strip to strip.
  15. Compare what was found in different types of leaves.

Going Further

  1. Try this on purple plants. Do they have chlorophyll too?
  2. Try this on white-leafed plants. Do they have chlorophyll too?
  3. Try this on leaves from trees before and after they change color in the fall. What happens to the chlorophyll as the leaves change color? Do new pigments emerge or were they there all along?
  4. Cover half of a wide green leaf with tin foil. Leave the plant in a sunny window for at least 4-5 days. Remove the tin foil and see what happened to the leaf. Compare chlorophyll extracted from the uncovered half of the leaf with chlorophyll extracted from the covered half. Is there any difference? On a separate leaf that underwent the same treatment, uncover the leaf and leave it in a sunny window. Does the chlorophyll come back?

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6. Cell Energy - Bubbling Plants

Elodea nuttallii: Image courtesy of Christopher Fischer.Elodea nuttallii: Image courtesy of Christopher Fischer.Summary
Students often believe that only animals “breathe”, but all things exchange gases with their environment. It’s just that the process is not so obvious in plants. Elodea is a very common water plant that can be found in aquarium stores. As photosynthesis occurs, oxygen is produced as a by-product. Elodea releases bubbles of oxygen as it photosynthesizes. In fact, the number or volume of bubbles in a certain amount of time can be used as a rough measure of photosynthetic rate.

The measure is rough because oxygen dissolves in water so may not always appear as a gas. Moreover, most light sources produce heat, which causes the water temperature to increase, which in turn causes lower gas solubility, and thus may produce bubbles just by turning the light on. Finally, the size of a bubble is not constant thus counting the number of bubbles per unit time is only a very rough measure. The total volume of gas produced is a better measure but again falls victim to the other caveats. The best measure is to use a dissolved oxygen meter which unfortunately costs a fair bit of money (between $400 to over $1000). You can also try disposable dissolved oxygen tests (see the Sources section of the Water Analysis activity).

An important note is that freshly cut Elodea stems produce more bubbles than the leaves. That is because Elodea stems contain large intracellular air passageways. As oxygen is produced, the plant transports the oxygen away from the leaves towards the roots. Thus, a freshly cut stem will produce oxygen bubbles at an observable rate. The cells in the leaves are much more tightly packed together and provide greater resistance to the emerging oxygen gas than the stems. Thus, to maximize oxygen gas production in this experiment, cut the stem of the Elodea then place the plant upside-down in the test tube. For more information about why the bubbles emerge from the stems, not the leaves, see this article by David Hershey of the Mad Scientist Network.

An excellent resource with more information about the use of Elodea in this experiment can be found at the Clifton College Science School website. There you will find detailed information about Elodea, how oxygen is produced, experiments by Frost Blackman, practical advice and more.

Materials

  • Elodea plants
  • Scissors
  • Large beaker
  • Clear test tube, preferably with fine graduations (< 1 ml) in order to measure the volume of the gas produced
  • Water
  • Sunlight or a lamp (best to find a light source that produces as little heat as possible)
  • Optional: heavy black cloth

Procedure

  1. Fill the large beaker almost to the top with water.
  2. Cut the stem of the Elodea plant at an angle (for greater surface area) so that it is just a little shorter than the test tube.
  3. Insert the plant, cut stem end in first, into the test tube.
  4. Fill the test tube to overflowing with water. Try to avoid introducing any bubbles to the test tube as you do this. Gently tap the test tube on a tabletop to dislodge any bubbles trapped between the leaves.
  5. Carefully cover the top of the test tube with your thumb, squeezing out some water as you do. Invert the test tube over the beaker and put the test tube with your thumb still covering the opening into the beaker.
  6. Release your thumb. And gently settle the test tube on the bottom of the container. Check to make sure there are no bubbles in the test tube.
  7. Place the beaker and test tube in sunlight or under a bright lamp. Observe what happens.
  8. At 5 minute intervals for a total of 15 minutes, record either the number of bubbles produced or the volume of bubbles produced.

Going Further

  1. Investigate the effect of light intensity. Compare bubble production between a plant in sunlight versus a plant in darkness, covered in a black cloth.
  2. Investigate the effect of temperature. Compare bubble production between a plant in the fridge versus a plant at room temperature.
  3. Investigate the effect of carbon dioxide levels. Compare bubble production between a plant in water that has been boiled and left to cool back to room temperature (little to no carbon dioxide) versus a plant in water that a person has blown bubbles through a straw for 3 minutes (lots of dissolved carbon dioxide). See the Colorful Respiration activity for more ideas along these lines.

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6. Cell Energy - Photosynthesis in a Jar

Summary
These experiments use a bell jar (or any other very large, clear, glass jar) to determine the identity of the gas produced by plants. It mirrors the famous experiments of Joseph Priestley and Jan Ingenhousz from the 1700’s that first demonstrated the existence of oxygen and its importance to plants and animals.

In 1771 and 1772, Priestly conducted a series of experiments using a bell jar. It was known that a candle placed in a sealed bell jar would eventually burn out and could not be relighted while still in the jar. Priestly discovered that a plant can survive indefinitely within a jar. Thus, he tried placing a plant into the jar with the burning candle. The candle went out as before and could not be relit right away. Priestly waited several days and tried again. The candle could be relit! The plant had restored the air inside the jar! (Do not try the next series of experiments since it harms animals!) Next priestly investigated what would happen to animals. He found that a mouse placed inside a sealed jar will eventually collapse. However, a mouse can survive in a sealed jar with a plant since the plant restores the air. Priestly was the first to demonstrate that oxygen is necessary for fire and animals but that given time, plants can create oxygen, allowing fires to burn and animals to breathe.

A few years later, Jan Ingenhousz investigated the effect of light on a plant’s ability to restore air. He found that a plant left in darkness cannot restore the air for a candle. To demonstrate this, he burned up all the oxygen in a jar with a plant then left the plant in sunlight for a few days to restore the air. Then without relighting the candle, he put the plant into darkness for several more days. At the end of the dark period, he was unable to relight the candle. He concluded that a plant in darkness acts like animals, using up the oxygen that it had created. Ingenhousz had discovered that plants can photosynthesize and create oxygen but only in the light. If left in the dark, plants do not photosynthesize and thus no oxygen is produced. Moreover plants are always performing respiration, just like animals. In sunlight, the rate of photosynthesis outstrips respiration so there is an excess of oxygen being produced. But in darkness, no photosynthesis takes place but respiration continues to occur. Thus, by keeping a plant in darkness you can demonstrate that plants need oxygen and use it up, just like animals.

For more information, see the wonderful website of Julian Rubin which describes many of these experiments and offers links and resources on how to recreate them in the classroom. Also, NSTA has produced a great set of photosynthesis related inquiry activities including the bell jar experiments.

Materials

  • Small plant in a pot, well watered
  • Candle or row of matches (I found the matches easier to light with the converging lens although it produces significantly more smoke.)
  • Flood lamp with a very high wattage bulb or bright sunlight
  • Magnifying glass
  • Bell jar or other large glass jar (Don’t use a plastic container like I did initially. Not only will it collapse with the vacuum produced following the burning of the candle but the smoke from the candle flame often deposits itself on the inside of the plastic, obscuring everything inside from view.)
  • Vacuum plate or large tray full of water (If you use a tray of water, beware that as the candle heats the air, the expanding gas will escape out from under the rim of the jar. When the air cools again, the level of the water inside the jar will rise so be sure to prop your plant up on a pedestal of some sort to prevent the whole thing from getting swamped. Also use a lot of water in the tray initially or air from outside will be pulled into the jar as the air cools.)
  • Heavy black cloth or dark closet

Procedure
A candle uses up the oxygen in the jar:

  1. Place a burning candle inside the bell jar and seal it. The candle will eventually go out.
  2. Focus a beam of light on the candle wick with the converging lens to show that the candle cannot be relit.

A plant restores the oxygen in the jar:

  1. Place a burning candle and a plant inside the bell jar and seal it. The candle will eventually go out.
  2. Try relighting the candle to show that the candle cannot be relit.
  3. Place the setup in a sunny window for 2 days.
  4. Try relighting the candle. The candle should relight.

A plant in darkness does not restore oxygen:

  1. Place a burning candle and a plant inside the bell jar and seal it. The candle will eventually go out.
  2. Try relighting the candle to show that the candle cannot be relit.
  3. Place the setup in the dark for 2 days.
  4. Try relighting the candle. The candle should not relight.

A plant in darkness uses oxygen:

  1. Place a burning candle and a plant inside the bell jar and seal it. The candle will eventually go out.
  2. Try relighting the candle to show that the candle cannot be relit.
  3. Place the setup in a sunny window for 2 days.
  4. Remove the setup from the sunny window and place it in darkness for 2 more days.
  5. Try relighting the candle. The candle should not relight.

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6. Cell Energy - Colorful Respiration

Summary
Blow through a straw into bluish liquid and watch it turn green then yellow before your eyes. Put some plants into the yellow liquid, leave it in a sunny window, come back the next day and the liquid is green. What if you leave the plants in the dark? What if you put some pond snails in? What if you put both pond snails and plants? What’s going on?

The liquid is bromthymol blue (BTB) a non-toxic acid-base indicator that can be used to indirectly measure levels of dissolved carbon dioxide (CO2). The amount of CO2 in a solution changes the pH. An increase in CO2 makes a solution more acidic (the pH gets lower). A decrease in CO2 makes a solution more basic (the pH gets higher). The reason for this is that carbon dioxide that is dissolved in water is in equilibrium with carbonic acid (H2CO3).

CO2 + H2O ↔ H2CO3

In any solution, while the majority of CO2 stays as CO2, some of it is converted to H2CO3, turning the solution slightly acidic. If CO2 is added to the water, the level of H2CO3 will rise and the solution will become more acidic. If CO2 is removed from the water, the amount of H2CO3 falls and the solution becomes more basic. Thus, acid-base indicators such as BTB can indirectly measure the amount of CO2 in a solution.

For more than you ever wanted to know about carbonic acid, see the Wikipedia article on carbonic acid. For the example lesson plans developed by Bob Culler through Access Excellence at the National Health Museum. For a great time lapse video showing BTB color changes using elodea and snails, see Activity C13 from Addison-Wesley’s Science 10 curriculum.

Materials

  • Bromthymol blue (BTB can be ordered from any science supply company such as Flinn Scientific $9 for 1 liter 0.04% BTB solution).
  • Several 2 liter soda bottles
  • Test tubes
  • 500 ml beakers or disposable plastic or paper cups
  • Water (since the pH of tap water varies, you may wish to use distilled water for your master BTB solution)
  • Drinking straws
  • Plastic wrap
  • Elodea
  • Pond snails

Procedure

  1. Before the lesson, the teacher should mix a master BTB solution in one or more 2 liter soda bottles. For each 2 liter bottle, mix 120 ml 0.04% BTB with 1800 ml water. The end result should be a medium blue master BTB solution, dilute enough to be safe for plants and snails but dark enough to see the color changes.
  2. Pour 200 ml diluted BTB in a beaker or cup.
  3. Take a deep breath then blow bubbles in the BTB solution through a drinking straw. What happened? Why?
  4. Set up a test tube rack with 3 tubes. In tube #1 put unbubbled BTB solution (blue). In tube #2 put bubbled BTB solution (yellow). Tubes #1 and #2 will be your comparison tubes. In tube #3 you have a choice of what to do. Choose one option from each of the following columns:
    BTB solution Living things
    Light conditions
    bubbled BTB (yellow) spring of Elodea Sunny window/bright light
    unbubbled BTB (blue) 5 pond snails Dark closet/drak heavy cloth
    both Elodea and 5 pond snails  
  5. Make a hypothesis about what will happen to your tube.
  6. After 24 hours, check the color of your tube. What happened? Why?

Going Further

  1. Investigate the effect of exercise. Compare blowing bubbles in BTB for 3 seconds before and after vigorous exercise (such as doing 2 minutes of jumping jacks).
  2. Investigate the effect of holding your breath. Compare blowing bubbles in BTB for 3 seconds before and after holding your breath for as long as possible (without passing out).
  3. Try this lesson developed by NASA. It describes how to capture various gases (room air, human exhalation, car exhaust, or carbon dioxide from a chemical reaction) in a balloon and use BTB to measure the carbon dioxide content.

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6. Cell Energy - Bubbling Yeast

Summary
Bubbling Yeast: Thanks to Ellen Loehman for creating this image.Bubbling Yeast: Thanks to Ellen Loehman for creating this image.Yeast are a single celled fungi that are a great model organism for studying respiration in the classroom. The species Saccharomyces cerevisiae is commonly used for leavening bread and fermenting beer but other species such as Candida albicans are known to cause infections in humans (vaginal yeast infections and diaper rash being the most common). In this investigation, students fill the bulb of a disposable pipet (eyedropper) with yeast, then submerge the pipet in a test tube of water. They can then measure the rate of respiration by counting the number of bubbles of carbon dioxide gas that emerge from the tip of the pipet in a certain length of time. By varying the temperature and the nutrient source, students can discover what variables affect the rate of respiration in yeast. By submerging the pipet in bromthymol blue (see Colorful Respiration activity), students can identify the gas being produced as carbon dioxide.

For more information about yeast in classroom experiments, see this experiment from the Exploratorium or this one from PBS Kids that has snippets of what different kids saw with different manipulations. The idea of using inverted disposable pipets to contain the yeast and measure their respiration rate came from a workshop led by Steve Ribisi of the University of Massachusetts – thanks Steve!

Materials

  • Fast-acting bread yeast (1 packet or 1/4 teaspoon per group)
  • 1 cup water
  • 2 tablespoons table sugar
  • Disposable plastic pipets (These can be ordered from most science supply companies such as Science Kit and Boreal Labs, around $6 for 100 pipets or $18 for 500 pipets. Note: don’t get the “microtip” style since the yeast solution is too viscous to be sucked into the tip.)
  • Metal washers from the hardware store (These will weigh the pipets down so that they don’t float up to the top of the tube. Make sure that the hole in the washers is large enough to sit around the neck of the pipet and rest on top of the bulb.)
  • Small test tubes for mixing yeast solution with sugar solution
  • Large test tubes (These must be wide enough to accommodate the pipets and washers comfortably but also tall enough to submerge the whole pipet. If you don’t have large enough test tubes, try using graduated 15 ml centrifuge tubes, a 100 ml graduated cylinder, or a small beaker.)
  • Optional: other nutrient sources for the yeast such as milk, apple juice, soda, Kool-aid, salt water, potato starch solution, flour in water, chicken broth, etc. Most of these work better if diluted in water 1:1.
  • Optional: bromthymol blue solution

Procedure

  1. an hour before the activity, mix 1 packet of bread yeast with 1/4 cup of luke warm water. Stir around 2 minutes until all the yeast is dissolved. Stir again just before use.
  2. Dissolve 1 tablespoon sugar in 1/2 cup of luke warm water. Stir around 1 minute until all the sugar is dissolved.
  3. In a small test tube, mix equal quantities of the yeast solution and sugar solution. Stir gently to combine. Use separate droppers for each solution to avoid contaminating the original stock solutions.
  4. Suck up some of this solution into a pipet. Invert the pipet and let the solution run down into the bulb. Carefully squeeze out the air and suck up some more yeast-sugar solution. Try to fill exactly half of the pipet bulb.
  5. Thread 2 washers over the neck of the pipet so that they come to rest on top of the bulb.
  6. Gently drop the pipet with washers into the large test tube.
  7. Fill the large test tube with luke warm water until the pipet is completely submerged.
  8. Wait 5 minutes to allow the yeast time to equilibrate and begin respiration.
  9. Count how many bubbles emerge from the top of the pipet each minute for 10 minutes.

Going Further

  1. Investigate the effect of temperature. Compare the respiration rate in yeast in cold water, luke warm water, and scalding hot water.
  2. Investigate the effect of different nutrient sources. Compare the respiration rate in yeast dissolved in different nutrient sources.
  3. Investigate the identity of the gas produced. Fill the test tube with BTB rather than water and see what happens to the color of the indicator over time. (See the Colorful Respiration activity.)

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6. Cell energy - Standards

Standards
Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
a. Students know cells function similarly in all living organisms.
b. Students know the characteristics that distinguish plant cells from animal cells, including chloroplasts and cell walls.
d. Students know that mitochondria liberate energy for the work that cells do and that chloroplasts capture sunlight energy for photosynthesis.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations. Students will:
a. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.
c. Communicate the logical connection among hypotheses, science concepts, tests conducted, data collected, and conclusions drawn from the scientific evidence.
e. Communicate the steps and results from an investigation in written reports and oral presentations.

Grade 8 Life Science
5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:
a. Students know reactant atoms and molecules interact to form products with different chemical properties.
b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.
c. Students know chemical reactions usually liberate heat or absorb heat.

Grades 9-12 Biology
Cell Biology
1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism's cells. As a basis for understanding this concept:
f. Students know usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.
g. Students know the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.

7. Flower and Frog Dissection

Sarracenia flower dissection: Image courtexy of Noah ElhardtSarracenia flower dissection: Image courtexy of Noah Elhardt Leopard frog in duckweed: Image courtesy of Steven DunlopLeopard frog in duckweed: Image courtesy of Steven Dunlop

Summary
To learn about the structure and function of living things, it is essential to explore the anatomy of real organisms up close and personal. While much can be accomplished by studying living things and their life cycles (see Raising Plants and Raising Trout projects), dissections offer a view of the internal structures and how they contribute to the whole. What follows are resources and information for teachers interested in conducting a flower and/or frog dissection. There are many excellent lesson plans and dissection guides on the web already. Rather than recreate these resources here, My Science Box provides nitty-gritty logistics and resources such as a selected list of great web resources, how to order frogs, what equipment you need, student handouts, and teaching strategies.

Objectives
Can identify the major parts of a plant and flower and describe the function of each part.
Can identify the major organs in a frog and describe the function of each organ.
Can thoughtfully, safely and respectfully complete an anatomical dissection.

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7. Flower Dissection

Materials

  • Flowers, possibly of several different species for cross-species comparisons. Almost any flower may be used although the anatomy is more easily distinguished in some flowers than others. Some common flowers with clearly differentiated parts include:Sarracenia flower dissection: Image courtexy of Noah ElhardtSarracenia flower dissection: Image courtexy of Noah Elhardt
    • Lily
    • Iris
    • Daffodil
    • Tulip
    • Wisconsin fast plant
    • Peas
    • Poppies
    • Gladiolus
  • Paper plates/plastic trays
  • Scissors or razor blade (to open the ovary)
  • Hand lens
  • Optional: tweezers
  • Optional: dissecting scope

Teaching Tips
The best resource that I have found for flower dissections is Gertrude Battaly’s website. There you will find comprehensive background information, step-by-step dissection directions, discussion questions and more. I recommend using her handout for the clarity of the directions. The handout I have provided includes only a summary table and conclusion questions.

Sources
To learn more about flower anatomy, see the following websites:

In addition to Gertrude Battaly’s site, other good lesson plans include:

  • A great cartoon-style interactive flower dissection can be found at BBC Kids. Some of the terminology differs between what is used on the BBC site and what is typically used in American classrooms.
  • San Diego State University has posted great lesson plans for a flower dissection followed by a fruit dissection. Solid scientific background information is found throughout the lesson plan.
  • Kids gardening provides a lesson plan appropriate for younger students.

Standards
Grade 7
Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.
f. Students know the structures and processes by which flowering plants generate pollen, ovules, seeds, and fruit.

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7. Frog Dissection

Materials

  • Frogs (order them from Carolina Biological catalog # 22-7444, 22-7445, 22-7446, 22-7464, 22-7465, 22-7466, between $3.35 - $5.95 depending on the quantity ordered and whether there is any color injection)
  • Paper plate or dissection tray
  • Scissors
  • Scalpel or razor blade
  • Forceps
  • Optional: dissection probes
  • Optional: dissection pins (especially useful if you have dissection trays on which to use them)

Teaching Tips
The best resource that I have found for frog dissections is Net Frog by Mabel Kinzie has a fabulous interactive virtual frog dissection including many multimedia resources such as videos and narration for every step of the dissection. It is an excellent resource for teachers, for students to preview or review the material, and as an alternative to an actual frog dissection.

Sources
To learn more about frogs, visit the following websites:

  • The Exploratorium had a great exhibit on frogs with excellent, student-friendly, web resources about frog behavior (listen to frog calls), biology (meet Dr. Tyrone Hayes, a frog researcher), and mythology (the Frog Prince and other stories).
  • The Amphibian Conservation Alliance provides an extensive set of articles on frog biology, behavior and conservation.
  • Check out the Animal Diversity Web, an extraordinary resource for learning about virtually any known species of animal. The site is organized by the classic kingdom-phylum-class taxonomy and includes photographs, diagrams, recordings of calls, and more. It is an indispensable resource for any class researching the classification of an organism.

In addition to Net Frog, other good lesson plans include:

  • The Virtual Frog Dissection by Steve Velie and Tim Hall is an exceptional resource, taking teachers and students step by step through a frog dissection and identifying structures both internally and externally. Their site was put together as part of a research study comparing the effectiveness of a virtual frog dissection versus an actual frog dissection. Every vocabulary word is linked to a comprehensive glossary of terms.
  • The Virtual Frog Dissection by Mrs. Mazanek of Batesville High School provides a similar virtual dissection experience using photographs and a glossary.
  • Lawrence Berkeley Labs has produced the Whole Frog Project, a 3 dimensional tool for dissecting a frog. They used MRI data from real frogs to allow users to rotate a digitized frog in 3 dimensions, while looking at only a selected set of organs. Teachers may find the labeled diagrams of selected body systems useful.

Standards
Grade 7
Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.
c. Students know how bones and muscles work together to provide a structural framework for movement.
d. Students know how the reproductive organs of the human female and male generate eggs and sperm and how sexual activity may lead to fertilization and pregnancy.

Physical Principles in Living Systems (Physical Sciences)
6. Physical principles underlie biological structures and functions. As a basis for understanding this concept:
j. Students know that contractions of the heart generate blood pressure and that heart valves prevent backflow of blood in the circulatory system.

Grades 9-12 Biology
Physiology
9. As a result of the coordinated structures and functions of organ systems, the internal environment of the human body remains relatively stable (homeostatic) despite changes in the outside environment. As a basis for understanding this concept:
a. Students know how the complementary activity of major body systems provides cells with oxygen and nutrients and removes toxic waste products such as carbon dioxide.
b. Students know how the nervous system mediates communication between different parts of the body and the body's interactions with the environment.
f. * Students know the individual functions and sites of secretion of digestive enzymes (amylases, proteases, nucleases, lipases), stomach acid, and bile salts.
g. * Students know the homeostatic role of the kidneys in the removal of nitrogenous wastes and the role of the liver in blood detoxification and glucose balance.

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Field Trip - Marine Science Institute

Summary
Sail aboard a research vessel and explore the living treasures of the San Francisco Bay. The Marine Science Institute (MSI) provides some of the best hands-on science and environmental education in the Bay Area. On the Discovery Voyage, students spend 4 hours learning about the San Francisco Bay ecosystem by examining water quality and collecting organisms at every level of the food web from microscopic plankton to mud dwellers to bat rays and fish. The diversity of life in the Bay is astounding and surprising to students who have spent their whole lives living by its water but never “diving in”.  If a half-day voyage isn’t for you, many other fantastic programs are available including Inland Voyages (where live marine organisms come to you), Ocean Lab (where students explore animals of the rocky coastal ecosystem in MSI’s Discovery Lab classrooms), and Tidepool Expeditions (where MSI naturalists provide a guided tour of the tidepool creatures at Pillar Point).

Objectives
Can apply knowledge about the characteristics of life to the organisms living in the San Francisco Bay.
Can conduct a scientific investigation.
Can use a dichotomous key to identify animals.
Can recognize the extraordinary diversity of life in an ecosystem from single cells to sharks.
HAVE FUN!

Time
The Discovery Voyage lasts 4 hours.
Other programs range in length from 1-4 hours or programs may be combined for a full day adventure.

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Marine Science Institute - Planning Guide

Planning Guide
MSI has an extraordinary team of instructors that quickly engage students’ curiosity about the Bay. All of their adventures have students collecting, measuring, and studying marine organisms up close and personal. They offer a wide range of programs for every grade K-12, suitable for any budget and timeframe. See their School Programs page for details.

While the land-based programs are excellent, my recommendation is to go on the Discovery Voyage. Their 90 foot research vessel, the Robert G. Brownlee, sails out on 2 voyages virtually every day of the school year. It is one of the most fun-filled learning experiences I have ever had. They also provide an extensive Educator’s Guide that include a complete overview of the voyage as well as pre- and post-trip activities for the classroom (download it from the MSI website).

The trip begins with an overview of the geography of the San Francisco Bay and a rough sketch of the many organisms within its boundaries. From there students divide into groups to rotate through 4 stations.

  1. Hydrology – Students collect a water sample and measure the temperature, salinity and dissolved oxygen content of the Bay’s water.
  2. Plankton – Students lower a plankton net and collect a rich sample of the various microscopic organisms populating the water column. Using a microscope hooked up to a projector, students can study and classify the many types of plankton from diatoms to copepods.
  3. Benthic invertebrates – Students lower a mud trap to bring up the fine, sticky mud lining the bottom of the Bay. There students discover worms, crabs, sea anemones, shrimp and more.
  4. Vertebrates – Students operate a trawl net and capture a wide variety of vertebrates including bug-eyed flounder, and maybe even a shark or bat ray.

The ship accommodates 42 students (up to 60 students may be accommodated with $200 extra fee) and costs between $1,000 – 1,600 depending on the level of sponsorship and the number of students (a very reasonable $25 - 40 per student for what you get). In addition to their home port in Redwood City, they sail from many other ports of call around the Bay including San Francisco, Richmond, and the Sacramento/San Joaquin River Delta.

To schedule a program, contact Gail Broderick at: 650-364-2760 ext. 10 or gail@sfbaymsi.org

Project - Raising Plants

Summary
To study the life cycle and structure of plants, students grow plants from seed, fertilize them, and collect seed, starting the process over again. With the right growing conditions, almost any plant can be grown successfully in the classroom – native plants for a restoration project, vegetables, cut flowers, etc. The instructions provided here are for growing Wisconsin Fast Plants since they are the most widely used species in classrooms across America. These plants have been artificially selected to grow well in small spaces, with indoor lighting, with little soil, and with an exceedingly short life cycle (14-20 days to flower and 21-40 days to set seed). Therefore, they are incredibly well adapted to survive in classroom conditions as well as participate in multi-generational studies such as plant life cycle studies, Mendelian crosses and artificial trait selection. However, the light boxes and terraqua columns lend themselves to growing virtually any

Objectives
Can observe and document the stages of a flowering plant’s life cycle from seed to flower to seed.

Vocabulary
Brassia rapa (Wisconsin Fast Plants)
Seed
Embryo
Seed coat
Germinate
Radicle (embryonic root)
Hypocotyl (early stem)
Cotyledons (early leaves)
Leaf
Stem
Root
Flower
Fruit/seed pod

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Raising Plants - Logistics

Time
40-50 min to build a light box
20 min to build terraqua columns (See Terraqua Columns activity for details)
20 min to plant seeds
5-10 min to build bee sticks
5-10 min to fertilize on day 14-20
5-10 min to harvest seeds on days 21-40
Time to conduct experiments and make observations varies.

Grouping
Each light box fits up to 9 terraqua columns constructed from 500 ml water bottles. Each water bottle terraqua column can accommodate 4 mature Fast Plants. Determine the grouping size based on the experiment you plan to try. Calculate the number of terraqua columns and light boxes required.

Materials
Light box
For one light box you need:

  • Scissors
  • Box cutter
  • 1 banker box or copy paper box
  • 1 Lights of America™ 30 watt CircleLite (order from Energy Federation Incorporated part # 1140.05 for $9.95 each)
  • 1 single socket electrical cord (available at most hardware stores for $5-10, often used for paper lanterns, garage utility lights, or lamp-making kits)
  • Tin foil
  • Glue
  • Clear scotch tape
  • Optional: window screen material and duct tape (bugs may be attracted to your light box and the screens can help keep the bugs out)

Don’t want to build light boxes? Have money to spare? Order one ready-made! Carolina Biological has several options:

  • Plant Light House™ (catalog # 15-8994, one light box for $85) is similar to the one described in this lesson
  • Plant Light Bank™ (catalog # 15-8998, one light bank for $145) is a table-top version with long fluorescent bulbs.

Terraqua columns
For 30 terraqua columns you need:

  • Seeds (A wide variety of Wisconsin fast plant seeds may be purchased from Carolina Biological. Standard seeds are catalog #15-8804 and 15-8805, 50 seeds for $10 or 200 seeds for $24)
  • 30 clear plastic water bottles (500 ml)
  • 30 6-inch long wicks (use a strip of cotton towel or a string from a janitor’s mop)
  • Soil. Fast plants grow best in medium or coarse vermiculite (Vermiculite is a mica-like mineral that expands in an accordion-like fashion in water, and is thus used as a soil additive for water-retention. You can find it in most garden centers for around $5-8 for an 8 quart bag.)
  • N-P-K fertilizer. Required for fast plants but may be unnecessary for other species.

Don’t want to build terraqua columns? Have money to spare? Order growing systems ready-made! Carolina Biological has several options:

  • Seed Challenge: Exploring Life Cycles Kit (catalog #15-8973, $60) provides everything needed for a class of 32 to raise Wisconsin fast plants from seed to seed - including a curriculum guide - except the light box (there are kits available for many other standard experiments as well, including monohybrid crosses, dihybird crosses, butterfly-flower interactions and more)
  • Growing System (catalog #15-8993, $35) provides everything for a class of 32 students except seeds and the light box
  • Watering System (catalog #15-8974, one watering system for $9.25) is designed for use with Quads (catalog #15-8960, 16 quads for $6.70) these are the watering system developed by Carolina Biological specifically for Wisconsin fast plants. Each quad holds 4 plants and each watering system holds 8 quads.

Bee sticks (for pollinating your plants)
For 30 bee sticks you need:

  • Dried bees (Carolina Biological catalog #15-8985, $5 for around 70 bees)
  • Toothpicks
  • Elmer’s glue

Setting
Classroom

Raising Plants - Background

Teacher Background
Wisconsin Fast Plants (Brassica rapa) are an extraordinary resource for teachers since they have been selected for over 30 years for traits that make them ideal model organisms for the classroom. They thrive under fluorescent lighting, need very little soil, complete their life cycle in about a month, and take up very little space. Moreover, for under $50, a teacher can set up a classroom greenhouse and growing system for 32 students (2 light boxes and 18 terraqua columns growing 4 plants each).

There are 4 growing requirements for Fast Plants:

  1. They need fluorescent lighting 24 hours a day. Ideally, the lights should be situated 5-10 cm from the plants. Directions for how to build a light box are provided.
  2. They need continuous water and fertilizer. The easiest way to accomplish this is to grow the plants in a self-watering terraqua column or growing system with fertilizer added directly to the water reservoir.
  3. They need consistent room temperature (between 65–78 °F or 18–26 °C). If the temperature goes above 90 °F, the flowers will be sterile. Make sure that the fluorescent lights don’t become hot.
  4. The roots need the aeration provided by a potting mixture and will not grow well in regular soil. Use coarse or medium grained vermiculite and even better in a 1:1 mixture of vermiculite and peat.

Student Prerequisites
None

Raising Plants - Getting Ready

Getting Ready

  1. Build your own light box and terraqua column as an example to show the students.
  2. Collect enough banker boxes or copy paper boxes for your group.
  3. Create light box building kits with scissors, a box cutter, aluminum foil, glue and scotch tape.
  4. You may want to print out a copy of the light box building instructions as an overhead or make enough copies for each group to have one.
  5. See getting ready steps in the Terraqua Column activity for how to set up for terraqua column construction.

Raising Plants - Procedures

Procedures
To build a light box:
See the light box assembly directions on the Wisconsin Fast Plant website for detailed information.

  1. Distribute boxes, single socket electrical cords, circular light bulb and light box building kits to each group.
  2. Have students set their box on the table with one of the small, square ends down. That is now the bottom of the box.
  3. Use the box cutter to cut a one inch diameter hole in the top of the box. The screw end of the circular light bulb should just squeeze into the hole.
  4. Use the box cutter to cut long rectangular slits (4x14 cm) in the sides and of the box, near the top edge. These are vents to prevent your plants from overheating.
  5. Line the inside of the box with aluminum foil. Use glue to glue the foil securely to all sides, and the top and bottom of the box. Make sure you leave the top hole and vent slit open.
  6. Working from the inside of the box, insert the circular light bulb through the top hole.
  7. While 1 person holds the light bulb, a second person should screw the light socket onto the light bulb.
  8. Make an aluminum foil curtain for the front of the box. The curtain should completely cover the opening. Tape the curtain to the top of the box and reinforce the sides if desired with clear tape.
  9. Optional: Cut pieces of window screen material to cover the vent holes from the outside. Use duct tape to secure them in place.

To build a terraqua column:
See the lesson plan of the Terraqua Column activity for a description of how to build terraqua columns with students.

Day 0 - Plant Wisconsin Fast Plant seeds:

See the planting and fertilizing tips on the Wisconsin Fast Plant website for detailed information.

  1. Moisten the vermiculite so that it expands and is damp to the touch.
  2. Saturate the wick in water.
  3. Mix the fertilizer into the water. Use a 1 part liquid fertilizer to 8 part water mixture or follow the directions for the N-P-K fertilizer you plan to use.
  4. Insert the wick through the hole in the cap. Screw the cap onto the opening of the bottle.
  5. Invert the planter onto the reservoir. Make sure that the wick reaches all the way from the bottom of the reservoir to the top of the planter.
  6. Add water to the reservoir.
  7. Add moist vermiculite to the planter. When adding the soil, hold the end of the wick up and fill in the vermiculite around the wick. Make sure that the wick is not stuck against the side of the planter. Bury the top of the wick in the vermiculite.
  8. Drop 8-12 seeds onto the surface of the vermiculite. Seedlings will be thinned later to a maximum of 4 plants per terraqua column.
  9. Lightly cover the seeds with a thin layer of vermiculite.
  10. Lightly water the soil.
  11. Place the system into the light boxes. Place the tops of the terraqua columns 5-10 cm from the lights. Use books to prop them up to the right height.
  12. Have students make initial observations of their terraqua columns, noting the number of seeds planted.

Day 4-5 – Thin seedlings
By now, seedlings should have pushed through the surface of the soil. Thin your seedlings so that there are no more than 4 seedlings per terraqua column or 1 seedling per cell in a quad. Try to leave seedlings that are spaced reasonably far apart.

Days 5-14 – Maintain your plants and make observations
By now, your plants should be growing well. Make sure the water reservoirs are full of nutrient rich water (especially before the weekend). Make sure the lights are 5-10 cm away from the plants (use books to prop them up). Make observations of your plants as they grow. Some traits that are easily measured:

  • Number of days to germinate
  • Ratio of seeds germinated to seeds planted
  • Plant height
  • Number of days to first leaf
  • Number of leaves
  • Number of hairs on leaf margins
  • Leaf color
  • Stem color
  • Number of days to first flower bud
  • Number of flower buds
  • Water usage
  • Number of seed pods
  • Pod length
  • Number of days to seed pod maturity (tips of pods will turn brown)
  • Total number of seeds collected per plant or per pod

Before day 14 – Make bee sticks

  1. Distribute one dried bee and one toothpick to each student.
  2. Set out glue.
  3. Remove the head, legs, and abdomen of the bee, leaving only the round, fuzzy thorax region and the wings if you wish.
  4. Put a drop of glue on the top of the toothpick. You do not need much glue.
  5. Insert the glue covered tip into the thorax. You may wish to put the toothpick into one of the holes left when you removed the head or abdomen.
  6. Set the bee stick aside for the glue to dry.

Day 14-20 – Fertilize flowers
By now, the flowers should have bloomed. Take the bee stick and rub it against the anthers of a blossomed flower. Move to the flowers of a different plant and rub against the pistil. Continue fertilizing until all the flowers in the classroom have been cross-fertilized. See the pollination directions on the Wisconsin Fast Plant website for detailed information.

Day 21-40 – Collect seeds
See the fertilization and seed development directions on the Wisconsin Fast Plant website for detailed information.

  1. 10-20 days after the last fertilization, some of the pistils will have turned into long seed pods. When the tips of the pods turn from green to brown, the plants are ready to be dried. Remove the water from the bottom reservoir.
  2. Let plants dry for 7 days. The pods should be brown and crispy.
  3. Cut the stem of the plant below the bottommost pod and place the whole plant into a labeled paper bag.
  4. Seal the bag with tape or staples then crush the plant inside, breaking up the pods thoroughly to release the seeds.
  5. In a shallow tray, pour out the contents of the bag. Pick out the large pieces of stem, leaves and pods.
  6. The smallest pieces of broken pod can be separated from the seeds by gently blowing across the surface of the tray. The pod pieces will blow away.
  7. Seeds may be stored in a labeled paper envelope. To store seeds for a year or more, place the envelope in a ziplock bag with silica gel (one of those packets often found with dried foods to absorb moisture).

Raising Plants - Experiment Ideas

Experiment Ideas
See activity ideas on the Wisconsin Fast Plant website for detailed information.

  1. Life Cycle – Raise Fast Plants from seed to seed. At each stage of the life cycle, discuss and study what the plant is doing. Discuss seeds, germination, growth, flowering, pollination, fruiting, and seed dispersal. Have students draw a life cycle diagram, adding a labeled picture of their plant at each stage of the life cycle. See the Fast Plants Life Cycle activity guide for a great diagram of the life cycle and information about the plants at each stage of life.
  2. Plant Traits – Examine the variation in plant traits. Pool the observations students made during the growth and flowering phases of the plant life cycle. Examine and graph the population data to determine whether there is a bell curve distribution of traits such as plant height. See the Growth, Development, and Flowering activity guide and the Getting a Handle on Variation activity guide for two different ways to conduct a study of plant traits and variation in a population.
  3. Artificial Selection - Sponsor an artificial selection program for hairiness (or height) in Fast Plants. Breed Fast Plants over several generations, always selecting either the most hairy or the least hairy plants to cross fertilize. For each generation, carefully quantify the number of hairs on each individual and construct a histogram showing data for the whole population. See the Hairy's Inheritance: Selection, Variation, and Inheritance activity guide for detailed information.
  4. Ecology – Experiment with environmental variables - salinity of the water, light conditions, nutrient supply, population density, pollution, or other factors – and monitor differences in plant growth and development. See any of the activities under Ecology, Environment, and Interactions Between Abiotic and Biotic Factors for detailed lesson plans.
  5. Coevolution – Investigate the coevolution of insects and flowering plants. Study the thorax of a bee under a dissecting microscope or strong magnifying glass. Look at the shape of the hairs on the bee’s body and its relationship to pollen. See the Flowering and Pollination - Pollination Biology activity guide for detailed information. Alternatively, raise Fast Plants and butterflies together in the same light box, studying their symbiotic relationship. See Brassica butterfly activities and rearing guide on the Wisconsin Fast Plant website.

Raising Plants - Sources and Standards

Sources
For information on Wisconsin Fast Plants, see:

  • The Fast Plants website with just about everything you ever wanted to know about Fast Plants including growing tips, activities and more.
  • Wisconsin Fast Plants Manual (Carolina Biological catalog #15-8950, $28)

Standards
Grade 6
Ecology (Life Sciences)
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
a. Students know energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs.
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
f. Students know that as multicellular organisms develop, their cells differentiate.

Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
a. Students know the differences between the life cycles and reproduction methods of sexual and asexual organisms.

Evolution
3. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.
f. Students know the structures and processes by which flowering plants generate pollen, ovules, seeds, and fruit.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.

Project - Raising Trout

Summary
Raising trout from eggs to fry in the classroom is a fabulous way for students to observe and study the life cycle of vertebrates and simultaneously learn about threatened species in local watersheds. Many states have programs where teachers and students raise trout in their classrooms in partnership with the Department of Fish and Wildlife for later release into a designated lake, creek or river. Described here is information for teachers on how to partner with state agencies, fish hatcheries, and local fly-fisher groups to raise rainbow trout in the classroom. A worksheet for the trout release field trip is provided. Best of all, many Trout in the Classroom Programs are fully supported by local fly-fisher groups and the California Department of Fish and Game (such as the California program that I participated in), and thus there is no materials cost to the teacher beyond the costs of organizing the trout release field trip at the end of the project.

FIsh Release: Atlantic salmon release in New Hampshire. Image contributed by the National Conservation Training Center.FIsh Release: Atlantic salmon release in New Hampshire. Image contributed by the National Conservation Training Center.Objectives
Can observe and document the stages of a trout’s life cycle from egg to fry.
Can describe the environmental conditions needed for trout survival in the classroom and in local habitats.

Vocabulary
Anadromous salmonids
Trout
Salmon
Steelhead/rainbow trout (Oncorhynchus mykiss)
Eggs
Alevin
Yolk sac
Fry
Juvenile
Smolt
Spawn
pH
Dissolved oxygen
Nitrates
Migration barrier
Diversion
Competition
Non-native species
Channelization

AttachmentSize
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Raising Trout - Logistics

Time
30 min set up tank
1 week for tank to equilibrate
1 month (approximately) between fertilization and hatching
2-3 weeks from hatching to release
Time required for the trout release field trip varies depending on the distance from your school and desired activities at the release site.

Grouping
The raising and care of the fry takes place as a whole class. During the trout release field trip, students may collect data in groups of 4 students.

Materials
Trout or salmon eggs are provided by your state’s Department of Fish and Wildlife, often through a local fish hatchery. Usually, a training workshop is required to participate, and a permit to transport and rear eggs is required from the state.

Aquarium set up (many state agencies and their partners offer the following equipment for classroom use for free):
1 10 gallon aquarium tank
1 undergravel filter
1 pump for undergravel filter (such as the Powerhead 201 pump from Hagen Aquaclear, available at most aquarium stores for $15-20)
Pea gravel, enough to cover the bottom of the aquarium to a depth of 1 inch
1 aquarium chiller or refrigeration unit that can maintain a 10 gallon tank at a stable 50°C (try the Cool Works Ice Probe Model IPWC-50W and power supply Cool Works P/N 5239, available at specialty aquarium supply companies for $100-120)
Aquarium thermometer that can monitor 1°C intervals between 40-60°C
10 gallons of non-chlorinated spring water
Aquarium net
Turkey baster (for siphoning away unhatched eggs
Aquarium insulation (make a Styrofoam box to surround your aquarium using insulating Styrofoam sheets available at most hardware stores)
Optional: if not using insulation, you will need a heavy black cloth to protect the alevins from UV radiation

For water testing
Dissolved oxygen test kit (see Water Analysis lesson for sources)
pH test strips

Setting
Trout are raised in the classroom then released on a field trip to a local lake, creek or river.

Raising Trout - Background

Salmon alevins: Just hatched salmon with yolk sacs. Image courtesy of U.S. Fish and Wildlife Service.Salmon alevins: Just hatched salmon with yolk sacs. Image courtesy of U.S. Fish and Wildlife Service.Teacher Background
Raising trout provide a fabulous way to introduce students to the life cycle and physiological requirements of other species. Moreover, you can use these fish to teach students about threatened and endangered species.

Oncorhynchus mykiss (rainbow trout or steelhead trout) are the most commonly encountered species in classrooms. They are native to the West coast of North America but have been introduced to oceans, lakes and rivers world wide. They are a highly prized game fish in many North American rivers.

They belong to a class of fish known as salmonids that includes salmon and trout. Salmonids are anadromous, that is, they are born in fresh water but may spend much of their adult lives in the ocean, returning to the rivers in which they were born to spawn and lay their eggs. The freshwater form of Oncorhynchus mykiss is called rainbow trout. These fish may spend their entire lives in fresh water. The saltwater form is known as steelhead trout. These are generally larger than rainbow trout and can find their way back to the stream of their birth to spawn and lay eggs. Steelhead are then able to migrate back to the ocean and repeat the cycle several times in their life. Salmon, the other genus of salmonids, die after spawning and do not return to the ocean. For more information on the trout life cycle, see the Nevada Trout in the Classroom website.

Rainbow trout: Image courtesy of US. Fish and Wildlife ServiceRainbow trout: Image courtesy of US. Fish and Wildlife ServiceIn order for young trout to survive to adulthood, several conditions must be met:

  1. They need high quality water. There must be high levels of dissolved oxygen (6-9 ppm), cold water (ideally 45-55°C), high winter flows and continuous summer flows.
  2. They need loose, pea-sized gravel for females to form nests and lay their eggs.
  3. They need cover for hiding from predators. Undercut banks, rocks, gravel and wood debris are ideal.
  4. They need a plentiful food supply. The hatchlings are known as alevins and will feed on their yolk sac until it is gone. Thereafter, they are known as fry and will eat plankton and aquatic invertebrates such as mayflies, caddisflies, damselflies, and other insects. When they reach maturity they smolt (change their physiology in order to survive in salt water), migrate to the ocean, and eat shrimp and small fish.

Each of these factors (besides the food supply since the alevin will have a yolk sac while in the classroom) must be carefully recreated in the classroom aquarium. Steelhead are classified as a threatened species since water diversion (dams), migration barriers (culverts, roads, and walls), habitat destruction, introduced species and creek disturbances (pollution, trash, dogs, erosion, etc.) have dramatically reduced the amount of acceptable habitat.

Different parts of the country have different programs for teachers to raise salmonids in their classrooms, each with its own set of rules and regulations. See the Procedures below to get in contact with a program near you. Information on how to set up a tank and care for your fish can be downloaded from Trout Unlimited. Curriculum resources may be downloaded from the Nevada Department of Wildlife.

Student Prerequisites
None

Raising Trout - Procedure

Procedure
To start a Trout in the Classroom program at your school, contact your state’s Department of Fish and Wildlife or find a local chapter of Trout Unlimited. These agencies sponsor training programs for teachers to show them how to set up an aquarium, get eggs, raise the fry, and release them into designated ecosystems. For specific resources, see the list of selected programs below:

  • Nationwide – A flourishing Trout in the Classroom program is administered through Trout Unlimited. Any state with a chapter of Trout Unlimited can participate (find your local chapter using this interactive map). For more information on the Trout in the Classroom program, contact Rochelle Gandour at (718)595-3503 or e-mail her at rgandour (at) tu.org
  • California – The California Department of Fish and Game sponsors the California Classroom Aquarium Education Project. Resources, training and equipment is provided by the state and by local fly-fishing groups.
  • Nevada – The Nevada Department of Wildlife sponsors the Trout in the Classroom program. Resources, training and equipment is provided by the state.
  • Washington – The Washington Department of Fish and Wildlife sponsors a Salmon in the Classroom project.
  • New England (New York, Massachusetts, New Hampshire, etc.) – The Adopt-a-Salmon program has partnerships with river associations throughout the region to sponsor salmonids in the classroom.
  • New Jersey – The New Jersey Division of Fish and Wildlife sponsors the Trout in the Classroom program in collaboration with Trout Unlimited.

On your trout release field trip, organize students into groups and assign each group an area of the creek, stream or river to survey. Groups are responsible for collecting data about the quality of the habitat and whether the newly released trout will have what they need to survive. Gather data on factors such as temperature, dissolved oxygen content, pH, shade, cover, and food availability. See the Water Analysis activity or the Habitat Survey activity or the Sediment Study project for details. A handout is provided but should be adapted to your specific release site.

Raising Trout - Standards

Standards
Grade 6
Ecology (Life Sciences)
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
a. Students know energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs.
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. As a basis for understanding this concept:
f. Students know that as multicellular organisms develop, their cells differentiate.

Genetics
2. A typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. As a basis for understanding this concept:
a. Students know the differences between the life cycles and reproduction methods of sexual and asexual organisms.

Evolution
3. Biological evolution accounts for the diversity of species developed through gradual processes over many generations. As a basis for understanding this concept:
a. Students know both genetic variation and environmental factors are causes of evolution and diversity of organisms.
e. Students know that extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient for its survival.

Structure and Function in Living Systems
5. The anatomy and physiology of plants and animals illustrate the complementary nature of structure and function. As a basis for understanding this concept:
a. Students know plants and animals have levels of organization for structure and function, including cells, tissues, organs, organ systems, and the whole organism.
b. Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.

Assessment - Life on Mars

Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.Mars Exploration Rovers: This special-effects image combines a model of the Mars rover Opportunity and 46 photogrpahs that Opportunity took of "Burns cliffs" near the edge of "Endurance Crater". Image courtesy of NASA/JPL-Caltech/Cornell.

Summary
In the summer of 2003, NASA’s Jet Propulsion Laboratory launched two Mars Exploration Rovers - Spirit and Opportunity - towards Mars. They landed on January 3rd and 4th, 2004. Their primary scientific goal was to study the geology of Mars and search for signs of water. Although they were expected to last only 3 months, they have been vigorously sending back data for over 2 years and are still going strong! In this activity, students receive simulated Martian soils and are given the task of designing 3 tests to determine whether the soil sample contains something alive or something that was once alive. They may use any of the tools from the previous lessons – agar plates, tests for organic molecules, microscopes, or something of their own design. This assignment allows students an opportunity to demonstrate what they have learned throughout the unit, both about scientific experimentation and about the special characteristics of living things.

Objectives
Can describe the necessary characteristics of life.
Can categorize objects as alive or not alive using self-generated data.
Can demonstrate that all living things will grow and reproduce when provided with the proper nutrients and environmental conditions.
Can demonstrate that living things are made of organic molecules.
Can test for the presence of protein, glucose and starch.
Can design an experiment.
Can make observations and keep track of data over several days.
Can interpret the results of an experiment.

Vocabulary
Characteristic
Agar
Nutrients
Yeast
Organic molecule
Protein
Biuret solution
Carbohydrates
Glucose
Benedict’s solution
Starch
Iodine
Microscope

AttachmentSize
assess_life_on_mars.doc68 KB
mars_soil_handout.doc2.13 MB
mars_soil_handout.pdf1.62 MB

Life on Mars - Logistics

Time
10 min introduction
20-30 min design experiments
35-50 min conduct experiments (some tests may need to be left overnight)
20-30 min discuss experiments

Grouping
Groups of 2-3 students

Materials
For all tests:

  • A copy of the Testing Martian Soils handout for each student
  • permanent markers
  • masking tape or labeling tape
  • hand lenses

For soil samples, enough for a class of 30 students in teams of 3:

  • 30 ziplock bags
  • 3 cups clean playground sand (no organic material should be present so carefully strain or wash the sand if necessary)
  • 8 packages fast-acting yeast (2 ounces total)
  • 4 Alkaseltzer® tablets, crushed

For nutrient milkshake:

  • 500 ml distilled water
  • 85 g table sugar (around 6 tablespoons)
  • 85 g all purpose white flour (around 6 tablespoons)
  • 1 liter bottle or flask

For agar plates (see Life Trap activity for ordering information):

  • 50 sterile disposable plastic 15 mm x 100 mm Petri dishes
  • 15 g agar agar powder
  • 2 beef bouillon cubes
  • 40 g table sugar (around 3 tablespoons) ** Unlike the plates made for the Life Trap activity, sugar is required for agar plates that yeast will happily grow on. If your agar agar powder is pre-sweetened, then no additional sugar is necessary. **
  • 1 liter distilled water
  • stove and large pot for preparing nutrient agar and steam sterilizing the Q tips
  • Q tips
  • paper towels
  • bleach

For organic molecules tests (see Testing for Life activity for ordering information):

  • Copy of test station directions at each test station (see Testing for Life activity)
  • Biuret solution
  • Benedict’s solution
  • Iodine tincture
  • beakers or cups
  • test tubes
  • test tube racks
  • eye droppers
  • trays or bins to keep the materials for each test station
  • small 100 ml beakers or squeeze bottles to contain test reagents
  • Optional: large squeeze bottles of water (500 ml disposable plastic water bottles are fine) for rinsing test tubes at test stations rather than going to a sink
  • large beakers or cups to dump waste materials
  • hot plate or source of boiling water
  • insulated containers such as a thermos or Styrofoam cup for creating a hot water bath
  • Optional: thermometers to monitor the temperature in the hot water bath
  • disposable latex gloves

For microscope test:

  • dissecting scope, although a light microscope at low power will also work
  • slides or Petri dishes


Optional for introduction:

  • computer with digital projector to show students slide shows or videos of the Mars Exploration Rover Mission (see Sources section for details)

Setting

Classroom 

Life on Mars - Background

Teacher Background
Mars, Blueberries, and Hematite
Mars Rover - Spirit: This special effects image of the Mars Exploration Rover Spirit was created using a rover model and an image taken by the Spirit navigation camera. Image courtesy of NASA/JPL-Caltech.Mars Rover - Spirit: This special effects image of the Mars Exploration Rover Spirit was created using a rover model and an image taken by the Spirit navigation camera. Image courtesy of NASA/JPL-Caltech.The Mars Exploration Rover mission provides the inspiration for exciting science experiences. These two rovers represent incredible feats of engineering and have contributed vast piles of data for geology and astrobiology research.

This lesson is built around the discovery of Martian “blueberries” by the rover Opportunity in Meridiani Planum. The blueberries aren’t really blue – they’re actually grey – nor are they the size of blueberries – they are only around 3 millimeters in diameter. When they were first observed scattered across the floor of Meridiani Planum, their composition was an enticing mystery.

Closeup of "blueberries": This image, taken by the rover&#39;s microscopic imager, clearly shows the sphere-like grains or "blueberries" that fill Berry Bowl. Image courtesy of NASA/JPL-Caltech.Closeup of "blueberries": This image, taken by the rover's microscopic imager, clearly shows the sphere-like grains or "blueberries" that fill Berry Bowl. Image courtesy of NASA/JPL-Caltech.What are they? Their uniformity and symmetrical shape calls to mind the bacterial and fungal colonies grown on agar plates. Could they once have been living things, now frozen or fossilized on the surface of Mars? What about the 3 fused berries in the picture? Does this capture the process by which berries reproduce? That is the question posed to students in this activity, however, this is not a theory supported by scientists. Scientists guessed that the blueberries were concretions, formed when water rich in minerals permeates into porous rock then evaporates, leaving behind the hardened minerals in the spaces. Although originally buried within the rock, as the surrounding rock weathered away, the concretions were freed and left to roll around on the Martian surface.

Berry Bowl with "blueberries": This image from the Mars Exploration Rover Opportunity&#39;s camera shows the rock called "Berry Bowl" in the "Eagle Crater" outcrop. Image courtesy of NASA/JPL-Caltech.Berry Bowl with "blueberries": This image from the Mars Exploration Rover Opportunity's camera shows the rock called "Berry Bowl" in the "Eagle Crater" outcrop. Image courtesy of NASA/JPL-Caltech.For several long weeks, the blueberries were too small and scattered to be analyzed accurately with Opportunity’s scientific instruments. Thus the scientists’ theory could not be confirmed. Finally the rover reached a spot nicknamed the “Berry Bowl”. There, enough blueberries had collected in one place for the rover to use its Mössbauer, thermal emission, and alpha particle X-ray spectrometers to decipher its chemical make-up. By comparing the berry cluster in the Berry Bowl with a berry-free patch nearby, scientists were able to determine that the blueberries are composed of hematite (or haematite).

Hematite is the mineral form of iron oxide (rust). It is very common on Earth and is generally found in places where there has been standing water or mineral hot springs. However, it may also be formed volcanically. So, does the hematite blueberries on Mars indicate the former presence of water or were the blueberries formed volcanically? The presence of fused blueberries, like the triplet berry near the center of the image strongly argues that these blueberries were formed through the action of liquid water. Volcanically formed beads are unlikely to fuse along a line in this fashion.

More information on the Mars Exploration Rover mission is available on the NASA/JPL website and specific links of interest to this lesson are provided in the Sources section.

Tips for Teachers
Be aware of several tips as you embark on this open-ended experiment.

The yeast will remain active when added to the nutrient milkshake for a few hours until they run out of nutrients to sustain their growth. Adding more milkshake will reinvigorate the culture.

For students to grow yeast on agar plates, the nutrient agar must include sugars for the yeast to digest. This differs from the agar plates described in the Life Trap activity in which no sugar was required. In addition, it is best to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water) and seed the plates with a Q tip dipped in the solution. Dry yeast get too little moisture from the plates alone to grow effectively.

To test for organic molecules, it is important to dissolve the yeast-soil sample in water first (approximately 1 part yeast-soil to 2 parts water). Only the protein test will yield a positive result. If you want to increase the rate of positive results, add 2 tablespoons of flour to the yeast-soil mixture. This will make the starch test give a positive result as well without interfering with any of the other tests the students might conduct.

Student Prerequisites

Students need a thorough understanding of the characteristics of life and must be equipped with several means of testing for life such as growing microbes on agar plates or nutrient-rich solutions, testing for organic molecules, observing cells under the microscope, etc. See the Life Trap, Testing for Life, and Seeing Cells activities.

Life on Mars - Getting Ready

Getting Ready 

For soil samples:

  • Sample #1 - Distribute 1 cup clean sand into 10 ziplock bags, around 1.5 tablespoons per bag. Label these “Sample #1”.
  • Sample #2 – Mix 1 cup clean playground sand with 4 thoroughly crushed Alkaseltzer® tablets. Distribute the mixture into 10 ziplock bags, around 1.5 tablespoons per bag. Label these “Sample #2”.
  • Sample #3 – Mix 1 cup clean playground sand with 8 packages yeast. Distribute the mixture into 10 ziplock bags, around 1.5 tablespoons per bag. Label these “Sample #3”.

For nutrient milkshake: combine 500 ml distilled water, 85 g table sugar, and 85 g all purpose white flour in a 1 liter bottle or flask.

For agar plates: see Life Trap activity for directions on how to mix nutrient agar and pour plates.

For organic molecules tests: see Testing for Life activity for directions on how to set up test stations.

Life on Mars - Lesson Plan

Lesson Plan

  1. Open the lesson with a description of the Mars Expedition Rover mission. Show students pictures and, if possible, videos of the rovers and the blueberries that were discovered.
  2. Pass out the handout and describe the challenge. NASA has given the class samples of “Martian soils” including “crushed blueberries”. It is the job of each team of students to design 3 tests to determine whether any of the soil samples contain something alive or something that once was alive. They must carefully select the “best” group of 3 tests and write down detailed procedures for how they plan to conduct each test.
  3. Describe the materials (especially the nutrient milkshake since this is new to the students) and the different tests available for the students to try. You may want to point out that most of the tests students conducted previously were done with liquids, not solid soil samples. Therefore, for SOME tests, students may wish to mix their sample with water (1 part sample to 2 parts water)
  4. Answer any questions then distribute soil samples and hand lenses.
  5. Get the students started making initial observations and discussing their experimental design in groups. The experiment should roll along from here. Once students have 3 tests designed and written down, they should come to you for approval before conducting the tests. Soon, students will be conducting various experiments and making discoveries. Expect teams to finish at different rates. Some tests, like the agar plate test, may require 24 hours to see results. Expect to spend at least 2 class periods or more on this activity. Encourage teams that finish early to work on the conclusion questions.
  6. When all the data has been collected, discuss the results and their conclusions as a class. Compare the results of the different tests and see whether a unified picture emerges. Discuss conflicting results and the reasons they might have appeared.
  7. Inform students that the soil samples weren’t actually from Mars. Allow them to discuss what they think was in each sample but don’t reveal the actual ingredients. Many of my students took some of the samples home to further experiment with them and figure out what was in each one.
  8. Tell the students what the actual Mars blueberries were found to be – hematite – and why that discovery is important for understanding the history of Mars and the possibility of discovering life on other planets. 

Life on Mars - Going Further

Going Further

  1. See the Imax movie “Roving Mars”. The animation is absolutely incredible. Sadly, little of the scientific discoveries on Mars itself are discussed in the movie but the engineering that went into designing the rovers and getting them to Mars is clearly and dramatically shown.
  2. After completing this activity, bake the soil samples at 200 degrees for 30 minutes, or microwave them on high for 5 minutes, to kill the yeast. Then do the activity again. The nutrient milkshake and agar plate tests should now show negative results but the protein test should still detect the presence of the yeast.
  3. Study other aspects of Mars such as its size, gravitation, planetary history, etc. NASA provides an extensive list of Mars-related lesson plans.
  4. Investigate what the “blueberries” really are – beads of hematite. Bring in samples of hematite and test some of its physical properties using methods described in the History of Rock activity. Hematite stats:
    • Hardness - 6.5, comparable to pyrite
    • Color – reddish grey, reddish brown, grey, dark grey
    • Density - 5.3
    • Luster – metallic
    • Streak – reddish brown
    • A neodymium magnet will show a weak attraction for hematite, regular magnets will not.

Life on Mars - Sources

Sources
This lesson was inspired by a workshop by Steve Ribisi of the University of Massachusetts and Mission 10 from the Life in the Universe curriculum, published by the SETI Institute.

To learn more about the Mars Rovers, go to the NASA/JPL website. The following are some of the highlights from this site that may be used in conjunction with this lesson:

  • NASA/JPL produced incredible computer animation sequences documenting the challenge of sending the rovers safely to Mars. I showed my students these videos as a prelude to assigning them an egg drop challenge - each student is given a chicken egg and must design a way to safely cushion the eggs fall from a third story window.
  • Read the latest update about the rovers to find out what they are up to.
  • To inspire girls in your class to pursue careers in engineering, show them this webcast of women engineers on the Mars NASA team.
  • Explore the Mars Fun Zone, a site packed with games and activities designed for kids to learn more about Mars.

To learn more about blueberries and hematite, see:

Standards
Grade 6
5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment. As a basis for understanding this concept:
e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.

Grade 7
Cell Biology
1. All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope.

Structure and Function in Living Systems