Huntington Library, Art Collections and Botanical Gardens
As You Like It Overview The class works as a team to gather evidence on what carnivorous plants like to “eat” and draws conclusions on why it likes or responds to certain foods over others. Introduction A plant is carnivorous if it attracts, captures, and kills animals. The sundew (Drosera) is an example of one such plant. After catching its prey, the sundew digests the animal using enzymes secreted from glands located in its leaves. The digestive enzymes dissolve the protein in the prey, much as we dissolve our own food. These enzymes include many of the enzymes we use in our digestion; proteases, esterase, acid phosphatase, and amylase. The sundew then absorbs the nutrients from the prey, leaving a desiccated body behind. More than 600 species and subspecies of carnivorous plants have been described (although humans have caused some to become extinct). There are many noncarnivorous plants that have some (but not all) of the characteristics of carnivory (attract, capture, kill). For example, flowers attract pollinators (such as bees, or birds); some plants (such as orchids, and waterlilies) temporarily trap insect pollinators to ensure pollen transfer. All plants absorb nutrients either through their roots or leaves. It is only carnivorous plants that do all these things together. So why do carnivorous plants capture animals? In the wetlands that house carnivorous plants, there are very few nutrients available for plants, particularly nitrogen and phosphorous. “Why?” you ask. In wetland environments where the water is not moving fast or refreshed by streams, chemicals like tannins released by decaying plant matter can become concentrated. These chemicals make the water acidic and because of this acidity, many microorganisms that aid in decomposition cannot function. Therefore, when plants die they don’t rot, they just become waterlogged. With little decomposition, there are few nutrients for plants. The soil also becomes very acidic and it is difficult for a plant to assimilate nutrients in acidic conditions. Noncarnivorous species that live there have a difficult time obtaining necessary nutrients and do not do well. However, with the carnivorous plants’ adaptations of capturing prey, they have found a different way to obtain nutrients, and so can survive. Catching bugs gives the carnivorous plants a competitive advantage over the noncarnivorous plants. In environments with plenty of available nutrients, the ability to catch bugs does not confer an advantage to carnivorous plants. So while a carnivorous plant would be using all this energy to capture prey, other plants would be putting energy into growing taller and stronger. The noncarnivorous plants would outcompete the carnivorous plants. Why is nitrogen so important to plants? The element nitrogen, while making up 80% of the atmosphere, is very hard to get in a bioavailable form. Some plants have evolved symbiotically with nitrogen fixing bacteria to help solve this problem. Nitrogen, despite being hard to get, is incorporated into all amino acids and therefore all proteins. It is also used in a number of high energy reactions, critical for everyday living.
It was Charles Darwin that discovered that it was the element nitrogen that these plants were after in their carnivory. He published his results in 1875. To test his hypothesis that plant carnivory was primarily a means to obtain nitrogen, he made extracts of a number of common sources that contained nitrogen and a control set that did not contain nitrogen. He tested these solutions to see which ones elicited a “prey” type response. Motivation Ask the class “Why do carnivorous plants ‘eat’ bugs? Is bug eating just a quick and tasty meal on the go for the busy plant, or is there a method to their madness?” Objectives Upon completion of the lab students will be able to 1. Draw the structure of a protein, a sugar, and of starch. 2. Discuss how plants acquire nitrogen, and especially how carnivorous plants acquire this element. 3. List the adaptations of the sundew (Drosera) to living in a bog. 4. Discuss how a plant or animal species adapts to an environment and how that is different from an individual adapting to adverse conditions. Materials · Sundews (Drosera sp.) · Distilled water · Saturated sugar solution · Starch solution (cornstarch and water in roughly a 1:2 ratio) · Olive oil · Whole milk
· Meat infusion · Decoction of chopped green cabbage leaves · Tea · Colored thread or tape · Egg · Droppers for each solution
Standards Addressed 1h. Students know most macromolecules (polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors. 5a. Students know the general structures and functions of DNA, RNA and protein. 6a. Students know biodiversity is the sum total of different kinds of organisms and is affected by alteration of habitats. 6d. Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the ecosystem and how oxygen cycles through photosynthesis and respiration. 6g. Students know how to distinguish between the accommodation of an individual organism to its environment and the gradual adaptation of a lineage of organisms through genetic change. 7a. Students know why natural selection acts on the phenotype rather than the genotype of an organism. 7c. Students know new mutations are constantly being generated in a gene pool. 8a. Students know how natural selection determines the differential survival of groups of organisms.
Procedure 1. Prepare small aliquots of each of the liquid solutions listed above. To make a decoction of cabbage leaves, chop and boil half a head of cabbage in about 2 cups of distilled water. Boil for about 1 hour until most of the water is gone, and the remaining liquid is cloudy and light green or yellow. To make a meat infusion, chop a small amount of raw meat and place in a small amount of water let sit in cold place sealed for 20 hrs. You will need to prepare enough solutions for each group. 2. Have the groups place a drop (~ .03 ml) of one test solution on the center of a sundew leaf. Make sure they pay close attention to what the leaf looks like at the start and have them sketch it. Recommend to students that they choose only leaves that are living, full grown, flat, and have no bugs on them already. 3. Have student groups label the leaf with the solution. A piece of tape works well. Colorcoded thread can be a good label as well. 4. Have students repeat this process with as many leaves as possible. 5. Have students make observations of leaf inflection at 24 and 48 hours and record their observations in the data table. 6. If you have abundant sundews you can have students test different solutions on the same day. This may not be practical, so you can perform this experiment over multiple days. Each round should be allowed 48 hours for observation. 7. If you want to have students test a leaf that had previously been tested with a non nitrogenous solution with a nitrogenous one, you can. This will demonstrate that the leaf was alive and capable of responding. The leaf will respond, but maybe a bit slower in response—it is “tired”. Evaluation The following questions are listed under the Analysis section of the student handout and may be used as part of a report, class discussion or assessment. 1. What is your control in this experiment and why is it the control? 2. What types of solutions does the sundew respond to most? Do these solutions have anything in common? 3. What solutions did the sundews respond least to? Are their any commonalities between these solutions? 4. If you tested a leaf that showed no response with a solution, how can you be sure the lack of response is due to the solution and not to the leaf itself (i.e., how do you know the leaf isn’t dead or dying)? 5. What are the molecular components of the solutions you tested? 6. On a separate sheet of paper, draw the basic chemical structure of: a protein’s monomers, a starch’s monomers, and a lipid. 7. Draw the basic chemical structure of a protein. 8. What do you think the sundew is responding to in the solutions you tested? 9. Where do sundews typically live? 10. Why do you think the sundew has evolved to “eat” insects, and how do you think this evolution might have occurred? 11. Discuss how plants in other habitats acquire nitrogen.
12. Discuss how humans obtain nitrogen and what they use it for. Extension Activities 1. Students can read Insectivorous Plants by Charles Darwin (particularly Chapter Five) and write a detailed report that illustrates the similarities and differences between their tests on sundews and those that Darwin performed. 2. Using the Internet or the library, students can write a report on a bog in the United States. Reports should include where the bog is, how large is it, what type of carnivorous plants live there, what animals live there, and how are these other plants and animals adapted to living in this bog. 3. Students can write an article for the rest of the class, based on research in newspapers, the library, and the Internet about the dangers of adding too much nitrogen into our environment. How does supplemental nitrogen affect plant growth and the health of our water systems? Students should include in the article a definition of eutrophication. Test Preparation 1. Selection acts directly on (A) the phenotype (B) the genotype (C) an allele (D) the entire genome (E) a community 2. Carnivorous adaptations of plants mainly compensate for soil that has a relatively low content of (A) potassium (B) nitrogen (C) calcium (D) water (E) phosphate
Student Sheet: As You Like It
Name:___________________
Procedure 1. Have one person from your group get the test solution(s) from your teacher. 2. Place a drop (~ .03 ml) of one test solution on the center of a sundew leaf (choose only leaves that are living, full grown, flat, and have no bugs on them already). 3. Pay close attention to what the leaf looks like at the start and sketch it on a piece of paper. 4. Label the leaf that you just placed the solution on. A piece of tape or colorcoded thread works well. Use the label material your teacher has prepared for you. 5. Repeat this process with as many leaves/solutions as possible. 6. Make observations of these leaves at 24 and 48 hours and record your observations in the data table. Also sketch the leaves at the various time points. Table of Leaf Response to Various Solutions Solution Total number Number of Number of leaves of sundew sundew leaves unaffected after 24 leaves tested affected after 24 hrs. hrs.
Number of leaves affected after 48 hrs.
Distilled water Olive oil Milk Tea Egg Sugar Cabbage leaf extract Corn Starch Raw meat extract
Analysis On a separate sheet of paper please complete the following: 1. What is your control in this experiment and why is it the control? 2. What types of solutions does the sundew respond to most? Do these solutions have anything in common? 3. What solutions did the sundews respond least to? Are their any commonalities between these solutions? 4. If you tested a leaf the showed no response with a solution, how can you be sure the lack of response is due to the solution and not to the leaf itself (i.e., how do you know the leaf isn’t dead or dying)? 5. What are the molecular components of the solutions you tested? 6. On a separate sheet of paper, draw the basic chemical structure of: a protein’s monomers, a starch’s monomers, and a lipid. 7. Draw the basic chemical structure of a protein. 8. What do you think the sundew is responding to in the solutions you tested?
9. Where do sundews typically live? 10. Why do you think the sundew has evolved to “eat” insects, and how do you think this evolution might have occurred? 11. Discuss how plants in other habitats acquire nitrogen. 12. Discuss how humans obtain nitrogen and what they use it for.
Huntington Library, Art Collections and Botanical Gardens
Supplement to “As You Like It” So you don’t have a field of sundews for your class to try this experiment on, or you need the answers much more quickly. Here is a variation that combines a demonstration using two plants, or even two different leaves of your plant and a tabulation of Darwin’s experimental data. Demo: Have a solution of distilled water and a solution of cabbage extract (boil cabbage in distilled water for 12 hours, until concentrated liquid and remove cabbage pieces). Place the solutions in bottles labeled “A” and “B”. It doesn’t matter which one is labeled “A or B” so long as you know which solution is which. Place a drop of each solution on different leaves, or on several leaves of different plants. Make sure you label each leaf with which solution was placed on it. You can use tape or colorcoded thread as label material. Make observations 24 hours and 48 hours later. Which solution did the sundew respond to? How can you tell it responded? Have students draw what the leaves look like before and after response. Discussion: Lead a discussion on what the plants might be responding to. Ask students where carnivorous plants live? What are bogs? Why are they nutrient poor? What types of nutrients do plants need? If a plant’s surroundings are poor in nutrients, what mechanisms does the plant adapt to getting those nutrients? What types of things do we eat that have nitrogen in them? What do our bodies use nitrogen for? Experimental Design: Have the students in small groups design an experiment to confirm the hypothesis that that plants are responding to solutions that have high nitrogen levels. Their experiment should include their experimental control; what solutions they would use; how they would make up those solutions; how many plants they will need; how they will know if the plants respond to the solution; how long will they wait to see if there is a response; and how many times they would repeat the experiment. Have the students’ hand in their experimental design as a research proposal. Evaluations of Darwin’s Data Once you’ve collected the students’ experimental designs, you can tell them that Darwin did such an experiment to discover if the sundew plant was trying to acquire nitrogen as he hypothesized. Hand them out the attached student worksheet with Darwin’s tabulated results.
Darwin’s Experimental Results
Solution Distilled water Olive oil Milk Tea Gum Arabic Human Urine Alcohol Egg Sugar Cabbage leaf extract Peas Corn Starch Raw meat extract
Number of sundew leaves inflected 0 0 16 0 0 12 0 7 0 18 4 0 1
Number of leaves not inflected after 24 hrs. 35 11 0 10 14 0 3 1 14 0 0 6 0
Analysis On a separate sheet of paper please complete the following: 13. What is the control in this experiment and why is it the control? 14. What types of solutions does the sundew respond to most? Do these solutions have anything in common? 15. What solutions did the sundews respond least to? Are their any commonalities between these solutions? 16. If you tested a leaf that showed no response with a solution, how can you be sure the lack of response is due to the solution and not to the leaf itself (i.e., how do you know the leaf isn’t dead or dying)? 17. What are the molecular components of the solutions you tested? 18. On a separate sheet of paper, draw the basic chemical structure of: a protein’s monomers, a starch’s monomers, and a lipid. 19. Draw the basic chemical structure of a protein. 20. What do you think the sundew is responding to in the solutions you tested? 21. Where do sundews typically live? 22. Why do you think the sundew has evolved to “eat” insects, and how do you think this evolution might have occurred? 23. Discuss how plants in other habitats acquire nitrogen. 24. Discuss how humans obtain nitrogen and what they use it for.