Biological Systems Interactions

Description of Activity:

Overview

In this long term experimental activity, students will build on skills and concepts gained through class discussions related to biological relationships found in nature. They will perform a short, pre-lab activity that introduces them to the use of Bromthymol blue to detect carbon dioxide. A problem will be posed: What is the biological relationship between a pond snail and a pond plant? The activity will provide students with the opportunity to generate and test alternative hypotheses, design an experimental investigation, and share and verify results with peers.

Duration of Activity

Lab investigation - two to three days

Verification labs, peer review, assessment - one to two days

Materials:

• Twenty pond snails
• Twenty Elodea sprigs
• 20-30 glass vials with screw cap lids
• 4-5 Dropper bottles of "Bromthymol blue" solution
  To make the stock solution add 0.04 g Bromthymol blue powder to a two liter bottle of distilled water. Shake, if not blue, add drops of 0.1 M NaOH.
• Labeling tape
• marker
• NaOH solution
  The Sodium hydroxide solution can be made by adding 4 g NaOH to one liter distilled water.

Students will also need access to areas in the classroom that are light for 24 hours (Grow lights work best) and areas that can remain dark for 24 hours (closets, cabinets, etc.). If using a sunny window for light, experiments may take longer than 24 hours.

Background Information:

Students should be comfortable using Bromthymol blue.

Teaching and Learning Strategies:

Ensure inquiry
The teacher should provide the purpose but not the answers in this investigation! Do not provide the hypotheses and experimental setups to the students. Allow them the opportunity to discover this themselves!

Elements of a good science experiment

Prior to this lab, give the students several experiences in following methods that scientists use to design and conduct experiments. Students should be grouped in collaborative teams of four to six.

Alternative strategies

• Have teams design experimental setups for more than one hypothesis. (Depending on time and number of students).
• To extend this investigation, have student teams create their own pond ecosystem models using terrariums or two liter. bottles. Students could experiment with water samples from their own ecosystem models and might also compare results with pond samples taken from a local outdoor area.

Development of Lab Skills and Tools:

Background

In order to teach the students how to use Bromthymol blue as an indicator for the presence of carbon dioxide in water, have the students conduct the following pre-lab and write observations on their data/write-up form. Explain to the students that carbon dioxide acidifies water. The color of Bromthymol blue is an indication of the presence or absence of carbon dioxide in a water sample. Carbon dioxide can introduced it to a water sample by exhaling through a straw then using the Bromthymol blue indicator solution to test for acidity.

Activity

Make sure you have students sign and keep the Safe Operating Procedures Contract in their binder.

Procedure

1. Fill a 50 ml. glass beaker about 1/3 full of tap water.
2. Add about 7 drops of Bromthymol blue. If the solution isn't blue add NaOH, one drop at a time, and stir until blue.
3. Gently blow through a straw into the Bromthymol blue solution. Note any color changes as you continue to blow until there is no more color change.
4. Carbon dioxide can be removed from a solution with NaOH. Add
   enough drops of 0.1 NaOH to the solution until it is blue again, and note the color changes that occur.
5. Answer the following questions in your data write-up:
   • When carbon dioxide is not present in water what color will the Bromthymol blue indicator be? (blue)
   • When carbon dioxide is present in water what color will the Bromthymol blue indicator be? (yellow- the solution is acidic.)
   • What is happening when the Bromthymol blue solution is green in color? (the solution has been neutralized).

Data and write up information

Invitation to Learn:

Problem: Determine the biological relationship between a pond animal such as a snail and a pond plant such as Elodea.

After completing the pre-lab, introduce several examples of the relationships between plants and animals in various environments. Introduce diagrams of different cycles and interactions that can occur (these can be found in most life science textbooks). Ask students to think about questions such as: (Do not give answers to students. To do so would compromise inquiry).

• Do you think that these interactions apply to all plants and animals? (The teacher should lead students to understand that the diagrams may not apply to all plants and animals, there might be exceptions).
• Do you think that these interactions occur in both light and dark?
• Do you think these relationships would apply to pond animals and plants?
  Assign students to generate diagrams of what they think the interactions might be between plants and animals in a pond environment (This could be homework). Have teams compare and contrast the interactions depicted in the student diagrams and tell them that the experiments they will conduct will help them to discover one such relationship found in nature. Tell the students that when scientists conduct investigations their hypotheses can either be supported, contradicted or not supported.

Instructions

1. Present the problem and ask the students to formulate as many hypotheses as possible related to the problem (list these on chalkboard or overhead projector). In order to make sure that they generate as many hypotheses as possible, remind them of the question: Does this happen in both light and dark?
2. Assign each team to be in charge of designing a setup, conducting an investigation, collecting data and reporting a conclusion for a hypotheses that has been generated.
3. Remind students not to leave Bromthymol blue solution in with snails.
4. Each team should prepare a summary report of findings to be communicated to other teams the following day in the form of an oral presentation.
5. Have teams exchange setups, verify lab findings, and do a peer review using the Scoring Rubric/Peer Review sheet attached at end of the activity.
6. After verification, teams should be allowed to move to other stations in order to observe, interpret, and record data related to carbon dioxide use and production.
   Possible hypotheses and experimental set-ups that might be tested by teams. (Remember - Do not give hypotheses to the students!)

Test	Expected Result
Snails produce CO2. Vial 1 (control): H2O, few drops Bromthymol blue Vial 2: H2O, Bromthymol blue, snail Place in light for 24 hour	All vials start out blue showing no CO2 present. After 24 hours, vials with snails should be yellow showing CO2 production. Control should remain blue.
Elodea uses CO2. Vial 1 (control): H2O, Bromthymol blue Vial 2: H2O, Bromthymol blue, Elodea Sprig Introduce CO2 with straw to both. Place in light for 24 hours.	Both vials start yellow. Vial with Elodea should turn blue in 24 hours. Elodea does use CO2 in light.
Elodea use CO2 that snails produce. Vial 1 (control): H2O, Bromthymol blue Vial 2: H2O, Bromthymol blue, snail, Elodea Sprig Place in light for 24 hours.	(This is a 2-day sequence). After 24 hours, the vial with the snail should be yellow. Exchange Elodea for snail and leave overnight. Vial should turn back to blue since Elodea do use the CO2 that snails produce. The vial in the dark should remain yellow. Elodea do not use CO2 in the dark (they produce it!) Some teams might want to put snail and Elodea in the same vial for 24 hours. Debate pros and cons of this later.
Snails produce CO2 in the dark. Vial 1 (control): H2O, few drops Bromthymol blue Vial 2: H2O, Bromthymol blue, snail Place in dark for 24 hours.	All vials start out blue showing no CO2 present. After 24 hours, vials with snails should be yellow showing CO2 production. Control should remain blue.
Elodea use CO2 in the dark. Vial 1 (control): H2O, Bromthymol blue Vial 2: H2O, Bromthymol blue, Elodea Sprig Place in dark for 24 hours.	Elodea solution should not turn blue since it does not take in CO2 in the dark.
Elodea use CO2 that snails produce in dark. Vial 1 (control): H2O, Bromthymol blue Vial 2: H2O, Bromthymol blue, snail, Elodea Sprig Place in dark for 24 hours.	(This is a 2-day sequence). After 24 hours, the vial with the snail should be yellow. Exchange Elodea for snail and leave overnight. Vial should turn back to blue since Elodea do use the CO2 that snails produce. The vial in the dark should remain yellow. Elodea do not use CO2 in the dark. Some teams might want to put snail and Elodea in the same vial for 24 hours. Debate pros and cons of this later.
Elodea produce CO2 in dark. Vial 1 (control): H2O, Bromthymol blue Vial 2: H2O, Bromthymol blue, Elodea Sprig Place in dark for 24 hours.	Both set-ups start out blue. After 24 hours, the experimental vial should be yellow. The control remains blue. Elodea does produce CO2 in the dark.

Hint:

An important and tricky part in doing this experiment is the color of the starting solutions. An alternative approach is to start with Bromthymol blue that is acidified with carbon dioxide but then brought back to the green neutral color. Then all experiments would start with the same Bromthymol blue solution. Some would stay green, some would turn yellow (more carbon dioxide produced), some would turn blue (carbon dioxide absorbed). For inquiry purposes, tell students they have different options for setting up the Bromthymol blue solutions at the start of the experiment.

Safe Operating Procedures

• Prior to the pre-lab activity, review with students the cautions on the Safe Operating Procedures Contract form. Remind students that sodium hydroxide is corrosive and contact with skin should be avoided. They should also be cautioned about not sucking on the straw. If contact occurs, skin should be flushed with water and teacher should be notified. Have students sign Safe Operating Procedures Contract forms.
• Students should also be reminded that caps on vials should be loose. About 2 to 3 cm. of air space should be left at top of vials during their experiments.
• In order to practice safe and humane handling of live organisms students should be reminded not to leave Bromthymol blue in with snails. For the sake of inquiry, allow them the opportunity to determine how to accomplish this!

Student Designed Experiment:

Experiments are performed to solve a problem or answer questions! Students will design and do experiments under guidelines such as the following:

1. Observations
2. Formulate a question, pose a problem, What If?, Wonder why, etc.
3. Predict an answer, formulate a hypothesis, prediction, guess, (hypothesis based upon observation and experiences).
4. Design a test of hypothesis, design a procedure, be clever, repeat test, include measurements, vary only one thing at a time (independent variable). Control other variables (control). The dependent variable is the thing that changes and you measure.
5. Test hypothesis, perform experiment, collect data on a data sheet, avoid bias, measure accurately.
6. Analyze Results, record data, graph data, compare and contrast data, avoid bias, use appropriate graphing techniques ( bar, line, pie ) report data.
7. Conclusions, meaning of results, hypothesis proven or disproved, conclusion should not exceed scope of the hypothesis.
8. Report experiment, write up experiment, discuss results, Oral Report. Results should communicate to the intended audience.
9. Verification of conclusion, other scientists verify findings.
10. Communicate findings.

Summary of Learning:

Assessment

Multiple choice questions

1. Draw a diagram (using plants and animals) to correctly illustrate the dependent relationships between animals and plants. Include the following:
   A. Solar radiation/energy
   B. Subsurface water
   C. Decomposition producing minerals
   D. Surface water
   E. Oxygen
   F. Producer (food source)
   G. Carbon dioxide
   H. Primary Consumer
2. When carbon dioxide is present in water what color will the Bromthymol blue indicator be? (B. yellow - the carbon dioxide has acidified the water)
   A. blue
   B. yellow
   C. red
   D. no color (clear)
3. The following statements are all true except: (c. Elodea produces carbon dioxide in the dark )
   A. Snails produce carbon dioxide in the light or dark.
   B. Elodea uses carbon dioxide that snails produce.
   C. Elodea uses carbon dioxide in the light or dark.
   D. Elodea produces carbon dioxide in the dark

Free response questions

1. Describe how the relationships discovered in the snail-Elodea lab are similar to the above illustration. How are the relationships different?
2. Of what value are chemical indicators to scientists? Could this lab have been performed without the use of the indicator? How?
3. Describe the effects upon balanced ecosystems when numbers of plants or animals are dramatically or suddenly altered.

Extensions:

Strategies and tools to share findings:

• Students may conduct verification labs between teams or class periods.\
• Students can record their activity in a "Journal of Findings".
• The entire lab may be written for a portfolio assessment.
• The lab design and findings may be published in the "WEB" newsletter of the Utah society for Environmental Education or the Utah Science Portfolio produced by the State Office of Education. Both documents encourage and publish student research.
• School newspapers and yearbooks should also be notified of student research projects.
• Investigate Internet communications to discuss experiment and share findings.