Carbon Transfer Through Snails and Elodea Lab
Name / # ________________________
Go to http://www.classzone.com/cz/books/bio_07/resources/htmls/virtual_labs/virtualLabs.html select California,
select the lab.
Procedure
Follow the steps to the lab given on the screen until you complete all seven (7) steps. You will need to fill in information
in the virtual lab notebook as you go to make the activity work, but you will only be graded on what you put on this
assignment sheet.
Problem
Read through the problem tab. What is the question that you are trying to investigate in this experiment?
a.
Explore:
Read and explore the lab to learn what is available to you in your investigation. You must click on each item in the
checklist. Describe the materials you will be using in this lab.
a. What is Bromthymol Blue/what does it test for? Why is the BTB in the beaker green?
b. If snails use lungs to breathe, which gas would they release into their environment as a result of respiration? ______
c. If Elodea is an aquatic plant, which gas would it release into its environment as a result of photosynthesis? ________
d. What is the purpose of the growth light? ____________________________________________________________
e. What is the purpose of the test tube rack cover? _______________________________________________________
f. Draw the picture seen on the CO2 – O2 Cycle poster.
g. Use the color key to determine: if no carbon dioxide is present in your test tube it will be a ____________ color. If
a medium amount of CO2 is present, your test tube will be a _______________ color. If a large amount of CO2 is
present, your test tube will be __________________.
Hypothesis:
Propose a reason why the Elodea is important to the snail.
__________________________________________________________________________________________________
__________________________________________________________________________________________________
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Now, transform your proposed reason into an if/then/because hypothesis that could be tested.
If (something testable)___________________________________________________________________________
then (an outcome goes here)_____________________________________________________________________
because (provide reasoning) _______________________________________________________________________
______________________________________________________________________________________________
The independent variable in an experiment is the variable which will be altered by you, the scientist. In the case of this
experiment, the independent variable will be the number of snails and/or number of elodea plants in each test tube.
a. Identify the dependent variable (what you, the scientist, will measure) in this experiment (given in notebook).
b. How will you measure it? Think back to the exploring the lab section!
Data/Results:
You will be using 8 test tubes for this experiment. Fill your test tubes and perform the experiment according to the data
chart found below.
First Test Tube Rack – Placed under the growth light:
Test Tube With BTB
Tube #1 (control)
Tube #2
Tube #3
Tube #4
Independent
Variables
No snails, No Elodea
2 snails
2 Elodea
2 snails, 2 Elodea
Beginning Color
Color Prediction
Color Results
Color Prediction
Color Results
Green
Green
Green
Green
Second Test Tube Rack – Placed under the test tube cover:
Test Tube with BTB
Tube #1 (control)
Tube #2
Tube #3
Tube #4
Independent
Variables
No snails, No Elodea
2 snails
2 Elodea
2 snails, 2 Elodea
Beginning Color
Green
Green
Green
Green
Analysis: Complete the following sentences AFTER filling in the results
a. In the test tubes which contained only snails…
b. In the test tubes which contained only Elodea under the light…
c. In the test tubes which contained only Elodea in the dark…
d. In the test tubes which contained both snails and Elodea under the light…
e. In the test tubes which contained both snails and Elodea in the dark…
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Discussion:
1. Analyze. Explain what happened in general with the following color changes in the Bromthymol Blue (BTB) solution.
From green to yellow:
From green to blue:
2. Determine possible error. What was the importance of a control in your experiment? What could you possibly
conclude if the color of the solution in the control changed to yellow? How would this alter your final conclusion?
3. Infer. When you began the experiment, was there CO2 in the water? In the test tubes that contained Elodea, what
happened with the CO2? Is there a difference between the light and dark reactions? Why?
4. Infer. Which gas did the snails release? What observation supports this inference?
5. Conclude/Apply. Based on the results of your experiment, explain why you need to add the Elodea to your snail
aquarium. Was your hypothesis supported?
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