Lab: Investigating Photosynthesis and Cellular Respiration

Name ______Date ______Period ______

Background: All organisms are dependent on a healthy carbon dioxide-oxygen balance. Photosynthesis and cellular respiration are key processes in maintaining this balance. Plants, through the process of photosynthesis, use energy absorbed from sunlight, water, and carbon dioxide to produce sugars and oxygen. Animals and plants, through the process of cellular respiration, use oxygen and sugars to produce carbon dioxide, water, and the energy needed to maintain life.

Purpose: To determine how carbon dioxide cycles through a biological system by performing the “Carbon Transfer Through Snails and Elodea” lab activity.

Procedure: 1. Read through the background information and purpose. Create your own question for what you are investigating in this experiment. a. Problem (in question form):

© 2014 – All rights reserved. www.cpalms.org 2. Obtain 8 test tubes of equal size/volume and number the test tubes 1-8. Fill each test tube with approximately 30 mL of deionized water. 3. Add enough bromothymol blue (BTB) indicator to solution to each test tube to change the water to a green color (about 3 mL). 4. What is Bromthymol Blue? Why is the BTB in the test tube green (Hint: recall the teacher demonstration)?

5. If snails use lungs to breathe, you can conclude that they release which gas into their environment as a result of respiration?

6. If Elodea is an aquatic plant, you can conclude that it releases which gas into its environment as a result of photosynthesis?

7. Next, place the following items in each appropriately labeled test tube. Test Tube Number Added Contents #1 and #5 Water Only #2 and #6 2 snails #3 and #7 2 sprigs of Elodea #4 and #8 2 snails and 2 sprigs of Elodea

8. Place test tubes 1-4 in a test tube rack and place the rack under a growth light. 9. What is the purpose of the growth light?

10. Place test tubes 5-8 in a test tube rack and place the rack under a test tube rack cover. 11. What is the purpose of the test tube rack cover?

© 2014 – All rights reserved. www.cpalms.org 12. Make your predictions below: Test Conditions Contents of Predict Color and Explain Tube Tube # 1 Light 2 Light 3 Light 4 Light 5 Dark 6 Dark 7 Dark 8 Dark

Predict - Explain how carbon dioxide (CO2) cycles in aquarium water through snails and Elodea. Complete the following statement to develop your own hypothesis.

If I add a snail and elodea to a test tube with bromthymol blue, then ______.

Explain: Why do you think this outcome will occur?

Read This: The independent variable in an experiment is the variable that 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.

1. Identify the dependent variable (what you, the scientist, will measure) in this experiment:

Now you must wait 24 hours. (make sure you clean up your station!)

© 2014 – All rights reserved. www.cpalms.org Data/Results: Yesterday, you filled 8 test tubes with the following contents. Carefully remove your test tube racks from the light or dark conditions and complete the tables below with your observations.

First Test Tube Rack – Placed under the growth light: Test Tube with Independent Beginning Color Color Result BTB Variables Color Prediction Tube # 1 Water Only Tube #2 2 snails Tube #3 2 Elodea Tube #4 2 snails, 2 Elodea

Second Test Tube Rack – Placed under the test tube cover: Test Tube with Independent Beginning Color Color Result BTB Variables Color Prediction Tube # 1 Water Only Tube #2 2 snails Tube #3 2 Elodea Tube #4 2 snails, 2 Elodea

Conclusions: Complete the following sentences.

1. In the test tubes which contained only snails, ______. 2. In the test tubes which contained only Elodea under the light, ______3. In the test tubes which contained only Elodea in the dark, ______. 4. In the test tubes which contained both snails and Elodea under the light ______.

2. Analyze. Why did the color of the Bromthymol Blue (BTB) solution change in certain test tubes?

3. Analyze. What was the importance of a control in your experiment? What would you conclude if the color of the solution in the control changed?

4. Infer. When you began the experiment, was there CO2 in the water? In the test tubes that contained Elodea, where did the CO2 go?

5. Infer. Which gas did the snails release? What observation supports this inference?

7. Assess.

Write the balanced chemical equation for photosynthesis below (label reactants and products).

Write the balanced chemical equation for cellular respiration below (label reactants and products).

Draw a diagram below of your results: