Do Photosynthetic Algae (cyanobacteria) Respond to CO2 Change?

Organisms and Carbon Dioxide
(Snails and Elodea)

Background Information

Organisms interact with many substances in nature.  One such substance is carbon dioxide which is exchanged during the processes of food-making in autotrophs, such as green plants, and breathing in most of Earth’s other living things.  Carbon dioxide is exchanged between these organisms and their environments.

In this investigation you will discover how organisms exchange carbon dioxide gas in their environments.  The investigation uses bromthymol blue, which turns yellow when carbon dioxide is added to a solution, and blue when carbon dioxide is removed from a solution.
 
 


Problem

How is carbon dioxide exchanged between organisms and their environments?

Materials

2 snails     light source
bromthymol blue solution   glass-marking pencil
aged tap water     2  300ml jars with lids
2 straws     graduated cylinder metric ruler
Elodea plant     2 test tube racks
10 large test tubes with corks
 

Procedure

  1. Fill both jars with aged tap water.  Add several drops of bromthymol blue to the water and shake the solutions gently.  The water should turn an even shade of blue.
  2. In one jar, gently exhale through a straw into the solution until it turns yellow.  You will use both the blue and the yellow solutions to set up your experiments.
  3. Label the test tubes 1 to 10.  Fill test tubes 1 to 6 with the blue solution.  Fill test tubes 7 to 10 with the yellow solution.
  4. Place a 4 cm  long piece of Elodea plant in test tubes 1, 2, 7, and 8.
  5. Place one snail in test tube 3 and one snail in test tube 4.
  6. Test tubes 5, 6, 9, and 10 will be the controls.
  7. Record initial observations of each test tube.
  8. Place test tubes 1, 3, 5, 7, and 9 near a strong light.  At the same time, place test tubes 2, 4, 6, 8, and 10 in a very dark area, such as in a closet, cabinet, or covered box.
  9. Observe each test tube for any color changes during the next laboratory period.  Record any changes in the Data Table.

Observations
Data Table
Color of  Solution

Test Tube Set-ups
Test Tube Set-up Initial Color  Color After 24 Hours (circle)
1 Elodea plant in light Blue Blue or Yellow
2 Elodea plant in dark Blue Blue or Yellow
3 Snail in light Blue Blue or Yellow
4 Snail in dark Blue Blue or Yellow
5 Blue solution in light Blue Blue or Yellow
6 Blue solution in dark Blue Blue or Yellow
7 Elodea plant in light Yellow Blue or Yellow
8 Elodea plant in dark Yellow Blue or Yellow
9 Yellow solution in light Yellow Blue or Yellow
10 Yellow solution in dark Yellow Blue or Yellow

Focus

1.  Why did the solution in test tube 2  change color?


2.  Why did you use a control in the experiment?  

3. Why did the solution in test tube 7 change color?  

4. Why did the solutions in test tubes 3 and 4 change color?
 

Research  Questions

1. During what processes is carbon dioxide exchanged between plants and their environments?  Explain your
answer?

 

2. What gas is present in the air you exhale?  What evidence do you have to support your answer?

 

3.   What gas is present in the air you exhale?  What evidence do you have to support your answer?

 

Inquiry Questions

1.  Design an experiment in which you would show that carbon dioxide is given off when bicarbonate of soda is added to water.

 2.  Test several different pond plants for the amount of carbon dioxide given off during respiration.  Obtain three different aquatic plants from a pond.  Fill three test tubes with bromthymol blue solution.  Place a piece of one plant in the first test tube, a piece of another plant in the second test tube, and a piece of the third plant in the third test tube.  Label each test tube with the name of the plant.  Place the test tubes in a covered box.  After 24 hours, record any color changes.  Add a drop of ammonia to the first test tube and stir once between drop until the solution turns blue.  In a chart, record the number of drops of ammonia needed.  The number of ammonia drops will represent the amount of carbon dioxide produced by the plant.  Repeat this for the remaining two test tubes.  Why did the plants utilize varying amounts of carbon dioxide when placed in the same conditions?

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