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NOTE: This lab is to be done under the supervision of an adult since it contains chemicals toxic to human life if ingested (eaten).

Introduction: The process of photosynthesis and respiration are vital to all life on earth. Photosynthesis, carried out by plants and algae provides the foodstuffs upon which most organisms depend for their existence. It is the only process which is able to trap the Sun's energy and convert it to usable food in the form of carbohydrates (glucose). Plants, animals, and humans, must carry out respiration. Carbon dioxide and water are the two end products of respiration. They are also the raw materials for photosynthesis. So both processes depend on each other. In this exercise the water plant Elodea will be used to study both processes.

Purpose: The purpose of this lab exercise is to study the relationship of carbon dioxide to the processes of respiration and photosynthesis.

Materials:

• Elodea plant
• Brom thymol blue (BTB)
• Indicator
• Cork
• 4 test tubes
• Test tube rack
• Straw
• China marking pencil
• Flask

Method:

1. Pour some brom thymol blue into a flask.
2. From the flask with the brom thymol blue blue solution, fill TWO test tubes about 2/3 full.
3. Create bubbles in the flask with the leftover BTB solution by breathing into a straw inserted into the flask with the BTB until the liquid turns yellow-green. (Warning: Do not under any circumstance ingest the BTB Solution, so only exhale into the straw, do not inhale through the straw as the BTB solution is TOXIC!!!!)
4. Pour the yellow-green BTB into the other 2 empty test tubes.
5. Prepare other the 4 test tubes as follows:
• #1. brom thymol blue + elodea plant - Place in the dark.

• #2. brom thymol blue + no plant - Place in the dark as a control.

• #3. brom thymol yellow-green + plant - Place in the light.

• #4. brom thymol yellow-green + no plant- Place in the light as a control.