Rate of Photosynthesis

Photosynthesis is the process by which plants take carbon dioxide from the atmosphere, add water, and use the energy of sunlight to produce sugar. Write the equation for photosynthesis:

Photosynthesis occurs in the chloroplast, an organelle in plant cells that contains the molecule chlorophyll. Chlorophyll absorbs the energy of sunlight. That light energy is converted to chemical energy through the steps of photosynthesis.
The reactions of photosynthesis can be divided into two major types: light-dependent reactions and light-independent reactions. The light-dependent reactions convert energy from the sun into a form that the chloroplast can then use to make sugar from carbon dioxide, in the process producing oxygen as a waste product. The light-independent reactions use that energy to make glucose from carbon dioxide and water.

Materials: test tube, Elodea cuttings, sodium bicarbonate (baking soda), beaker with water, lamp

Procedure:

1. Obtain a sprig of elodea. Remove several leaves from around the cut end of the stem. Slice off a portion of the stem at an angle and lightly crush the cut end of the stem.
2. Place the sprig in a test tube, cut side up. Add water to test tube and a pinch of baking soda.
3. Place the test tube into a beaker filled with tap water.
3. Place a lamp next to the beaker. - The water in the beaker will help to absorb the heat from the light, thus reducing the variables in the experiment
4. Turn on the lamp. As soon as see small bubbles coming from the cut end of the stem, time the reaction for 10 minutes. If you do not see bubbles, cut the stem again and recrush.
5. Calculate the net photosynthesis in bubbles/min. (Divide the number of bubbles by 10 minutes.)
6. Remove your test tube from the bright light. Observe and record the rate of bubbles without direct light.

Data

Analysis

1. What are the bubbles? Explain why bubbles happen.

2. Did the number of bubbles change when the light intensity was reduced? Explain why this would occur.

3. Why was the test tube placed in a beaker of water? What is a variable and why is it important to eliminate them?

4. What was the purpose of adding sodium bicarbonate (baking soda) to the plant? Hint: look at the formula for photosynthesis