Effect of Light on Photosynthesis

Purpose: This experiment served to determine the affects of light intensity on the rate of photosynthesis in the underwater plant elodea. It was found that the rate of photosynthesis in the plant was accelerated when placed in closer proximity to a constant light source. The rate of photosynthesis was measured by counting the amount of oxygen, a product of photosynthesis, generated by the plant. When the plant placed closer to the light source in a given time it generated more bubbles than when it was placed farther away from the light source.

Photosynthesis can be described by the following chemical reaction:

Light + 6CO2 + 6 H2O -> Glucose + 6O2

With this in mind, the efficiency of photosynthesis during a specified time period can be calculated by measuring the amount of product formed from the above reaction. The plants tested in this experiment were underwater plants (Elodea) and the rate of photosynthesis was measured by the amount of oxygen produced by the plant through photosynthesis. The amount of oxygen produced was measured by counting of the number of bubbles that formed and floated to the surface from the submerged plant. The affects of different light intensities was determined by the amount of bubbles produced from various intensities of light.

Hypothesis: If photosynthesis is more efficient in stronger light, then more products will be formed faster in photosynthetic reactions.

Materials:

1) Aquatic plant (Elodea) 

2) Test tubes 

3) Watch 

4) Water (at room temperature) 

5) Lamp (light source) 

6) Knife/Scissors 

7) Ruler

Limiting factors: The main factors affecting the rate of photosynthesis are light intensity, CO2 concentration and temperature. In any given situation any one of these may become a limiting factor, in other words the factors that directly affects the rate at which photosynthesis can take place masking the effects of the other factors.

Method:

1) A segment of plant of approximately 8cm was cut with scissors.

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