Rate of Photosynthesis in Elodea Underwater Plant Vs. Light Intensity

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.

Introduction:

Purpose: to determine the effects of light intensity to rate of photosynthesis.

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

Methods:

Procedure:

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

2) The end of the stem at the site of incision was gently crushed.

3) The plant was fully submerged into a test tube filled with room temperature water.

4) That tube was set on a test tube stand.

5) A light source was placed 50 cm away facing the test tube.

6) The light source was powered on and observations were made.

7) The number of bubbles generated was counted in10 second, 30 second, and 1 minute intervals for each trial.

8) Steps one through seven were repeated with different conditions on each consecutive experiment. On the second trial the light source was placed at 40 cm from the test tube with the plant. On the third trial the light source was 30 cm away. On the fourth trial the test tube was 20 cm away. On the fifth trial the light source was placed 10 cm away from the test tube.

9) Lastly, room conditions were used for the control group. This was done by observing the plant by itself at room lighting without the extra lamp light source. Bubbles generated were counted in 10 second, 30 second, and 1 minute intervals.

Results:

Data Table:

Number of Bubbles Counted (bubbles) vs. Distance of plant from Light Source

10 seconds30 seconds1 minute
No Lamp92850
50 cm1549110
40 cm1755112
30 cm1854115
20 cm2470145
10 cm3094201

It was difficult to count all of the bubbles generated in 1 minute. There may have been several errors in counting in the experiment because bubbles formed quickly. Therefore we used some estimates in our calculations for number of bubbles formed per minute. There was a trend that showed that more bubbles were formed when the lamp was placed closer to the test plant.

Conclusion/Discussion:

Under the given conditions, the plants being tested were able to undergo photosynthesis. This is apparent by the product created by the plants. Oxygen released by the plants showed that photosynthetic reactions had taken place. Furthermore the amount of oxygen generated indicated the rate of which photosynthesis reactions were occurring. In plants where the light source was of closer proximity more oxygen products were found to be produced. The closer the light was to the plant, the greater light intensity it provided. This demonstrates that greater light intensity enabled more accelerated photosynthesis as more products were able to form faster.