Sunscreen Experiment

Experiment to demonstrate that light is necessary for the process of photosynthesis:

Requirements: Light screen, a potted plant and iodine.

Method:

1. Take a potted plant and make its leaves destrached by keeping it in dark for one or two days.

2. Fix a leaf of this plant in between the Ganong’s screen.

3. In the black paper or black tin foil disc of the screen, cut a pattern of some kind (like P) and fix it on the screen.

4. Keep the whole apparatus in sunlight.

Due to this light screen, some parts of the leaf are covered whereas other remaining parts are exposed to light.

5. Remove the leaf from the screen after a few hours, and test for starch with the help of iodine.



Observations

In the region of the letter ‘P’ the leaf shows positive iodine test. 

Results:

The observations indicate that the iodine test is positive only in the regions of the leaf which were exposed to sunlight (P) while on the other hand the unexposed regions show negative iodine test for starch. Because the ultimate product of photosynthesis is starch, hence it can be concluded that it is formed only in those regions which remain exposed to sunlight and not in others. So, light is essential for photosynthesis.