How can you prove the essentiality of CO 2 and sunlight for photosynthesis?

The carbon dioxide and sunlight are the two factors which are essential for photosynthesis. This can be proved by experiments. i) Experiment to prove CO 2 is essential for photosynthesis. Take two healthy potted plants and keep them in dark for 24 hours to destarch the leaves. After that cover them with glass jars. Take some crystals of KOH and place it under one of the jars. Keep the set up airtight. Keep the plants in sunlight for 2-3 hours. Collect a leaf from each of the plants. Boil the leaves in water and alcohol to remove chlorophyll. Now conduct the iodine test for starch in each leaf. OBSERVATION: Only one leaf turned blue-black which shows the presence of starch. CONCLUSION: KOH absorbed CO 2 present in one jar. So photosynthesis did not occur in this case and starch is not synthesised because of the unavailability of CO 2. This shows that CO 2 is essential for photosynthesis. ii) Experiment to prove Sunlight is essential for photosynthesis. Take a potted plant in dark for 24 hours. Then stick black paper on both sides of a leaf. Now place this plant in sunlight for a few hours. Pluck the leaf and remove the tape from it. Boil the leaf in water and alcohol to remove the chlorophyll from it. Now conduct an iodine test on it. OBSERVATION: The covered region did not turn black, indicating the absence of starch. CONCLUSION: This covered region did not receive light and no starch was formed because photosynthesis did not occur in the absence of light. This shows that sunlight is essential for photosynthesis.