Question

Describe an experiment to show that sunlight is essential for photosynthesis

Answer 1

We know that oxygen gas supports combustion. When a glowing matchstick is brought close to the mouth of a test tube containing oxygen gas, it relights. This confirms the presence of oxygen gas. So, we can show that oxygen is evolved during photosynthesis with the help of following activity :

1) Take an aquatic plant such as hydrilla (a few twigs).

2) Place these twigs in a glass jar or a beaker containing water. Add a small amount of NaHCO3 to the beaker to ensure the availability of CO2 to the plant. 

3) Place an inverted glass funnel over these twigs. 

4) Invert a test tube filled with water over the stem of the funnel. Keep this set up undisturbed for sometime in sunlight. 

5) Carefully remove the test tube and bring a burning matchstick close to the mouth of the test tube. The matchstick burns more brightly. This proves that oxygen is evolved during photosynthesis