Question

Explain with activities that plants need $H_2O$ and $CO_2$.

Answer 1

Plants are the photoautotrophs. They can convert carbon dioxide present in the atmosphere to a chemical energy source that is carbohydrate or glucose. This process is known as photosynthesis. In this process, water is also essential along with sunlight.

Complete answer:
To solve this question, we need to perform one experiment which will prove that water and carbon dioxide are essential for plants.
For this we need a healthy potted plant, a glass bottle with cork, KOH solution and iodine solution.

Procedure:
• The healthy potted plant was kept in the dark for 2-3 days.
• In a wide mouth glass bottle, 10-15 ml of KOH solution was added and the cork was split vertically.
• The half of the leaf part was put into a glass bottle and the other was exposed to the air. This was left for 4 hours.
• The leaf from the plant was removed and was tested for starch.

Observation:
• The part of the leaf kept inside the KOH solution did not show any colour change.
• The other part turned dark brown which shows the presence of starch.
• From the above experiment we can conclude that carbon dioxide and water are key factors for photosynthesis. The part inside the glass bottle did not receive carbon dioxide and carbon dioxide so the photosynthesis did not take place.

Note: Iodine solution is an indicator for starch. It turns black-brown in the presence of starch. Potassium hydroxide absorbs carbon dioxide liberating potassium carbonate. It is widely used to absorb carbon dioxide from the surface.