Question

A sudden increase in carbon dioxide concentration around a leaf will cause
A. Wider opening of stomata
B. Increase in transpiration
C. Closure of stomata
D. Decrease in transpiration due to closure of stomata

Answer 1

The opening and closing of stomata depends on light, water and carbon dioxide and due to their opening and closing, transpiration rate also gets affected.

Complete answer:
Stomata are the tiny pores which are present on plant tissue and it functions in exchange of gases. These are typically found in the plant leaves but can also be found in some stems. Guard cells surround the stomata and it controls the opening and closing of the stomata. It allows the exchange of gases for entry of carbon dioxide and releasing of oxygen which allows plants to take carbon dioxide for photosynthesis. It's one more important function is to regulate water movement through transpiration.

The opening and closing of stomata is affected by three environmental factors which are:
- Light
- Water
- Carbon dioxide
In this question the cause when sudden increase in carbon dioxide is asked. So, we will look at this factor only. Since the stomata allows the carbon dioxide to enter and oxygen to exit therefore if there will be sudden increase in carbon dioxide concentration around the leaf will happen then the stomata will get closed so that the excess gas does not enter the cell and this will further decrease the rate of transpiration too.

If we look at the options now. We know that stomata will get closed and transpiration will increase.

Option A is a wider opening of the stomata which is completely incorrect as the stomata gets closed not open.
Option B is Increase in transpiration which is also completely wrong as there is decrease in the rate of transpiration not increase.
Option C is Closure of stomata which seems correct but its incomplete since there is closing of stomata but along with this there is decrease in the rate of transpiration too.
Option D is Decrease in transpiration due to closure of stomata which is the most correct one as due to closing of stomata there is decrease in the rate of transpiration too.

Hence, the correct answer is option (D).

Note: Carbon dioxide is required by cell in a particular amount but if there will be excess of it then stomata will get closed so that it does not reach the cells otherwise the function will be disturbed in the cell and thus this is followed by the decrease in the transpiration too as it depends on opening and closing of stomata. Therefore, the correct answer is Decrease in transpiration due to closure of stomata.