Question

Phenylmercuric acetate is known to

• A. Reduce transpiration rate
• B. Reduce photosynthesis
• C. Kill the plant
• D. Reduce respiration

Answer 1

The correct option is A Reduce transpiration rate

PMA functions as an antitranspirant when it is applied directly to the leaves of a plant. It reduces the amount of water lost through transpiration by closing the plant’s stomata. PMA induces stomatal closure at low concentrations of short duration. Prolonged contact will eventually kill the guard cells surrounding the stoma, causing the pores to reopen. Stomata are designed to be very sensitive to changes in carbon dioxide concentration. Even a small increase in the cellular concentration of carbon dioxide can induce stomatal closure. Increased amounts of carbon dioxide inside the plant cells can be caused by increased respiration or decreased photosynthesis. PMA increases the plant’s compensation point so that more light must be absorbed to perform photosynthesis and fix carbon dioxide. If the plant is unable to obtain enough energy to surpass the compensation point carbon dioxide may build up in the cell, causing stomatal closure.

Therefore, the correct answer is option A.