Question

Which one of the following is not an antitranspirant?
A. PMA
B. BAP
C. Silicone oil
D. All the above

Answer 1

Antitranspirants are defined as compounds which can be applied to the leaves of plants. They reduce transpiration and are used on flowers, on new transplanted shrubs, and on other applications for preserving and protecting plants from quickly drying out. Also, they are used to protect leaves from salt burn as well as fungal diseases.

Complete answer:
You should know, Antitranspirants are divided into two types:

metabolic inhibitors and
film-forming antitranspirants.
Metabolic inhibitors are defined as substances that reduce the stomatal opening and increase the leaf resistance to water vapour diffusion without affecting uptake of carbon dioxide. Its examples are- phenylmercury acetate, abscisic acid (ABA), and aspirin.
Remember, antitranspirants -blocks the active excretion of hydrogen cation from the guard cells. And because of the presence of carbon dioxide, a rapid acidification of cytoplasm results in stomatal closure. Milbarrow in 1974 - described the formation of these chemical compounds in the chloroplast, and it moves to the stomata- here it is responsible to check up the intake of Potassium ion and for inducing loss of potassium ion from the guard cells.
Let’s recap, Transpiration is a process of loss of water in the form of water vapour, from plant parts. This happens with the help of stomata which are mostly present on the lower surface of leaves. The chemicals applied on leaves of plants for reducing the rate of transpiration are known as antitranspirants. Antitranspirants are widely used for improving the crop yield in drought affected areas. Remember, Phenyl mercuric acetate (PMA) as well as low viscosity silicone oil are antitranspirants. Benzo[a]pyrene (BAP) is not considered as an antitranspirant.

Therefore, the correct answer is option B.

Additional information:
Keep in mind, Anti-transpirants are liquid chemicals, that you can spray on your plants to shield them from moisture loss and once these products are sprayed on your plants, these spray dries into a transparent clear and flexible protective coating which don’t interfere with plant growth, osmosis or photosynthesis.

Note: Remember, Antitranspirants are chemical substances which are applied to the plants for the purpose of reducing transpiration or water loss, without causing a major effect on other plant processes, like photosynthesis & growth.