Question

Which of the following is a plant showing scotoactive opening of stomata?
A. Opuntia
B. Nerium
C. Arachis
D. All of the above

Answer 1

Hint: In order for you to answer the question, you must first understand the meaning of scotoactive stomata. By scotoactive stomata we mean those stomata that open at night. Can you tell why will and under which conditions will a stomata of a plant open at night?

Complete answer:
As mentioned earlier, scotoactive stomata are a type of stomata that open at night. They are found in mainly succulent plants which form a part of CAM plants. The abbreviation CAM stands for Crassulacean acid metabolism, also known as CAM photosynthesis. It is a specific type of carbon fixation pathway that has evolved in those plants that are present in semi arid and arid regions in response to certain conditions. For example, plants present in semi arid regions show certain modifications so that they are able to store water due to water scarcity in those regions. They show sunken stomata or an extensive root system or the presence of spines rather than leaves. Presence of leaves reduces loss of water by transpiration and sunken stomata also helps to prevent water loss by transpiration. In normal conditions, carbon fixation goes on in the presence of light .However in the plants of semi- arid regions, if the stomata is open during the day, then all the water will be lost. So, they have a modified pathway. Their stomata remain open at night so that carbon dioxide diffuses to reach the mesophyll cells.

So, the correct answer is option A Opuntia.

Note:
CAM was first observed by the botanists Ranson and Thomas in the Crassulaceae family or the succulent family. It generally refers to the acid metabolism that occurs in this family and not the acid metabolism of Crassulacean acid which does not actually exist.