Question

Among these plants ,the ones which show physiological process referred to as a "necessary evil" are
A)Potamogeton
B)Sagittaria
C)Limnophila
D)Nymphaea
A)b,c,d
B)a,b,c
C)a,b,d
D)a,e,d

Answer 1

Hint: From the given option three plants show this physiological process. One plant is commonly known as marsh weeds. They show cuticles and stomata. The second plant shows the stomata on the upper epidermis and cuticle. The third plant contains many stomata and belongs to the genus of hardy and tender aquatic plants.

Complete answer:
Here necessary evil refers to " transpiration". Transpiration mainly occurs through stomata. Stomata are the minute opening on the surface of leaves that allow them to carry some important functions like the easy passage of water vapor, carbon dioxide, and oxygen. The primary function of stomata is the absorption of carbon dioxide but it also releases water vapor through the process called transpiration. Transpiration is an unavoidable process thus refers to a necessary evil as transpiration as it doesn’t do any good for plants but on the other hand without transpiration suction pool will not create in plants and water will not evenly distribute to all parts of the plant. Also without the transpiration, cooling mechanisms will also not occur in plants.
-Sagittaria, Limnophilia, Nymphaea plants have stomata on their leaves which is meant for gaseous exchange and has cuticles also which prevents the loss of excess water through transpiration. On the other hand, Potamogeton is a submerged aquatic plant and they don't have stomata for gaseous exchange and cuticles also.

Additional Information: Advantage of transpiration
1)It helps in the evaporation of the excess amounts of water.
2)It causes the opening and closing of stomata. Hence indirectly control the process of photosynthesis and respiration in plants.
3)It creates suction force.
4)It causes the absorption of minerals and waters from the root.
Disadvantage of transpiration
1)About 99% of water is lost from plants due to transpiration.
2)It causes dwarfism in plants due to the increase in the rate of transpiration.
3)Most of the plants like xerophytes modify their structures to reduce the amount of transpiration.

So,the correct answer is, "b,c,d ".

Note: -Cuticle is a waxy layer that presents in all the above-ground plants which serve as a barrier for plants to prevent excess loss of water.
-The number of stomata present in plants totally depends on environmental conditions.