Question

Osmoregulation in all animals involves epithelium which forms a continuous barrier. This ensures that all solutes entering and leaving the area (osmoregulatory organ) must pass through
A. Plasma membrane.
B. Stratified epithelium membrane.
C. Both A and B.
D. None of these.

Answer 1

Hint:- The regulation of solute movement and hence water movement (which follows solute by osmosis) is called osmoregulation. It is the maintenance of salt water concentration in the steady state. On the basis of osmoregulation animals are either osmoconformers or osmoregulator.

Complete answer:
Osmoconformers-these animals cannot actively control the osmotic condition of their body fluids,instead of this they change or adapt osmolality of body fluids according to the osmolality of the surrounding medium.
For example, all marine invertebrates and some freshwater invertebrates.
Osmoregulators-these animals maintain an internal osmolality different from the surrounding medium in which they inhabit.Osmoregulator animals must either eliminate excess water if they are in hypertonic medium or they should continue to take in water to compensate for water the loss if they are in hypotonic medium.Due to the osmoregulator animals have to spend energy. For example, most vertebrates.
Different animals have different osmoregulatory organs such as in all vertebrates this is kidney. In
most insects there are malpighian tubules,in annelids this is nephridia,in platyhelminthes this is protonephridia. The kidney is the main organ responsible for osmoregulation in humans. Water, amino acids and glucose are reabsorbed by the kidneys. From these osmoregulatory organs many solute exit and enter in the body via permeable membranes.Plasma membrane is permeable but stratified epithelium membrane is impermeable. So all the solute crosses the area via plasma membrane.

Therefore the correct answer is (A).

Note:- Osmoregulators have to spend more energy as compared to the osmoconformers to move in or out and maintain osmotic gradient by manipulating solute concentration in their body fluid. In the human body Whenever the water level in the body is increased, it releases a large amount of hypotonic urine. When the water level is decrese it retains water and produces a low amount of hypertonic urine. Thus, the kidneys maintain the electrolytic balance of the body.