Question

If the external solution balances the osmotic pressure of cytoplasm, it is said to be isotonic.
A. True
B. False

Answer 1

Isotonic solution is the solution having same osmotic pressure and the concentration of solute is same as that of the other solution. If the two solutions that are isotonic in nature pass through the semipermeable membrane then the water (acts as a solvent) will flow in equal parts out of each solution and into the other.

Complete Answer:
Tonicity refers to the measure of the effective osmotic pressure gradient and the water potential of the given two solutions is separated by the semipermeable membrane.
It can be of three types:
- Hypertonic solution: The solution in which the one solution is having the greater concentration of solutes than another solution. When these solutions are passed through the semipermeable membrane then the exo-osmosis takes place to maintain the osmolarity.
- Hypotonic solution: The solution in which the one solution is having the lower concentration of solutes than another solution. When these solutions are passed through the semipermeable membrane then the endo-osmosis takes place to maintain the osmolarity.
- Isotonic solution: The solution in which the same solute concentration is present in the two solutions.

The correct option is A i.e. the statement is TRUE.

Additional information: Osmolarity plays a very vital role in the living organisms either they are belonging to lower primitive class like monera, Protista or belonging to higher class like amphibian, aves, mammals etc.
- If the hypotonic cell is placed in the normal solution then the cell swells up while if the hypertonic cell is placed then it shrunk.
- Various biological mechanisms are truly based on the process of osmolarity like excretion of wastes from the body, circulation of nutrients and gases in the body and many more.

Note: In amoeba belonging to the lower class of living organisms is having subcellular organelle named as contractile vacuole that are responsible for maintaining osmolarity in the cell and thus performing the functions of osmoregulation.