Question

Gas exchange in the gills of a teleost fish is enhanced by having the blood flow in direction opposite to the direction of water flow, a process known as
A) Counter gas exchange
B) Ventilation
C) Facilitated diffusion
D) Active respiration

Answer 1

Hint: It involves the active secretion of body fluids in many vertebrates' kidneys. As an example, transfer of heat from heat to cold.

Complete answer:
Let’s discuss the options and find the correct answer.
A) When two fluids flow in opposite directions, it is known as countercurrent flow. In biological terms, it is widely used. In fishes, gaseous exchange occurs through their gills or in case of birds, countercurrent exchange occurs in the form of heat exchange through the blood vessels for keeping their body warm.
B) Ventilation is the other term of breathing. It is the gaseous exchange between the lungs and the atmosphere. It may be the exchange of oxygen and carbon dioxide through alveoli. Inhalation and exhalation are included.
C) Process of passive transport of ions or molecules that occurs spontaneously is called Facilitated diffusion. It is the diffusion of biological molecules or ions through some integral proteins that present in the transmembrane. It does not require energy from ATP which is acquired by hydrolysis hydrolysis. The concentration of ions and molecules are diffusive in nature.
D) Contraction between the muscles that are involved in breathing is known as active respiration. It increases the volume of cavity upper ribs are elevated for this.

Hence the correct answer is option ‘A’ Counter gas exchange

Note: Opposite direction secretion in vertebrate kidney or passive exchange of gases in fish gills like teleost gills comes under this point. The advantage of this system is that,
i) The fishes can extract a very high proportion of oxygen from water when compared to other animals.
ii) As there is not much oxygen available in water, this helps it to absorb more and more oxygen.