Question

The process of moving air or water across the gas-exchange surfaces of an animal is known as:
(A) Ventilation
(B) Active respiration
(C) Facilitated diffusion
(D) Countercurrent exchange

Answer 1

Hint: The movement of oxygen from the lungs to the bloodstream and the elimination of carbon-dioxide is the exchange of gases that takes place inside the animal body. In some animals it is maintained in the through diffusion process and in some lower animals the exchange is made directly with the environment.

Complete answer: The ventilation is a technique used in medical science to provide any animal with a lower oxygen rate inside the body. This required a ventilation machine through which the oxygen is maintained inside the body.
1. Now, the active respiration required the contraction of the skeletal muscles. It includes the diaphragm and external intercostals muscles for the movement of gases throughout the body.
2. The facilitated diffusion involves the gas exchange process for the movement of gases or water with the external environment of the animal body.
3. The countercurrent exchange is the process in which the substance gets exchanged between the fluids that are flowing in the opposite direction.

Additional information: It is a physical process in which the gases can move passively through diffusion in the surface.
In animals the exchange of gas is very important for the respiration process. In multicellular organisms, specialised respiratory organs are present that are lungs or gills.
These organs provide adequate surface area for the gas exchange with the external environment.
The gas is entered in the surface through a diffusion process but to reach the deeper tissues the gas distributing circulatory system is required.

Hence, the correct option is C. Facilitated diffusion.

Note: Some of the multicellular organisms like flatworms have very low surface area as they are very thin, exchanging gases through their outer surface of the body.
Similarly, in some multicellular organisms like sponge, they have large surface area and have pores in the body and through this pores exchange of gases or water takes place.