Question

Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?
A. The amount of dissolved oxygen is fairly low in water than air
B. Aquatic organisms like fishes obtain oxygen from water present in dissolved state.
C. Both A and B
D. None of the above

Answer 1

The aquatic organisms are the organisms who live in water. These organisms breathe using their gills. Terrestrial organisms have direct access to oxygen as opposed to aquatic organisms.

Complete step by step answer:
Terrestrial organisms are the ones who spend their life on land. These animals have a respiratory system that breathes air through the lungs. On the other hand, the organisms living in water do not breathe with lungs but have specialized organs called gills to help them sustain inside water. Terrestrial organisms have a lot of oxygen which is present in the air around them, which makes it easy to breathe. So, a small volume of air at a time can be sufficient to provide oxygen to each and every part of the body. And hence the rate at which these animals breathe is also slow, as ample amounts of oxygen are available in the air and they can have a longer time interval between two breathes. Contrary to this situation, the amount of dissolved oxygen present in the water is much lower than the oxygen present in the air. With each breath, the amount of oxygen these organisms get is much smaller and hence it is required for them to breathe more frequently than the terrestrial organism to fulfill the need for oxygen by their body. That is why the rate at which these organisms breathe is much more than that of the terrestrial organisms.
So, the correct answer is option C, i.e., Both A and B

Additional information: Some aquatic organisms also breathe through their skin. Aquatic mammals like Dolphins and Whales, even though aquatic animals have lungs for respiration and often come to the surface of the water for breathing oxygen from the air.

Note: Air has roughly around 21% oxygen along with other gases. And the amount of oxygen dissolved in water depends on its solubility in water, which in turn depends upon various other physical factors like temperature, pressure, salinity, etc. Therefore, aquatic organisms have to struggle more to get the same amount of oxygen as terrestrial organisms do.