Question

(a) Why is diffusion insufficient to meet the oxygen requirements of large multicellular organisms like humans?
(b) What type of arrangement exists in the bodies of large animals to meet their oxygen requirements adequately?
(c) What advantage a terrestrial animal has over an aquatic animal with regard to obtaining oxygen for respiration?

Answer 1

(a) In small unicellular animals, such as Amoeba, the volume of their body is so small that oxygen can be introduced quickly into the whole body by the process of diffusion. This is because the cell of Amoeba is so small that the oxygen does not have to go far. But in case of large multicellular animals like humans, the volume of the body is so big that oxygen cannot quickly diffuse into all the cells of the body. This is because in these cases, the oxygen has to travel a very large distance to reach each and every cell of the body.

(b) In large animals, there is a blood circulatory system to quickly carry the oxygen to all the parts of the body.

(c) A terrestrial animal is surrounded by an oxygen-rich atmosphere from where it can take any amount of oxygen. An aquatic animal uses the oxygen dissolved in water to carry out respiration. The amount of oxygen dissolved in water is low as compared to the amount of oxygen in the air.