48. 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?

• In multicellular organisms like humans the transport of oxygen by diffusion is more as compared to other unicellular organisms. Due to a large number of cells and the huge size of the body the oxygen cannot diffuse quickly into all cells of the body. In unicellular organisms, the size of the organism is small and the cell present is also singular. Hence, diffusion is insufficient to meet the oxygen requirements of large multicellular organisms like humans.

• In large animals, the blood circulatory system contains hemoglobin which carries blood to all parts of the body.
• A terrestrial animal has over an aquatic animal with regard to obtaining oxygen for respiration. It’s because the air in the atmosphere contains the maximum amount of Aquatic animals have only

dissolved oxygen in water which is in minimal amount. Hence, terrestrial animal has over an aquatic animal with regard to obtaining oxygen for respiration.