Question

why is diffusion is sufficient to meet the oxygen required in multicellular oxygen

Answer 1

The oxygen requirements of an animal cannot be met by the process of diffusionas diffusion is a very slow process. To overcome this, multicellular organisms have specialized cells and tissues for performing various necessary functions of the body such as intake of oxygen and food.

Answer 2

In multicellular organisms, only the cells of skin are in direct contact with the environment and cells of rest of the body are not in direct contact with the environment. Thus, if all the raw materials required to sustain life are transported by the process of diffusion it will take a very long time to reach all parts of the body. To overcome this problem, multicellular organisms have specific organs for the transport of various substances like digested food, oxygen, carbon dioxide, water and waste products.