*In multi-cellular organisms, all the cells, may not be in direct contact with the surrounding environment. Thus simple diffusion will not meet the requirements of all the cells.

*Therefore, in human beings, there are specialized tissues and organs that help to meet the oxygen requirements of the body

Diffusion is a process where molecules move from an area of high concentration to an area of low concentration. This process is the primary mode of gas exchange in unicellular organisms and small aquatic animals. In unicellular organisms, diffusion is sufficient to meet their oxygen requirements as their surface area to volume ratio is high, and the distance over which oxygen has to diffuse is small.



Multicellular organisms, like humans, have a low surface area to volume ratio as compared to unicellular organisms. The distance over which oxygen has to diffuse is also significant. Therefore, diffusion alone cannot meet the oxygen requirements of multicellular organisms.



Multicellular organisms have different types of life processes, which require oxygen. Some of them are:

• Respiration: Respiration is a process where glucose is broken down to release energy. This process requires oxygen, and the waste product produced is carbon dioxide. Respiration is essential for the survival of multicellular organisms.


• Circulation: Multicellular organisms have a circulatory system to transport oxygen and nutrients to different parts of the body. The circulatory system consists of a heart, blood vessels, and blood. Oxygen is transported by the red blood cells in the blood.


• Activity: Multicellular organisms are active and require energy for their daily activities. This energy is obtained through the process of respiration, which requires oxygen.

Multicellular organisms require nutrients for growth and development. The nutrients are obtained through the process of digestion. The process of digestion requires energy, which is obtained through the process of respiration, which requires oxygen.



In conclusion, diffusion is insufficient to meet the oxygen requirements of multicellular organisms like humans. Multicellular organisms require a circulatory system to transport oxygen to different parts of the body. They also require energy for their daily activities, growth, and development. This energy is obtained through the process of respiration, which requires oxygen. Therefore, the respiratory system is essential for the survival of multicellular organisms.