➡ Diffusion is insufficient to meet the oxygen requirements of multicellular organisms like humans because of several reasons:
1. Size and Complexity:
- Multicellular organisms are much larger and more complex than single-celled organisms. They have many cells that are located deep within their bodies, and diffusion alone is not efficient enough to transport oxygen to all these cells quickly and effectively.
2. Distance:
- Cells in multicellular organisms can be far from the external environment where oxygen is obtained. Diffusion is limited by the distance over which molecules must travel. Oxygen would have to diffuse through multiple cell layers and tissues to reach deep-seated cells, leading to a slow rate of delivery.
3. Oxygen Demand:
- Multicellular organisms have a higher oxygen demand due to their larger size and higher metabolic rates. Diffusion cannot supply oxygen at the required rate to support the energy needs of such organisms.
4. Limited Surface Area:
- The surface area available for diffusion is limited by the organism's size. As an organism becomes larger, its surface area-to-volume ratio decreases, reducing the efficiency of diffusion for gas exchange.
➟ To overcome these limitations, multicellular organisms like humans have evolved specialized respiratory systems, such as lungs, that facilitate the efficient exchange of oxygen and carbon dioxide. These systems use mechanisms like active pumping, circulation, and respiratory surfaces with large surface areas to ensure an adequate oxygen supply to all cells in the body.