Question

What is the process of diffusion, and how does it limit the size of an organism? Can this be counteracted? What else might limit the size of an organism? What is the difference between an endothermic animal and an ectothermic animal?  

Answer 1

Diffusion is movement of particles from the region where they are more to the region where they are less till the concentration of the particles becomes equal on both the sides. The rate of diffusion depends on the difference in the concentration of particles , temperature etc. It also depends on the surface area available for diffusion to occur. Normally in a cell , the diffusion occurs through the cell membrane. So the larger surface area of the cell membrane, more diffusion of the particles possible.

Diffusion can limit the size of a cell. Because diffusion always occurs through cell membrane. When a cell is growing, the volume of cell increase much faster than the surface area. As the cell is growing faster with more volume increase, material requirement also increases. But the surface area is not increasing as much as volume. It cant get all the substances that the cell requires by diffusion as cell surface is not growing faster. So this limits further growth of the cell . That is how the diffusion process limits the cell size. If it is a unicellular organism, we can say that the diffusion limits the size of the organism. But in case of multicellular organism, diffusion has no effect on the size of multicellular organism. The size here is due to genes and other environmental factors.

Animals whiich can control their own body temperature are endothermic animals. Their body temperature does not change with surounding temperature. Ectothermic animals are those whose body temperature changes with the surounding temperature. If the surounding temperature increases the body temperature of ectothermic animals also increases. If the temperature of the suroundings decreases, the body temperature decreases in ectothermic animals.