What factors limit the effectiveness of diffusion in larger organisms?

The effectiveness of diffusion in larger organisms is limited by factors such as size, surface area to volume ratio, and distance.

Diffusion is a passive process that relies on the random movement of particles from an area of high concentration to an area of low concentration. It is an effective means of transport for small, unicellular organisms. However, in larger, multicellular organisms, the effectiveness of diffusion is limited by several factors.

Firstly, the size of the organism plays a significant role. As the size of an organism increases, the distance that substances need to travel from the outer surface to the inner cells also increases. This makes diffusion a slower and less efficient process. For example, in a large organism like a human, it would take an extremely long time for oxygen to diffuse from the lungs to cells in the feet solely by diffusion.

Secondly, the surface area to volume ratio also limits the effectiveness of diffusion. As organisms become larger, their volume increases at a much faster rate than their surface area. This means that there is less surface area available for diffusion to occur relative to the volume of the organism. This can limit the rate at which substances can enter or leave the organism, making diffusion less effective.

Lastly, the distance that substances need to travel can also limit the effectiveness of diffusion. In larger organisms, cells are often located far from the surface. This means that substances need to travel a greater distance to reach these cells, which can slow down the rate of diffusion. This is why larger organisms have developed specialised transport systems, like the circulatory system in humans, to help transport substances around the body more efficiently.

In conclusion, while diffusion is an effective means of transport in small, unicellular organisms, its effectiveness is limited in larger organisms due to factors such as size, surface area to volume ratio, and distance.