Exchange of substances with the environment takes place at the surface of an organism, but the materials absorbed are used throughout the whole volume of the organism.As organisms get larger, their volume increases faster than their surface area. Their surface area increases at the rate of the square of a factor whilst the volume increases at the rate of the cube of the factor. As a result, simple diffusion alone is not fast enough to meet the metabolic needs of active organisms. It would take too long for substances to reach the middle of the organism.Adaptations to increase surface area to volume ratio:
a flattened shape means that no cell is ever far from the surface.
Specialised exchange surfaces (e.g. lungs, gills) which provide large surface areas to increase the surface area to volume ratio.
a flattened shape means that no cell is ever far from the surface.
Specialised exchange surfaces (e.g. lungs, gills) which provide large surface areas to increase the surface area to volume ratio.