Surface area: The total number of cells in direct contact with the surrounding environment
Volume: The total three-dimensional space occupied by metabolically active tissues
Surface area affects the rate of exchange of materials at exchange surfaces.
It also influences the rate of supply of metabolites to tissues.
Volume of metabolically active tissue influences the demand for metabolites.
Effect of Size
As an organism’s size increases, its surface area increases less than its volume.
This is because many cells are not in direct contact with the surrounding environment.
- Therefore large animals have a small surface area to volume ratio and
- Small animals have a large surface area to volume ratio.