Investigating the effect of surface area
As a cell’s volumeHow much space an object occupies. increases, the more substances (e.g. oxygen) it needs for cell reactions.
When a cell’s surface area increases, the amount of substances diffusing into the cell increases.
As volume and surface area increase, the volume increases faster, so much so that the surface area available to allow substances in halves each time the cell volume doubles.
This is known as the surface area/volume ratio (SA/V ratio).
A cell will eventually become so large there is not enough surface area to allow the diffusion of sufficient substances like oxygen and it will die.
As organisms need a large enough surface area (large SA/V ratio) to supply substances for cell reactions, multi-celled organisms have developed internal gas exchange organs (lungs) in order to provide an increased surface area.
With the lungs far away from other body cells, a transport system circulatory systemBodily system made up of the heart, blood vessels and blood that delivers nutrients and other essential materials to cells whilst removing waste products. has also developed in order to provide all cells with substances like oxygen.