Exchange surfaces

• The need for specialised exchange surfaces arises as the size of the organism, and its surface area to volume ratio decreases
• In the case of single celled organisms, the substances can easily enter the cell as the distance that needs to be crossed over is short
• However, in multicellular organisms that distance is much larger due to a lower surface area to volume ratio
• As a result of that, multicellular organisms required specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Features of an efficient exchange surface include large surface area, for instance the root hair cells or folded membranes, such as those of the mitochondria
• An efficient exchange surface should also be thin to ensure that the distance that needs to be crossed by the substance is short.
• The exchange surface also requires a good blood supply/ventilation to maintain a steep gradient, for example that of the alveoli