Do single-celled organisms have a high or low surface area to volume ratio?
Single-celled organisms have a high surface area to volume ratio.
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How do single-celled organisms exchange gases with their external environment?
By diffusion across the cell-surface membrane.
This is possible because their surface area to volume ratio is sufficiently high.
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Describe how the size of an organism tends to affect its surface area to volume ratio.
As the size of an organism increases, its surface area to volume ratio decreases.
Some larger organisms have different shapes and structures that give them a slightly larger surface area to volume ratio, for instance they may be thinner and flatter.
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What needs to be exchanged between an organism and its environment?
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What is an exchange surface?
A specialised structure that allows materials to be transferred between cells and an organism’s surrounding environment.
Exchange surfaces always involve plasma membranes.
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State some key features of specialised exchange surfaces.
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How does the metabolic rate of an organism affect the amount of material that it needs to exchange?
Organisms with higher metabolic rates need to exchange more materials.
They need a higher surface area to volume ratio, and/or a specialised exchange system, to exchange these substances at a faster rate.
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