The Need for Exchange Surfaces (A-level Biology)
The Need for Exchange Surfaces
Exchange Surfaces
Specialised Exchange Surfaces
- Multicellular organisms need substances – metabolic reactions and the removal of other substances require substances to carry out.
- Specialised exchange surfaces increase in demand as the surface are to volume ration (SA:V) decreases.
- Diffusion rate is quick – this is due to the surface area to volume (SA:V) being very high.
- Passive transport – a single-celled organism’s substances are able to to directly diffuse into and out of the cell across the cell surface membrane by passive transport.
- Direct diffusion across the outer membrane is too slow in multicellular organisms – this is due cells lying deep within the body, making the distance substances need to travel very large.
- The larger the animal, the lower the SA:V – this makes it difficult for enough substances to exchange through a relatively small outer surface
- Multicellular organisms use up substances faster – a higher metabolic rate compared to single-celled organisms means substances such as oxygen and glucose get used up in reactions quicker.
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