| Exchange surfaces in single celled organisms | - substances diffuse directly into (or our of) the cell across the cell surface membrane
- the diffusion rate is quick because of the short distances substances have to travel
- relatively high surface area to volume ratio |
| Exchange surfaces in multicellular organisms | - some cells are deep within the body = big distance between them and the outside environment
- larger surface area to volume ratio
- they have higher metabolism rate, so they use up oxygen and glucose faster |
| Exchange surface of root hair cells | - has large surface area which helps increase rate of absorption of water (by osmosis) and mineral ions (by active transport) from the soil |
| Exchange surface of alveoli | - made from a single layer of thin, flat cells called alveolar epithelium
- this helps decrease the distance over which oxygen and carbon dioxide diffusion takes place |
| Blood supply to alveoli | - alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply
- this allows oxygen to be taken away and bring more carbon dioxide
- the lungs are also ventilated, so air in each alveolus is constantly replaced
- this helps maintain concentration gradient of oxygen and carbon dioxide |
| Blood supply in fish gills | - fish gills contains a large network of capillaries keeping them well supplied with blood
- they are also well ventilated as fresh water is constantly passing over them
- this helps maintain concentration gradient of oxygen, increasing the rate of diffusion |
