Exchange surfaces
Single-celled organisms have relative large surface area to volume ratios. Larger Having more than one cell. organisms have smaller surface area to volume ratios. So, they have evolved exchange surfaces to exchange molecules with their surroundings.
The effectiveness of exchange surfaces in plants and animals is increased by having:
A large surface area:
- the flattened shape of structures such as leaves
- the Tiny air sacs in the lungs, where gas is exchanged during breathing. in the respiratory system
- the Finger-like projections in the small intestine that provide a large surface area for the absorption of food. in the digestive system
A short distance required forThe movement of molecules from an area of higher concentration to an area of lower concentration.:
- the membranes of cells
- the flattened shape of structures such as leaves
- the walls of blood Tiny blood vessels with walls one-cell thick where exchange of materials occurs. are one cell thick
- the Type of tissue that lines or covers surfaces of an organism. It is made up of epithelial cells. of alveoli in the respiratory system and the villi in the small intestine are only one cell thick
Animals have additional adaptations for effective exchange surfaces.
An efficient blood supply to transport molecules to and from the exchange surface increases effective exchange. Examples of this include:
- the network of blood capillaries that surrounds each of the alveoli in the lungs
- the network of blood capillaries in each of the villi in the small intestine
The process of breathing, or Breathing in and out., brings air to, and removes air from the exchange surface – the alveoli.
The moving blood and ventilated surfaces mean that a steep The difference in the concentration of a chemical across a membrane. can be maintained. This increases effective exchange.
