Organisms must transfer materials between themselves and their environment.
Materials must be rapidly distributed to the cells requiring them and waste products returned to exchange surface for removal.
Size and metabolic rate of an organism affects amount of each material needed - influences type of exchange surface and transport system that has evolved to meet requirements of organism.
Things that need to be interchanged between an organism and its environment:
- Respiratory gases (CO2 and O2)
- Nutrients (glucose, fatty acids, amino acids, vitamins, minerals).
- Excretory products (urea and CO2)
Exchange can take place in two ways:
- Passively by diffusion and osmosis.
- Actively by active transport (energy required).
Surface area to volume ratio
Surface area of organism must be large in comparison to its volume for exchange to be effective.
Small organisms have surface area large enough compared with volume for effecient gas exchange across…