Plants also rely on a number of exchange systems. Two main systems are:

• carbon dioxide entering the leaves by diffusion
• water and mineral ions entering the roots

Roots

In plants, water is mainly absorbed through the roots. The roots are well adapted to this because:

• their surface area is increased by root hairs
• the root hairs are very thin so that the distance required for osmosis is greatly reduced

Water is mainly absorbed into the root cells by osmosis but it can also be absorbed by active diffusion.

Plants also need to absorb mineral ions. However, there are only very small amounts of these in the soil and so root cells need to actively transport these through their membranes.

Leaves

Leaves are adapted for efficient gaseous exchange:

• In terms of their structure, they’re very thin so that the distance of diffusion is reduced.
• They also tend to have a large surface so that more diffusion can happen simultaneously.
• They contain a large number of internal air spaces so that gases can move easily inside the leaf.