How a tree functions - part 2
The other two key processes are osmosis and transpiration. Together they move water and dissolved materials through the tree.
Osmosis is the movement of water through a semi-permeable membrane from an area of higher water concentration to an area of lower concentration. Root hairs help maximise this absorption.
Transpiration is the movement of water and nutrients through the tree and out through the stomata in the leaves. As water evaporates from the leaves, it pulls more water upward behind it.
Osmosis
Minerals and sugars in the roots lower the water concentration inside root cells, so water moves inward from the surrounding soil. If the soil becomes too mineral-rich, the flow can reverse and the tree can lose water instead.
Transpiration
Water moves up from roots to trunk to leaves and then leaves through the stomata. During the growing season this creates a continuous stream that carries both water and nutrients.
Key takeaway
Osmosis gets water into the roots. Transpiration keeps that water moving through the whole tree.
Knowledge check
What is reverse osmosis in this context?