Exchange of substances in roots

Root hair cells

Roots anchor many plants into the ground. They are also responsible for absorbing water and mineral ions like nitrates from the soil. Roots have specialised cells called root hair cells. These have long thin projections that stick out into the soil.

A diagram of the root epidermal cell

This massively increases the surface area of the root and allows it to absorb more water and mineral ions.

Uptake of water by osmosis

Osmosis is the net movement of water molecules from an area where they are in higher concentration to an area where they are in lower concentration across a partially permeable membrane. This happens naturally and does not require energy from respiration.

The water then moves through root cortex cells to xylem vessels which transport it to the leaves for photosynthesis, or where it evaporates into the surrounding air. This process is called transpiration.

Uptake of mineral ions by active transport

Active transport is required for the movement of molecules from an area of low to higher concentration. Because this process moves molecules up the concentration gradient, it requires the use of energy from respiration.

Plants require mineral ions in high concentrations. They are found in low concentrations in the soil. Therefore, plants must use active transport to move them from the soil into their root hair cells.

These mineral ions are carried around the plant dissolved in water in xylem vessels.