#68 Summary of plant transport

In plants, xylem vessels transport water and mineral ions from the roots upwards to the leaves. Phloem tubes transport sucrose and other organic nutrients, from the leaves where they are made to all parts of the plant. This is called translocation.

• Xylem vessels are made of dead, empty cells with strong lignin in their walls. As well as transporting water, they help to support the plant.

• Water is drawn up xylem vessels by the evaporation of water from the leaves, called transpiration. Transpiration happens fastest when it is hot, dry, windy and sunny.

• Water enters root hairs by osmosis, and then moves across the cortex of the root into the xylem.

• Root hairs take up mineral ions by active transport, using energy supplied by respiration to move them against their concentration gradient.

• Phloem is made of living cells with sieve plates at their ends. A companion cell is associated with each phloem sieve tube element.

• Systemic pesticides are translocated in phloem.

• Sucrose is translocated from sources to sinks. Different parts of a plant may become sources and sinks in different seasons.