Concept preview

What you will be able to do

1. 01Explain how water is transported up the xylem by transpiration, cohesion-tension and root pressure.
2. 02Explain how sugar is transported in the phloem from source to sink (translocation).
3. 03Describe the parts of a flower and their roles in reproduction.
4. 04Outline pollination, fertilisation, and the formation and dispersal of seeds and fruit.

Tall trees must move water from soil to leaves high above the ground. The main upward drive in the xylem is the tension created as water evaporates from leaf surfaces and vapour diffuses out. Cohesion helps transmit this tension through water columns, while xylem walls resist collapse. The physical lift does not require a metabolic pump along the xylem, although living root and guard cells use energy in regulating uptake and water loss.