GCSE Biology · Edexcel 1BI0 · Topic 6B
Transport in plants
Key points
- Root hair cells have a large surface area to absorb water by osmosis and mineral ions by active transport.
- Xylem is made of dead cells with no end walls, strengthened with lignin; it carries water and minerals up from the roots.
- Phloem is made of living cells with sieve plates; it moves sugars up and down the plant (translocation), which needs energy.
- Transpiration: water evaporates from leaf cells and diffuses out through stomata, pulling more water up the xylem.
- Guard cells open stomata when turgid and close them when flaccid.
- Transpiration rate increases with higher temperature, light intensity and air movement, and decreases with higher humidity. Measure it with a potometer; rate = distance the bubble moves ÷ time.
- Adaptations: cacti have spines and thick cuticles; plants in shade have larger leaves.
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A plant has to move water and minerals up from its roots and sugars from its leaves to wherever they are needed. This sub-topic explains the cells and tissues that do it, the process of transpiration and how plants are adapted to their…
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