GCSE Biology · AQA 8461 · Topic 4.2.3
Plant tissues, organs and systems
Key points
- Plant tissues include epidermis, palisade mesophyll (most photosynthesis), spongy mesophyll (air spaces for gas exchange), xylem, phloem and meristem.
- Xylem is made of dead cells strengthened with lignin; it carries water and mineral ions up from the roots.
- Phloem carries dissolved sugars both ways around the plant; this is translocation.
- Transpiration is water evaporating from leaves through stomata, which pulls water up the xylem. Guard cells open and close the stomata.
- Transpiration is faster when it is warmer, drier, windier or brighter. A potometer measures water uptake.
- Root hair cells give a large surface area to absorb water by osmosis and mineral ions by active transport.
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A plant has no heart, yet it still moves water from the soil to the top of a tree and sugars from leaves to roots. This sub-topic explains the tissues that make this possible and the factors that control water loss from leaves.
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