Transpiration and xerophytes
Introduced| English | Meaning |
|---|---|
| transpiration/trænspəˈreɪʃn/ | The loss of water vapour from a plant's aerial parts, mainly through its stomata. |
| water vapour/ˈwɔːtə ˈveɪpə/ | Water in its gaseous state. |
| stomata/ˈstəʊmətə/ | Small pores in plant epidermis, controlled by guard cells, through which gases and water vapour pass. |
| cohesion/kəʊˈhiːʒn/ | The attraction between molecules of the same substance, helping them remain together. |
| tension/ˈtenʃn/ | A pulling force transmitted through a stretched string, cable or similar object. |
| adhesion/ədˈhiːʒn/ | Attraction between molecules of different substances. |
| xerophyte/ˈzɪərəfaɪt/ | A plant adapted to live where water is scarce. |
| cuticle/ˈkjuːtɪkl/ | A protective surface layer; on a leaf it is a waxy covering that helps reduce water loss. |
Pulling water up a tree
- A tall tree lifts water tens of metres — with no pump.
- The "engine" is water leaving the leaves: transpiration 蒸腾作用.
- Sticky water molecules let the whole column be pulled up.
Transpiration
- Transpiration is the loss of water vapour 水蒸气 from a plant.
- Water evaporates from the wet cell surfaces inside the leaf.
- The water vapour then diffuses out through the stomata 气孔 into the air.
Transpiration pulls water up the xylem by cohesion 内聚力 and tension 张力
Transpiration is:
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Transpiration is water evaporating inside the leaf and the vapour diffusing out through the stomata.
Water vapour leaves the leaf mainly by diffusing out through pores called ______.
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After evaporating from leaf cell surfaces, the vapour diffuses out through the stomata.
Cohesion and tension
- Water molecules attract each other by hydrogen bonds, so they stick together — this is cohesion.
- Loss at the top puts the column under tension (a pull), and cohesion lets the whole column be drawn up — the cohesion–tension idea.
- Water also sticks to the cellulose walls — adhesion 附着力 — which helps hold the column in place.
The transpiration stream
Step through how water is pulled up a tree — evaporation at the top creates a tension that drags the whole cohesive column upward.
Cohesion in the cohesion–tension theory means:
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Cohesion is water-to-water attraction (hydrogen bonds); it lets the whole column be pulled up under tension.
Match each term in the cohesion–tension theory.
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Evaporation creates tension; cohesion holds the column together so it is pulled up; adhesion helps it cling to the walls.
Xerophytes 旱生植物
- A xerophyte is a plant adapted to live where water is scarce. It cuts transpiration with:
- a thick waxy cuticle 角质层,
- stomata sunk in pits,
- hairs that trap moist air,
- leaves that can roll up.
Xerophyte leaf adaptations that reduce water loss
Which feature helps a xerophyte reduce water loss?
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Sunken stomata, a thick cuticle, trapped moist air and rolled leaves all cut transpiration.
Xerophytes are plants adapted to reduce water loss, with features like a thick cuticle and sunken stomata.
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Small or rolled leaves, a thick waxy cuticle, hairs and sunken stomata all trap moist air and cut transpiration.
You've got it
- transpiration = loss of water vapour: evaporates inside the leaf, diffuses out the stomata
- cohesion (hydrogen bonds) holds the water column together; it's pulled up under tension
- adhesion = water sticking to the cell walls
- xerophytes cut water loss: thick cuticle, sunken stomata, hairs, rolled leaves