Transpiration and xerophytes
| English | Chinese | Pinyin |
|---|---|---|
| transpiration | 蒸腾作用 | zhēng téng zuò yòng |
| water vapour | 水蒸气 | shuǐ zhēng qì |
| stomata | 气孔 | qì kǒng |
| cohesion | 内聚力 | nèi jù lì |
| tension | 张力 | zhāng lì |
| adhesion | 附着力 | fù zhuó lì |
| xerophyte | 旱生植物 | hàn shēng zhí wù |
| cuticle | 角质层 | jiǎo zhì céng |
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:
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 ______.
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:
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.
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?
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.
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