Transpiration
Introduced| English | Meaning |
|---|---|
| stomata/ˈstəʊmətə/ | Small pores in plant epidermis, controlled by guard cells, through which gases and water vapour pass. |
| transpiration/trænspəˈreɪʃn/ | The loss of water vapour from a plant's aerial parts, mainly through its stomata. |
| humidity/hjuːˈmɪdɪti/ | The amount of water vapour in the air, measured in a specified way. |
| guard cells/ɡɑːd selz/ | One of a pair of specialised cells whose changes in shape control the opening of a stoma. |
The price of open pores
- To let carbon dioxide in, a leaf must open its stomata 气孔 — but water vapour escapes at the same time.
- This loss of water is transpiration 蒸腾作用.
Transpiration is the loss of:
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Transpiration is water vapour loss, mainly through stomata.
Most water vapour is lost through pores called ______.
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Stomata are the main route for transpiration.
What transpiration is
- Transpiration is the loss of water vapour from a plant's leaves, mainly through the stomata.
- It pulls the transpiration stream of water up from the roots.
The transpiration stream
Water is pulled up the plant in a continuous stream, from the roots to the leaves where it evaporates.
Which increase the rate of transpiration? (Select all that apply.)
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Higher humidity slows transpiration; the others speed it up.
Increasing the humidity of the air around a leaf will:
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Moist air reduces evaporation, slowing transpiration.
Factors affecting the rate
- Transpiration speeds up with more light, higher temperature, more wind, and lower humidity 湿度.
- Each makes evaporation from the leaf faster.
Each environmental factor that speeds up evaporation raises the transpiration rate.
A plant wilts if it loses water faster than it can take it up.
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Flaccid cells can no longer support the plant.
Wilting and control
- If a plant loses water faster than it takes it up, cells become flaccid and it wilts.
- Guard cells 保卫细胞 can close the stomata to reduce water loss.
Higher humidity SLOWS transpiration. When the air is already moist, there's less difference between the leaf and the air, so less water evaporates. Dry, windy, hot, bright conditions speed it up.
You've got it
- transpiration = loss of water vapour from leaves (through stomata)
- rate rises with more light, higher temperature, more wind, lower humidity
- excessive loss causes wilting; guard cells close stomata to reduce it