Homeostasis in plants
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. |
| guard cell/ɡɑːd sel/ | One of a pair of specialised cells whose changes in shape control the opening of a stoma. |
| turgid/ˈtɜːdʒɪd/ | Describing a plant cell swollen and firm because water entering by osmosis produces pressure against its cell wall. |
| water stress/ˈwɔːtə stres/ | A condition in which water availability is insufficient to support normal plant functions. |
| abscisic acid/əbˈsɪzɪk ˈæsɪd/ | A plant hormone involved in responses to water shortage, stomatal closure and seed dormancy. |
How plants control water loss
- Stomata 气孔 are pores in a leaf.
- The plant opens and closes them to balance two needs.
- A drought hormone can shut them to save water.
Guard cells close the stomata to reduce water loss when the plant is short of water.
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Closing the stomata is how a plant conserves water — part of homeostasis in plants.
A plant opens and closes its stomata to balance:
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Open stomata let CO₂ in for photosynthesis but also let water escape, so the plant must balance the two.
A balancing act
- Open stomata let in carbon dioxide for photosynthesis.
- But open stomata also lose water by transpiration 蒸腾作用.
- So stomata usually open by day and close at night, on a daily rhythm.
How a stoma opens
Step through it. Guard cells pump in ions, draw in water by osmosis, swell turgid and bend apart — opening the pore.
Guard cells open a stoma by:
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Taking in ions lowers their water potential; water enters, the guard cells swell turgid and bend apart.
Put the opening of a stoma in order.
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Pump ions → water in by osmosis → turgid → bend apart → open. Losing the ions reverses it and the stoma closes.
How guard cells 保卫细胞 work
- Each stoma is opened and closed by two guard cells:
- to open: guard cells pump in ions → water potential falls → water enters by osmosis → they swell turgid 膨胀 and bend apart, opening the pore.
- to close: ions leave → water follows out → guard cells go floppy → the pore shuts.
Guard cells swell turgid to open the stoma, and go floppy to close it
When a plant is short of water, abscisic acid (ABA):
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ABA is released under water stress and triggers stomatal closure to conserve water.
When a plant is short of water, the hormone ______ makes its stomata close.
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ABA is the stress hormone that triggers stomatal closure to save water.
Inside the guard cells, the second messenger in ABA signalling is:
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Calcium ions act as the second messenger that brings about stomatal closure in response to ABA.
Water stress 水分胁迫 and ABA
- When the plant is short of water (water stress), it releases the hormone abscisic acid 脱落酸 (ABA).
- ABA makes the guard cells lose ions and water, so the stomata close and save water.
- Inside the guard cells, calcium ions act as a second messenger.
You've got it
- stomata balance CO₂ in (photosynthesis) vs water loss (transpiration)
- guard cells open the pore by taking in ions + water (turgid); close it by losing them (floppy)
- under water stress, ABA makes stomata close to save water
- calcium ions act as the second messenger in the guard cells