CIE A Level Biology復(fù)習(xí)筆記14.2.1 Stomata
Stomata
- Plants carry out?homeostasis?– just like animals they need to maintain a?constant internal environment
- For example, mesophyll cells in leaves require a?constant supply of carbon dioxide?for?photosynthesis
- Stomata?(specifically the?guard cells) control the diffusion of gases in and out of leaves
- This means stomata?control the entry of carbon dioxide?into leaves
Response of guard cells & stomata table
- Regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion with the need to minimise water loss by transpiration
Advantages & disadvantages of stomatal opening & closure table
Exam Tip
A stoma is actually the aperture (hole) between two guard cells, but the term is often used to refer to the whole unit (the two guard cells and the hole between them).Don’t forget – stoma (singular) refers to one of these units, whereas stomata (plural) refers to many!
Opening & Closing of Stomata
- Stomata?open?and?close?in a?daily rhythm
- Even when the plant is kept in?constant light?or?constant darkness, the daily rhythm of opening and closing of the stomata continues
- Opening of stomata?during the day:
- maintains the?inward diffusion of carbon dioxide?and the?outward diffusion of oxygen
- allows the?outward diffusion of water?vapour?in transpiration
- Closing of stomata?at night?when photosynthesis cannot occur:
- reduces?the rate of?transpiration
- conserves water
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