Structure and Function
Stomata (singular: stoma) are pores in the leaf epidermis controlled by pairs of guard cells. These kidney-shaped cells regulate gas exchange and water loss.
Opening Mechanism
Guard cells control stomatal opening through changes in turgor pressure:
- Light triggers: Blue light receptors activate potassium pumps
- Ion movement: Kโบ ions actively pumped into guard cells
- Water influx: Water follows by osmosis, increasing turgor
- Shape change: Guard cells become turgid and curved
- Pore opens: Inner walls pulled apart creating opening
Closing Mechanism
- Kโบ ions pumped out of guard cells
- Water follows by osmosis
- Guard cells become flaccid
- Pore closes as cells straighten
This deep dive covers Stomata: The Control Valves within Transpiration for GCSE Biology. Transpiration process, stomatal control, factors affecting rate, plant adaptations, measuring transpiration, and practical investigations It is section 5 of 21 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Transpiration
What is transpiration?
Describe the three stages of transpiration in a leaf.
Quick recall flashcards
What is a potometer?
An apparatus that measures the rate of water uptake by a plant shoot. Used to estimate transpiration rate (though actually measures uptake, not loss).
What is a xerophyte?
A plant adapted to survive in dry/arid conditions with limited water availability (e.g., cacti, marram grass).