Higher Guard Cell Ion Mechanism in Detail
Part of Transpiration — GCSE Biology
This higher tier covers Higher Guard Cell Ion Mechanism in Detail within Transpiration for GCSE Biology. Transpiration process, stomatal control, factors affecting rate, plant adaptations, measuring transpiration, and practical investigations It is section 17 of 20 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
Topic position
Section 17 of 20
Practice
20 questions
Recall
25 flashcards
Higher Guard Cell Ion Mechanism in Detail
At Higher tier, you may need to explain the guard cell mechanism with precise reference to active transport and osmosis:
- In light, blue light receptors in the guard cell plasma membrane are activated.
- This activates H⁺-ATPase pumps, which actively pump H⁺ ions out of the guard cell. This creates a negative charge inside the cell.
- The negative interior attracts K⁺ (potassium) ions from neighbouring epidermal cells — K⁺ enters via ion channels.
- The accumulation of K⁺ lowers the water potential inside the guard cell.
- Water enters by osmosis down the water potential gradient, making the guard cell turgid.
- The guard cell wall is unevenly thickened — the inner wall (facing the pore) is much thicker than the outer wall. As turgor increases, the thinner outer wall expands more than the inner wall, bowing the cell into a curved (kidney) shape.
- This bowing pulls the two guard cells apart, opening the pore.
Closing is the reverse: in darkness or drought, K⁺ is pumped back out, water follows by osmosis, cells become flaccid, and the pore closes.