CAIE A-Level Biology A2 14.2.3 Guard Cells Questions

Explain guard cells and their role in stomatal control using evidence from each question and mark scheme.

Exam points

Explain guard cells and their role in stomatal control.

[Maximum number: 4]

Stomata in leaves respond to changes in environmental conditions by opening and closing. This regulates carbon dioxide uptake and water loss.

Describe the mechanism by which stomata open in sunlight.

any four from:
1 protons / $\mathrm{H}^{+}$ ions, pumped, from guard cells / into guard cell wall ;
2 ref. to negative potential (inside cell) or $\mathrm{Cl}^{-}$ ions enter (cell) ;
3 (voltage-gated) $\mathrm{K}^{+}$ channels open or $\mathrm{K}^{+}$ ions enter (guard) cells ;
4 water enters cell, by osmosis / down water potential gradient ;
5 (guard) cells, become turgid / swell / increase in volume ;

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CAIE A-Level Biology A2 14.2.3 Guard Cells Questions question 1