Biological termModerate1 mark
2(iv)
Read the explanations given below and name the structures:
Regulation of the opening and closing of stomata.
Topic: Guard cells
Previous-year question practice database
Answer
Exam answer
GUARD CELLS.
Explanation
Each stoma is bounded by two bean-shaped GUARD CELLS, and they are the only epidermal cells containing chloroplasts.
HOW THEY WORK: when the guard cells take in water they become TURGID. Because their inner wall (facing the pore) is THICKER and less elastic than the outer wall, the cells bend outwards as they swell, and the pore OPENS. When they lose water they become FLACCID, straighten, and the pore CLOSES.
That unequal thickening is the whole mechanism, and it is what examiners want explained — not simply that the cells swell.
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