Page 43 - Q & A STPM 2022 Biology

Biology STPM Chapter 7 Gaseous Exchange
7.3 Gaseous Exchange in Plants

Section A Multiple-choice Questions

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Question 1
Which of the following condition causes the opening of a stoma?
A The influx of potassium ions from the guard cells
B The decrease in the concentration of glucose in the guard cells
C The increase in the concentration of carbon dioxide in the guard cells
D The increase in the concentration of the abscisic acid when plants are
exposed to stress

Answer: A
According to the potassium ion accumulation hypothesis, the opening of the
stomata is associated with the influx of K ions into the guard cells from the
+
Semester
2 epidermal cells

Section B Structured Questions

Question 1
(a) With the aid of a diagram, describe the structure of stomata.
(b) Explain the mechanism of stomatal opening and closing.

Answer:
(a) – The stomata consist of a pair of guard cells.
– that surround a small pore known as the stomatal aperture
– The guard cells are kidney-shaped.
– The guard cell contains chloroplasts, nuclei, dense cytoplasm, vacuole
and mitochondria.
– It has a thicker, less elastic inner wall and a thinner outer wall.
– There are cellulose microfibrils that are radially orientated in the cell
walls of the guard cells.
– The guard cells are joined at the ends.
– The epidermal cells surrounding these cells are called subsidiary cells.

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