1. Which plant hormone promotes stomatal closure during water stress?
A.
Auxin
B.
Abscisic acid
C.
Gibberellin
D.
Cytokinin
Correct Answer:
Abscisic acid
Explanation:
Abscisic acid promotes stomatal closure when the plant experiences water stress, helping to reduce water loss.
2. What is the main purpose of stomatal closure during drought?
A.
To increase water loss
B.
To reduce water loss
C.
To increase leaf size
D.
To promote flowering
Correct Answer:
To reduce water loss
Explanation:
Closing the stomata reduces the escape of water vapour from the leaves through transpiration.
3. Which cells change their shape to open or close a stoma?
A.
Root hair cells
B.
Guard cells
C.
Xylem cells
D.
Palisade cells
Correct Answer:
Guard cells
Explanation:
Guard cells surround each stoma and control its opening and closing.
4. During water stress, abscisic acid causes guard cells to become less:
A.
Turgid
B.
Lignified
C.
Divided
D.
Elongated
Correct Answer:
Turgid
Explanation:
Abscisic acid promotes loss of water from guard cells, making them less turgid and causing the stomatal pore to close.
5. Stomatal closure directly decreases which process?
A.
Transpiration
B.
Seed germination
C.
Root growth
D.
Cell division
Correct Answer:
Transpiration
Explanation:
When stomata close, less water vapour leaves the leaf, so the rate of transpiration decreases.
6. In which condition is abscisic acid most likely to promote stomatal closure?
A.
Adequate water supply
B.
Drought
C.
High nutrient availability
D.
Rapid cell division
Correct Answer:
Drought
Explanation:
Drought causes water stress, which increases the role of abscisic acid in closing stomata.
7. What happens to the stomatal pore when guard cells lose water?
A.
It becomes wider
B.
It closes
C.
It changes into a root
D.
It produces pollen
Correct Answer:
It closes
Explanation:
Loss of water lowers guard-cell turgor, causing the guard cells to close the stomatal pore.
8. Stomatal closure helps a plant survive mainly by conserving:
A.
Water
B.
Starch
C.
Oxygen
D.
Pollen
Correct Answer:
Water
Explanation:
Closing stomata limits transpiration and helps conserve water during stressful conditions.
9. Which structure is closed by the action of guard cells during water stress?
A.
Stomatal pore
B.
Root cap
C.
Leaf vein
D.
Seed coat
Correct Answer:
Stomatal pore
Explanation:
Guard cells regulate the stomatal pore, closing it when water stress signals such as abscisic acid are present.
10. What is a likely effect of abscisic acid on the stomata of a water-stressed leaf?
A.
They remain permanently open
B.
They close to limit water loss
C.
They produce more chlorophyll
D.
They develop into roots
Correct Answer:
They close to limit water loss
Explanation:
Abscisic acid signals the guard cells to close the stomata, thereby reducing water loss from the leaf.
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