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Xylem Hydrostatic Pressure
MCQ questions and answers.
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MCQ Questions
1. What is xylem hydrostatic pressure?
A.
Positive pressure developed in the xylem
B.
Negative pressure developed in the phloem
C.
Pressure developed in the stomata
D.
Pressure inside the root hairs only
Correct Answer:
Positive pressure developed in the xylem
Explanation:
Xylem hydrostatic pressure is the positive pressure that develops inside the xylem vessels, mainly due to the movement of water and dissolved minerals from the roots.
2. Which process mainly contributes to the development of hydrostatic pressure in the xylem?
A.
Active absorption of mineral ions by root cells
B.
Loss of water from leaves through stomata
C.
Breakdown of starch in guard cells
D.
Movement of sugars through phloem
Correct Answer:
Active absorption of mineral ions by root cells
Explanation:
Active absorption of mineral ions lowers the water potential of root cells, causing water to enter and build positive hydrostatic pressure in the xylem.
3. What happens to water in the xylem when xylem hydrostatic pressure increases?
A.
It is pushed upward through the xylem
B.
It moves into the phloem
C.
It changes into mineral ions
D.
It immediately leaves through the roots
Correct Answer:
It is pushed upward through the xylem
Explanation:
Positive hydrostatic pressure in the xylem can push water and dissolved minerals upward through the continuous xylem vessels.
4. Which condition favors the development of xylem hydrostatic pressure?
A.
Adequate soil moisture and active roots
B.
Completely dry soil and dead roots
C.
Blocked xylem vessels
D.
Absence of mineral ions in the soil
Correct Answer:
Adequate soil moisture and active roots
Explanation:
Active roots can absorb mineral ions and water when soil moisture is available, helping positive hydrostatic pressure develop in the xylem.
5. Xylem hydrostatic pressure is commonly associated with which form of pressure in plants?
A.
Root pressure
B.
Turgor pressure in guard cells
C.
Osmotic pressure in phloem sieve tubes
D.
Atmospheric pressure around leaves
Correct Answer:
Root pressure
Explanation:
Root pressure is the positive hydrostatic pressure produced in the xylem of roots and may help push water into the stem.
6. What is one visible effect of high xylem hydrostatic pressure in some herbaceous plants?
A.
Guttation from leaf margins
B.
Closing of all xylem vessels
C.
Formation of phloem sap
D.
Immediate drying of leaf surfaces
Correct Answer:
Guttation from leaf margins
Explanation:
When xylem hydrostatic pressure is high, water may be forced out through hydathodes at leaf margins, producing guttation.
7. Through which structures can water be released during guttation caused by xylem hydrostatic pressure?
A.
Hydathodes
B.
Lenticels only
C.
Sieve plates
D.
Root hairs only
Correct Answer:
Hydathodes
Explanation:
Hydathodes are specialized structures, usually located at leaf margins or tips, through which xylem water may escape during guttation.
8. Why can xylem hydrostatic pressure help water reach the leaves?
A.
It provides a pushing force from below
B.
It pulls water into the roots from the leaves
C.
It converts water into food
D.
It prevents water from entering the xylem
Correct Answer:
It provides a pushing force from below
Explanation:
Positive pressure in the root xylem pushes water upward, helping its movement toward the leaves.
9. When is guttation due to xylem hydrostatic pressure most likely to occur?
A.
When soil water is available and transpiration is low
B.
When soil is completely dry and transpiration is very high
C.
When roots are no longer absorbing minerals
D.
When all hydathodes are permanently closed
Correct Answer:
When soil water is available and transpiration is low
Explanation:
Adequate soil water allows root absorption, while low transpiration permits positive xylem pressure to build and force water out through hydathodes.
10. What type of pressure is present in the xylem during root pressure?
A.
Positive pressure
B.
Negative pressure
C.
Zero pressure
D.
Pressure found only in phloem
Correct Answer:
Positive pressure
Explanation:
Root pressure produces positive hydrostatic pressure in the xylem, which can push water and minerals upward through the plant.
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