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Root Pressure Evidence
MCQ questions and answers.
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MCQ Questions
1. What happens when the stem of a well-watered plant is cut near the base?
A.
Water may ooze out from the cut end
B.
The roots immediately stop absorbing water
C.
Air enters the roots and pushes water upward
D.
The leaves release no water at all
Correct Answer:
Water may ooze out from the cut end
Explanation:
The oozing of water or sap from a cut stem is evidence of positive root pressure generated in the roots.
2. The exudation of sap from a cut stem mainly indicates the presence of:
A.
Negative pressure in the leaves
B.
Positive pressure developed in the roots
C.
High temperature in the stem
D.
Low water absorption by the roots
Correct Answer:
Positive pressure developed in the roots
Explanation:
Sap exuding from a cut stem shows that pressure produced by the roots is pushing water upward through the xylem.
3. Which observation provides evidence for root pressure?
A.
Water droplets appearing at leaf margins
B.
Leaves becoming dry during a hot day
C.
Flowers opening in sunlight
D.
Seeds germinating in moist soil
Correct Answer:
Water droplets appearing at leaf margins
Explanation:
Water droplets at leaf margins, called guttation, can occur because root pressure pushes water through leaf hydathodes.
4. In which condition is root pressure most clearly observed through guttation?
A.
During a cool, humid night
B.
During a hot, dry afternoon
C.
During strong wind and low humidity
D.
When the soil is completely dry
Correct Answer:
During a cool, humid night
Explanation:
Guttation is common at night or early morning when transpiration is low but root pressure continues to push water toward the leaves.
5. Where do guttation droplets usually appear on a leaf?
A.
At the leaf margins or tips
B.
Only on the upper surface near the midrib
C.
Inside the leaf veins
D.
Only on the stem below the leaf
Correct Answer:
At the leaf margins or tips
Explanation:
Guttation droplets emerge through hydathodes, which are commonly located at the margins or tips of leaves.
6. Which experimental observation supports the existence of root pressure in a herbaceous plant?
A.
Sap rises from a cut stump
B.
The plant bends toward light
C.
The leaves turn green in sunlight
D.
The stem produces flowers
Correct Answer:
Sap rises from a cut stump
Explanation:
Sap rising or flowing from a cut stump shows that pressure from the roots is forcing water upward through the xylem.
7. Root pressure can be demonstrated most easily when the plant has:
A.
Adequate water in the soil
B.
Completely dry soil
C.
No living roots
D.
Leaves removed and roots dried
Correct Answer:
Adequate water in the soil
Explanation:
A well-watered plant can develop root pressure, making evidence such as sap exudation or guttation easier to observe.
8. What does the appearance of water droplets on the tips of grass leaves in the early morning commonly show?
A.
Guttation caused partly by root pressure
B.
Evaporation caused by strong sunlight
C.
Water loss through leaf stomata only
D.
Absorption of water from the atmosphere by leaves
Correct Answer:
Guttation caused partly by root pressure
Explanation:
Early-morning droplets on grass leaf tips are often produced by guttation, in which root pressure forces xylem sap out through hydathodes.
9. Why does sap continue to come out of a cut stem for some time after the cut is made?
A.
Root pressure continues to push water into the xylem
B.
The leaves begin producing extra water
C.
The cut stem absorbs water directly from the air
D.
The roots stop taking in mineral salts
Correct Answer:
Root pressure continues to push water into the xylem
Explanation:
Continued exudation occurs because active roots maintain positive pressure and keep forcing water into the xylem.
10. Which of the following is direct evidence of positive pressure in the xylem caused by roots?
A.
Bleeding of sap from a cut plant stem
B.
Closing of stomata during drought
C.
Wilting of leaves in dry air
D.
Growth of roots toward water
Correct Answer:
Bleeding of sap from a cut plant stem
Explanation:
The bleeding or exudation of sap from a cut stem directly demonstrates that pressure generated in the roots is pushing xylem water upward.
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Root Pressure Evidence
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