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in Botany
In the nitrogen cycle, the conversion of atmospheric N2 into ammonia is carried out by:
A
Nitrosomonas
B
Rhizobium
C
Nitrobacter
D
Thiobacillus
Correct Answer:
B. Rhizobium
EXPLANATION
Rhizobium bacteria in root nodules of legumes fix atmospheric nitrogen into ammonia through nitrogenase enzyme.
The pulling force that moves water upward in xylem vessels is primarily due to:
A
Root pressure alone
B
Capillary action alone
C
Transpirational pull (tension) in xylem
D
Gravitational force
Correct Answer:
C. Transpirational pull (tension) in xylem
EXPLANATION
Cohesion-tension theory explains that water is pulled upward due to transpirational pull creating negative pressure in xylem.
Which of the following plants exhibits CAM (Crassulacean Acid Metabolism) photosynthesis?
A
Wheat
B
Rice
C
Pineapple
D
Maize
Correct Answer:
C. Pineapple
EXPLANATION
CAM plants like pineapple, cactus, and agave fix CO2 at night into organic acids and release during day for photosynthesis.
The enzyme RuBisCO catalyzes the fixation of CO2 by combining it with:
A
Glyceraldehyde-3-phosphate
B
Ribulose-1,5-bisphosphate
C
Phosphoenolpyruvate
D
Pyruvate
Correct Answer:
B. Ribulose-1,5-bisphosphate
EXPLANATION
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes CO2 fixation with RuBP in the Calvin cycle.
In the light-dependent reactions, the splitting of water molecules produces oxygen, hydrogen ions, and:
A
NADP+
B
NADPH
C
Electrons
D
ATP alone
Correct Answer:
C. Electrons
EXPLANATION
Water photolysis (2H2O → O2 + 4H+ + 4e-) releases electrons that are transferred through electron transport chains.
The process by which plants lose water as water vapour through stomata is called:
A
Guttation
B
Transpiration
C
Imbibition
D
Exudation
Correct Answer:
B. Transpiration
EXPLANATION
Transpiration is the loss of water vapour from aerial parts of plants, primarily through stomata during daytime.
Which type of phloem tissue is responsible for translocation of sugars in plants?
A
Sieve tube members only
B
Companion cells only
C
Sieve tube members with companion cells
D
Phloem fibers
Correct Answer:
C. Sieve tube members with companion cells
EXPLANATION
Sieve tube members conduct sugars while companion cells provide ATP and metabolic support for active transport.
The osmotic potential of a solution is directly related to:
A
Temperature only
B
Solute concentration and temperature
C
Pressure only
D
Volume of solvent only
Correct Answer:
B. Solute concentration and temperature
EXPLANATION
Osmotic potential (Ψs) = -iCRT, where it depends on solute concentration (C) and absolute temperature (T).
In plant tissue culture, which growth regulator ratio promotes callus formation?
A
High auxin : Low cytokinin
B
Low auxin : High cytokinin
C
Equal ratio of auxin and cytokinin
D
Neither auxin nor cytokinin
Correct Answer:
A. High auxin : Low cytokinin
EXPLANATION
High auxin to low cytokinin ratio promotes callus formation, while the ratios determine the type of organogenesis.
The phenomenon of leaf fall in deciduous plants before winter is regulated by which hormone?
A
Abscisic acid
B
Ethylene
C
Gibberellin
D
Cytokinin
Correct Answer:
A. Abscisic acid
EXPLANATION
Abscisic acid (ABA) accumulates during water stress and environmental changes, promoting abscission layer formation and leaf fall.
