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in Botany
In C4 plants, the first stable compound formed during carbon fixation is:
A
3-Phosphoglycerate
B
Oxaloacetate
C
Ribulose-1,5-bisphosphate
D
Glucose
Correct Answer:
B. Oxaloacetate
Explanation:
In C4 photosynthesis, CO2 combines with PEP (3-carbon) to form oxaloacetate (4-carbon compound) via the enzyme PEP carboxylase.
The root pressure phenomenon in plants can be measured using a device called:
A
Potometer
B
Barograph
C
Manometer
D
Tensiometer
Correct Answer:
C. Manometer
Explanation:
Root pressure is measured using a manometer connected to the cut end of a plant stem, showing the positive pressure generated by roots.
Which of the following statements about stomatal opening is correct?
A
Guard cells lose turgor pressure when stomata open
B
Potassium ions accumulate in guard cells during stomatal opening
C
Stomata open in complete darkness
D
Guard cells have thick outer walls and thin inner walls
Correct Answer:
B. Potassium ions accumulate in guard cells during stomatal opening
Explanation:
During stomatal opening, potassium ions (K+) actively accumulate in guard cells, increasing osmotic potential and causing water influx.
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.
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 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).
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.
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 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.
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.
