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in Plant Physiology
Which of the following is a characteristic feature of bundle sheath cells in C4 plants?
A
Rich in chloroplasts with well-developed grana
B
Absence of starch grains
C
Tightly packed with few intercellular spaces
D
Directly exposed to stomata
Correct Answer:
A. Rich in chloroplasts with well-developed grana
EXPLANATION
Bundle sheath cells in C4 plants contain large chloroplasts with well-developed grana for the Calvin cycle, unlike mesophyll cells.
In C4 plants, the first stable product of CO2 fixation is:
A
3-Phosphoglycerate
B
Oxaloacetate
C
Malate
D
Phosphoenolpyruvate
Correct Answer:
B. Oxaloacetate
EXPLANATION
In the Hatch-Slack pathway, PEP carboxylase catalyzes formation of oxaloacetate (4-carbon compound) in mesophyll cells.
Which statement about ATP synthase is correct?
A
It synthesizes ATP using proton gradient energy
B
It functions in both photosynthesis and aerobic respiration
C
The F0 subunit is embedded in the membrane
D
All of the above are correct
Correct Answer:
D. All of the above are correct
EXPLANATION
ATP synthase works in both processes using chemiosmotic gradient; F0 is the membrane-spanning unit; F1 synthesizes ATP from ADP.
The phenomenon where plants lose water in liquid form through hydathodes is called:
A
Transpiration
B
Guttation
C
Exudation
D
Imbibition
Correct Answer:
B. Guttation
EXPLANATION
Guttation occurs when root pressure forces water out through hydathodes (water pores) as liquid water droplets, typically at night.
At saturating light intensity, photosynthesis is primarily limited by:
A
Light wavelength
B
Photosynthetic pigments
C
CO2 concentration
D
Chloroplast number
Correct Answer:
C. CO2 concentration
EXPLANATION
When light is saturating, CO2 becomes the limiting factor as RuBisCO activity depends on substrate availability.
Which of the following best describes the Pasteur effect?
A
Inhibition of photosynthesis by high light intensity
B
Inhibition of fermentation by aerobic respiration
C
Enhancement of fermentation under anaerobic conditions
D
Increased photosynthesis at high CO2 levels
Correct Answer:
B. Inhibition of fermentation by aerobic respiration
EXPLANATION
The Pasteur effect describes how aerobic respiration inhibits the rate of fermentation, as aerobic respiration is more efficient.
The rate-limiting step of photosynthesis under normal conditions is:
A
Light absorption
B
CO2 fixation
C
Electron transport
D
Water photolysis
Correct Answer:
B. CO2 fixation
EXPLANATION
The carboxylation of RuBP by RuBisCO is typically the slowest step in photosynthesis under normal light conditions.
Which organelle is responsible for amino acid synthesis in plants?
A
Ribosome
B
Chloroplast
C
Peroxisome
D
Endoplasmic reticulum
Correct Answer:
B. Chloroplast
EXPLANATION
Chloroplasts synthesize amino acids using carbon skeletons from the Calvin cycle and nitrogen from nitrite reduction.
In photorespiration, the primary substrate is:
A
3-Phosphoglycerate
B
Ribulose-1,5-bisphosphate
C
Glyceraldehyde-3-phosphate
D
Phosphoenolpyruvate
Correct Answer:
B. Ribulose-1,5-bisphosphate
EXPLANATION
RuBisCO catalyzes oxygenation of RuBP instead of carboxylation under high O2/CO2 ratios, initiating the photorespiratory pathway.
The grana in chloroplasts are composed of:
A
Stacked thylakoids
B
Unstacked thylakoids
C
Stroma lamellae
D
Cristae
Correct Answer:
A. Stacked thylakoids
EXPLANATION
Grana are stacks of thylakoids arranged vertically, while stroma lamellae are unstacked thylakoids connecting different grana.
