The casparian strip in plant roots is composed primarily of:
A
Cellulose and pectin
B
Suberin and lignin
C
Chitin and protein
D
Keratin and elastin
Correct Answer:
B. Suberin and lignin
Explanation:
The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.
The quantum yield of photosynthesis (φ) represents:
A
The number of CO₂ molecules fixed per photon absorbed
B
The wavelength of light absorbed
C
The rate of electron transport
D
The concentration of chlorophyll
Correct Answer:
A. The number of CO₂ molecules fixed per photon absorbed
Explanation:
Quantum yield is the ratio of CO₂ fixed to photons absorbed, typically 0.05-0.1 (5-10 CO₂ per 100 photons).
Guttation in plants occurs due to:
A
Transpiration
B
Root pressure and high humidity conditions
C
Photorespiration
D
Osmotic stress
Correct Answer:
B. Root pressure and high humidity conditions
Explanation:
Guttation is the exudation of xylem sap through hydathodes, caused by positive root pressure, especially in early morning when transpiration is low.
The turgor pressure in plant cells is maintained by which osmotically active substances?
A
Cellulose and starch
B
Soluble sugars, organic acids, and mineral ions
C
Proteins and lipids
D
Chlorophyll and carotenoids
Correct Answer:
B. Soluble sugars, organic acids, and mineral ions
Explanation:
Osmotically active solutes like glucose, sucrose, malate, and K⁺ ions accumulate in vacuoles to maintain turgor pressure and cell rigidity.
The Hatch-Slack cycle in C4 plants first produces which compound?
A
Oxaloacetate (4-carbon)
B
3-Phosphoglycerate (3-carbon)
C
Malate (4-carbon)
D
Pyruvate (3-carbon)
Correct Answer:
A. Oxaloacetate (4-carbon)
Explanation:
In C4 photosynthesis, CO₂ combines with phosphoenolpyruvate (PEP) to form oxaloacetate (4-carbon), catalyzed by PEP carboxylase.
The transpiration pull mechanism in xylem transport depends on which principle?
A
Osmotic gradient
B
Cohesion-tension theory and water's high surface tension
C
Active transport of ions
D
Pressure exerted by companion cells
Correct Answer:
B. Cohesion-tension theory and water's high surface tension
Explanation:
Transpiration creates negative pressure (tension) in xylem; water cohesion allows continuous columns to be pulled upward against gravity.
The non-cyclic photophosphorylation in photosystem II produces:
A
ATP only
B
NADPH only
C
Both ATP and NADPH, and releases O₂
D
Glucose directly
Correct Answer:
C. Both ATP and NADPH, and releases O₂
Explanation:
Non-cyclic photophosphorylation involves PSII and PSI, producing ATP, NADPH, and O₂ from water photolysis.
The reduction phase of Calvin cycle produces which molecule as the final product?
A
Pyruvate
B
Glucose
C
Glyceraldehyde-3-phosphate
D
Oxaloacetate
Correct Answer:
C. Glyceraldehyde-3-phosphate
Explanation:
G3P (Glyceraldehyde-3-phosphate) is the final product of the reduction phase where 3-PG is reduced using ATP and NADPH from light reactions.
C3 plants show a phenomenon of photorespiration. What is the primary substrate that reacts with RuBP when O2 concentration is high?
A
Phosphoenolpyruvate
B
Phosphoglycolate
C
Oxygen (O2)
D
Carbon monoxide
Correct Answer:
C. Oxygen (O2)
Explanation:
When O2 concentration is high, RuBisCO catalyzes oxygenase activity, causing O2 to react with RuBP instead of CO2, initiating photorespiration.
The phenomenon where plants lose water as liquid droplets from leaf margins is called:
A
Transpiration
B
Exudation
C
Imbibition
D
Osmosis
Correct Answer:
B. Exudation
Explanation:
Exudation or guttation occurs when root pressure forces water out through specialized pores (hydathodes) as liquid water droplets, typically observed in early morning.
