The calcium pump in plant cell vacuole membrane is primarily involved in:
Answer: C
Calcium pumps actively transport Ca²⁺ into vacuoles, serving as a calcium reservoir for second messenger signaling in plant cells.
Q.22Medium
The phenomenon where plants show reduced photosynthesis when exposed to high oxygen concentrations is called:
Answer: A
The Warburg effect in plants refers to photorespiration, where high O₂ competes with CO₂ for Rubisco binding, reducing net photosynthesis.
Q.23Medium
Mycorrhizal associations in plants primarily enhance the uptake of which nutrients?
Answer: B
Arbuscular mycorrhizal fungi increase plant access to phosphorus and micronutrients (Zn, Cu) through their extensive hyphal networks in soil.
Q.24Medium
The casparian strip in plant roots is composed primarily of:
Answer: B
The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.
Q.25Medium
The quantum yield of photosynthesis (φ) represents:
Answer: A
Quantum yield is the ratio of CO₂ fixed to photons absorbed, typically 0.05-0.1 (5-10 CO₂ per 100 photons).
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Q.26Medium
Guttation in plants occurs due to:
Answer: B
Guttation is the exudation of xylem sap through hydathodes, caused by positive root pressure, especially in early morning when transpiration is low.
Q.27Medium
The turgor pressure in plant cells is maintained by which osmotically active substances?
Answer: B
Osmotically active solutes like glucose, sucrose, malate, and K⁺ ions accumulate in vacuoles to maintain turgor pressure and cell rigidity.
Q.28Medium
The Hatch-Slack cycle in C4 plants first produces which compound?
Answer: A
In C4 photosynthesis, CO₂ combines with phosphoenolpyruvate (PEP) to form oxaloacetate (4-carbon), catalyzed by PEP carboxylase.
Q.29Medium
The transpiration pull mechanism in xylem transport depends on which principle?
Answer: B
Transpiration creates negative pressure (tension) in xylem; water cohesion allows continuous columns to be pulled upward against gravity.
Q.30Medium
The non-cyclic photophosphorylation in photosystem II produces:
Answer: C
Non-cyclic photophosphorylation involves PSII and PSI, producing ATP, NADPH, and O₂ from water photolysis.
Q.31Medium
The reduction phase of Calvin cycle produces which molecule as the final product?
Answer: C
G3P (Glyceraldehyde-3-phosphate) is the final product of the reduction phase where 3-PG is reduced using ATP and NADPH from light reactions.
Q.32Medium
C3 plants show a phenomenon of photorespiration. What is the primary substrate that reacts with RuBP when O2 concentration is high?
Answer: C
When O2 concentration is high, RuBisCO catalyzes oxygenase activity, causing O2 to react with RuBP instead of CO2, initiating photorespiration.
Q.33Medium
The phenomenon where plants lose water as liquid droplets from leaf margins is called:
Answer: B
Exudation or guttation occurs when root pressure forces water out through specialized pores (hydathodes) as liquid water droplets, typically observed in early morning.
Q.34Medium
Which plant hormone is known to have antagonistic effects to gibberellins in seed germination?
Answer: B
Abscisic acid (ABA) promotes seed dormancy and inhibits germination, acting antagonistically to gibberellins which promote germination.
Q.35Medium
Which of the following transport mechanisms does NOT require energy in plant cells?
Answer: B
Osmosis is passive transport of water molecules across a semipermeable membrane in response to water potential differences.
Q.36Medium
The phenomenon of senescence in plants is primarily controlled by which hormone?
Answer: D
Ethylene is the major hormone controlling senescence (aging) in plants, promoting leaf yellowing, fruit ripening, and abscission.
Q.37Medium
Which of the following is a chemosynthetic organism commonly found in soil?
Answer: B
Nitrosomonas is a chemosynthetic bacterium that oxidizes ammonia to nitrite, obtaining energy without requiring light (unlike photosynthetic organisms).
Q.38Medium
The rate of photosynthesis increases with an increase in CO2 concentration until it reaches a plateau. This plateau is called:
Answer: B
The saturation point is the CO2 concentration beyond which photosynthesis rate does not increase further, limited by other factors like temperature or light.
