The phenomenon where certain seeds require light for germination is called:
Answer: B
Photomorphogenesis refers to light-dependent development processes including light-mediated seed germination. Phytochrome is the photoreceptor involved. This is distinct from photoperiodism (flowering response to day length).
Q.22Medium
In the Calvin cycle, how many ATP and NADPH molecules are required to fix one molecule of CO2?
Answer: B
The reduction phase of Calvin cycle requires 3 ATP per CO2 fixed. NADPH requirement is 2 molecules per CO2. These are stoichiometric ratios essential for understanding photosynthetic efficiency.
Q.23Medium
Which of the following is a synthetic auxin used in agriculture?
Answer: B
2,4-D is a synthetic auxin widely used as a selective herbicide. Natural auxin is IAA (Indole-3-acetic acid). This is application-based knowledge relevant for agricultural science in UPSC.
Q.24Medium
The casparian strip in the endodermis of roots is composed of:
Answer: B
The Casparian strip is a band of suberin (waterproof lipid polymer) that prevents passive transport across the endodermis, forcing minerals to undergo active transport. This ensures selective ion uptake - a key NCERT concept.
Q.25Medium
The rate of photosynthesis increases with increasing CO2 concentration only up to a certain point. This point is called:
Answer: A
CO2 saturation point is where further increase in CO2 doesn't increase photosynthesis rate because other factors (like enzyme activity) become limiting. Compensation point is where photosynthesis equals respiration.
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Q.26Medium
Abscisic acid (ABA) functions primarily as which type of hormone?
Answer: B
ABA is a stress hormone that accumulates during drought, regulating stomatal closure and promoting seed dormancy. It antagonizes gibberellins and cytokinins. This is crucial for understanding plant responses to environmental stress.
Q.27Medium
In woody dicots, the wood primarily consists of:
Answer: B
Wood is composed of secondary xylem with thick-walled tracheids and vessel elements that provide mechanical support and water transport. Annual rings visible in wood represent secondary xylem produced by vascular cambium.
Q.28Medium
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.29Medium
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.30Medium
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.31Medium
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.32Medium
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).
Q.33Medium
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.34Medium
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.35Medium
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.36Medium
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.37Medium
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.38Medium
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.39Medium
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.40Medium
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.
