Abscisic acid (ABA) functions primarily as which type of hormone?
AGrowth promoter
BStress hormone
CFlowering hormone
DRipening hormone
Correct Answer:
B. Stress hormone
Explanation:
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.
The rate of photosynthesis increases with increasing CO2 concentration only up to a certain point. This point is called:
ASaturation point
BCompensation point
COptimal point
DLight-saturation point
Correct Answer:
A. Saturation point
Explanation:
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.
The casparian strip in the endodermis of roots is composed of:
ACutin and wax
BSuberin
CCellulose and hemicellulose
DLignin only
Correct Answer:
B. Suberin
Explanation:
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.
Which of the following is a synthetic auxin used in agriculture?
AGibberellic acid
B2,4-Dichlorophenoxyacetic acid (2,4-D)
CAbscisic acid
DKinetin
Correct Answer:
B. 2,4-Dichlorophenoxyacetic acid (2,4-D)
Explanation:
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.
In the Calvin cycle, how many ATP and NADPH molecules are required to fix one molecule of CO2?
A1 ATP, 1 NADPH
B3 ATP, 2 NADPH
C2 ATP, 1 NADPH
D6 ATP, 3 NADPH
Correct Answer:
B. 3 ATP, 2 NADPH
Explanation:
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.
The phenomenon where certain seeds require light for germination is called:
APhototropism
BPhotomorphogenesis
CPhotoperiodism
DHeliotropism
Correct Answer:
B. Photomorphogenesis
Explanation:
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).
In C4 photosynthesis, the first stable compound formed after CO2 fixation is:
A3-Phosphoglycerate (3-PGA)
BOxaloacetate
CRibulose-1,5-bisphosphate
DGlucose
Correct Answer:
B. Oxaloacetate
Explanation:
In C4 plants, PEP carboxylase fixes CO2 into oxaloacetate (4-carbon compound), unlike C3 plants where RuBisCO produces 3-PGA. This adaptation reduces photorespiration and is efficient in hot climates.
Which of the following pigments is primarily responsible for absorbing light in the red and far-red regions of the spectrum in photosynthesis?
AChlorophyll a
BPhytochrome
CCarotenoids
DXanthophyll
Correct Answer:
B. Phytochrome
Explanation:
Phytochrome exists in two interconvertible forms (Pr and Pfr) and absorbs maximally in red (~660 nm) and far-red (~730 nm) regions. It's crucial for seed germination and photoperiodism - important for UPSC agriculture-related questions.
The root pressure phenomenon in plants is primarily due to which of the following?
ATranspiration pull alone
BCapillary action in soil
CActive transport of mineral ions into xylem, creating osmotic gradient
DGravitational force on water column
Correct Answer:
C. Active transport of mineral ions into xylem, creating osmotic gradient
Explanation:
Root pressure is generated by active transport of mineral ions into the xylem sap, creating a concentration gradient that draws water in osmotically. This is distinct from transpiration pull and is a key concept in plant physiology.
