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Difficulty: All Easy Medium Hard 51–60 of 96
Topics in General Science
Q.51 Medium Physics
A lens has a focal length of 15 cm. What is its power?
A +6.67 D
B -6.67 D
C +2.25 D
D -2.25 D
Correct Answer:  A. +6.67 D
EXPLANATION

Power P = 1/f (in meters). P = 1/0.15 = 6.67 Diopters (positive for converging lens)

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Q.52 Medium Botany
The rate of photosynthesis increases with an increase in CO2 concentration until it reaches a plateau. This plateau is called:
A Compensation point
B Saturation point
C Optimum point
D Threshold point
Correct Answer:  B. Saturation point
EXPLANATION

The saturation point is the CO2 concentration beyond which photosynthesis rate does not increase further, limited by other factors like temperature or light.

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Q.53 Medium Botany
Which of the following is a chemosynthetic organism commonly found in soil?
A Cyanobacteria
B Nitrosomonas
C Chlorella
D Spirogyra
Correct Answer:  B. Nitrosomonas
EXPLANATION

Nitrosomonas is a chemosynthetic bacterium that oxidizes ammonia to nitrite, obtaining energy without requiring light (unlike photosynthetic organisms).

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Q.54 Medium Botany
The phenomenon of senescence in plants is primarily controlled by which hormone?
A Gibberellin
B Cytokinin
C Abscisic acid
D Ethylene
Correct Answer:  D. Ethylene
EXPLANATION

Ethylene is the major hormone controlling senescence (aging) in plants, promoting leaf yellowing, fruit ripening, and abscission.

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Q.55 Medium Botany
Which of the following transport mechanisms does NOT require energy in plant cells?
A Active transport of mineral ions
B Osmosis across the cell membrane
C Uptake of glucose by epidermal cells
D Loading of sugars in sieve tubes
Correct Answer:  B. Osmosis across the cell membrane
EXPLANATION

Osmosis is passive transport of water molecules across a semipermeable membrane in response to water potential differences.

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Q.56 Medium Botany
Which plant hormone is known to have antagonistic effects to gibberellins in seed germination?
A Cytokinin
B Abscisic acid
C Ethylene
D Auxin
Correct Answer:  B. Abscisic acid
EXPLANATION

Abscisic acid (ABA) promotes seed dormancy and inhibits germination, acting antagonistically to gibberellins which promote germination.

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Q.57 Medium Botany
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.

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Q.58 Medium Botany
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.

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Q.59 Medium Botany
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.

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Q.60 Medium Botany
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.

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