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.
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.
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.
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).
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.
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)
An object is placed 30 cm in front of a concave mirror with focal length 10 cm. Where is the image formed?
A
15 cm behind the mirror
B
15 cm in front of the mirror
C
20 cm in front of the mirror
D
20 cm behind the mirror
Correct Answer:
A. 15 cm behind the mirror
Explanation:
Using mirror formula 1/f = 1/u + 1/v, where f = -10 cm, u = -30 cm, we get v = -15 cm (behind mirror)
A transformer has 500 turns in primary and 100 turns in secondary coil. If primary voltage is 220V, what is the secondary voltage?
A
44 V
B
1100 V
C
22 V
D
110 V
Explanation:
Using transformer equation Vs/Vp = Ns/Np, we get Vs = 220 × (100/500) = 44 V
A current-carrying conductor is placed in a magnetic field perpendicular to it. What force acts on it?
A
Gravitational force
B
Lorentz force
C
Electrostatic force
D
Frictional force
Correct Answer:
B. Lorentz force
Explanation:
The force on a current-carrying conductor in a magnetic field is called the Lorentz force, given by F = BIL
A radioactive element has a half-life of 10 years. After 30 years, what fraction of the original sample remains?
Explanation:
After 3 half-lives (30 years), the fraction remaining = (1/2)³ = 1/8
