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
