1. Which enzyme catalyzes the conversion of atmospheric nitrogen (N₂) to ammonia (NH₃) and is irreversibly inhibited by oxygen?

  • A. Nitrate reductase
  • B. Nitrite reductase
  • C. Nitrogenase
  • D. Glutamate dehydrogenase

Answer: C. Nitrogenase

Explanation: Nitrogenase catalyzes biological nitrogen fixation and is highly sensitive to oxygen, requiring protective mechanisms such as leghemoglobin in root nodules.

2. In soil chemistry, the Sodium Adsorption Ratio (SAR) is primarily used to assess the:

  • A. Nitrogen supplying capacity
  • B. Salinity hazard of irrigation water
  • C. Sodicity hazard of irrigation water
  • D. Organic carbon content

Answer: C. Sodicity hazard of irrigation water

Explanation: SAR indicates the relative concentration of sodium to calcium and magnesium and predicts the sodicity hazard of irrigation water.

3. Which molecular marker is co-dominant, highly reproducible, PCR-based, and widely used for fingerprinting crop varieties?

  • A. RAPD
  • B. AFLP
  • C. SSR (Microsatellite)
  • D. ISSR

Answer: C. SSR (Microsatellite)

Explanation: SSR markers are co-dominant, highly polymorphic, reproducible, and extensively used in plant breeding and genetic diversity studies.

4. Which pathogen causes late blight of potato?

  • A. Alternaria solani
  • B. Phytophthora infestans
  • C. Fusarium oxysporum
  • D. Sclerotium rolfsii

Answer: B. Phytophthora infestans

Explanation: Late blight of potato is caused by the oomycete Phytophthora infestans, responsible for the historic Irish potato famine.

5. Which statistical distribution is commonly assumed for quantitative traits controlled by many genes and environmental effects?

  • A. Poisson distribution
  • B. Binomial distribution
  • C. Normal distribution
  • D. Exponential distribution

Answer: C. Normal distribution

Explanation: Quantitative traits typically exhibit continuous variation that approximates a normal distribution due to polygenic inheritance.

6. Which plant growth regulator is commercially used to break dormancy in potato tubers?

  • A. Ethylene
  • B. Gibberellic acid (GA₃)
  • C. Abscisic acid
  • D. Maleic hydrazide

Answer: B. Gibberellic acid (GA₃)

Explanation: Gibberellic acid promotes sprouting and is commonly used to overcome dormancy in potato tubers.

7. Which insect order is characterized by forewings modified into hardened elytra?

  • A. Lepidoptera
  • B. Coleoptera
  • C. Hemiptera
  • D. Orthoptera

Answer: B. Coleoptera

Explanation: Beetles belonging to the order Coleoptera possess hardened forewings called elytra that protect the membranous hind wings.

8. Which enzyme of the Krebs cycle directly produces GTP (or ATP) through substrate-level phosphorylation?

  • A. Citrate synthase
  • B. Isocitrate dehydrogenase
  • C. Succinyl-CoA synthetase
  • D. Succinate dehydrogenase

Answer: C. Succinyl-CoA synthetase

Explanation: Succinyl-CoA synthetase converts succinyl-CoA to succinate while generating one molecule of GTP (or ATP).

9. The crop coefficient (Kc) is defined as the ratio of:

  • A. Actual rainfall to irrigation water
  • B. Crop evapotranspiration (ETc) to reference evapotranspiration (ET₀)
  • C. Water use efficiency to irrigation efficiency
  • D. Consumptive use to effective rainfall

Answer: B. Crop evapotranspiration (ETc) to reference evapotranspiration (ET₀)

Explanation: Kc = ETc/ET₀ and is used to estimate crop water requirements under standard conditions.

10. Which quantitative genetic parameter estimates the expected improvement in a trait after one cycle of selection?

  • A. Genetic advance
  • B. Broad-sense heritability
  • C. Dominance variance
  • D. Environmental variance

Answer: A. Genetic advance

Explanation: Genetic advance predicts the expected gain from selection based on heritability, phenotypic variability, and selection intensity.