1. Which enzyme catalyzes the conversion of sucrose into UDP-glucose and fructose during sucrose metabolism in higher plants?

  • A. Invertase
  • B. Sucrose synthase
  • C. Hexokinase
  • D. Phosphoglucomutase

Answer: B. Sucrose synthase

Explanation: Sucrose synthase catalyzes the reversible conversion of sucrose and UDP into UDP-glucose and fructose, especially in sink tissues.

2. Which soil horizon is characterized by the maximum accumulation of silicate clay, iron, or aluminum due to illuviation?

  • A. O horizon
  • B. A horizon
  • C. B horizon
  • D. C horizon

Answer: C. B horizon

Explanation: The B horizon is the zone of illuviation where clay, iron oxides, aluminum, and other materials accumulate.

3. Which plant disease is caused by the bacterium Xanthomonas oryzae pv. oryzae?

  • A. Rice blast
  • B. Sheath blight
  • C. Bacterial leaf blight of rice
  • D. Brown spot of rice

Answer: C. Bacterial leaf blight of rice

Explanation: Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, one of the most destructive diseases of rice.

4. Which type of gene action is primarily responsible for the expression of hybrid vigor (heterosis)?

  • A. Additive gene action
  • B. Dominance and overdominance
  • C. Cytoplasmic inheritance
  • D. Maternal inheritance

Answer: B. Dominance and overdominance

Explanation: Dominance and overdominance hypotheses are widely accepted explanations for heterosis in crop plants.

5. Which insect order is characterized by piercing-sucking mouthparts and forewings modified into hemelytra?

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

Answer: B. Hemiptera

Explanation: True bugs belonging to Hemiptera possess piercing-sucking mouthparts and forewings called hemelytra.

6. Which nutrient is considered the central atom of the chlorophyll molecule?

  • A. Iron
  • B. Manganese
  • C. Magnesium
  • D. Calcium

Answer: C. Magnesium

Explanation: Magnesium occupies the central position in the chlorophyll porphyrin ring and is essential for photosynthesis.

7. Which statistical measure represents the square root of variance?

  • A. Standard deviation
  • B. Coefficient of variation
  • C. Standard error
  • D. Mean deviation

Answer: A. Standard deviation

Explanation: Standard deviation is the positive square root of variance and measures the dispersion of observations around the mean.

8. Which cereal crop exhibits protandry as a natural mechanism promoting cross-pollination?

  • A. Rice
  • B. Wheat
  • C. Pearl millet
  • D. Barley

Answer: C. Pearl millet

Explanation: Pearl millet is highly cross-pollinated due to protandry and the emergence of stigmas after pollen shedding.

9. Which physiological process is primarily responsible for the ascent of sap in tall trees?

  • A. Root pressure
  • B. Osmosis
  • C. Transpiration pull
  • D. Capillary action alone

Answer: C. Transpiration pull

Explanation: According to the cohesion-tension theory, transpiration pull is the major force responsible for the ascent of sap in plants.

10. Which enzyme is inhibited by the herbicide glyphosate in susceptible plants?

  • A. Acetolactate synthase (ALS)
  • B. EPSP synthase
  • C. ACCase
  • D. Glutamine synthetase

Answer: B. EPSP synthase

Explanation: Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, blocking the synthesis of aromatic amino acids.