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1. The technique of growing plants in a nutrient solution without soil is called:
A. Hydroponics
B. Aeroponics
C. Geoponics
D. Aquaculture
Answer: A. Hydroponics
Explanation: Hydroponics is the technique of growing plants in a defined nutrient solution in complete absence of soil, first demonstrated by Julius von Sachs.
2. Who among the following demonstrated for the first time that plants could be grown to maturity in a defined nutrient solution?
A. Julius von Sachs
B. Melvin Calvin
C. Joseph Priestley
D. Jan Ingenhousz
Answer: A. Julius von Sachs
Explanation: In 1860, Julius von Sachs, a prominent German botanist, demonstrated that plants could be grown to maturity in a defined nutrient solution in complete absence of soil.
3. How many essential elements are recognized for plant growth and metabolism?
A. 17
B. 10
C. 21
D. 60
Answer: A. 17
Explanation: Only 17 elements are considered absolutely essential for plant growth and development based on strict criteria of essentiality.
4. Macronutrients are generally present in plant tissues in large amounts exceeding:
A. 10 mmole/kg of dry matter
B. 1 mmole/kg of dry matter
C. 100 mmole/kg of dry matter
D. 0.1 mmole/kg of dry matter
Answer: A. 10 mmole/kg of dry matter
Explanation: Macronutrients are generally present in plant tissues in large amounts, greater than 10 mmole/kg of dry matter.
5. Which of the following is a essential micronutrient for plants?
A. Zinc
B. Calcium
C. Magnesium
D. Phosphorus
Answer: A. Zinc
Explanation: Micronutrients or trace elements include Fe, Mn, Cu, Mo, Zn, B, Cl, and Ni. Calcium, Magnesium, and Phosphorus are macronutrients.
6. Which element is an essential component of middle lamella as calcium pectate in plant cell walls?
A. Calcium
B. Magnesium
C. Potassium
D. Iron
Answer: A. Calcium
Explanation: Calcium is required for the synthesis of plant cell walls, particularly as calcium pectate in the middle lamella.
7. Which mineral element constitutes the central atom of the ring structure of chlorophyll?
A. Magnesium
B. Iron
C. Manganese
D. Copper
Answer: A. Magnesium
Explanation: Magnesium ($Mg^{2+}$) is a constituent of the porphyrin ring of chlorophyll and helps maintain ribosome structure.
8. The element involved in the opening and closing of stomata by maintaining anion-cation balance is:
A. Potassium
B. Sodium
C. Chlorine
D. Calcium
Answer: A. Potassium
Explanation: Potassium ($K^+$) helps determine anion-cation balance in cells and is involved in opening and closing of stomata.
9. Which element is required for the photolysis (splitting) of water during photosynthesis?
A. Manganese
B. Zinc
C. Copper
D. Molybdenum
Answer: A. Manganese
Explanation: The best-defined function of manganese ($Mn^{2+}$) is in the splitting of water to liberate oxygen during photosynthesis, along with chlorine.
10. Zinc is required for the synthesis of which essential plant growth regulator (hormone)?
A. Auxin
B. Gibberellin
C. Cytokinin
D. Ethylene
Answer: A. Auxin
Explanation: Zinc ($Zn^{2+}$) activates various enzymes, especially carboxylases, and is needed for auxin synthesis.
11. Boron is required for which of the following physiological processes in plants?
A. Pollen germination
B. Chlorophyll synthesis
C. Nitrogen fixation
D. Stomatal closure
Answer: A. Pollen germination
Explanation: Boron is required for $Ca^{2+}$ uptake and utilization, membrane functioning, pollen germination, cell elongation, and carbohydrate translocation.
12. Which element is a component of nitrogenase and nitrate reductase enzymes involved in nitrogen metabolism?
A. Molybdenum
B. Boron
C. Iron
D. Zinc
Answer: A. Molybdenum
Explanation: Molybdenum ($Mo$) is a component of several enzymes, including nitrogenase and nitrate reductase, both of which participate in nitrogen metabolism.
13. Yellowing of leaves due to the loss of chlorophyll is known as:
A. Chlorosis
B. Necrosis
C. Etiolation
D. Albinism
Answer: A. Chlorosis
Explanation: Chlorosis is the loss of chlorophyll leading to yellowing in leaves, caused by deficiency of elements like N, K, Mg, S, Fe, Mn, Zn, and Mo.
14. Death of tissue, particularly leaf tissue, due to deficiency of Ca, Mg, Cu, and K is termed:
A. Necrosis
B. Chlorosis
C. Plasmolysis
D. Stunting
Answer: A. Necrosis
Explanation: Necrosis, or death of tissue (particularly leaf tissue), is caused by deficiency of Ca, Mg, Cu, and K.
15. Deficiency symptoms of actively mobile elements like N, K, and Mg first appear in:
A. Older senescent leaves
B. Young buds
C. Root tips
D. Flowers
Answer: A. Older senescent leaves
Explanation: For elements that are actively mobilized within the plant (like N, Mg, K), deficiency symptoms show up first in the older tissues as elements move to younger leaves.
16. The conversion of atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) is termed:
A. Nitrogen fixation
B. Nitrification
C. Ammonification
D. Denitrification
Answer: A. Nitrogen fixation
Explanation: The process of conversion of atmospheric nitrogen ($N_2$) to ammonia ($NH_3$) is called nitrogen fixation.
17. Decomposition of organic nitrogen of dead plants and animals into ammonia is called:
A. Ammonification
B. Nitrification
C. Denitrification
D. Nitrogen assimilation
Answer: A. Ammonification
Explanation: Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
18. The oxidation of ammonia to nitrite ($NO_2^-$) is performed by which soil bacteria?
A. Nitrosomonas and Nitrococcus
B. Nitrobacter
C. Pseudomonas
D. Rhizobium
Answer: A. Nitrosomonas and Nitrococcus
Explanation: Ammonia is oxidized to nitrite by Nitrosomonas/Nitrococcus. Nitrite is then oxidized to nitrate by Nitrobacter.
19. The process of converting soil nitrate ($NO_3^-$) back into atmospheric nitrogen ($N_2$) is called:
A. Denitrification
B. Nitrification
C. Ammonification
D. Nitrogen fixation
Answer: A. Denitrification
Explanation: Nitrate present in soil is reduced to nitrogen gas by the process of denitrification, carried out by bacteria like Pseudomonas and Thiobacillus.
20. Which free-living, anaerobic nitrogen-fixing bacterium is present in the soil?
A. Rhodospirillum
B. Azotobacter
C. Beijerinckia
D. Rhizobium
Answer: A. Rhodospirillum
Explanation: Azotobacter and Beijerinckia are free-living aerobic nitrogen fixers, while Rhodospirillum is anaerobic.
21. Symbiotic nitrogen-fixing bacteria found in root nodules of leguminous plants belong to the genus:
A. Rhizobium
B. Frankia
C. Azospirillum
D. Clostridium
Answer: A. Rhizobium
Explanation: Rhizobium species form symbiotic associations with roots of leguminous plants like sweet pea, lentils, alfalfa, and garden peas.
22. Frankia forms nitrogen-fixing root nodules in non-leguminous plants such as:
A. Alnus
B. Pisum
C. Cicer
D. Glycine
Answer: A. Alnus
Explanation: The microbe Frankia produces nitrogen-fixing nodules on the roots of non-leguminous plants like Alnus.
23. The pink-colored pigment present in root nodules of leguminous plants that protects nitrogenase from oxygen is:
A. Leghemoglobin
B. Myoglobin
C. Cytochrome
D. Hemocyanin
Answer: A. Leghemoglobin
Explanation: Leghemoglobin acts as an oxygen scavenger to protect the oxygen-sensitive nitrogenase enzyme during nitrogen fixation.
24. How many ATP molecules are required for the biological reduction of one molecule of nitrogen ($N_2$) into two molecules of ammonia?
A. 16 ATP
B. 8 ATP
C. 12 ATP
D. 24 ATP
Answer: A. 16 ATP
Explanation: The reduction of one $N_2$ molecule to $2NH_3$ requires 8 electrons, 8 protons, and 16 ATP molecules (8 ATP per $NH_3$ produced).
25. Export of fixed nitrogen from root nodules of plants like soyabean occurs mainly in the form of high-nitrogen compounds called:
A. Ureides
B. Nitrates
C. Ammonium ions
D. Amino acids
Answer: A. Ureides
Explanation: Nodule exports of plants like soyabean translocate fixed nitrogen as ureides (such as allantoin and allantoic acid), which have a high N/C ratio.
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