Nitrogen Cycle MCQs for Class 8 Science
CBSE Class 8 Science – MCQs with Answers & Explanations
Section 2: Microorganisms – Friend and Foe
Topic: Nitrogen Cycle MCQs for Class 8 Science
Based on NCERT | CBSE Board Examinations
These Multiple Choice Questions (MCQs) are designed strictly as per the NCERT syllabus, making them ideal for CBSE Class 8 Science examination preparation.
1. The nitrogen cycle refers to the circulation of nitrogen between:
Answer: B
Explanation: Nitrogen moves through air, soil, plants, animals, and microorganisms in a continuous cycle.
Explanation: Nitrogen moves through air, soil, plants, animals, and microorganisms in a continuous cycle.
2. Percentage of nitrogen in atmosphere is about:
Answer: C
Explanation: Nitrogen forms the major component of air but cannot be used directly by most organisms.
Explanation: Nitrogen forms the major component of air but cannot be used directly by most organisms.
3. Conversion of atmospheric nitrogen into usable form is:
Answer: B
Explanation: Nitrogen fixation converts N₂ into ammonia or nitrates usable by plants.
Explanation: Nitrogen fixation converts N₂ into ammonia or nitrates usable by plants.
4. Nitrogen fixation is done by:
Answer: A
Explanation: Rhizobium lives in legume root nodules and fixes nitrogen.
Explanation: Rhizobium lives in legume root nodules and fixes nitrogen.
5. Lightning helps nitrogen fixation by:
Answer: B
Explanation: High temperature during lightning forms nitrogen oxides that dissolve in rain.
Explanation: High temperature during lightning forms nitrogen oxides that dissolve in rain.
6. Plants absorb nitrogen mainly as:
Answer: C
Explanation: Soil bacteria convert nitrogen into nitrates/nitrites absorbed by roots.
Explanation: Soil bacteria convert nitrogen into nitrates/nitrites absorbed by roots.
7. Animals get nitrogen through:
Answer: C
Explanation: Animals obtain nitrogen by eating plants or other animals.
Explanation: Animals obtain nitrogen by eating plants or other animals.
8. Decomposers convert dead matter into:
Answer: B
Explanation: Decomposition releases ammonia back into soil.
Explanation: Decomposition releases ammonia back into soil.
9. Conversion of ammonia into nitrates is:
Answer: C
Explanation: Nitrifying bacteria convert ammonia into nitrates.
Explanation: Nitrifying bacteria convert ammonia into nitrates.
10. Denitrifying bacteria convert nitrates into:
Answer: B
Explanation: Denitrification returns nitrogen to atmosphere.
Explanation: Denitrification returns nitrogen to atmosphere.
11. Blue‑green algae fix nitrogen in:
Answer: B
Explanation: Cyanobacteria enrich soil fertility.
Explanation: Cyanobacteria enrich soil fertility.
12. Leguminous plants include:
Answer: C
Explanation: Pea roots contain nitrogen‑fixing nodules.
Explanation: Pea roots contain nitrogen‑fixing nodules.
13. Nitrogen is essential for making:
Answer: B
Explanation: Proteins require nitrogen atoms.
Explanation: Proteins require nitrogen atoms.
14. Excess fertilizers disturb:
Answer: B
Explanation: Artificial nitrogen alters natural balance.
Explanation: Artificial nitrogen alters natural balance.
15. Root nodules contain:
Answer: B
Explanation: Symbiotic nitrogen fixation occurs here.
Explanation: Symbiotic nitrogen fixation occurs here.
16. Ammonification produces:
Answer: B
Explanation: Decomposers release ammonia.
Explanation: Decomposers release ammonia.
17. Which returns nitrogen to air?
Answer: C
Explanation: They release nitrogen gas.
Explanation: They release nitrogen gas.
18. Nitrogen cycle maintains:
Answer: B
Explanation: Ensures nitrogen availability.
Explanation: Ensures nitrogen availability.
19. Main reservoir of nitrogen:
Answer: C
Explanation: Atmosphere stores most nitrogen.
Explanation: Atmosphere stores most nitrogen.
20. Nitrogen is vital for plant growth because it forms:
Answer: A
Explanation: Nitrogen is key for chlorophyll and protein synthesis.
Explanation: Nitrogen is key for chlorophyll and protein synthesis.
