CBSE Class 11 Biology – Mineral Nutrition | Case-Based / Source-Based Questions with Answers (NCERT Based)

Course & Examination Details

Course: CBSE Class 11 Biology
Unit: Unit IV – Plant Physiology
Chapter: Chapter 12 – Mineral Nutrition
Prescribed Textbook: NCERT
Board: CBSE

CBSE Board Examination Context

• Case-based questions assess application of concepts and analytical ability
• Aligned with competency-based assessment pattern
• Answers must be NCERT-specific, logical, and concept-driven

Section A: Essential Elements (Case-Based Questions 1–7)

Case 1

A farmer notices poor vegetative growth and yellowing of older leaves in his crop.

Q1. Which mineral element is likely deficient?
Ans: Nitrogen is deficient, as it causes chlorosis and stunted growth, especially in older leaves due to its mobility.

Q2. Why do symptoms appear first in older leaves?
Ans: Nitrogen is a mobile element and is translocated from older leaves to younger growing regions.

Case 2

A plant shows weak stems and marginal leaf necrosis.

Q3. Identify the deficient element.
Ans: Potassium deficiency causes marginal necrosis and weak stems.

Q4. State one function of this element.
Ans: Potassium activates enzymes and regulates stomatal movement and osmotic balance.

Case 3

Leaves show interveinal chlorosis but veins remain green.

Q5. Which element is likely deficient?
Ans: Magnesium deficiency causes interveinal chlorosis, particularly in older leaves.

Q6. Why is magnesium important for plants?
Ans: Magnesium is the central atom of chlorophyll and activates photosynthetic enzymes.

Case 4

Death of root and shoot tips is observed in a crop field.

Q7. Which mineral deficiency causes this condition?
Ans: Calcium deficiency causes death of growing regions due to its role in cell wall formation.

Section B: Deficiency Symptoms & Toxicity (Case-Based Questions 8–13)

Case 5

A plant shows yellowing of young leaves while older leaves remain green.

Q8. Identify the deficient element.
Ans: Iron deficiency causes chlorosis in young leaves as iron is immobile.

Q9. Why does iron deficiency affect chlorophyll synthesis?
Ans: Iron is required for chlorophyll synthesis though it is not a structural component.

Case 6

Excess manganese in soil leads to yellowing of leaves.

Q10. What condition does this represent?
Ans: This is mineral toxicity caused by excess manganese.

Q11. How does manganese toxicity affect plants?
Ans: Excess manganese inhibits iron absorption, causing iron deficiency symptoms.

Case 7

Plants show delayed flowering and reduced yield.

Q12. Which deficiency is responsible?
Ans: Nitrogen deficiency causes delayed flowering and poor yield.

Q13. Why does nitrogen deficiency reduce yield?
Ans: Nitrogen is essential for protein synthesis and vegetative growth.

Section C: Nitrogen Cycle (Case-Based Questions 14–19)

Case 8

Soil microorganisms convert ammonia into nitrates.

Q14. Name this process.
Ans: The process is nitrification.

Q15. Name the bacteria involved.
Ans: Nitrosomonas converts ammonia to nitrite and Nitrobacter converts nitrite to nitrate.

Case 9

Nitrates are converted back into nitrogen gas in waterlogged soil.

Q16. Identify the process.
Ans: Denitrification is responsible for this conversion.

Q17. Why is denitrification harmful to soil fertility?
Ans: It removes usable nitrogen from soil, reducing nutrient availability.

Case 10

Decomposers convert organic nitrogen into ammonia.

Q18. Name the process involved.
Ans: The process is ammonification.

Case 11

Plants absorb nitrates and synthesize amino acids.

Q19. What is this process called?
Ans: This process is nitrogen assimilation.

Section D: Biological Nitrogen Fixation (Case-Based Questions 20–25)

Case 12

Root nodules are observed in leguminous plants.

Q20. Name the bacterium present in root nodules.
Ans: Rhizobium is the symbiotic bacterium present in root nodules.

Case 13

A red pigment is found inside root nodules.

Q21. Identify the pigment.
Ans: The pigment is leghaemoglobin.

Q22. State its function.
Ans: Leghaemoglobin maintains low oxygen concentration to protect nitrogenase.

Case 14

Nitrogen fixation stops when oxygen concentration increases.

Q23. Why does this happen?
Ans: Nitrogenase enzyme is oxygen-sensitive and becomes inactive in high oxygen.

Case 15

Free-living organisms enrich soil nitrogen.

Q24. Name one such organism.
Ans: Azotobacter is a free-living nitrogen-fixing bacterium.

Case 16

Legumes are grown before cereal crops.

Q25. Why is this practice beneficial?
Ans: Legumes enrich soil nitrogen through symbiotic nitrogen fixation, improving fertility.

Best Suited For

• CBSE Class 11 Annual Examinations
• Competency-based and case-study questions
• NCERT-aligned conceptual assessment