CBSE Class 11 Biology – Mineral Nutrition | Very Short Answer 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 Focus

• VSAs test definitions, facts, and core concepts
• Frequently asked in annual exams and unit tests
• Answers must be precise, NCERT-based, and well-structured

Section A: Essential Elements (Questions 1–15)

Q1. What are essential elements in plants?
Ans: Essential elements are mineral nutrients required for normal growth and completion of life cycle; their absence results in abnormal growth or failure to reproduce.

Q2. State the criteria of essentiality of elements.
Ans: An element is essential if its absence prevents life cycle completion, deficiency is specific, and the element directly participates in plant metabolism.

Q3. Who proposed the criteria of essentiality?
Ans: The criteria of essentiality for mineral nutrients were proposed by Arnon and Stout.

Q4. Define macronutrients.
Ans: Macronutrients are essential elements required by plants in large amounts, generally more than one milligram per gram of dry plant weight.

Q5. Name any four macronutrients.
Ans: Nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur are macronutrients required in large quantities.

Q6. Define micronutrients.
Ans: Micronutrients are essential elements required by plants in very small quantities, usually less than one milligram per gram of dry weight.

Q7. Name any four micronutrients.
Ans: Iron, manganese, zinc, copper, boron, molybdenum, and chlorine are important micronutrients in plants.

Q8. Why is nitrogen considered the most important macronutrient?
Ans: Nitrogen is a major component of amino acids, proteins, nucleic acids, and chlorophyll, making it essential for growth and metabolism.

Q9. State one role of phosphorus in plants.
Ans: Phosphorus is a component of ATP and nucleic acids and plays a key role in energy transfer reactions.

Q10. Mention one function of potassium.
Ans: Potassium activates several enzymes and regulates stomatal opening and closing in plants.

Q11. Why is magnesium essential for photosynthesis?
Ans: Magnesium is the central atom of chlorophyll molecule and also acts as an activator of photosynthetic enzymes.

Q12. Name one role of calcium in plants.
Ans: Calcium is required for cell wall formation and helps maintain membrane integrity and permeability.

Q13. Which element is a component of sulphur-containing amino acids?
Ans: Sulphur is a component of amino acids like cysteine and methionine, essential for protein synthesis.

Q14. Why are micronutrients required in small amounts?
Ans: Micronutrients act mainly as enzyme cofactors or activators and are effective even in very small concentrations.

Q15. What is the functional classification of mineral nutrients?
Ans: Mineral nutrients are functionally classified as structural components, enzyme activators, and elements maintaining osmotic and ionic balance.

Section B: Deficiency Symptoms (Questions 16–30)

Q16. What are deficiency symptoms?
Ans: Deficiency symptoms are visible abnormalities in plant growth and development caused by inadequate supply of essential mineral elements.

Q17. Why do deficiency symptoms appear first in older leaves for some elements?
Ans: Mobile elements move from older to younger leaves, so deficiency symptoms appear first in older leaves.

Q18. Name two mobile elements.
Ans: Nitrogen and magnesium are mobile elements whose deficiency symptoms appear first in older leaves.

Q19. Why do calcium deficiency symptoms appear in younger leaves?
Ans: Calcium is an immobile element and cannot be transported from older tissues to younger growing regions.

Q20. What is chlorosis?
Ans: Chlorosis is yellowing of leaves due to reduced chlorophyll synthesis, commonly caused by nitrogen, magnesium, or iron deficiency.

Q21. What is necrosis?
Ans: Necrosis is the death of plant tissues resulting in brown or black patches on leaves due to severe mineral deficiency.

Q22. Name one element whose deficiency causes interveinal chlorosis.
Ans: Magnesium deficiency causes interveinal chlorosis, especially in older leaves.

Q23. Which deficiency leads to delayed flowering?
Ans: Nitrogen deficiency often results in delayed flowering and reduced vegetative growth.

Q24. What happens due to potassium deficiency?
Ans: Potassium deficiency causes marginal leaf necrosis, weak stems, and reduced resistance to diseases.

Q25. Which deficiency causes death of growing points?
Ans: Calcium deficiency causes death of root tips and shoot apical meristems.

Q26. Why is iron deficiency common in young leaves?
Ans: Iron is immobile in plants, so its deficiency symptoms appear first in young leaves.

Q27. What is mineral toxicity?
Ans: Mineral toxicity occurs when excess accumulation of certain elements interferes with uptake or function of other nutrients.

Q28. Which micronutrient toxicity induces iron deficiency symptoms?
Ans: Excess manganese causes iron deficiency symptoms by inhibiting iron absorption.

Q29. How does nutrient deficiency affect cell division?
Ans: Deficiency of nitrogen or calcium inhibits cell division, leading to stunted growth.

Q30. Why are deficiency symptoms specific?
Ans: Each mineral element performs unique functions, so its deficiency produces characteristic and specific symptoms.

Section C: Nitrogen Cycle (Questions 31–40)

Q31. What is the nitrogen cycle?
Ans: The nitrogen cycle is the cyclic movement of nitrogen between atmosphere, soil, plants, animals, and microorganisms.

Q32. Why cannot plants use atmospheric nitrogen directly?
Ans: Atmospheric nitrogen exists as N₂, which is chemically inert and cannot be directly absorbed by plants.

Q33. What is nitrogen fixation?
Ans: Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia or related compounds usable by plants.

Q34. Name two nitrogen-fixing bacteria.
Ans: Rhizobium and Azotobacter are nitrogen-fixing bacteria found in soil or symbiotic associations.

Q35. What is nitrification?
Ans: Nitrification is the conversion of ammonia into nitrite and nitrate by nitrifying bacteria in soil.

Q36. Name the bacteria involved in nitrification.
Ans: Nitrosomonas converts ammonia to nitrite, while Nitrobacter converts nitrite to nitrate.

Q37. What is ammonification?
Ans: Ammonification is the conversion of organic nitrogen from dead organisms into ammonia by decomposer microorganisms.

Q38. Define denitrification.
Ans: Denitrification is the conversion of nitrate into atmospheric nitrogen by anaerobic bacteria, resulting in nitrogen loss from soil.

Q39. Which bacteria carry out denitrification?
Ans: Denitrification is carried out by anaerobic bacteria such as Pseudomonas.

Q40. Why is denitrification harmful to soil fertility?
Ans: Denitrification removes nitrogen from soil, reducing availability of nitrates for plant absorption.

Section D: Biological Nitrogen Fixation (Questions 41–50)

Q41. What is biological nitrogen fixation?
Ans: Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia by living microorganisms.

Q42. Name two free-living nitrogen-fixing organisms.
Ans: Azotobacter and Nostoc are free-living organisms capable of fixing atmospheric nitrogen.

Q43. What is symbiotic nitrogen fixation?
Ans: Symbiotic nitrogen fixation occurs when nitrogen-fixing bacteria live in association with host plants, especially legumes.

Q44. Name the symbiotic bacterium found in leguminous plants.
Ans: Rhizobium forms a symbiotic association with leguminous plants and fixes atmospheric nitrogen.

Q45. Where are root nodules found?
Ans: Root nodules are specialized structures formed on roots of leguminous plants housing nitrogen-fixing bacteria.

Q46. What is the role of leghaemoglobin?
Ans: Leghaemoglobin maintains low oxygen concentration in root nodules, protecting nitrogenase enzyme from oxygen damage.

Q47. Why is nitrogenase enzyme sensitive to oxygen?
Ans: Nitrogenase is inactivated by oxygen, hence it functions only under low oxygen conditions.

Q48. Which enzyme is responsible for nitrogen fixation?
Ans: Nitrogenase enzyme catalyses the reduction of atmospheric nitrogen to ammonia.

Q49. Why is biological nitrogen fixation important in agriculture?
Ans: It enriches soil fertility naturally and reduces dependence on chemical nitrogen fertilizers.

Q50. How does biological nitrogen fixation benefit plants?
Ans: It supplies plants with usable nitrogen for protein synthesis, promoting healthy growth and development.

Ideal For

• CBSE Class 11 Annual Examinations
• NCERT-based internal assessments
• Rapid revision & concept reinforcement