CBSE Class 11 Biology – Mineral Nutrition | Short Answer Type 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 Relevance

• Short answer questions assess concept clarity, explanation ability, and accuracy
• Frequently asked as 3–4 mark questions
• Answers must be concise, structured, and NCERT-specific

Section A: Essential Elements (Q1–Q15)

Q1. What are essential elements in plants? Explain their importance.

Ans:
Essential elements are mineral nutrients required by plants to complete their life cycle normally. Their absence results in abnormal growth or failure to reproduce. These elements are directly involved in metabolic processes such as enzyme activation, synthesis of biomolecules, and maintenance of structural integrity. Essential elements ensure proper growth, development, and physiological functioning of plants.

Q2. State and explain the criteria of essentiality of mineral elements.

Ans:
An element is considered essential if its absence prevents completion of the plant life cycle, the deficiency is specific and cannot be replaced by another element, and the element directly participates in plant metabolism. These criteria, proposed by Arnon and Stout, help distinguish essential nutrients from beneficial elements.

Q3. Differentiate between macronutrients and micronutrients.

Ans:
Macronutrients are required in large quantities, usually more than one milligram per gram of dry weight, such as nitrogen, phosphorus, and potassium. Micronutrients are required in very small amounts, less than one milligram per gram of dry weight, such as iron, zinc, and copper. Both are essential for normal plant growth.

Q4. Describe the functional classification of essential elements.

Ans:
Functionally, essential elements are classified into three groups: constituents of cell structures like nitrogen and phosphorus; enzyme activators such as potassium and magnesium; and elements involved in maintaining osmotic and ionic balance like calcium and potassium. This classification explains the specific physiological roles of mineral nutrients.

Q5. Explain the role of nitrogen in plants.

Ans:
Nitrogen is a major component of amino acids, proteins, nucleic acids, and chlorophyll. It is essential for vegetative growth and metabolic activities. Nitrogen deficiency leads to stunted growth, chlorosis, and reduced yield. It is considered the most important macronutrient for plants.

Q6. Describe the importance of phosphorus in plant metabolism.

Ans:
Phosphorus is a component of ATP, nucleic acids, and phospholipids. It plays a crucial role in energy transfer, photosynthesis, respiration, and cell division. Phosphorus deficiency results in poor root development, delayed flowering, and reduced growth.

Q7. State the functions of potassium in plants.

Ans:
Potassium activates many enzymes involved in photosynthesis and respiration. It regulates stomatal opening and closing, maintains osmotic balance, and enhances disease resistance. Potassium deficiency causes weak stems, marginal leaf necrosis, and reduced crop quality.

Q8. Why is calcium considered an important structural element?

Ans:
Calcium is required for cell wall formation and stabilization of cell membranes. It maintains membrane permeability and is essential for proper functioning of growing regions like root and shoot tips. Calcium deficiency leads to death of meristematic tissues.

Q9. Explain the role of magnesium in plants.

Ans:
Magnesium is the central atom of the chlorophyll molecule and is essential for photosynthesis. It also acts as an enzyme activator in respiration and nucleic acid synthesis. Magnesium deficiency causes interveinal chlorosis, especially in older leaves.

Q10. What is the importance of sulphur in plants?

Ans:
Sulphur is a component of sulphur-containing amino acids such as cysteine and methionine. It is essential for protein synthesis and enzyme function. Sulphur deficiency leads to stunted growth and yellowing of young leaves.

Q11. Why are micronutrients essential despite being required in small amounts?

Ans:
Micronutrients act as enzyme cofactors or activators and play catalytic roles in metabolic reactions. Even in small concentrations, they regulate critical biochemical pathways. Their deficiency can severely affect plant metabolism and growth.

Q12. Explain the role of iron in plants.

Ans:
Iron is involved in chlorophyll synthesis and functions as a component of cytochromes and ferredoxin in electron transport. Iron deficiency causes interveinal chlorosis in young leaves due to its immobility in plants.

Q13. What is the significance of molybdenum in plants?

Ans:
Molybdenum is required for nitrogen metabolism as it is a component of nitrate reductase and nitrogenase enzymes. Its deficiency affects nitrogen assimilation and leads to poor growth and reduced nitrogen fixation.

Q14. What are beneficial elements? Give examples.

Ans:
Beneficial elements are those not essential for all plants but helpful for certain species. Examples include sodium, silicon, and cobalt. They improve growth, yield, or stress tolerance under specific conditions.

Q15. Why are mineral nutrients absorbed mainly as ions?

Ans:
Mineral nutrients dissolve in soil water and exist as charged ions. Roots absorb them in ionic form through diffusion or active transport, enabling easy movement across cell membranes and participation in metabolic processes.

Section B: Deficiency Symptoms (Q16–Q30)

Q16. What are deficiency symptoms? Explain their cause.

Ans:
Deficiency symptoms are visible abnormalities in plant growth caused by inadequate supply of essential elements. They occur because minerals play specific roles in metabolism. Lack of a nutrient disrupts biochemical pathways, leading to characteristic symptoms like chlorosis or necrosis.

Q17. Why do deficiency symptoms differ among nutrients?

Ans:
Each nutrient performs specific functions in plants. Therefore, its deficiency affects particular physiological processes, producing unique and characteristic symptoms. This specificity helps identify the deficient element.

Q18. Explain the significance of nutrient mobility in deficiency symptoms.

Ans:
Mobility of nutrients determines where deficiency symptoms appear. Mobile elements like nitrogen move to young leaves, causing symptoms in older leaves first. Immobile elements like calcium cannot move, so symptoms appear in younger leaves.

Q19. What is chlorosis and which elements cause it?

Ans:
Chlorosis is yellowing of leaves due to reduced chlorophyll formation. It is commonly caused by deficiency of nitrogen, magnesium, iron, or manganese, affecting photosynthesis.

Q20. Define necrosis and state its causes.

Ans:
Necrosis is death of plant tissues resulting in brown or black patches on leaves. It is caused by severe deficiency of elements like calcium, potassium, and magnesium, which are vital for cell integrity.

Q21. Explain interveinal chlorosis.

Ans:
Interveinal chlorosis is yellowing of leaf areas between veins while veins remain green. It commonly occurs due to magnesium or iron deficiency, affecting chlorophyll synthesis in specific leaf regions.

Q22. How does nitrogen deficiency affect plant growth?

Ans:
Nitrogen deficiency causes stunted growth, reduced leaf size, chlorosis of older leaves, and delayed flowering. Since nitrogen is vital for protein synthesis, its deficiency severely affects metabolism and growth.

Q23. What are the effects of potassium deficiency?

Ans:
Potassium deficiency leads to marginal leaf necrosis, weak stems, poor root growth, and reduced disease resistance. It also affects stomatal regulation and enzyme activity.

Q24. Why does calcium deficiency affect growing regions?

Ans:
Calcium is immobile and essential for cell division and wall formation. Its deficiency affects actively growing regions like root and shoot tips, causing death of meristems.

Q25. Explain iron deficiency symptoms.

Ans:
Iron deficiency causes interveinal chlorosis in young leaves because iron is immobile. Chlorophyll synthesis is affected, although iron is not a structural component of chlorophyll.

Q26. What is mineral toxicity?

Ans:
Mineral toxicity occurs when excess accumulation of certain nutrients interferes with plant metabolism. It may inhibit absorption of other nutrients, leading to deficiency symptoms.

Q27. How does manganese toxicity affect plants?

Ans:
Excess manganese inhibits absorption of iron and magnesium, causing deficiency symptoms like chlorosis. It also interferes with enzyme activity, affecting photosynthesis and respiration.

Q28. Why are deficiency symptoms delayed in some cases?

Ans:
Plants may store minerals temporarily. Symptoms appear only when reserves are exhausted and supply falls below critical levels required for normal metabolism.

Q29. How does mineral deficiency affect flowering and yield?

Ans:
Mineral deficiency disrupts energy metabolism and hormone synthesis, leading to delayed flowering, poor fruit set, and reduced yield, especially in nitrogen and phosphorus deficiency.

Q30. Why are deficiency symptoms reversible in early stages?

Ans:
In early stages, restoring the deficient nutrient can resume normal metabolic functions. Severe deficiency causes irreversible damage, making recovery difficult.

Section C: Nitrogen Cycle & Biological Nitrogen Fixation (Q31–Q50)

Q31. Explain the importance of nitrogen in plants.

Ans:
Nitrogen is essential for synthesis of proteins, nucleic acids, enzymes, and chlorophyll. It promotes vegetative growth and is a major component of plant biomass. Despite its abundance in atmosphere, plants depend on fixed nitrogen.

Q32. What is the nitrogen cycle?

Ans:
The nitrogen cycle is the circulation of nitrogen between atmosphere, soil, plants, animals, and microorganisms. It includes nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

Q33. Why is nitrogen fixation necessary?

Ans:
Atmospheric nitrogen is inert and unavailable to plants. Nitrogen fixation converts it into ammonia or nitrates, making it usable for plant metabolism.

Q34. Describe nitrification.

Ans:
Nitrification is the biological oxidation of ammonia to nitrite by Nitrosomonas and then to nitrate by Nitrobacter. Nitrates are the main form absorbed by plants.

Q35. What is ammonification?

Ans:
Ammonification is the conversion of organic nitrogen from dead organisms into ammonia by decomposer microorganisms, recycling nitrogen in soil.

Q36. Explain denitrification and its effect.

Ans:
Denitrification is the conversion of nitrates into atmospheric nitrogen by anaerobic bacteria like Pseudomonas. It reduces soil fertility by removing usable nitrogen.

Q37. What is biological nitrogen fixation?

Ans:
Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia by microorganisms, either free-living or symbiotic, using nitrogenase enzyme.

Q38. Explain symbiotic nitrogen fixation with example.

Ans:
In symbiotic nitrogen fixation, bacteria like Rhizobium live in root nodules of legumes and fix atmospheric nitrogen, benefiting both plant and bacteria.

Q39. Describe the structure of root nodules.

Ans:
Root nodules contain infected zones with bacteroids, vascular tissue, and leghaemoglobin. They provide anaerobic conditions necessary for nitrogen fixation.

Q40. What is the role of leghaemoglobin?

Ans:
Leghaemoglobin maintains low oxygen concentration in nodules, protecting nitrogenase enzyme while ensuring oxygen supply for respiration.

Q41. Why is nitrogenase oxygen-sensitive?

Ans:
Nitrogenase is inactivated by oxygen, so it functions only under anaerobic or low-oxygen conditions provided by leghaemoglobin.

Q42. Name two free-living nitrogen-fixing organisms.

Ans:
Azotobacter and Nostoc are free-living nitrogen-fixing organisms that enrich soil nitrogen independently.

Q43. How does biological nitrogen fixation benefit agriculture?

Ans:
It naturally enriches soil fertility, reduces use of chemical fertilizers, and supports sustainable agriculture.

Q44. What is assimilation of nitrogen?

Ans:
Assimilation is the incorporation of absorbed nitrates or ammonia into organic compounds like amino acids and proteins in plants.

Q45. Why are legumes important in crop rotation?

Ans:
Legumes enrich soil nitrogen through symbiotic nitrogen fixation, improving fertility for subsequent crops.

Q46. What is the role of nitrate reductase?

Ans:
Nitrate reductase converts nitrates into nitrites during nitrogen assimilation in plants.

Q47. How does nitrogen deficiency affect chlorophyll?

Ans:
Nitrogen deficiency reduces chlorophyll synthesis, leading to chlorosis and decreased photosynthetic efficiency.

Q48. Explain the ecological significance of nitrogen cycle.

Ans:
The nitrogen cycle maintains balance of nitrogen in ecosystems, ensuring continuous availability for living organisms.

Q49. Why is excessive fertilizer use harmful?

Ans:
Excess fertilizers cause nutrient imbalance, soil degradation, water pollution, and disruption of natural nitrogen cycle.

Q50. State two differences between nitrification and denitrification.

Ans:
Nitrification converts ammonia to nitrates under aerobic conditions, increasing nitrogen availability. Denitrification converts nitrates to nitrogen gas under anaerobic conditions, reducing soil nitrogen.

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