CBSE Class 11 Biology Mineral Nutrition NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

This chapter delves into the crucial topic of Mineral Nutrition in plants, providing detailed NCERT Solutions for Class 11 Biology. It covers the essential elements required for plant growth, their specific roles, and the consequences of their deficiency or toxicity. The solutions explain concepts like critical concentration, mobile vs. immobile elements, and the symptoms associated with various nutrient deficiencies. Furthermore, it elaborates on the complex process of biological nitrogen fixation, including the roles of nitrogenase and leghemoglobin. These solutions are designed to help students grasp the fundamental principles of plant nutrition and prepare effectively for their examinations by offering clear explanations and step-by-step problem-solving.

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Board	CBSE
Class	Class 11
Subject	Biology Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 12

Chapter summary

Chapter 12, Mineral Nutrition, focuses on the essential elements plants need for survival and growth. The NCERT Solutions cover the functions of these elements, how to identify deficiencies through symptoms, and the concept of critical concentration. It also explains the mobility of elements within the plant and details the biological nitrogen fixation process, including the enzymes and pigments involved. The exercises are designed to test understanding of these key concepts in plant physiology.

Learning outcomes

Understand the criteria for essentiality of mineral elements for plants.
Identify the roles of various essential elements in plant metabolism.
Recognize and explain deficiency symptoms of essential elements.
Define and apply the concept of critical concentration.
Explain the process of biological nitrogen fixation.
Describe the function of nitrogenase and leghemoglobin.

Topics covered

Paper topics

Essential elements for plant growth
Macronutrients and Micronutrients
Roles of essential elements
Deficiency symptoms
Toxicity of elements
Critical concentration
Mobile and immobile elements
Nitrogen cycle
Biological nitrogen fixation
Nitrogenase enzyme
Leg-haemoglobin
Nitrification

Important topics

Criteria for essentiality of elements
Roles and deficiency symptoms of key elements (N, P, K, Mg, S)
Concept of critical concentration
Biological nitrogen fixation process
Function of nitrogenase and leghemoglobin
Distinguishing mobile vs. immobile elements

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Questions and Solutions

Question 1

Which one of the following roles is not characteristic of an essential element?

Being a component of biomolecules
Changing the chemistry of soil
Being a structural component of energy related chemical compounds
Activation or inhibition of enzymes

Solution: Changing the chemistry of the soil is not a direct role of an essential element within the plant. Essential elements are crucial for plant metabolism and physiology. They function as components of vital biomolecules (like chlorophyll or nucleic acids), structural parts of energy-carrying compounds (like ATP), and as activators or inhibitors of enzymes, directly influencing metabolic processes. The other options listed are indeed characteristic roles of essential elements in plants.

Question 2

Which one of the following statements can best explain the term critical concentration of an essential element?

Essential element concentration below which plant growth is retarded.
Essential element concentration below which plant growth becomes enhanced.
Essential element concentration below which plant remains in the vegetative phase.
None of the above.

Solution: The critical concentration of an essential element is defined as the concentration below which the plant's growth is significantly retarded. If the availability of a particular essential element falls below this critical level, the plant begins to exhibit deficiency symptoms. This concentration serves as a threshold for normal physiological functioning and growth.

Question 3

Deficiency symptoms of an element tend to appear first in young leaves. It indicates that the element is relatively immobile. Which one of the following elemental deficiencies would show such symptoms?

Sulphur
Magnesium
Nitrogen
Potassium

Solution: The deficiency symptoms of an element that is relatively immobile within the plant typically appear first in the younger leaves or growing apices. This is because the plant cannot easily translocate the element from older tissues to supply the actively growing regions. Among the given options, Sulphur (S) is an example of such an immobile element. Its deficiency often manifests as reduced growth, a hard and woody stem, extensive root growth, and chlorosis (yellowing) of the young leaves. Magnesium (Mg), Nitrogen (N), and Potassium (K) are generally considered mobile elements, and their deficiency symptoms usually appear first in older leaves.

Question 4

Which one of the following symptoms is not due to manganese toxicity in plants?

Calcium translocation in shoot apex is inhibited.
Deficiency in both iron and nitrogen is induced.
Appearance of brown spots surrounded by chlorotic veins.
None of the above.

Solution: Manganese (Mn) is an essential micronutrient, but its toxicity can occur when absorbed in excessive amounts. Symptoms of manganese toxicity include the inhibition of calcium translocation to the shoot apex, the induction of deficiencies in other essential elements like iron (Fe) and magnesium (Mg) (and sometimes nitrogen), and the appearance of necrotic brown spots on leaves, often surrounded by chlorotic (yellowish) veins. Therefore, all the symptoms listed (a), (b), and (c) can be associated with manganese toxicity. Option (d) 'None of the above' is incorrect because the question asks which symptom is NOT due to manganese toxicity, and all listed symptoms ARE related to it. Thus, none of the provided symptoms are exempt from being caused by Mn toxicity.

Question 5

Reactions carried out by N2 fixing microbes include:

$2NH_3 + 3O_2 → 2NO_2^- + 2H^+ + 2H_2O \quad \dots(i)$

$2NO_2^- + O_2 → 2NO_3^- \quad \dots(ii)$

Which of the following statements about these equations is not true?

Step (i) is carried out by Nitrosomonas or Nitrococcus.
Step (ii) is carried out by Nitrobacter.
Both steps (i) and (ii) can be called nitrification.
Bacteria carrying out these steps are usually photoautotrophs.

Solution: The statement that is not true is (d). The bacteria involved in these steps, namely Nitrosomonas (or Nitrococcus) for step (i) and Nitrobacter for step (ii), are not photoautotrophs. Instead, they are chemoautotrophs. Chemoautotrophs obtain energy from the oxidation of inorganic substances. In this case, Nitrosomonas oxidizes ammonia (NH3) to nitrite (NO2-), and Nitrobacter oxidizes nitrite (NO2-) to nitrate (NO3-), using the energy released from these reactions to synthesize their own food. Both steps (i) and (ii) are indeed part of the nitrification process, which converts ammonia into nitrates, making nitrogen available for plant uptake.

Question 6

With regard to the biological nitrogen fixation by Rhizobium in association with soyabean, which one of the following statement/ statements does not hold true.

Nitrogenase may require oxygen for its functioning.
Nitrogenase is Mo-Fe protein.
Leg-haemoglobin is a pink coloured pigment.
Nitrogenase helps to convert N2 gas into two molecules of ammonia.

Solution: The statement that does not hold true is (a). The enzyme nitrogenase, which is responsible for reducing atmospheric nitrogen (N2) to ammonia (NH3), is exclusively found in prokaryotes like Rhizobium. This enzyme is extremely sensitive to oxygen (O2) and gets irreversibly inactivated when exposed to it. Therefore, nitrogenase functions under strictly anaerobic conditions and does not require oxygen for its activity; rather, oxygen must be excluded. Statements (b), (c), and (d) are true: nitrogenase is indeed a molybdenum-iron (Mo-Fe) protein, leg-haemoglobin is a pink pigment that helps maintain anaerobic conditions in the root nodule, and the enzyme's primary function is to convert N2 into ammonia.

Common mistakes

Confusing roles of essential elements with general plant growth factors.
Misinterpreting deficiency symptoms for mobile vs. immobile elements.
Incorrectly identifying the type of bacteria involved in nitrogen fixation (chemoautotrophs vs. photoautotrophs).
Overlooking the oxygen sensitivity of the nitrogenase enzyme.

Revision tips

Create flashcards for essential elements, their roles, and deficiency symptoms.
Draw diagrams to illustrate nitrogen fixation and the role of leghemoglobin.
Focus on understanding the difference between mobile and immobile elements and their symptom locations.
Practice identifying which element's deficiency causes specific symptoms described in the questions.

Practice MCQs

Q1. Which of the following is NOT a characteristic role of an essential element in plants?

Q2. What does 'critical concentration' of an essential element refer to?

Q3. If deficiency symptoms of an element appear first in young leaves, it suggests the element is:

Q4. Which of the following symptoms is NOT typically caused by manganese toxicity in plants?

Q5. The bacteria involved in the conversion of ammonia to nitrite and then to nitrate are classified as:

Q6. Which statement about biological nitrogen fixation by Rhizobium is incorrect?

Frequently asked questions

What is the main focus of Chapter 12, Mineral Nutrition, in Class 11 Biology?

Chapter 12 focuses on the essential mineral elements required by plants, their specific functions in plant growth and metabolism, the symptoms that arise due to their deficiency or toxicity, and the process of biological nitrogen fixation.

What is meant by the 'critical concentration' of an essential element?

Critical concentration refers to the specific concentration of an essential mineral element in plant tissues below which the plant's growth is significantly retarded, and deficiency symptoms begin to appear.

How do mobile and immobile elements differ in showing deficiency symptoms?

Deficiency symptoms of mobile elements appear first in older leaves because the plant can translocate them to younger, growing parts. Immobile elements, however, are not easily moved, so their deficiency symptoms appear first in the younger leaves or growing points.

What is the role of nitrogenase in biological nitrogen fixation?

Nitrogenase is the key enzyme responsible for biological nitrogen fixation. It catalyzes the conversion of atmospheric nitrogen gas (N2) into ammonia (NH3), a form that plants can utilize.

Why is leg-haemoglobin important in nitrogen fixation by Rhizobium?

Leg-haemoglobin is a pink pigment that binds oxygen, creating an anaerobic environment within the root nodule. This is crucial because the nitrogenase enzyme, essential for nitrogen fixation, is highly sensitive to oxygen and would be inactivated in its presence.

Are the bacteria involved in nitrification photoautotrophs or chemoautotrophs?

The bacteria involved in nitrification, such as Nitrosomonas and Nitrobacter, are chemoautotrophs. They derive energy from the oxidation of inorganic nitrogen compounds (like ammonia and nitrite) rather than from light.

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