NCERT Solutions Class 11 Biology Chapter 12

NCERT Solutions for Class 11 Biology Chapter 12

NCERT Class 11 Biology Chapter 12 – Mineral Nutrition educates students about inorganic plant nutrition and elements essential for the growth of a plant. Students will also learn about the role these essential elements play in plant growth, the mechanism by which they are absorbed, and the symptoms of serious deficiency in this chapter. 

NCERT Solutions offered by Extramarks provide accurate answers to the questions given at the end of every chapter of the NCERT textbook. Extramarks offers NCERT Solutions for Class 11 Biology Chapter 12 to help students answer the questions and perform better in exams. The solutions also aid in understanding the concepts in a better way.

NCERT Solutions for Class 11 Biology Chapter 12 – Mineral Nutrition 

The subject-matter experts at Extramarks prepare NCERT Solutions keeping the latest CBSE guidelines in mind. You can easily access NCERT Solutions for Class 11 Biology Chapter 12 on Extramarks in offline and online modes.

NCERT Biology Class 11 Mineral Nutrition 

NCERT Solutions for Class 11 Biology Chapter 12 provided by Extramarks are curated in a way that makes referring to all answers to textbook questions easy. The answers have detailed explanations and are broken down into smaller parts for better understanding.

Solutions have been prepared by subject-matter experts following the latest CBSE syllabus and guidelines so that students can give accurate answers and perform better in examinations.

NCERT Solution Class 11 Biology Chapter 12 Mineral Nutrition 

All living creatures have certain fundamental needs such as the consumption of macromolecules (like starches, fats, and proteins), water, and minerals to promote development and advancement. The chapter discusses inorganic plant sustenance, and students will learn the technique for recognising components that play a basic part in plant development and advancement. Students will also read about the functions of the fundamental components, their lack of indications, and the retention of the basic components.

In 1860, the German botanist Julius Von Sachs demonstrated that plants could be developed without the presence of soil. It was done with the help of a defined nutrient solution. This process that does not require soil but the nutrient solution is known as tank-farming. Tank farming is used for vegetable farming for business purposes. It should be noted that circulation for nutrition solutions with sufficient air is a must for a plant’s ideal development. 

From then on, multiple techniques were utilised to decide the mineral solution ideal for plants. The different techniques all include growing plants in a mineral solution without soil. Filtered water and mineral solutions like salts are required in these techniques. 

A series of tests were conducted where plants were grown in nutrient solutions and a component was either added, removed, or given in shifted fixation. After these tests, the most appropriate mineral solution for plant development was obtained. It was possible to distinguish basic components and find out their inadequacy indicators. 

Distribution of Marks for Mineral Nutrition 

The Mineral Nutrition chapter is covered under Unit IV, which carries a topic weightage of 18 marks. 1 mark or 5 marks questions may be asked in exams from it.

Advantages of Class 11 Biology Mineral Nutrition NCERT Solution 

NCERT Solutions for Class 11 Biology Chapter 12 contain comprehensive answers that students can refer to while attempting to practice questions given at the end of the Chapter 12 NCERT textbook. 

Extramarks NCERT Solutions are reliable enough to be considered the best guide option for examination preparation. All questions which are a part of Chapter 12 Mineral Nutrition are covered well in Class 11 Chapter 12 Biology NCERT Solutions.

Related Questions 

Q1. A cut apple that has been kept for a while in the air turns brown. This occurs due to the presence of :

  • Ferrous ions
  • An enzyme action
  • Ferric ions
  • Magnesium ion

 

Answer: An enzyme action

Explanation: When an apple is cut, the enzyme polyphenol oxidase (PPO) present in the apple comes in contact with the oxygen molecules in the air. Oxygen molecules oxidise polyphenol into o-quinones which react with amino acids to produce melanins. The production of melanins gives the apple its brownish appearance.

Q2. The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements is involved in this reaction?

  • Magnesium and chlorine
  • Manganese and potassium
  • Manganese and chlorine
  • Magnesium and molybdenum

 

Answer: Manganese and Chlorine

Explanation: The photolysis of water is aided by chlorine, manganese, and calcium during the light reaction of photosynthesis.

Q3. Mention the functions of Leghaemoglobin.

Leghaemoglobin is a hemoprotein found in nitrogen-fixing root nodules of leguminous plants and has the following functions:

  • It protects nitrogenase (an enzyme) from being deactivated by oxygen as nitrogenase is sensitive to oxygen. 
  • It provides enough oxygen to bacteria for respiration. 

Q4. Explain the steps involved in the formation of root nodules.

The formation of root nodules involves multiple steps and sequencing of a series of interactions between the roots of the host plant and Rhizobium. Here are the steps involved:

Step 1: Rhizobia multiplies and colonizes the surroundings of the roots and epidermal. The root hair cells get attached to it. When the root hair curls, the invasion of bacteria begins.

Step 2: Upon the production of an infection thread, the bacteria are carried into the cortex of the root, and nodule formation is initiated.

Step 3: The bacteria is released from the thread into the cells which lead to the differentiation of specialized cells for nitrogen fixation.

Step 4: This leads to the formation of a direct vascular connection with the host with the help of nodules. It helps in the exchange of nutrients.

 

Q.1 ‘All elements that are present in a plant need not be essential to its survival’. Comment.

The statement that “all the elements that are present in a plant need not be essential to its survival” holds true as only the elements which fulfill the below-mentioned criteria are essential for the survival of the plant, rest are not essential.

  • The element must be absolutely necessary for supporting growth and reproduction. In the absence of these elements, plants cannot grow or produce seeds.
  • The element cannot be replaced with any other element which means that the requirement is very specific. Deficiency of that particular element cannot be met by replacing it with other elements.
  • The element must be directly involved in the metabolism of the plant.

There are cases where elements like gold, selenium, etc., have been found in plants but these are not essential.

Q.2 Why is purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?

The purification of water and nutrient salts is very important in studies involving mineral nutrients using hydroponics because the presence of impurities in a mineral solution may alter the concentration of the solution therefore, altering the optimum growth conditions like pH required for Hydroponics. Due to such alterations, the standardised mineral solution might be rendered non-useful for the growth of the plant. These impurities could be in the form of inorganic elements or compounds that are detrimental to the plants. For example, Sodium (Na) if greater than 70 ppm, Boron (B) if greater than 2.0 ppm, anions of chloride (Cl–) if greater than 100 ppm and bicarbonate (HCO3–) if greater than 40 ppm can be very harmful to the growth of the plants. Also, in order to determine the exact nature and amount of mineral required, it is necessary that the nutrient is present in known amounts. Any kind of impurity from water or nutrient salt will hamper the validity of the experiment.

Q.3 Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.

Macronutrients: They have the following features:

  • Essential for the growth of the plant
  • Required in large amounts
  • Directly involved in the metabolism of the plant
  • Cannot be replaced with any other nutrients
  • Generally present in large amounts (in excess of 10 mmole Kg-1 of dry matter).

Example: carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur etc.

Micronutrients: They have the following features:

  • Essential for the growth of the plant
  • Required in small amounts
  • Directly involved in the metabolism of the plant
  • Cannot be replaced with any other nutrient
  • Generally present in very small amounts (less than 10 mmole Kg-1 of dry matter).

Example: iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel.

Beneficial Nutrients: The elements which are not essential but their presence enhances the growth of the plants are known as beneficial nutrients. In addition to the essential elements, beneficial elements are also required by some higher plants for better growth. These elements have been reported to enhance the resistance of the plant to biotic and abiotic stresses. Example: sodium, silicon, cobalt and selenium.

Essential Elements: Essential elements are elements that have the following features:

  • Absolutely necessary for supporting normal plant growth
  • Cannot be replaced by any other element
  • Directly involved in the metabolism of the plant
  • Can be macronutrients or micronutrients (depending upon the quantities in which they are required by the plant)
  • 17 essential elements which carry out essential functions in the plants
  • Classified into four subgroups based on the function.

Example: carbon, hydrogen, oxygen, nitrogen, iron, manganese, copper, molybdenum, zinc.

Q.4 Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.

The different deficiency symptoms in plants are as follows:

  • Chlorosis is the loss of chlorophyll leading to yellowing of leaves. This is caused by the deficiency of elements like N, K, Mg, S, Fe, Mn, Zn and Mo.
  • Necrosis is the death of tissues, particularly leaf tissue. This is caused by the deficiency of elements like Ca, Mg, Cu, K.
  • Delayed flowering is the result of low levels of elements like N, S or Mo.
  • Stunted plant growth is the result of deficiencies of Cu and K.
  • Inhibition of cell division is caused by lack or low levels of N, K, S or Mo.

[N-Nitrogen, K-Potassium, Mg-Magnesium, S-Sulphur, Fe-Iron, Mn-Manganese, Ca-Calcium, Cu-Copper, Zn-Zinc and Mo-Molybdenum]

Q.5 If a plant shows a symptom which could develop due to deficiency of more than one nutrient, how would you find out experimentally, the real deficient mineral element?

If a plant shows a symptom which could develop due to deficiency of more than one nutrient, the real deficient mineral element can be found by following steps:

  • Observe the morphological changes in all the parts of the plant.
  • Compare the changes with the available standard tables.
  • Design an experiment where one can add the nutrient one by one and then look for the recovery of the plants after addition of the particular element.

This strategy helps in finding out the real deficient mineral element.

Q.6 Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?

The reason behind the appearance of deficiency symptoms first in younger parts of the plant as compared to that of mature organs is due to the difference in the mobility of the element under study. When the elements are relatively immobile and are not transported out of the mature organs, the deficiency symptoms first appear in younger growing parts. For example, elements like sulphur and calcium are part of the structural component of the cell and are not easily released from the older tissues making it deficient in the younger and newer organs. The elements that are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms first appear in the older tissues. For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves. In the older leaves, biomolecules containing these elements are broken down, making it available for younger leaves.

Q.7 How are the minerals absorbed by the plants?

The main organ of the plant through which minerals are absorbed from the soil is root. The process of absorption has two well-demarcated phases.

  • In the initial phase, rapid uptake of ions occurs passively into the space outside the cell membrane of the cells (known as apoplast). This uptake occurs through ion-channels which are transmembrane proteins that function as selective pores.
  • In the second phase of uptake, the ions are taken in slowly into the ‘inner space’ or the space inside the plasma membrane (known as symplast) of the cell. This process is energy-driven and thus an active process. The movement of ions is called flux.

Q.8 What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobium. What is their role in N2 -fixation?

Nitrogen is one of the most prevalent elements in living organisms. The atmospheric nitrogen cannot be absorbed by plants as such – it needs to be fixed as nitrates before plants can absorb and transport it to leaves. Reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation and few prokaryotic species are capable of fixing nitrogen. These prokaryotic microbes, which have the enzyme nitrogenase, are capable of nitrogen reduction and are called N2 fixers. Rhizobium is one such N2 fixer. The conditions necessary for fixation of atmospheric nitrogen by Rhizobium are as follows:

  1. The most important condition required for fixation of atmospheric nitrogen by Rhizobium is the presence of the anaerobic condition. The enzyme nitrogenase, that is required for the conversion of atmospheric nitrogen to ammonia cannot function in the presence of oxygen. The nodule where the bacteria reside, provide the anaerobic condition.
  2. The presence of leguminous haemoglobin, an oxygen scavenger is required for the process of nitrogen fixation to occur.
  3. The process of ammonia synthesis by nitrogenase requires a high input of energy and this is obtained from the respiration of the host cells.

Role in N2-fixation: The free-living aerobic bacteria Rhizobium enters into a symbiotic relationship with leguminous plants and starts fixing free nitrogen of the atmosphere into ammonia which can be utilised by the host plant. The important features of Rhizobium are

  • It occurs inside the anaerobic nodule which carries all the necessary biochemical components such as the enzyme nitrogenase and leghaemoglobin, which is an oxygen scavenger.
  • The enzyme nitrogenase of Rhizobium is a Mo-Fe protein and catalyzes the below-written reaction. Ammonia is the first stable product of nitrogen fixation. The reaction is as follows-

N2+ 8e–+ 8H+ + 16ATP → 2NH3+ H2+ 16ADP+16Pi

  • The ATP required for the above reaction is provided by the host.
  • Ammonia formed following nitrogen fixation is incorporated into amino acids as the amino groups.

Q.9 What are the steps involved in formation of a root nodule?

The formation of nodule requires a series of interaction between the Rhizobium, which is free-living aerobic bacteria and the roots of the host leguminous plants. Rhizobium is capable of fixing free nitrogen of the atmosphere into ammonia which can be utilised by the host plant. This reaction occurs inside the anaerobic conditions maintained inside nodule which carries all the necessary biochemical components. Main stages in the formation of the nodule are described below:

  • Rhizobia multiply, colonise the root surroundings and get attached to epidermal and root hair cells.
  • Root hairs curl and bacteria invade the root hair.
  • Infection thread carries the bacteria into the root cortex, where nodule formation is initiated.
  • Bacteria are released from the infection thread into the cells – specialised nitrogen-fixing cells start differentiating.
  • The nodule is formed – it has a direct vascular connection with the host for exchange of nutrients.

Q.10 Which of the following statements are true? If false, correct them:

(a) Boron deficiency leads to stout axis.

(b) Every mineral element that is present in a cell is needed by the cell.

(c) Nitrogen as a nutrient element, is highly immobile in the plants.

(d) It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.

(a) True

(b) False. All the mineral elements that are present in a cell are not needed by the cell. For example, gold and selenium are found accumulated in plants but they are not used in any plant process.

(c) False. Nitrogen as a nutrient is highly mobile in the plants. Its deficiency results in deficiency symptoms to show up first in older tissues.

(d) False. It is very difficult to establish the essentiality of micronutrients because of the trace requirements

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FAQs (Frequently Asked Questions)

Mineral salt is absorbed by plants easily through the roots with the help of root hair and zones of extension. Minerals that plants have collected from the soil are assimilated as ions. Absorption of minerals takes place in two phases: Initial and Metabolic. 

The initial stage involves ions being taken up rapidly into the apoplast (free spaces of the cells). Apoplast includes cell dividers and intercellular spaces. The particles that are absorbed by the free space are not interchangeable (eg: unlabelled K+ particles cannot be replaced with labelled K+ particles). The absorption of minerals from soil by root hair occurs with a simple diffusion process and does not require energy. The diffusion process involves the movement of solute and minerals from a place they are highly concentrated (soil) to a place of lower concentration (root hair). The initial stage can be considered as passive transport of minerals. 

The metabolic stage involves ions passing into internal space. The transport of minerals here takes up energy and hence this stage can be considered an active transport of minerals. Flux is the movement of ions. Influx on the other hand is the movement of ions into the cell while efflux is the outwards movement. 

 

In plants, Chlorosis, Necrosis, Delay in flowering, Deformation, and Inhibition of cell division are the five deficiency symptoms. Here is how they occur:

Chlorosis: This is caused because of N, K, Mg, S, Fe, Mn, Zn, and Mo deficiency.

Inhibition of cell division: N, Mo, K, and S deficiency are the reasons for this. 

Delay in flowering: This occurs because of reduced levels of Mo, S, and N.

Necrosis: This is caused because of Mg, Ca, Cu, and K deficiency.

Deformation: This is caused by Boron deficiency.

 

As explained in Class 11 Biology Chapter 12 Mineral Nutrition, observing the morphological changes in every part of the plant is what should be followed to determine the real deficient mineral. The standard tables and the changes should then be compared. One has to check experimentally (which is done by adding the nutrients one after the other) by noting the recovery of the plant in response to adding a particular nutrient. The deficient mineral element can be found with the help of this method.

The nitrogen cycle includes converting Nitrogen into biologically accessible forms. This can be done in three ways:

  • Lightning And UV radiation: Lightning And UV radiation convert Nitrogen gas to Nitrate. 
  • Industrial processes: Through industrial processes, nitrogen can be reduced to Ammonia and Urea.  
  • Nitrogen-fixing bacteria: Nitrogen-fixing bacteria aid in converting nitrogen to ammonia.

When lightning occurs, pressure and high temperature in the air convert nitrogen to its oxides. These oxides keep revolving in the air until rainwater dissolves them into nitric and nitrous acids. Multiple life forms then use these acids. Rain causes the nitric and nitrous acids to merge with the soil and form soil organic nitrogen. This process of nitrogen being converted into a biologically accessible form is called atmospheric nitrogen fixation. 

Particular deficiency characteristics can be seen in every element. An element’s deficiency cannot be fulfilled by supplying some other element. Noting down all the symptoms in different parts of the plants is the first step while the next one is comparing the collected information and the standard symptoms in a table to determine the mineral deficiency. 

NCERT Solutions Class 11 Biology Chapter 12 by Extramarks have been curated to help students prepare all the answers that are a part of the exercise questions of NCERT Class 11 Chapter 12 Biology. Diagrams are used to make them more understandable. Clear explanations of the answers help in learning and understanding them more easily and quickly.