NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition

The focus of chapter 12 'Mineral Nutrition' is on the concept of inorganic plant nutrition, in which the methods that are used to trace the elements required for the growth and development of plants will be studied along with the criteria or conditions that prove the essentiality or necessity of those elements for plants. Students will also gain knowledge of the role these essential elements play in the plants' growth, the mechanism through which these elements are absorbed, and what are their serious deficiency signs.

The students will also be given a gist about the mechanism and importance of biological nitrogen fixation. Now, it's time to get a brief look at the topics covered in this chapter.

• Modus Operandi to study the demand for minerals by Plants
• What are the vital mineral elements?
• The process of absorption of elements
• Translocation of Solutes
• Soil, considered as a warehouse of essential elements
• Nitrogen Metabolism

All living entities have the same necessities, for example, macromolecules, like proteins, starches, water, fats, and minerals to advance and develop themselves. Therefore, this chapter focuses on the inorganic nutrients that organisms require to grow. Overall, the topics mentioned above talk about the techniques required to identify the constituents that are primary to the advancement and development of plants and find the rules necessary to build up the vitality. The nutrients that are demanded in large quantities are called macronutrients, and those needed in lesser quantities are referred to as micronutrients.

In this chapter, students will examine the functions the fundamental constituents play, a serious lack of indications,i.e. deficiency symptoms in them, and the retention capacity of these basic components. Additionally, students will get acquainted with the system of organic nitrogen fixation through the topics stated above.

Q1. 'All elements that are present in a plant need not be essential to its survival. Comment
Answer: A plant tends to accumulate a variety of mineral elements. Out of these elements, not all of them are essential for the survival of plants. For example, the plants which grow near radioactive sites, accumulate radioactive elements, which are not essential for survival. Similarly, some plants can accumulate elements like gold, selenium, etc. which are also not essential for the survival of the plant. Hence, the importance of any element to the survival of a plant is dependent on its role in the physiology and metabolism of the plant. If an element does not have an important role to play in plant physiology, then it is not essential for survival, and if it has a role in plant physiology then it is essential for survival. Thus, all elements that are present in a plant need not be essential to its survival.

Q2. Why is the purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?
Answer: The technique of growing plants in soil-less conditions in solution cultures is called hydroponics. Hydroponic studies are used to identify the functions and roles of different mineral elements in the physiology of plants. During such studies, it is important to purify water and nutrient salts because if there are impurities in water and nutrient salts the exact physiological role and deficiency symptoms of elements could not be identified. 
Therefore, in studies involving mineral nutrition using hydroponics, purification of water and nutrient salts is essential so as to maintain an optimum growth of the plants.

Q3. Explain with examples:
1. macronutrients,
Answer: Macronutrients- These are the nutrients required by plants in large amounts. Macronutrients are mostly present in plant tissues in amounts of more than 10 m mole/kg Of dry matter. Examples of macronutrients include Nitrogen, Phosphorus and Potassium.

2. micronutrients,

Answer: Micronutrients- These are also called trace elements and are present in plant bodies in very small amounts, i.e., amounts less than 10 m mole/kg of dry matter. Examples of micronutrients include cobalt, manganese, zinc, etc.

3. beneficial nutrients,

Answer: Beneficial nutrients: These are plant nutrients that are not essential, but are beneficial to the plants. Nutrients like sodium, silicon, cobalt, and selenium are beneficial to higher plants.

4. toxic element

Answer: Toxic elements: The micronutrients that are required by plants in extremely small quantities. An excess of these nutrients may induce toxicity in plants. For example, if manganese is present in large amounts, it can induce deficiencies of iron, magnesium, and calcium by interfering with their metabolism.

5. essential elements.

Answer: Essential elements- The essential elements are absolutely necessary for the growth and reproduction of the plants. The requirement of these elements is specific and non-replaceable. Essential elements are further classified as macronutrients and micronutrients on the basis of size.

Q4. Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.
Answer: Deficiency symptoms- In the absence of any particular element, the plant shows certain morphological changes. These morphological changes are called deficiency symptoms. Five different deficiency symptoms in plants are as follows:

Chlorosis- It refers to the loss of chlorophyll causing yellowing of the leaves. This symptom is visible during the deficiency of Mg, Mn, Zn, Fe etc.
Necrosis- The term necrosis signifies the death of tissues. Necrosis is seen during the deficiency of Calcium.
Exanthema- It refers to the splitting of skin and exudation of gummy matter. Exanthema is seen due to the deficiency of Copper.
Delayed flowering- The flowering is delayed due to the deficiencies of nitrogen..
Stunted plant growth- This deficiency symptom caused a decrease in the growth of the stem. Stunted plant growth is a result of the deficiencies of copper and sulphur.

Q5. 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?
Answer: In plants, the deficiency of a nutrient can cause multiple symptoms. Similarly, deficiency of one nutrient may cause the same symptom as that caused by the deficiency of some other nutrients. For example, the deficiency of nitrogen can cause chlorosis as well as delayed flowering. Similarly, necrosis can be caused by the deficiency of nutrients like calcium.. If a plant shows a symptom that could develop due to deficiency of more than one nutrient then to find out experimentally, the real deficient mineral element, we have to first prepare the dilute solutions of all the possible deficient nutrients. A number of plants will be grown in small pots using nutrient-deficient soil. Dilute solutions of different nutrients will be added in different pots. In one set the growth of plants will become normal. The nutrient supplied to these plants had been deficient.

Q6. Why is it that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?
Answer: Deficiency symptom refers to the morphological changes in plants that indicate a deficiency of a particular nutrient. The occurrence of deficiency symptoms in plant parts depends on the mobility of the deficient element in the plant. For example, elements such as nitrogen, potassium, and magnesium are highly mobile. These elements can move from the mature organs to the younger parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the older parts of the plant. Similarly, elements like calcium and sulfur are relatively immobile and are not transported out of the older parts of a plant. Therefore, the symptoms for the deficiencies of these elements first appear in the younger parts of the plant. Hence, certain plant deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs.

Q7. How are the minerals absorbed by the plants?
Answer: Process of mineral absorption by plants

Minerals are absorbed by cells of the root apex, zone of elongation, and root hairs. The minerals absorbed by the root hair zone are meant for passage to shoot while the ones absorbed by the root apex and zone of elongation remain in the root. The process of mineral absorption is an active process. It occurs in two phases i.e. initial phase and the metabolic phase. The initial phase is a passive process wherein ions absorbed from the outside pass in the outer or free space of the cells. It comprises intercellular spaces and cell walls i.e. apoplast.

The metabolic phase is an active process wherein ions enter the cytoplasm and cell vacuoles i.e symplast. The movement of ions is called flux. The inward movement is called influx and outward movement is called efflux.

Q8. What are the conditions necessary for the fixation of atmospheric nitrogen by Rhizobium? What is their role in N2- fixation
Answer: The conditions necessary for fixation of atmospheric nitrogen by Rhizobium and their roles in nitrogen fixation are as follows:

Reducing environment- A reducing environment is necessary for the action of enzyme nitrogenase which is sensitive to free oxygen.
The presence of nitrogenase enzyme- a Mo-Fe protein — helps in the conversion of atmospheric free nitrogen into ammonia.
Presence of leghaemoglobin- The root nodules containing Rhizobium contains leghemoglobin, which protects nitrogenase from oxygen.
Source of energy as ATP- Nitrogen fixation is an energy-requiring process thus ATP is required.
Source of reducing power NAD(P), H2, or FMNH2-

Ferredoxin as the electron donor- Ferredoxin makes nitrogen reactive.
Magnesium ions as cofactors- Magnesium acts as a cofactor and helps in the activity of nitrogenase.

Q9. What are the steps involved in the formation of a root nodule?
Answer: Formation of root nodules - The process of nodule formation involves a sequence of interaction between root and Rhizobium which occurs in the following manner:

The Rhizobia present around the roots multiply and increase in number. These Rhizobia attach themselves with the epidermis of the roots. The root hairs curls and bacteria invade it. An infection thread is formed that carries the bacteria into the cortex of the root. Nodule formation starts in the cortex of the root. Then, the bacteria are released from thread to cells which leads to the formation of specialized nitrogen-fixing cells. The nitrogen-fixing cells by repeated divisions increase in number and form nodules. The nodules establish a direct vascular connection with the host for the exchange of nutrients. These nodules contain all necessary biochemical components like enzyme nitrogenase and leg-hemoglobin. Due to the presence of leghaemoglobin, nodules are pinkish in color.

Q10. Which of the following statements are true? If false, correct them:

1. Boron deficiency leads to the stout axis.

2. Every mineral element that is present in a cell is needed by the cell.

3. Nitrogen as a nutrient element is highly immobile in plants.
4. It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.

Answer:

1. Boron deficiency leads to the stout axis.

True statement

2. Every mineral element that is present in a cell is needed by the cell.

False statement. Only essential mineral elements are needed by the cells.

3. Nitrogen as a nutrient element is highly immobile in plants.

False statement. Nitrogen is a highly mobile nutrient.

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

True statement.