NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition

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The “Mineral Nutrition” chapter of Biology Class 11 discusses the role of essential elements, symptoms of mineral deficiency, inorganic plant nutrition, mineral deficiency symptoms, the significance of biological nitrogen fixation, route of absorption and transport, what defines a mineral as essential, and much more.

Question 1:

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


All the elements present in a plant need not be essential for its survival but only few elements are found to be essential for growth and metabolism. Such essential elements are specific to plants and are not replaceable by another element. These are directly involved in the nutrition of the plant. There are some elements such as Zn, Mo, B etc. are non-essential and present in traces. They take part in some metabolic reactions but are not essential for survival.

Question 2:

Why is purification of water and nutrient salts so important in studies involving minerals nutrition using hydroponics ?


It is important for the studies of physiological role and deficiency symptoms of specific mineral element involving hydroponics.

Question 3:

Explain with examples: macro-nutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.


Macronutrients. An element such as potassium, nitrogen, calcium essential in large quantities for plant growth is termed macronutrient. They are generally present in plant tissues in concentrations of at least 10 m-mol kg–1 of dry matter. Examples Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, silicon and iron. Micronutrients or trace elements, are needed in very small amounts (equal to or less than 10 m-mol kg–1 of dry matter). These include iron, manganese, copper, molybdenum, zinc, boron, chlorine and nickel. Beneficial nutrients. They are required by higher plants in large quantities. Examples are sodium, silicon, cobalt and selenium. Toxic element. Any mineral ion that reduces the dry weight of tissues by about 10% is called a toxic element. Example—excess of Manganese causes the development of brown spots in plants. Essential elements. Such elements without whom the physiological functions of plants are affected are called essential elements. These include calcium, hydrogen, oxygen etc.

Question 4:

Name atleast five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral deficiency.


The names of five different deficiency symptoms are :

  1. Chlorosis. It is the loss of chlorophyll leading to yellowing of leaves. It is caused by the deficiency of elements N, K, Mg, S, Fe, Mn, Zn and Mo.
  2. Necrosis. It is the death of tissue particularly leaf tissue and appears due to the deficiency of Ca, Mg, Cu, K.
  3. Inhibition of cell division which affects the general growth of the plant and elongation of parts like roots is caused because of the deficiency of N, K, S, Mo.
  4. Some elements like N, S, M delay flowering if their concentrations in the plant are low.
  5. Stunted growth occurs due to deficiency of N, P, Ca.
Question 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 ?


In such a case in order to find out the real cause of the symptom, one has to study all the symptoms developed in all the various parts of the plant and compare them with the available standard tables. To observe the real deficient mineral element, a series of experiments are done in which the roots of the plants are inmersed in nutrient solutions and wherein and an element was added/removed or given in varied concentration, a mineral solution suitable for the plant growth is obtained. By this method, essential element is identified and its deficiency symptoms can be discovered.

Question 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 parts of the plants that show the deficiency symptoms depend on the mobility of the element in the plants. Where elements are actively mobilised within the plants and exported to young developing tissues, the deficiency symptoms tend to appear first 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 these elements available for mobilising to younger leaves.
The deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs, for example, elements like sulphur and calcium are a part of the structural component of the cell and hence are not easily modified.

Question 7:

How are the minerals absorbed by the plants ?


The process of intake of nutrients from the soil is called absorption. Plants absorb minerals from the soil through the roots by two ways—(a) Passive absorption and (b) Active absorption.
(a) Passive absorption. It is simple process of diffusion of ions from higher concentration to lower concentration into root cells.
(b) Active absorption. The uptake of mineral ions against concentration gradient is called active absorption. Such a movement of ions is carried out with the expenditure of energy (ATP). Carriers are involved in active mineral absorption.
Carrier+ionCarrier ion complexCarrier ion enters inner space.

Question 8:

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


The most important condition necessary for fixation of atmospheric nitrogen by Rhizobium is that it should occur in a symbiotic relationship with the roots of leguminous plants like alfalfa, sweet clover, sweet pea, lentils, peas, beans etc. Although Rhizobium also occurs as free living but can carry out fixation of atmospheric nitrogen fixation as a symbiont.

Question 9:

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

  1. Boron deficiency leads to 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 the plants.
  4. It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.
  1. True. Boron deficiency leads to death of root and shoot tips, loss of apical dominance etc.
  2. False. Every element that is present in the plant may not be required by the plant.
  3. False. Nitrogen as a nutrient is high mobile element.
  4. True.