NCERT Solutions for Class 11 Biology Mineral Nutrition [Old Book]

NCERT
SOLUTIONS
CLASS - 11th

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Class : 11th
Subject : Biology
Chapter : 12
Chapter Name : Miniral Nutrition

Q1 ‘All elements that are present in a plant need not be essential to its survival’. Comment.

Answer. Plants tend to absorb different kinds of nutrients from soil. However, a nutrient is
inessential for a plant if it is not involved in the plant's physiology and metabolism. For example,
plants growing near radioactive sites tend to accumulate radioactive metals. Similarly, gold and
selenium get accumulated in plants growing near mining sites. However, this does not mean that
radioactive metals, gold, or selenium are essential nutrients for the survival of these plants.

Q2 Why is puri cation of water and nutrient salts so important in studies involving mineral
nutrition using hydroponics?

Answer. Hydroponics is the art of growing plants in a nutrient solution in the absence of soil.
Since the plant roots are exposed to a limited amount of the solution, there are chances that the
concentrations of oxygen and other minerals in the plant roots would reduce. Therefore, in studies
involving mineral nutrition using hydroponics, puri cation of water and nutrient salts is essential
so as to maintain an optimum growth of the plants.

Q3 Explain with examples: macronutrients, micronutrients, bene cial nutrients, toxic elements
and essential elements.

Answer. Macronutrients: They are the nutrients required by Plants in large amounts. They are
present in plant tissues in amounts more than 10 m mole/kg Of dry matter. Examples include
hydrogen, oxygen, and nitrogen.
Micronutrients: They 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 include cobalt,
manganese, Zinc, etc.
Bene cial nutrients: They are plant nutrients that may not be essential, but are bene cial to
plants. Sodium, silicon, cobalt and selenium are bene cial to higher plants.
Toxic elements: Micronutrients are required by Plants in small quantities. An excess Of these
nutrients may induce toxicity in Plants. For example, when manganese iS present in large
amounts, it induces de ciencies of iron, magnesium, and calcium by interfering with their
metabolism. Essential elements: These elements are absolutely necessary' for plant growth and

reproduction. The requirement Of these elements is speci c and non-replaceable. They are further
classi ed as macro and micro-nutrients.

Q4 Name at least ve different de ciency symptoms in plants. Describe them and correlate them
with the concerned mineral de ciency.

Answer. The ve main de ciency symptoms arising in plants are:

Chlorosis

Necrosis

Inhibition of cell division

Delayed owering

Stunted plant growth

Chlorosis or loss of chlorophyll leads to the yellowing of leaves. It is caused by the de ciencies of
nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc, and molybdenum. Necrosis is
the death of plant tissues as a result of the de ciencies of calcium, magnesium, copper, and
potassium. Inhibition of cell division is caused by the de ciencies of nitrogen, potassium, sulphur,
and molybdenum. Delayed owering is caused by the de ciencies of nitrogen, sulphur, and
molybdenum. Stunted plant growth is a result of the de ciencies of copper and sulphur.

Q5 If a plant shows a symptom which could develop due to de ciency of more than one nutrient,
how would you nd out experimentally, the real de cient mineral element?

Answer. In plants, the de ciency of a nutrient can cause multiple symptoms. For example, the
de ciency of nitrogen causes chlorosis and delayed owering.
In a similar way, the de ciency of a nutrient can cause the same symptom as that caused by the
de ciency of another nutrient. For example, necrosis is caused by the de ciency of calcium,
magnesium, copper, and potassium. Another point to be considered is that different plants
respond in different ways to the de ciency of the same nutrient. Hence, to identify the nutrient
de cient in a plant, all the symptoms developed in its different parts must be studied and
compared with the available standard tables.

Q6 Why is that in certain plants de ciency symptoms appear rst in younger parts of the plant

while in others they do so in mature organs?

Answer. De ciency symptoms are morphological changes in plants, indicating nutrient de ciency.
De ciency symptoms vary from one element to another. The plant part in which a de ciency
symptom occurs depends on the mobility of the de cient element in the plant. Elements such as
nitrogen, potassium, and magnesium are highly mobile. These elements move from the mature
organs to the younger parts of a plant. Therefore, the symptoms for the de ciencies of these
elements rst appear in the older parts of the plant. Elements such as calcium and sulphur are
relatively immobile. These elements are not transported out of the older parts of a plant.
Therefore, the symptoms for the de ciencies of these elements rst appear in the younger parts of
the plant.

Q7 How are the minerals absorbed by the plants?

Answer. The absorption of soil nutrients by the roots of Plants occurs in two main phases —
apoplast and symplast.
During the initial phase or apoplast, there is a rapid uptake of nutrients from the soil into the free
spaces of plant cells. This process is passive and it usually occurs through transmembrane proteins
and ion-channels.
In the second phase or symplast, the ions are taken slowly into the inner spaces of the cells. This
pathway generally involves the expenditure of energy in the form of ATP.

Q8 What are the conditions necessary for xation of atmospheric nitrogen by Rhizobium. What is
their role in N - xation?
2

Answer. Rhizobium iS a symbiotic bacteria present in the root nodules of leguminous plants. The
basic requirements for Rhizobium to carry out nitrogen xation are as follows:
(a) Presence Of the enzyme nitrogenase
(b) Presence Of leg-haemoglobin
(c) Non-haem iron protein, ferredoxin as the electron-carrier
(d) Constant supply Of ATP
(e) M g ions as cofactors
2+

Rhizobium contains the enzyme nitrogenase — a Mo-Fe protein — that helps in the conversion of
atmospheric free nitrogen into ammonia.
The reaction is as follows:
N +8e + 8H + 16 ATP - 2 N H + H + 16 ADP + 16Pi
− +
2 3 2

The Rhizobium bacteria live as aerobes under free-living conditions, but require anaerobic
conditions during nitrogen xation. This is because the enzyme nitrogenase is highly sensitive to
molecular oxygen. The nodules contain leg-haemoglobin, which protects nitrogenase from
oxygen.

Q9 What are the steps involved in formation of a root nodule?

Answer. Multiple interactions are involved in the formation of root nodules. The Rhizobium
bacteria divide and form colonies. These get attached to the root hairs and epidermal cells. The
root hairs get curled and are invaded by the bacteria. This invasion is followed by the formation of
an infection thread that carries the bacteria into the cortex of the root. The bacteria get modi ed
into rod-shaped bacteroides. As a result, the cells in the cortex and pericycle undergo division,
leading to the formation of root nodules. The nodules nally get connected with the vascular
tissues of the roots for nutrient exchange increases in region C.

Q10 Which of the following statements are true? If false, correct them:
(a) Boron de ciency 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.

Answer. (a) True
(b) All the mineral elements present in a cell are not needed by the cell. For example, plants
growing near radioactive mining sites tend to accumulate large amounts of radioactive
compounds. These compounds are not essential for the plants.
(c) Nitrogen as a nutrient element is highly mobile in plants. It can be mobilised from the old and
mature parts of a plant to its younger parts.
(d) True