NCERT
Biology Grade 11 Chapter 12 Mineral nutrition
CBSE NCERT Solutions for Class 11 biology Chapter 12
Exercises
Q.1. ‘All elements that are present in a plant need not be essential to its survival’.
Comment.
Solution: Out of all the nutrients absorbed by plants, the following are the criteria which makes it essential or non-
essential for plant survival:
The element that is very necessary for supporting normal plant growth and reproduction.
The requirement of an element cannot be replaced by a substitute element.
The element must play a direct role in plant metabolism.
If the element satisfies all these criteria it is considered essential.
Q.2. Boron deficiency leads to a stout axis.
True
Solution: Boron is a micronutrient found in the plants. Its deficiency leads to the death of stem and root apices, the
disintegration of internal tissues, and a decrease in flowering and fruiting. The given statement is correct as
boron takes part in the formation of pectin in the walls causing stout axis.
False
Q.3. Every mineral present in the cell is needed by the cell.
TrueFalse
Solution: Every mineral present in the cell is not necessarily needed by the cell. Only elements that are involved directly
in plant metabolism, have no substitute for it and is very essential for growth and reproduction in plants. There
are a total of 17 elements essential for plant survival.
Q.4. Nitrogen as a nutrient element is highly immobile in the plants.
TrueFalse
Solution: Mobile elements move from old plant parts to the new young growing part of the plants. Nitrogenous
compounds play a role in protein synthesis. Nitrogen in plants is highly mobile as it moves in the form of
nitrates. The other immobile nutrients in plants are magnesium, calcium, zinc, chlorine, iron.
Q.5. It is very easy to establish the essentiality of micronutrients because they are required in trace quantities.
True
Solution: Micronutrients are needed for the growth and development of plants but are required in very minute quantities.
Even though these are needed only in small quantities, their deficiency affects the plants and causes some
symptoms and disorders. Hence, it is very easy to establish the essentiality of micronutrients.
False
Q.6. Why is the purification of water and nutrient salts so important in studies involving mineral nutrition using hydroponics?
Solution: Hydroponics is a method of growing plants to maturity in a nutrient solution. The purification of water and
nutrient salts is essential since the method is artificial and any impurities in water or unwanted nutrient salts
can disrupt the growth or development of the plant.
It also produces wrong results in the studies involving mineral nutrients and the optimisation of the essentiality
or the concentration of mineral required will get altered.
Q.7. Explain with examples: macronutrients, micronutrients, beneficial nutrients, toxic elements and essential elements.
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NCERT Biology Grade 11 Chapter 12 Mineral nutrition
Solution: Macronutrients – Macronutrients are the nutrients required in large quantities, more than 10mmole /kg of dry
matter. Carbon, Hydrogen, Nitrogen, Oxygen, Sulphur, Phosphorus, Magnesium, Potassium and Calcium.
They are also called major elements. They contribute to the development of osmotic potential in the cells.
They are not toxic in a slightly excessive amount.
Micronutrients - Micronutrients are the nutrients required in small quantities, i.e., less than 10mmole /kg of
dry matter. These include Zinc, Copper, Molybdenum, Chlorine, Boron, Nickel, Iron, Manganese. They are
also called trace elements. They do not play any role in the development of osmotic potential in the cell and
are toxic even in slight excess.
Beneficial nutrients – Apart from the 17 elements categorised into macro and micronutrients, there are
beneficial elements that include Selenium, Cobalt, Sodium and Silicon. They are required by the higher plants
for various purposes like compensatory or regulative effect for toxic elements.
Toxic elements – The micronutrients are always required in lower concentrations, and any slight decrease in
their concentration can lead to deficiency symptoms while an increase in the concentration can lead to toxicity.
A decrease in 10 per cent of dry weight in tissues due to any mineral ion concentration can cause toxicity.
While the level of toxicity varies from plant to plant, it is also not easily detected. Most of the mineral toxicity
is such that it hinders the uptake of other minerals. Example: Deficiency of nitrogen causes Chlorosis.
Essential elements – The substance that must be obtained from the diet because the body cannot make it in
sufficient quantity to meet its needs. They are used (a) As components of energy-related chemical compounds
in plants e.g. Magnesium and Phosphorous. (b) Activators or inhibitors of enzymes e.g. Magnesium, Zinc. (c)
For regulation of osmotic potential e.g. Potassium.
Q.8. Name at least five different deficiency symptoms in plants. Describe them and correlate them with the concerned mineral
deficiency.
Solution: Mineral deficiency in plants occurs when a specific element present in the plant is below the critical
concentration. It can be observed in plants through morphological changes and are known as deficiency
symptoms.
Some of the deficiency diseases and its symptoms in plants are :
1. Chlorosis: It is the yellowing in leaves caused by the loss of chlorophyll, and the elements that are deficient
in N, K, Mg, S, Fe, Mn, Zn and Mo. 2. Necrosis: It is the death of leaf tissue due to the deficiency of elements
like Ca, Mg, Cu, K. 3. Inhibition of cell division: It is the inhibition of the normal cell division, caused due to
lack or deficiency of elements like N, K, S, Mo.
4. Deformation: The deformation, disorganisation and discolouration of meristematic tissue and finally, the
death of plant can occur due to deficiency of Boron.
5. Delayed flowering: The flowering in plants can be delayed due to deficiency or lack of elements like N, S,
Mo.
Q.9. 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?
Solution: It often happens that a deficiency symptom in plants can occur due to deficiency of nutrients associated with
many symptoms. Hydroponics can be employed to study the actual mineral element deficiency for a particular
plant deficiency symptom.
A plant that has fast growth can be used in 3 sets.
SET 1 SET 2 SET 3
It is
Plant is supplemented A plant with deficiency symptoms is taken and
kept with a nutrient supplementing the nutrient solution with that
inside solution without specific mineral element to which it has shown
the one specific the deficiency symptoms. It will make the plant
nutrient element of grow in normal conditions, thus suppressing the
medium. known deficiency symptoms.
deficiency.
Therefore, by listing out the deficiency in different regions of the plants must be studied and compared to
available standard tables. If the actual deficient element is supplemented in set 3 then it will result in normal
growth of plant, hence the mineral will be identified.
Q.10. 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?
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NCERT Biology Grade 11 Chapter 12 Mineral nutrition
Solution: In certain individual plants, the deficiency symptoms first appear in younger tissues or regions of the plant
since the elements remain relatively immobile and shall not be transported out, through the mature organs.
Elements such as sulphur and calcium, which belong to the structural components of the cell are not quickly
released.
Whereas, if the mineral elements are mobile, the deficiency symptoms are indicated in the mature plant
organs. Hence, the deficiency symptoms in a plant depend on the mobility of the nutrient elements. This
characteristic of mineral nutrition in plants has a significant role in horticulture and agriculture.
Q.11. How are the minerals absorbed by the plants?
Solution: The process of mineral absorption from soil solution can be distinguished into two phases.
The apoplast phase or passive phase – It is the initial phase in which there is a rapid uptake of the ions into the
free or 'outer space', where the nutrients move in the intercellular spaces and do not enter the cytoplasm. It
takes place through the ion-channels in which the transmembrane proteins act as selective pores.
The symplast phase or active phase – It is the second phase in which there is slow uptake of ions into the inner
space with the utilisation of metabolic energy, where water moves between cytoplasm and vacuoles of adjacent
cells. Flux refers to the movement of ions, where, the outward movement of ions is called efflux, and inward
movement is called influx.
Q.12. What are the conditions necessary for fixation of atmospheric nitrogen by Rhizobium. What is their role in N2 -fixation?
Solution: The conditions necessary for atmospheric nitrogen fixation include:
(a) A strong reducing agent
(b) The energy in the form of ATP
(c) Anaerobic environment
(d) Enzyme nitrogenase
The bacteria Rhizobium has a symbiotic relationship with the roots of leguminous plants such as garden pea,
sweet pea, alfalfa etc., Several biochemical components such as leghaemoglobin and enzyme nitrogenase (
Mo-Fe protein) are present in the root nodules, which catalyses the formation of ammonia from free
atmospheric nitrogen. It is the first stable product in the process of nitrogen fixation.
The rhizobium converts the free nitrogen into a usable form such as the ammonia by utilising the enzyme
nitrogenase, and it is in turn benefitted by the carbohydrates, proteins and oxygen of plants which helps the
bacteria grow. The leghaemoglobin scavenges any free oxygen to prevent the damage to nitrogenase enzyme.
The reaction is :
N2 + 8e-+ 8H++ 16ATP→ 2NH3 + H2+ + 16ADP + 16Pi
Q.13. What are the steps involved in formation of a root nodule?
Solution: Root nodules are formed to maintain the symbiotic association between Rhizobium and roots of the leguminous
plants. The Nitrogen-fixing bacteria, Rhizobium helps in fixation of atmospheric nitrogen into a useful form
like nitrates, which can be utilized by plants for their growth.
The steps in the formation of root nodule are as follows:
The Rhizobium bacteria come in contact with vulnerable root hair and start dividing around it. This
bacteria then infect the root hair, which causes it to curl, in case of successful infection.
The infected threads carry the bacteria into the inner cortex, where the bacteria modify into rod-shaped
bacteroids. It causes the division of cells of inner cortex and pericycle, thus leading to nodule formation
The vascular connection with the plant is established by the nodules which are in continuity with those
in the roots.
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