NCERT Class 11-Biology: Chapter – 12 Mineral Nutrition Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 3:

What are essential elements for plants? Give the criteria of essentiality? How are minerals classifieds depending upon the amount in which they are needed by the plants?


Essential elements are the elements which are necessary for a plant to grow and reproduce. The deficiency of these elements cannot be replaced by any other. There are two types of essential elements which are:

(A) Macro elements: These are present in large amounts like Calcium, Magnesium etc.

(B) Micro Elements: Present in small amounts like Iron, Zinc etc.

Criteria of essentiality: The essentiality not only depends on the presence of an element in the plant but also on the following criteria:

1. If the plant is unable to grow and reproduce without the presence of an element.

2. The element is specific and cannot be replaced by any other element.

3. The element is directly involved in the metabolism process.

Question 4:

With the help of examples describe the classification of essential elements based on the function they perform.


Classification of essential elements based on the function they perform is as follows:

1. Essential elements as components of energy related compounds

For example: Magnesium in Chlorophyll and Phosphorus in ATP molecule.

2. Essential elements as components of Structural elements of cells

For example: Hydrogen bonds are seen in secondary structure of proteins, Carbon and Oxygen in proteins, lipids, carbohydrates and nucleic acids.

3. Essential elements as Activator and Inhibitor of enzymes:

For example: Magnesium (Mg2 + ) is an activator of both Ribulose Bisphosphate and Phosphoenol pyruvate enzyme which are involved in photosynthetic carbon fixation.

4. Essential elements which can alter osmotic pressure:

For example Potassium plays an important role in opening and closing of Stomata.

Question 5:

We know that plants require nutrients. If we supply these in excess, will it be beneficial to the plants? If yes, how/If no, why?


Question 6:

Trace the events starting from the coming in contact of Rhizobium to a leguminous root till nodule formation. Add a note on importance of leg haemoglobin


The following events take place:

1. Rhizobium multiply and colonise around the surrounding of the roots and get attached to the epidermal and root hair cells.

2. Now, the root hair cells curl and the bacteria enters the root hairs.

3. After entering the root hair an infection thread is formed. Which carries the bacteria to the cortex of the root.

4. In the cortex nodule formation starts taking place.

5. Here, the bacteria are released from the thread in the cells, which leads to differentiation of nitrogen fixing cells.

6. A vascular connection is established with the host for exchange of nutrients.

Leghaemoglobin is a red coloured pigment present in the root nodules of a legume. It is also considered as oxygen molecule scavenger because it combines with the oxygen molecule and helps in its removal. Thus helping enzyme nitrogenase in nitrogen fixation, which only works in absence of molecular

Question 7:

Give the biochemical events occurring in the root nodule of a pulse plant. What is the end product? What is its fate?


Nodule consists of all the biochemical like enzyme nitrogenase and Leg Hemoglobin. The process of nitrogen fixation involves the conversion of free nitrogen in the air into Ammonia or other nitrogenous compounds in the presence of enzyme Nitrogenase.

The end product of the biochemical events is Ammonia .

Fate of Ammonia: The Ammonia produced through nitrogen fixation is incorporated in the amino acids as amino group. At physiological group is protonated to group.

The two events by which group is incorporated into amino acids are:

1. Reductive Amination: In this reaction alpha Ketoglutaric acid forms glutamate. In this reaction Ammonia reacts with a-ketoglutaric acid to form glutamate.

Reductive Amination

2. Transamination: In this reaction amino group transfers from one amino acid to another amino acid transaminase enzyme catalyses this reaction.