CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from Chapter 14 - Biomolecules

Check important questions for CBSE 12th Chemistry Board Exam 2020 and prepare for the upcoming CBSE Class 12th Chemistry Board Exam 2020.
Mar 6, 2020 16:12 IST
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Chapter 14
Chapter 14

The CBSE Class 12th Chemistry Examination will be held on March 7, 2020. The students who are appearing for CBSE Class 12th Examination can go through the important questions mentioned in this article. The questions mentioned in this article are based on the previous year question papers, sample papers and NCERT textbook. 

Key Points to be mentioned while writing the answers to the below mentioned important questions: 

Question 1- Define:   

(i) peptide linkage

(ii) glycosidic linkage

(iii) Invert Sugar

(iv) Polypeptides

Answer: (i) peptide linkage: Chemically, peptide linkage is an amide formed between –COOH group and –NH2 group.

(ii)  Glycosidic linkage: The two monosaccharide units are joined together through an ethereal or oxide linkage formed by loss of a molecule of water.

(iii) Invert Sugar: An equimolar mixture of glucose and fructose obtained by hydrolysis of sucrose in the presence of an acid such as dil. HCl or the enzyme invertase or sucrase is called invert sugar.

(iv) Polypeptides: They are formed when several molecules of a-amino acids are joined together by peptide bonds.

Question 2- Answer the following: 

(a)Name two water-soluble vitamins along with their sources and the diseases caused due to their deficiency in the diet.




Deficiency disease

Vitamin B2

(Riboflavin or Lactoflavin)

Milk, yeast, green vegetables, meat, liver, kidney, egg white etc. The daily dosage is 2-3 mg.

Retards growth, causes inflammation of the tongue (glossitis), dermatitis and cheilosis (cracking or fissuring) at comers of mouth and lips.

Vitamin C (Ascorbic acid)

Citrus fruits, green leafy vegetables, chillies, sprouted pulses and germinated grains. The daily dosage is 75 mg.

Scurvy (bleeding) of gums), pyorrhea (loose­ning and bleeding of teeth).


(b) Name two fat-soluble vitamins along with their sources and the diseases caused due to their deficiency in the diet.




Deficiency disease

  Vitamin A

Milk, butter, eggs, fish, liver oil, rice, kidney, green vegetables etc.

Xerophthalmia(hardening of the cornea), night blindness and xerosis (drying of skin).

Vitamin D

Fish liver oil, butter, milk, eggs, liver and meat.

Rickets, osteomalacia (soft bones and joint pain).


Question 3- Answer the following: 

(a)Name the four bases present in DNA. Which one of these is not present in RNA? 

(b)  essential and non-essential amino acids in human food. 

(c) the amine produced by the Hoffmann degradation of benzamide. 

Answer: (a) (i) Adenine (A)

(ii) Guanine (G)

(iii) Cytosine (C)

(iv) Thymine (T)

In RNA, Thymine (T) is absent. It has Uracil (U) in place of Thymine.

(b) Essential amino acids: Amino acids which the body cannot synthesize are called essential amino acids.

Example: Valine, leucine etc.

Non-essential amino acids: Amino acids which the body can synthesize are called non-essential amino acids. Therefore, they may or may not be present in the diet.

Example: Glycine, alanine etc.

(c) Benzamide is an aromatic amide containing seven carbon atoms. Hence, the amine formed from benzamide is aromatic primary amine-containing six carbon atoms.  Therefore, the IUPAC name will be either Aniline or benzenamine. 


Question 4- : (a) Differentiate between the following :

(i) nucleoside and nucleotide

(ii) Fibrous and globular proteins.

(iii) a-helix and P-pleated sheet structure of the protein

Answer: (a) (i)  A nucleoside contains only two basic components of nucleic acids, i.e., a pentose sugar and a nitrogenous base. It is formed by the attachment of a base to V position of the sugar while A nucleotide contains all the three basic components of nucleic acids, i.e., a phosphoric acid group, a pentose sugar and nitrogenous base. These are formed by the esterification of C5—OH of the sugar of the nucleoside with phosphoric acid.

Structure of Nucleoside: 

Structure of Nucleotide: 

(ii) Globular Proteins have almost spheroidal shape due to the folding of the polypeptide chain while Polypeptide chains of fibrous proteins consist of thread-like molecules which tend to lie side by side to form fibres. Globular proteins are soluble in water while Fibrous proteins are insoluble in water. Globular proteins are sensitive to small changes of temperature and pH and undergo denaturation on heating or on treatment with acids/bases whereas Fibrous proteins are stable to moderate changes of temperature and pH. Globular proteins possess biological activity that’s why they act as enzymes while Fibrous proteins do not have any biological activity but serve as the chief structural material of animal tissues. Example: Maltase, invertase etc., hormones (insulin) antibodies, transport agents (haemoglobin), etc.Example: Keratin in skin, hair, nails and wool, collagen in tendons, fibroin in silk etc.

(iii) In α-Helix structure, the polypeptide chains are held together (stabilized) by intramolecular H-bonding whereas in β-Pleated sheet structure the two neighbouring polypeptide chains are held together by intermolecular, H-bonding.

Question 5- (i) Write the name of two monosaccharides obtained on hydrolysis of lactose sugar.

(ii) Why Vitamin C cannot be stored in our body?

(iii) Write the structural difference between starch and cellulose.

Answer: (i) On hydrolysis, lactose gives β-D-galactose and β-D-glucose.

(ii) Vitamin C is mainly ascorbic acid which is water-soluble and is readily excreted through urine and thus cannot be stored in the body.

(iii) Starch contains the β-D-glucose as its monomer units while cellulose contains β-D- glucose as its monomer units.

Question 6- How are vitamins classified? Name the vitamin responsible for the coagulation of blood. 

Answer: Vitamins are classified into:

  1. Water-insoluble vitamins: These are fat-soluble substances E.g. Vitamin A, D, E and K.
  2. Water-soluble vitamins: These include Vitamin B-Complex and Vitamin C (except B12).
    Vitamin K or phylloquinone is responsible for the coagulation of blood.

These were some of the important questions from previous year question paper, sample papers and the NCERT textbooks. Students can also check other important articles from the links given below: 

CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from Chapter 13 - Amines

CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from All Chapters of NCERT Textbooks - Part I & II

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