# NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules

NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules- It is fascinating to know that the living systems (like humans, plants, animals) are made up of non-living atoms and molecules. These molecules can be very complex as well as simple in nature and are simply known as biomolecules for eg. Carbohydrates, Proteins, Lipids and Nucleic acids, etc. The solutions of NCERT for class 12 chemistry chapter 14 biomolecules deals with characteristics, functions, and structures of biomolecules. The basic definition of biomolecules is that they are the chemicals that are produced by living organisms to sustain life, promote growth and reproduce. It is an important and very basic chapter of biochemistry which you may study in your higher classes. Although this chapter will involve cramming you need not worry as you will get all CBSE NCERT solutions for class 12 chemistry chapter 14 biomolecules here.

This chapter holds 4 marks in the CBSE Board exams. In this chapter, there are a total of 8 topic wise questions and 25 questions in the exercise. The NCERT solutions for class 12 chemistry chapter 14 Biomolecules are presented in a very comprehensive manner. These NCERT solutions help students in their preparation of CBSE boards exams as well as in the competitive exams like NEET, JEE Main, etc. After completing the NCERT solutions for class 12 chemistry chapter 14 Biomolecules you will be able to explain the characteristics of biomolecules like proteins, carbohydrates, and nucleic acid; classify proteins, carbohydrates, nucleic acid, and vitamins on the basis of their structures; describe the role of biomolecules in biosystem and also able to explain difference between RNA and DNA.

Important points of NCERT solutions for Class 12 Chemistry Chapter 14 Biomolecules

• Carbohydrates and proteins are essential constituents of our food.
• Carbohydrates are optically active polyhydroxy molecules or ketones or aldehydes. Carbohydrates are classified into 3 groups- monosaccharides, disaccharides, and polysaccharides.
• Proteins are the polymers of 20 different $\alpha$-amino acids. These amino acids are linked by peptide bonds.
• Vitamins additional food factors required in the diet.

## 14.1 Carbohydrates

14.2 Proteins

14.3 Enzymes

14.4 Vitamins

14.5 Nucleic Acids

14.6 Hormones

## NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules Exercises 14.1 to 14.8

We know that water is a polar molecule. It is also known that "like dissolves like". So either polar molecule or the compounds which can form hydrogen bonds with water molecules will get dissolved in water.

Glucose and sucrose have five and eight -OH groups respectively. So they are likely to form hydrogen bonds with molecules with water. In the case of cyclohexane and benzene, these are non-polar molecules because of very low electronegativity difference. So these are not soluble in water.

Question

The expected product in the hydrolysis of lactose is Galactose and Glucose.

When pentaacetate of glucose is made to react with hydroxylamine, it does not react indicating the absence of free —CHO group.

In aqueous solution, the cyclic structure (have -OH group at C-1 ) should get converted to open chain structure which has an aldehyde group at C-1. It then should react with hydroxylamine and give glucose oxime. But such case is not observed. This suggests that in aqueous solution open chain structure doesn't exist and as a result, the aldehyde group is absent in pentaacetate of glucose.

Amino acids have both acidic and basic group(amine) which lead to the formation of zwitterions and make them dipolar compounds. Due to this property, they form strong molecular bonds themselves and also with water. This result high melting point and good solubility in water as compared to haloacids.

Halo acids doesn't exhibit the property of dipolar compounds. Only carboxyl group of haloacid is involved in H-bonding, not the halogen atom. That's why they have low melting points and less solubility than amino acids.

Question

Due to denaturation of proteins, globules unfold and helix gets uncoiled which changes its biological activity. In denaturation, secondary and tertiary structures are destroyed whereas primary structure remains the same.

Due to this process (denaturation of proteins) coagulation of egg take place while boiling. In egg, the globular protein changes into a rubber-like structure which is responsible for absorption of water.

Question

Vitamin C is a water-soluble vitamin which is excreted from the body in the form of urine and cannot be stored. So they must be supplied in the diet regularly.

When a nucleotide from the DNA containing thymine is hydrolyzed, the products are thymine β-D-2-deoxyribose and phosphoric acid.

When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained, this fact suggests that RNA is a single strand structure. Unlike DNA which is a double strand structure in which pairing of bases occurs (for e.g. adenine pairs with thymine). Thus, on hydrolysis, the amount of adenine produced will be the same as the amount produced by thymine. In RNA there is no relationship with quantities of bases, meaning bases don't occur in pairs or it is single strand structure.

## NCERT Solutions for Class 12 Chemistry Chapter 14 Biomolecules- Exercise Questions

Question

Monosaccharides are the carbohydrates that cannot be hydrolysed further to give simpler units of polyhydroxy aldehyde or ketone. Nearly 20 monosaccharides are known to occur in nature. The general formula of monosaccharides is $\dpi{80} (CH_{2}O)_{}n$ where, n =3 to 7. Some common examples of monosaccharides are glucose, fructose.

Question

The carbohydrate which can reduce Fehling’s solution and Tollens’ reagent is referred to as reducing sugar. Also, all monosaccharides whether ketose or aldose are reducing sugars.

Question

The importance of carbohydrates in plants:-

(i) Carbohydrates are used as storage molecules as starch in plants.

(ii) The cell wall of the plants is made up of cellulose

Question

(1)     Ribose

Ribose is a monosaccharide carbohydrate since it doesn't give simpler units upon hydrolysis.

Question

(2)    2-deoxyribose

It is a monosaccharide carbohydrate because upon hydrolysis it doesn't break into simpler ketone or aldehyde.

Question

(3)    maltose

Maltose is a disaccharide carbohydrate i.e., upon hydrolysis it yields two monosaccharide units.

Question

(4)    galactose

Galactose is a monosaccharide carbohydrate.

Question

(5)    fructose

It is a monosaccharide carbohydrate because upon hydrolysis it doesn't break into simpler compounds of ketone and aldehyde.

Question

(6)  lactose.

Lactose is a disaccharide carbohydrate since it breaks into two simpler monosaccharide units.

Question

It is the linkage by which two monosaccharide units are joined together by an oxygen atom. This linkage is formed by loss of water molecule.

Question

Glycogen is a polysaccharide carbohydrate which is stored in the body of animals or human beings. Whenever our body requires glucose (energy), glycogen breaks down to glucose with the help of the enzyme. It is present in liver, brain and muscles. Whereas starch is a polysaccharide carbohydrate stored in plants.

Question

(i)    sucrose

Upon hydrolysis sucrose breaks into $\alpha - D\ Glucose\ and$    $\beta - D\ Fructose$.

Question

(ii)    lactose

Hydrolysis of lactose gives    $\beta - D\ Galactose\ and$   $\beta - D\ Glucose$.

Cellulose is a long straight-chain polysaccharide made of  $\beta$ -  D - glucose units and has 1,4 - glycoside linkage.

Whereas starch is made up of 2 components:- Amylose and amylopectin.

Amylose is a long straight chain made of $\alpha$ - D - glucose units and joined by 1,4 - glycosidic linkage.

Amylopectin is a branched structure and chains are formed at 1,4 - glycoside linkage and branching occurs at 1.6 - glycosidic linkage.

Question

(i)    HI

When glucose is treated with HI for long time, n - Hexane is formed.

Question

(ii)    Bromine water

Since bromine water is an oxidising agent so it will oxidise aldehyde group to carboxylic acid group. Thus glucose is converted to gluconic acid.

Question

(iii) HNO3

On reacting glucose with nitric acid, oxidation takes place and glucose is converted into saccharic acid.

Below are the few reactions which cannot be explained by the open structure of glucose:-

1.  Even if glucose has an aldehyde group, it does not give Schiff’s test and as a result, it does not form the hydrogen sulphite addition product with NaHSO3.

2. The pentaacetate of glucose does not react with hydroxylamine, which indicates the absence of free —CHO group.

3. It is found that glucose exists in two different crystalline forms which are named as α and β. This property can only be explained by the cyclic structure of glucose.

The amino acids which are required for the body and can be synthesised in the body are known as non-essential amino acids.  E.g  Glycine, Alanine. Whereas, the amino acids which are required for our body but cannot be synthesised by our body and should be taken through diet are known as essential amino acids. E.g.  Valine, Leucine

Question

Peptide linkage is an amide bond formed between –COOH group and –NH2 group. The reaction between two molecules of either different or similar amino acids proceeds by the combination of the amino group of one molecule with the carboxyl group of the other molecule. This will result in the elimination of a water molecule and formation of a peptide bond –CO–NH–.

Question

(ii) Primary structure

Primary structure of proteins: Each and every polypeptide present in a protein has amino acids linked with each other in a specific sequence and it is this sequence of amino acids that are known to be the primary structure of that protein. Any change in this primary structure that is, the sequence of amino acids creates a different protein.

Question

(iii) Denaturation

When a protein in its raw form, is subjected to change like change in temperature e.g boiling in hot water or chemical change like a variation in pH, the hydrogen bonds are disturbed. This results in unfolding of globules and uncoiling of the helix and thus protein loses its biological activity. This is called denaturation of the protein.

Question

Secondary structures of proteins are found to exist in two types of structure:-

(i)  $\alpha -$ Helix structure:-  α-Helix is a way in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw or helix with the –NH group of each amino acid and residue hydrogen bonded to the of$C= O$ an adjacent turn of the helix.

(ii)  $\beta -$pleated sheet:-  In this structure, all peptide chains are stretched out to maximum extension and then laid side by side which is held together by strong intermolecular hydrogen bonds.

Hydrogen bonding is the intermolecular bonding which helps in stabilising the $\alpha$-helix structure of proteins. Hydrogen bonds are formed between -NH- of amino acid and $C = O$ of the adjacent turn of helix.

Question

The difference between fibrous protein and globular protein is given below :-

 Fibrous Protein Globular Protein When the polypeptide chains run parallel and are held together with the help of hydrogen and disulphide bonds. In case of a globular protein, the chains of polypeptides coil around and give a spherical shape These proteins are generally insoluble in water. These proteins are generally soluble in water. E.g.  keratin, myosin E.g.,               Insulin, albumins

Question

Amino acid has both acidic group  $\dpi{80} (C=O)\left$  and basic group $\dpi{80} (N-H)$. Thus in aqueous solution, the carboxyl group can lose a proton and the basic group (amine group) can accept a proton. In this way, it forms zwitter ion which can act in both ways i.e., acidic as well as basic. Hence amino acids are amphoteric in nature.

Question 14.17     What are enzymes?

Enzymes are the biocatalysts i.e., they catalyse biological reactions. Enzymes are very specific in nature and a particular enzyme can be used for a particular substrate. They are generally named after the name of a compound on which they act. For e.g conversion of maltose to glucose requires enzyme maltase.

Question

In denaturation of protein, globules get unfolded and helix gets uncoiled and also globular protein converts into fibrous protein. The primary structure remains the same but secondary and tertiary structure of the protein are destroyed so its biological activity changes.

On the basis of their solubility in water vitamins are classified as:-

1.  Water-soluble vitamins:-   Water soluble vitamins such as Vitamin C need to taken through diet regularly as they are excreted in the form of urine.

2. water-insoluble and fat-soluble vitamin:-  Since these vitamins are not soluble in water so we don't need to take them regularly through diet. They are stored in liver and adipose. E.g. Vitamin D

Vitamin K is responsible for the coagulation of blood.

Vitamin A:-   Sources of this vitamin are carrots, butter and milk. Its deficiency causes Xerophthalmia (hardening of the cornea of the eye).

Vitamin C:-   Sources of this vitamin are citrus fruits, amla and green vegetables. Its deficiency causes Scurvy (bleeding gums).

Question

Nucleic acids are biomolecules found in nuclei of a cell. They are of two types

(i)  DNA - Deoxyribonucleic acid

(ii)  RNA -  Ribonucleic acid.

The two important functions of nucleic acid are:-

(i) DNA present in chromosomes is responsible for heredity by transferring genes.

(ii) Both the nucleic acids are responsible for the protein synthesis in a cell.

Question

 Nucleoside Nucleotide 1.  It has base and sugar. 1. It has base, sugar and phosphoric acid. 2. The base is attached to 1' position of sugar. 2. In this, the base is attached to 1' positon and phosphoric acid to 5' position of sugar moiety.

Question

The two strands in DNA are not identical but they held together because they form hydrogen bonds with each other. So they are not identical but complementary to each other. Cytosine forms a hydrogen bond with guanine and adenine forms a hydrogen bond with thymine. SO, that's why the two strands act as a complementary for each other.

Structural differences between DNA and RNA:-

(i) The sugar moiety in DNA is D-2-deoxyribose whereas sugar moiety in RNA is D-ribose.

(ii) DNA contains thymine but it is absent in RNA.

(iii) The helical structure of DNA is double-stranded whereas it is single-stranded in case of RNA.

Functional differences between DNA and RNA:-  The main function of DNA is to provide heredity but the main function of RNA is a synthesis of protein in a cell.

Question

The three types of RNA found in the cell are:-

(i) messenger RNA    (m - RNA)

(ii) ribosomal RNA     (r - RNA)

(iii) transfer RNA       (t - RNA)

## NCERT Solutions Class 12 Chemistry

 Chapter 1 CBSE NCERT solutions for class 12 chapter 1 The Solid State Chapter 2 NCERT solutions for class 12 chemistry chapter 2 Solutions Chapter 3 Solutions of NCERT class 12 chemistry chapter 3 Electrochemistry Chapter 4 CBSE NCERT solutions for class 12 chemistry chapter 4 Chemical Kinetics Chapter 5 Solutions of NCERT class 12 chemistry chapter 5 Surface chemistry Chapter 6 NCERT solutions for class 12 chemistry General Principles and Processes of isolation of elements Chapter 7 CBSE NCERT solutions for class 12 chemistry chapter 7 The P-block elements Chapter 8 Solutions of NCERT class 12 chemistry chapter 8 The d and f block elements Chapter 9 NCERT solutions for class 12 chemistry chapter 9 Coordination compounds Chapter 10 Solutions of NCERT class 12 chemistry chapter 10 Haloalkanes and Haloarenes Chapter 11 CBSE NCERT solutions for class 12 chemistry Alcohols, Phenols, and Ethers Chapter 12 Solutions of NCERT class 12 chemistry chapter 12 Aldehydes, Ketones and Carboxylic Acids Chapter 13 NCERT solutions for class 12 chemistry chapter 13 Amines Chapter 14 CBSE NCERT solutions for class 12 chemistry chapter 14 Biomolecules Chapter 15 Solutions of NCERT class 12 chemistry chapter 15 Polymers Chapter 16 NCERT solutions for class 12 chemistry chapter 16 Chemistry in Everyday life

## NCERT Solutions for Class 12 Subject wise

 Solutions of NCERT class 12 biology NCERT solutions for class 12 maths CBSE NCERT solutions for class 12 chemistry Solutions of NCERT class 12 physics

## Benefits of NCERT solutions for class 12 chemistry chapter 14 Biomolecules

• The answers presented in a step-by-step manner in the NCERT solutions for class 12 chemistry chapter 14 Biomolecules will help in understanding chapter easily.

• It will be easy to revise because the detailed solutions will help you remember the concepts and fetch you good marks.

• Homework problems won't bother you anymore, all you need to do is check the detailed NCERT solutions for class 12 chemistry and you are ready to sail.

If you have a doubt or question that is not available here or in any of the chapters, contact us. You will get all the answers that will help you score well in your exams.