NCERT Solutions for Class 11 Biology Chapter 9 Biomolecules
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Page 1
NCERT
SOLUTIONS
CLASS - 11th
aglase .co
SOLUTIONS
CLASS - 11th
aglase .co
Page 2
Class : 11th
Subject : Biology
Chapter : 9
Chapter Name : Biomolecules
Q1 What are macromolecules? Give examples.
Answer. Macromolecules are large complex molecules that occur in colloidal state in intercellular
uid. They are formed by the polymerization of low molecular weight micromolecules.
Polysaccharides, and nucleic acids are common examples of macromolecules.
Page : 160 , Block Name : Exercises
Q2 Illustrate a glycosidic, peptide and a phosphodiester bond.
Answer. (a) Glycosidic bond is formed normally between carbon atoms, 1 and 4, of neighbouring
monosaccharide units.
(b) Peptide bond is a covalent bond that joins the two amino acids by - NH - CO linkage.
(c) Phosphodiester bond is a strong covalent bond between phosphate and two sugar groups. Such
bonds form the sugar phosphate backbone of nucleic acids.
Subject : Biology
Chapter : 9
Chapter Name : Biomolecules
Q1 What are macromolecules? Give examples.
Answer. Macromolecules are large complex molecules that occur in colloidal state in intercellular
uid. They are formed by the polymerization of low molecular weight micromolecules.
Polysaccharides, and nucleic acids are common examples of macromolecules.
Page : 160 , Block Name : Exercises
Q2 Illustrate a glycosidic, peptide and a phosphodiester bond.
Answer. (a) Glycosidic bond is formed normally between carbon atoms, 1 and 4, of neighbouring
monosaccharide units.
(b) Peptide bond is a covalent bond that joins the two amino acids by - NH - CO linkage.
(c) Phosphodiester bond is a strong covalent bond between phosphate and two sugar groups. Such
bonds form the sugar phosphate backbone of nucleic acids.
Page 3
Page : 160 , Block Name : Exercises
Q3 What is meant by tertiary structure of proteins?
Answer. The helical polypeptide chain undergoes colling and folding to form a complex three-
dimensional shape referred to as tertiary structure of proteins. These coils and folds are arranged
to hide the non-polar amino acid chains and to expose the polar side chains. The tertiary structure
is held together by the weak bonds formed between various parts of the polypeptide chain.
Page : 160 , Block Name : Exercises
Q4 Find and write down structures of 10 interesting small molecular weight biomolecules. Find if
there is any industry which manufactures the compounds by isolation. Find out who are the
buyers.
Answer.
(a)
Q3 What is meant by tertiary structure of proteins?
Answer. The helical polypeptide chain undergoes colling and folding to form a complex three-
dimensional shape referred to as tertiary structure of proteins. These coils and folds are arranged
to hide the non-polar amino acid chains and to expose the polar side chains. The tertiary structure
is held together by the weak bonds formed between various parts of the polypeptide chain.
Page : 160 , Block Name : Exercises
Q4 Find and write down structures of 10 interesting small molecular weight biomolecules. Find if
there is any industry which manufactures the compounds by isolation. Find out who are the
buyers.
Answer.
(a)
Page 5
(b)
Page : 160 , Block Name : Exercises
Q5 Proteins have primary structure. If you are given a method to know which amino acid is at
either of the two termini (ends) of a protein, can you connect this information to purity or
homogeneity of a protein?
Answer. Yes, if we are given a method to know the sequence of proteins, we can connect this
information to the purity of a protein. It is known that an accurate sequence of a certain amino
acid is very important for the functioning of a protein. If there is any change in the sequence, it
would alter its structure, thereby altering the function. If we are provided with a method to know
the sequence of an unknown protein, then using this information, we can determine its structure
and compare it with any of the known correct protein sequence. Any change in the sequence can
be linked to the purity or homogeneity of a protein. For example, any one change in the sequence
of haemoglobin can alter the normal haemoglobin structure to an abnormal structure that can
Page : 160 , Block Name : Exercises
Q5 Proteins have primary structure. If you are given a method to know which amino acid is at
either of the two termini (ends) of a protein, can you connect this information to purity or
homogeneity of a protein?
Answer. Yes, if we are given a method to know the sequence of proteins, we can connect this
information to the purity of a protein. It is known that an accurate sequence of a certain amino
acid is very important for the functioning of a protein. If there is any change in the sequence, it
would alter its structure, thereby altering the function. If we are provided with a method to know
the sequence of an unknown protein, then using this information, we can determine its structure
and compare it with any of the known correct protein sequence. Any change in the sequence can
be linked to the purity or homogeneity of a protein. For example, any one change in the sequence
of haemoglobin can alter the normal haemoglobin structure to an abnormal structure that can
Page 6
cause sickle cell anaemia.
Page : 160 , Block Name : Exercises
Q6 Find out and make a list of proteins used as therapeutic agents. Find other applications of
proteins (e.g., cosmetics, etc.)
Answer. Proteins used as therapeutic agents are as follows:
1. Thrombin and brinogen — They help in blood clotting.
2. Antigen (antibody) It helps in blood transfusion.
3. Insulin — It helps in maintaining blood glucose level in the body.
4. Renin — It helps in osmoregulation.
Proteins are also commonly used in the manufacture of cosmetics, toxins, and as biological
buffers.
Page : 160 , Block Name : Exercises
Q7 Explain the composition of triglyceride.
Answer. Triglyceride is a glyceride, which is formed from a single molecule of glycerol, esteri ed
with three fatty acids. It is mainly present in vegetable oils and animal fat.
The general chemical formula of triglyceride is R COO − CH CH (−OOCR ) CH − OOCR ,
2 2 1 2 3
where R 1, R and R are fatty acids. These three fatty acids can be same or different. and are
2, 3
fatty acids.
Page : 160 , Block Name : Exercises
Q8 Can you describe what happens when milk is converted into curd or yoghurt from your
understanding of proteins.
Answer. Proteins are macromolecules formed by the polymerization of amino acids. Structurally,
proteins are divided into four levels.
(a) Primary structure — It is the linear sequence of amino acids in a polypeptide chain.
(b) Secondary structure The polypeptide chain is coiled to form a three dimensional structure.
(c) Tertiary structure — The helical polypeptide chain is further coiled and folded to form a
complex structure.
(d) Quaternary structure — More than one polypeptide chains assemble to form the quaternary
structure.
Page : 160 , Block Name : Exercises
Q6 Find out and make a list of proteins used as therapeutic agents. Find other applications of
proteins (e.g., cosmetics, etc.)
Answer. Proteins used as therapeutic agents are as follows:
1. Thrombin and brinogen — They help in blood clotting.
2. Antigen (antibody) It helps in blood transfusion.
3. Insulin — It helps in maintaining blood glucose level in the body.
4. Renin — It helps in osmoregulation.
Proteins are also commonly used in the manufacture of cosmetics, toxins, and as biological
buffers.
Page : 160 , Block Name : Exercises
Q7 Explain the composition of triglyceride.
Answer. Triglyceride is a glyceride, which is formed from a single molecule of glycerol, esteri ed
with three fatty acids. It is mainly present in vegetable oils and animal fat.
The general chemical formula of triglyceride is R COO − CH CH (−OOCR ) CH − OOCR ,
2 2 1 2 3
where R 1, R and R are fatty acids. These three fatty acids can be same or different. and are
2, 3
fatty acids.
Page : 160 , Block Name : Exercises
Q8 Can you describe what happens when milk is converted into curd or yoghurt from your
understanding of proteins.
Answer. Proteins are macromolecules formed by the polymerization of amino acids. Structurally,
proteins are divided into four levels.
(a) Primary structure — It is the linear sequence of amino acids in a polypeptide chain.
(b) Secondary structure The polypeptide chain is coiled to form a three dimensional structure.
(c) Tertiary structure — The helical polypeptide chain is further coiled and folded to form a
complex structure.
(d) Quaternary structure — More than one polypeptide chains assemble to form the quaternary
structure.
Page 7
Milk has many globular proteins. When milk is converted into curd or yoghurt, these complex
proteins get denatured, thus converting globular proteins into brous proteins. Therefore, by the
process of denaturation, the secondary and tertiary structures of proteins are destroyed.
Page : 161 , Block Name : Exercises
Q9 Can you attempt building models of biomolecules using commercially available atomic models
(Ball and Stick models).
Answer. Ball and stick models are 3D molecular models that can be used to describe the structure
of biomolecules. In ball and stick model, the atoms are represented as balls whereas the bonds
that hold the atoms are represented by the sticks. Double and triple bonds are represented by
springs that form curved connections between the balls. The size and colour of various atoms are
different and are depicted by the relative size of the balls. It is the most fundamental and common
model of representing biomolecular structures.
In the above ball and stick model of D-glucose, the oxygen atoms are represented by red balls,
hydrogen atoms by blue balls, while carbon atoms are represented by grey balls.
Page : 161 , Block Name : Exercises
Q10 Attempt titrating an amino acid against a weak base and discover the number of dissociating (
ionizable ) functional groups in the amino acid.
Answer. Titrating a neutral or basic amino acid against a weak base will dissociate only one
functional group, whereas titration between acidic amino acid and a weak acid will dissociate two
or more functional groups.
Page : 161 , Block Name : Exercises
Q11 Draw the structure of the amino acid, alanine.
Answer. Structure of alanine
proteins get denatured, thus converting globular proteins into brous proteins. Therefore, by the
process of denaturation, the secondary and tertiary structures of proteins are destroyed.
Page : 161 , Block Name : Exercises
Q9 Can you attempt building models of biomolecules using commercially available atomic models
(Ball and Stick models).
Answer. Ball and stick models are 3D molecular models that can be used to describe the structure
of biomolecules. In ball and stick model, the atoms are represented as balls whereas the bonds
that hold the atoms are represented by the sticks. Double and triple bonds are represented by
springs that form curved connections between the balls. The size and colour of various atoms are
different and are depicted by the relative size of the balls. It is the most fundamental and common
model of representing biomolecular structures.
In the above ball and stick model of D-glucose, the oxygen atoms are represented by red balls,
hydrogen atoms by blue balls, while carbon atoms are represented by grey balls.
Page : 161 , Block Name : Exercises
Q10 Attempt titrating an amino acid against a weak base and discover the number of dissociating (
ionizable ) functional groups in the amino acid.
Answer. Titrating a neutral or basic amino acid against a weak base will dissociate only one
functional group, whereas titration between acidic amino acid and a weak acid will dissociate two
or more functional groups.
Page : 161 , Block Name : Exercises
Q11 Draw the structure of the amino acid, alanine.
Answer. Structure of alanine
Page 8
Page : 161 , Block Name : Exercises
Q12 What are gums made of ? Is Fevicol different?
Answer. Gums are heteropolysaccharides. They are made from two or more different types of
monosaccharides. On the other hand, fevicol is polyvinyl alcohol (PVA) glue. It is not a
polysaccharide.
Page : 161 , Block Name : Exercises
Q13 Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice,
saliva, sweat and urine for them.
Answer. (a)Test for protein
Biuret's test — If Biuret reagent is added to protein, then the colour of the reagent changes from
light blue to purple.
(b) Test for fats and oils Grease or solubility test
(c) Test for amino acid Ninhydrin test — If Ninhydrin reagent is added to the solution, then the
colourless solution changes to pink, blue, or purple, depending on the amino acid.
Q12 What are gums made of ? Is Fevicol different?
Answer. Gums are heteropolysaccharides. They are made from two or more different types of
monosaccharides. On the other hand, fevicol is polyvinyl alcohol (PVA) glue. It is not a
polysaccharide.
Page : 161 , Block Name : Exercises
Q13 Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice,
saliva, sweat and urine for them.
Answer. (a)Test for protein
Biuret's test — If Biuret reagent is added to protein, then the colour of the reagent changes from
light blue to purple.
(b) Test for fats and oils Grease or solubility test
(c) Test for amino acid Ninhydrin test — If Ninhydrin reagent is added to the solution, then the
colourless solution changes to pink, blue, or purple, depending on the amino acid.
Page 9
Page : 161 , Block Name : Exercises
Q14 Find out how much cellulose is made by all the plants in the biosphere and compare it with
how much of paper is manufactured by man and hence what is the consumption of plant material
by man annually. What a loss of vegetation!
Answer. Approximately, 100 billion tonnes of cellulose are made per year by all the plants in the
biosphere and it takes 17 full grown trees to make one ton of paper. Trees are also used to ful l the
other requirements of man such as for timber, food, medicines, etc. Hence, it is dif cult to
calculate the annual consumption of plant material by man.
Page : 161 , Block Name : Exercises
Q15 Describe the important properties of enzymes.
Answer. Properties of enzymes
(1) Enzymes are complex macromolecules with high molecular weight.
(2) They catalyze biochemical reactions in a cell. They help in the breakdown of large molecules
into smaller molecules or bring together two smaller molecules to form a larger molecule.
(3) Enzymes do not start a reaction. However, they help in accelerating it.
(4) Enzymes affect the rate of biochemical reaction and not the direction.
(5) Most of the enzymes have high turnover number. Turnover number of an enzyme is the number
Q14 Find out how much cellulose is made by all the plants in the biosphere and compare it with
how much of paper is manufactured by man and hence what is the consumption of plant material
by man annually. What a loss of vegetation!
Answer. Approximately, 100 billion tonnes of cellulose are made per year by all the plants in the
biosphere and it takes 17 full grown trees to make one ton of paper. Trees are also used to ful l the
other requirements of man such as for timber, food, medicines, etc. Hence, it is dif cult to
calculate the annual consumption of plant material by man.
Page : 161 , Block Name : Exercises
Q15 Describe the important properties of enzymes.
Answer. Properties of enzymes
(1) Enzymes are complex macromolecules with high molecular weight.
(2) They catalyze biochemical reactions in a cell. They help in the breakdown of large molecules
into smaller molecules or bring together two smaller molecules to form a larger molecule.
(3) Enzymes do not start a reaction. However, they help in accelerating it.
(4) Enzymes affect the rate of biochemical reaction and not the direction.
(5) Most of the enzymes have high turnover number. Turnover number of an enzyme is the number
Page 10
of molecules of a substance that is acted upon by an enzyme per minute. High turnover number of
enzymes increases the ef ciency of reaction.
(6) Enzymes are speci c in action.
(7) Enzymatic activity decreases with increase in temperature.
(8) They show maximum activity at an optimum pH of 6 — 8.
(9) The velocity of enzyme increases with increase in substrate concentration and then, ultimately
reaches maximum velocity.
Page : 161 , Block Name : Exercises
enzymes increases the ef ciency of reaction.
(6) Enzymes are speci c in action.
(7) Enzymatic activity decreases with increase in temperature.
(8) They show maximum activity at an optimum pH of 6 — 8.
(9) The velocity of enzyme increases with increase in substrate concentration and then, ultimately
reaches maximum velocity.
Page : 161 , Block Name : Exercises
Document Details
| Board / Org | NCERT |
| Exam | Class 11 |
| Type | Solution |
| Pages | 10 |
| Updated | 22 Jul 2026 |