NCERT Solutions Class 11 Biology Chapter 9

NCERT Solutions for Class 11 Biology Chapter 9

NCERT Solutions Class 11 Biology Chapter 9 discusses the diverse variety of living organisms along with their chemical compounds. There are questions given in the exercise section to help students gauge their understanding of the topics covered in Chapter 9. Students looking for answers to these questions can refer to Chapter 9 Biology Class 11 NCERT Solutions by Extramarks. The solutions are prepared by subject-matter experts at Extramarks, which makes them a credible reference material for students.

NCERT Solutions for Class 11 Biology Chapter 9 – Biomolecules 

Class 11 Bio Chapter  9 NCERT Solutions can help students prepare better for the exams. As answers are written in a simple and step-by-step manner, students will get an idea of how to attempt a question paper in the right way.

Access NCERT Solutions for Class 11 Biology 

Class 11 Biology Chapter 9 NCERT Solutions Download 

Students can access the Class 11 Biology Chapter 9 NCERT Solutions on Extramarks, anytime and anywhere, and prepare well for the exams. Solutions help students study in both – online and offline modes.

NCERT Solutions Of Biology Class 11 Biomolecules 

Chapter 9 – Biomolecules discusses the chemical constituents of living cells, enzyme action, properties, enzyme types, structure and function of proteins, lipids, etc. 

Imparting information about diverse living organisms and helping in building a mindset of coexisting with other living beings is the main purpose of this chapter. A complex biological phenomenon exists in our surroundings and the Biology Chapter 9 of Class 11 attempts to expose students to just that. 

NCERT Biology Class 11 Biomolecules Marks Distribution

Class 11 Biology examination has a practical exam of 30 marks and a theoretical exam of 70 marks. Biology Class 11 Chapter 9 under Unit III carries 4 marks for practical questions (of which Practical Record and Viva Voice are not a part) and 12 marks for theory, as per the latest marking scheme. 

Class 11 Biology Biomolecules NCERT Solutions 

NCERT Solutions Class 11 Biology Chapter 9 answer the questions given at the end of the chapter. Questions from the following topics are included in the Chapter 9 Class 11 Biology NCERT Solutions:

Ex 9.1 – How to Analyse Chemical Composition?

Ex 9.2 – Primary and Secondary Metabolites

Ex 9.3 – Biomacromolecules

Ex 9. 4 – Proteins

Ex 9.5 – Polysaccharides

Ex 9.6 – Nucleic Acids

Ex 9.7 – Structure of Protein

Ex 9.8 – Nature of Bond Linking Monomers in a Polymer

Ex 9.9 – Dynamic State of Body Constituents – Concept of Metabolism

Ex 9.10 – Metabolic Basis of Living

Ex 9.11 – The Living State

Ex 9.12 – Enzymes

Benefits of Class 11 Ch 9 NCERT Solutions

NCERT Solutions Class 11 Biology Chapter 9 have been framed in an easy language so that concepts are easy to understand and the students can score more marks in the subject. Here are some of the benefits of referring to Chapter 9 Biology Class 11 NCERT Solutions:

  • Teachers who specialise in the field of science have curated the questions and answers in the NCERT Solutions. This way the students get the best study material to prepare from. 
  • The solutions have been prepared in a concise way and in simple language.
  • These expert teachers have also incorporated illustrations in the form of diagrams and images along with explanations in the Chapter 9 Class 11 Biology NCERT Solutions to make understanding topics easier.

Q.1 What are macromolecules? Give examples.


A macromolecule is a very large molecule of relatively high molecular weight (of more than one thousand daltons) which is created by polymerization of smaller subunits, called monomers. Example: Proteins, nucleic acids, carbohydrates. Large lipids molecules are though non-polymeric, but they come under the category of macromolecules.

Q.2 Illustrate a glycosidic, peptide and a phospho-diester bond.


Glycosidic bond: A glycosidic bond is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. Water molecule is released during the formation of glycosidic bond.

Peptide bond: The covalent bond between two neighbouring amino acids in a protein molecule, formed due to a condensation reaction between the carboxyl group of one and the amino group of another is known as peptide bond.

Phospho-diester bond: The covalent diester bond between phosphoric acid and two sugar molecules linking two nucleotides together to form the backbone of DNA and RNA is known as a phosphor-diester bond. It exists between the phosphate of one nucleotide and the sugar 3′ carbon of the next nucleotide.

Q.3 What is meant by tertiary structure of proteins?


The tertiary structure of a protein is the actual shape of the protein molecule. It describes the structure of the complex and irregular folding of the peptide chain in three dimensions. It depicts the way alpha helices and beta sheets are arranged depending upon the particular amino acids in the primary structure. These complex structures are held together by a combination of several molecular interactions (like hydrogen bond, ionic bond, covalent bond, hydrophobic interactions between R groups) that involve the R-groups of each amino acid in the primary chain. The tertiary structure of the protein is important for the biological activity of the protein.

Q.4 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.


Structures of 10 interesting small molecular weight biomolecules are:

Industries manufacturing small Biomolecules are:

Biomolecule Manufacturing Industries
Glucose M/S.Vinayak Ingredients (India) Pvt ltd.
Glycine Triveni Aromatics And Perfumery Private Limited, Vapi
Glycerol P & G Chemicals (USA),

The Tata Oil Mills Co. Ltd (India)

Research laboratories, educational institutes and other industries use biomolecules as precursors for making other products.

Q.5 Proteins have a 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?


Proteins are heteropolymers containing strings of amino acids. There are 20 different amino acids. The sequence of amino acids in the protein which conveys the positional information of each amino acid is known as primary structure of the protein. This sequence of amino acid is very important for the protein as it will determine the final structure as well as function of the protein. Any deviation in the sequence of amino acids in the primary structure results in the malfunctioning of the protein. If we have a method to determine the entire amino acid sequence in the primary structure of the protein, we can connect the information to the purity or homogeneity of the protein. However, just the information about the two amino acids sitting at two ends of a protein will not tell about the purity as we will not know the composition of amino acids in the middle of the protein chain.

Q.6 Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics etc.)


List of proteins used as therapeutic agents:

Protein Therapeutic Role
Thrombin and fibrinogen Blood clotting
Insulin Maintaining blood glucose level in the body
Renin Osmoregulation
Trypsin Enzyme
Antibody Treatment of auto-immune diseases and cancer
Tissue Plasminogen Activator Thrombolytic agent
Factor VIII Treatment of Haemophilia A
Live and inactivated viral and bacterial proteins Vaccination
Human interferons To fight against viral infections
DNase I For treatment of Cystic Fibrosis
Human growth hormone For inducting growth

Other applications of Proteins:

  • Pectinases used in food industry since 1930 in fruit juice manufacturing.
  • Amylases are used in detergents to remove starch based stains.
  • Cellulases are used in detergents.
  • Alpha-amylases have been most widely studied in connection with improved bread quality and increased shelf life.
  • Leather industry uses proteolytic and lipolytic enzymes in leather processing.

Q.7 Explain the composition of triglyceride.


A triglyceride is an ester derived from condensation reaction of one glycerol molecule and three fatty acids. The glycerol is an alcohol with three hydroxyl (OH) groups. Each fatty acid has carboxyl group (COOH). In the triglyceride molecule, hydroxyl groups of the glycerol join the carboxyl groups of the fatty acid to form the ester bond. They are also referred to as neutral fats because unlike their component parts, they lack polar groups that can hydrogen bond with water. The hydrocarbon chain of the fatty acid in a triglyceride can be saturated or unsaturated depending upon the presence or absence of double bonds between carbon atoms. Triglyceride like butter which is solid at room temperature contains saturated fatty acid whereas oil contains unsaturated fatty acids and thus remains in liquid state at all temperatures.

Q.8 Can you describe what happens when milk is converted into curd or yoghurt, from your understanding of proteins.


The main protein in dairy milk is caseins which contains all the essential amino acids. Caseins are composed of several similar proteins which form a multi-molecular, granular structure called a casein micelle. The casein micelle also contains water and salts. The individual casein molecules are not very soluble in the aqueous environment of milk however the casein micelle granules are maintained as a colloidal suspension in milk. Bacteria found in the milk or when added externally, ferment the sugar lactose into lactic acid. This fermentation results in the acidic environment causing the micellar structure to break and the casein comes out of solution or coagulates. The resulting gelatinous material with creamy texture is known as yoghurt or curd.

Q.9 Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).


Yes, we can attempt building models of biomolecules using commercially available atomic models (Ball and Stick model).

Ball and Stick models are made to represent the three-dimensional structure of a chemical compound showing the position of atoms and the bonds in the 3-D space. The round balls of different colours are used to represent various atoms with sticks as bonds between these atoms. The angle and the distance between the atoms in the model are proportional to the actual molecule/compound.

Structure of cysteine


Q.11 Draw the structure of the amino acid, alanine.


The structure of the amino acid alanine:

Q.12 What are gums made of? Is Fevicol different?


Gums are heteropolysaccharide substances made up of two or more kinds of monosaccharide units.

Fevicol is a branded synthetic product with excellent adhesive properties. It is made up of polyvinyl acetate (PVAc) glue, not a polysaccharide. There are several variations available.

Q.13 Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.


Qualitative tests

  1. Proteins: Biuret Test (It is used to determine the presence of peptide bonds in protein. In the presence of peptide bond, a purple coloured compound is formed.)
  2. Fats and Oils: Grease spot test/Brown paper test (lipids leave translucent spots (grease spots) on unglazed brown paper bags) OR Sudan Red test (Sudan red is a fat-soluble dye that stains lipids red).
  3. Amino acids: Ninhydrin Test (Ninhydrin is used to detect amino acids. When about 0.5 mL of a 0.1% solution of Ninhydrin is boiled for one or two minutes with a few mL of dilute amino acid or protein solution, a blue colour develops indicating presence of amino acids).
Item Test Procedure Result Interpretation
Fruit Juice Biuret Test Add Biuret’s reagent to Fruit Juice Colour changes from light blue to purple Protein is present

or solubility Test

Put a drop of fruit juice on unglazed brown paper bag No translucent spot No oil or fat is present
Ninhydrin Test Boil Ninhydrin solution with fruit juice Colourless solution changes to Blue Amino acids are present
Saliva Biuret Test Add Biuret’s reagent to saliva Colour changes from light blue to purple Protein is present

or solubility Test

Put a drop of saliva on an unglazed brown paper bag No translucent spot No oil or fat is present
Ninhydrin Test Boil Ninhydrinsolution with saliva Colourless solution changes to Blue Amino acids are present
Sweat Biuret Test Add Biuret’s reagent to sweat No change in colour No proteins are present

or solubility Test

Put a drop of sweat on an unglazed brown paper bag Translucent spot appears Fats or oils present
Ninhydrin Test Boil Ninhydrin solution with sweat Solution remains colourless No amino acids are present
Urine Biuret Test Add Biuret’s reagent to urine Colour changes from light blue to purple Protein is present

or solubility Test

Put a drop of urine on an unglazed brown paper bag No translucent spot No oil or fat is present
Ninhydrin Test Boil Ninhydrin solution with urine Colourless solution changes to Blue Amino acids are present

Q.14 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!


Cellulose is a complex carbohydrate that consists of 3,000 or more glucose units. It forms the basic structural component of plant cell walls. Cellulose comprises about 33 percent of all vegetable matter (90 percent of cotton and 50 percent of wood are cellulose) and is the most abundant of all naturally occurring organic compounds. Cellulose is found in the cell walls of secondary xylem and it is the ultimate source of production of paper. Paper is nothing but 90% secondary xylem or wood. The remaining 10% comes from the fibres of rags, straw, grass or old newspapers. According to a report, each person in the United States uses about 749 pounds of paper every year and almost 4 billion trees are cut down each year for the production of paper. The world uses 400 percent more paper now than it did 40 years ago. Used paper and paper products make up the largest portion of our trash – about 40 percent. This is indeed a huge loss of vegetation.

Q.15 Describe the important properties of enzymes.


The important properties of enzymes are:

  • All enzymes are proteins and some of the nucleic acids also behave like enzymes.
  • All enzymes have a primary structure determined by the amino acid sequence followed by secondary and tertiary structure.
  • They reduce the activation energy required for the reaction to occur and thereby fasten the process many folds.
  • Specificity: Each enzyme catalyzes a very specific chemical reaction and are also known as biocatalysts. The folding of the protein backbone gives rise to an active site of the enzyme where the substrate for the enzyme fits and undergoes modification resulting in product formation. This is explained by the lock and key mechanism. Enzymes remain unchanged after the chemical reaction.
  • Denaturation: Since enzymes are proteins, they get denatured at higher temperatures and thereby lose their ability to function.
  • Regulation: Enzyme activity is regulated in the cell depending upon the metabolic necessity.
  • Enzyme is affected by pH and temperature of the solution. They work best under optimum pH.

Attempt titrating an amino acid against a weak base and discover the number of dissociating (ionisable) functional groups in the amino acids.

The titration curves help in identifying the existence of different ionic groups present in the amino acids. In the case of neutral and basic amino acids, the number of dissociating groups is usually one and in acidic amino acids, the number of dissociating groups are usually two.

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FAQs (Frequently Asked Questions)

1. Explain Macromolecules with an Example.

Polymerised biomolecules that contain an array of macromolecules that have a high molecular weight are called Macromolecules. In simpler words, large complex molecules occurring in an intercellular fluid in a colloidal state are called macromolecules. Macromolecules are not visible to the naked eye. They are larger than other molecules with their molecular weight lying between 18-800 daltons (Da). Nucleic acids, proteins, polysaccharides, etc. are some of the broad examples of macromolecules. Some other examples include RNA, DNA, polyester, keratin in hair, nylon, waxes, grease, steroids, hormones, etc.

2. Throw some light on Micro Molecules.

Micro means “small”. Molecules that are small or in mini size are known as micro molecules. As compared to macromolecules, they have a low molecular weight. These molecules are also known as “monomers”. Monomers combine to form large molecules or “polymers”. Metabolic processes lead to the formation of micro molecules.

3. What are the benefits of NCERT solutions for Class 11 Biology Chapter 9 Biomolecules?

The free NCERT Solutions Class 11 Biology Chapter 9 that are available on Extramarks have multiple benefits. All the questions and answers are given in the same place so studying becomes easy for students. The solutions are given chapter-wise and are written in easy language. These solutions contain to-the-point explanations in great detail and are curated by biology experts. 

4. What are the types of enzymes?

All proteins are not enzymes but all enzymes are proteins. Enzymes, like proteins, have multiple structures such as primary, secondary, and tertiary structures. An active site in the enzyme helps in binding the substrate molecule. Enzymes function as catalysts but they are not used up during the reaction. Some enzymes need a coenzyme or cofactor to function.

The major enzyme types are as follows:

  • Transferases 
  • Ligases 
  • Hydrolases
  • Oxidoreductases
  • Lyases
  • Isomerases

5. What is a nucleotide?

A nucleotide is the basic unit of nucleic acid. DNA and RNA are made up of the Nucleic acid biomolecules. Genetic codes along with all the information needed to build a body are contained in the nucleic acid. 

6. What are DNA and RNA?

Deoxyribonucleic acid or DNA can be found in humans as well as other organisms. This hereditary material can be found in every cell and carries genetic instructions about how to live, develop, and reproduce. Ribonucleic acid or RNA together with DNA makes up the nucleic acid. RNA is involved in several functions of the cell and has three types. 

Different forms of DNA are:

  • A-DNA: A-DNA is similar to B-DNA and is a right-handed double helix. 
  • B-DNA: B-DNA is a double helical structure that is right-handed. This type of DNA is found in humans.
  • Z-DNA: This form is a left-handed double helix.

Different types of RNA are:

  • Ribosomal RNA (rRNA)
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)

7. What are the functions of RNA and DNA?

The functions of RNA are:

  • RNA helps in the translation of DNA into proteins. 
  • Functions as a messenger that connects the DNA and the ribosomes.
  • It helps ribosomes choose the right amino acid. In order to build up new proteins in the body, this choice is essential. 
  • It works in the process of protein synthesis as an adapter molecule.
  • It carries genetic information in all living cells. 

The functions of DNA and the processes it’s involved in are:

  • It stores genetic information.
  • During the replication process, it transfers this genetic information to the daughter cells of the cell, from one generation to the next. 
  • Transcription
  • DNA fingerprinting 
  • Cellular metabolism
  • Gene therapy.

8. What is the reason for DNA being called Polynucleotide?

The DNA molecules are composed of nucleotides – deoxycytidylate (C), deoxyadenylate (A), deoxyguanylate (G), and deoxythymidylate (T). These nucleotides are combined to form long chains known as polynucleotides. DNA includes two chains of polynucleotides. 

9. What are lipids?

Compounds that are insoluble (poorly or completely) in water are known as lipids. However, lipids are soluble in other non-polar solvents like benzene, chloroform, and ether.

Lipids store energy that can be used later. Protecting insects, animals, plants, and vertebrates is one of their other functions. In the structure of the membrane, lipids are a major component. 

10. Can you use protein as a therapeutic agent? What are the other applications of protein? List them.

Yes, utilising proteins as therapeutic agents is possible. Due to many pharmaceutical needs, proteins have been formulated in laboratories by scientists. These kinds of proteins are called therapeutic proteins. Therapeutic proteins include antigens, renin, diastase, streptokinase, insulin, enzymes, bone morphogenetic proteins, antibody-based drugs, vasopressin, engineered protein scaffolds, and Fc fusion proteins.

Proteins happen to be a useful element in textile industries, biological buffers, research techniques, and cosmetics. However, there has been a significant transformation in the healthcare sector due to therapeutic proteins.

Therapeutic proteins are considered an important part of cancer treatment, HIV, and many more serious ailments such as solubility, tertiary structural stability, cellular interactions, pharmacokinetics, and immunogenicity are affected by therapeutic proteins with carbohydrate profile. 

11. List out the main physical properties of Amino Acids

Molecules that combine to form protein are called Amino acids. Methionine, tryptophan, leucine, valine, lysine, etc. are some examples of the same.

Amino acids have the following main physical properties;

  • When amino acids are heated to higher temperatures, they decompose.
  • Amino acids usually exist in the d and I form.
  • Their melting point is quite high (more than 200 degrees Celsius).
  • Amino acids are colourless.
  • All amino acids are quite active except glycerine which is quite inactive.