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 NCERT Solutions for Class 11 Biology Chapter 9 - Biomolecules


Our Biosphere has diversified living organisms where each organism has a different chemical composition and molecules inside them. And, this is what will be taught in the NCERT Solutions Class 11 Biology Chapter 9. Topics students will learn are How Chemical Composition in Living Organisms is Analyzed?, about Biomacromolecules, Primary & Secondary Metabolites, Polysaccharides, Proteins, Structure of Proteins, and Nucleic Acids.

Other topics that are included in this chapter and are relevant from the exam's perspective are What is the Nature of Bond that Links Monomers with Polymer, Dynamic State of Body Constituents, i.e. Metabolism Concepts, The Living State, Enzymes, and Metabolic Basis of Living. Let's briefly take a look at the topic taught in this chapter.

  • How is chemical composition analyzed?
  • Primary and Secondary Metabolites
  • About Biomacromolecules
  • Proteins
  • Polysaccharides
  • Nucleic Acids
  • Arrangement of Proteins
  • Nature of Bonds connecting Monomers in a Polymer
  • Dynamic State of Body Components - Theory of Metabolism
  • Metabolic basis for Living
  • The Living State
  • Enzymes

The presence of elements, like oxygen, carbon, hydrogen, etc., in living tissues per unit mass as regards to the earth's crust has been taught under this chapter. Coming under Unit III 'Structure and Functions of Cells' of class 11 Biology syllabus, this chapter takes students through the chemical composition of living cells, different chemical reactions and their conversions, nature of different enzymes actions, the role of enzymes, factors that affect the activities of enzymes, and how different enzymes are classified and named. This chapter promotes knowledge on the diversity of living organisms and how to develop a positive co-existence behavior with other living organisms.

Q1. What are macromolecules? Give examples.


The large-sized complex molecules that get separated in acid-insoluble fractions using trichloroacetic acid are called macromolecules. These are polymers having a molecular mass of 10,000 daltons or more. Examples of macromolecules include proteins, carbohydrates, nucleic acids, etc. Lipids are found to be present in the acid-insoluble fraction, however, they are not of high molecular weight.


Q2. Illustrate a glycosidic, peptide, and phospho-diester bond.


Glycosidic bond- This bond is formed between the 1st carbon atom of one monosaccharide with 4 carbon atoms of the neighboring monosaccharide units. During the formation of this bond, a water molecule is released. A representation of a glycosidic bond is as follows

Peptide bond- This is a covalent bond formed between the carboxyl group of one amino acid and the amino group of neighboring amino acids. A water molecule is released as a by-product in the formation of a peptide bond. A representation of a peptide bond is as follows

Phosphodiester bond- It refers to the phosphate-hydroxyl linkage between two nucleotides. In this bond, the phosphate attached to the hydroxyl group at the 5' carbon of pentose sugar is in turn bonded to the hydroxyl group of the 3' carbon of the pentose sugar of the next nucleotide.



Q3. What is meant by the tertiary structure of proteins?


The three-dimensional structure of the protein which is formed after repeated coiling and folding of helical and pleated polypeptide chains is called its tertiary structure. By repeated coiling and folding, the polar side chains are exposed while non-polar amino acids are hidden. Tertiary structure is bonded via weak bonds. The functionality of a protein lies in its tertiary structures.


Q4. Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry that manufactures the compounds by isolation. Find out who are the buyers.


The structures of 10 small molecular weight biomolecules are as follows:


These biomolecules are manufactured in biotechnology industries.


Q6. Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins (e.g., Cosmetics, etc.)


Proteins with therapeutic uses are insulin, oxytocin, ADH, thrombin, fibrinogen, renin, immunoglobulin, diastase, streptokinase, etc.

Other applications of proteins are

  1. As cosmetics- Protein such as casein is used in beauty creams, shampoos, etc.
  2. Sweeteners- Thaumatin and monellin are sweet proteins.
  3. Dietary supplements- Proteins can be used as dietary supplements.


Q7. Explain the composition of triglycerides.


A triglyceride is a chemical formed by the esterification of three molecules of fatty acids with one molecule of trihydric alcohol called glycerol. All the three fatty acids of triglyceride can be similar as in tripalmitin or dissimilar as in palmito-oleo stearin, dipalmitostearin, etc.



Q8. Can you describe what happens when milk is converted into curd or yogurt, from your understanding of proteins?


Milk contains a protein called casein. When we add a little amount of curd to the milk, the protein casein gets coagulated due to the action of lactic acid bacteria and as a result, this milk is converted into curd. Coagulation disrupts the structure of the protein casein.


Q9. 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 such as ball and stick models. In these models, the stick is assumed to be a bond while balls of different colors are assumed to be atoms.


Q10. Attempt titrating an amino acid against a weak base and discover the number of dissociating ( ionizable ) functional groups in the amino acid.


When we titrate an amino acid against a weak base, it dissociates into its functional groups i.e. -COOH (carboxylic group) and -NH (amino group).


Q11. Draw the structure of the amino acid, alanine.


The structure of amino acid alanine is represented below



Q13. Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat, and urine for them.


A qualitative test for proteins is the xanthoproteic test. When urine is tested for protein with the help of the xanthoproteic test, the presence of a yellow precipitate confirms the presence of protein in it.

The qualitative test for fats is the emulsification test. In this test, the experimental material is treated with ethanol and then dissolved in water. The formation of emulsion confirms the presence of fats.

The qualitative test for oils is the paper test. The experimental material is put on paper. If oil marks are left, the presence of oil is confirmed.

The qualitative test for amino acids is the ninhydrin test.


Q14. Find out how much cellulose is made by all the plants in the biosphere and compare it with how much paper is manufactured by man and hence what is the consumption of plant material by man annually. What a loss of vegetation!


Paper is made up of pulp of wood which is mainly constituted by cellulose. Cellulose is a polymer of glucose molecules joined together. About 85 billion tonnes of cellulose is formed annually in the biosphere. Paper manufacture consumes 0.5 billion tonnes of wood. The increase in consumption of wood has led to a great loss in vegetation.


Q15. Describe the important properties of enzymes.


Enzymes are proteinaceous substances that are capable of catalyzing chemical reactions of biological origin without themselves undergoing any change. They are commonly called biocatalysts. The properties of enzymes are as follows:

  1. Enzymes are proteins by nature.
  2. Optimum temperature - An enzyme is active within a narrow range of temperature. The temperature at which an enzyme is most active is called the optimum temperature. The enzyme activity decreased above and below this temperature.
  3. Optimum pH - Every enzyme has an optimum pH at which it is maximum active. Most of the intracellular enzymes work at neutral pH.
  4. Enzymes are substrate specific i.e. one enzyme catalyzes only a particular substrate. Every enzyme has specific sites called active sites for the binding of substrates.
  1. Only a small quantity of enzyme is capable of forming the desired product.
  2. Enzyme activity is sensitive to certain chemicals called inhibitors or modulators.

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Also See    
NCERT Solutions for Class 11 Biology Chapter 1 - The Living World NCERT Solutions for Class 11 Biology Chapter 2 - Biological Classification NCERT Solutions for Class 11 Biology Chapter 3 - Plant Kingdom
NCERT Solutions for Class 11 Biology Chapter 4 - Animal Kingdom NCERT Solutions for Class 11 Biology Chapter 5 - Morphology of Flowering Plants NCERT Solutions for Class 11 Biology Chapter 6 - Anatomy of Flowering Plants
NCERT Solutions for Class 11 Biology Chapter 7 - Structural Organization in Animals NCERT Solutions for Class 11 Biology Chapter 8 - Cells: The Unit of Life NCERT Solutions for Class 11 Biology Chapter 10 - Cell Cycle and Division
NCERT Solutions for Class 11 Biology Chapter 11 - Transport in Plants NCERT Solutions for Class 11 Biology Chapter 12 - Mineral Nutrition NCERT Solutions for Class 11 Biology Chapter 13 - Photosynthesis in Higher Plants
NCERT Solutions for Class 11 Biology Chapter 14 - Respiration in Plants NCERT Solutions for Class 11 Biology Chapter 15 - Plant Growth and Development NCERT Solutions for Class 11 Biology Chapter 16 - Digestion and Absorption
NCERT Solutions for Class 11 Biology Chapter 17 - Breathing and Exchange of Gases NCERT Solutions for Class 11 Biology Chapter 18 - Body Fluids and Circulation NCERT Solutions for Class 11 Biology Chapter 19 - Excretory Products and their Elimination
NCERT Solutions for Class 11 Biology Chapter 20 - Locomotion and Movement NCERT Solutions for Class 11 Biology Chapter 21 - Neural Control and Coordination NCERT Solutions for Class 11 Biology Chapter 22 - Chemical Coordination and Integration

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