The VIDYANKER team has thoughtfully prepared the NCERT Solutions for Class 11 Biology Chapter 9, "Biomolecules" These solutions are designed to help you tackle the NCERT textbook questions with ease. We recommend going through the chapter's theory before diving into the solutions for a deeper understanding. Feel free to share these NCERT Solutions for Class 11 Biology with others—learning is always better when shared!
NCERT TEXTBOOK QUESTIONS SOLVED
1. What are macromolecules? Give examples.
Ans. The big-sized complicated molecules that get divided in acid-insoluble fractions by using trichloroacetic acid are macromolecules. These are the polymers which have a molecular weight of 10,000 daltons and above. The examples of macromolecules include proteins, carbohydrates, nucleic acids, etc.
Lipids are identified to be located in the acid-insoluble fraction, but they are not of high molecular weight.
2. Illustrate a glycosidic, peptide, and a phospho- diester bond.
Ans. (i) Glycosidic bond is the type of chemical linkage between the monosaccharide units of disaccharides, oligosaccharides and polysaccharides, which is formed by the removal of a molecule of water. 
(ii)Peptide bonds are formed by the reaction between carboxyl (- COOH) of one amino acid and amino (- NH2) group of other amino acid with the elimination of water.
(iii) In a polynucleotide chain, adjacent nucleotides are joined together by a bond called phosphodiester bond. This bond links a phosphate group and sugar group of two adjacent nucleotides by means of an oxygen bridge.
3. What is meant by tertiary structure of proteins?
Ans. The helical polypeptide molecule can fold back upon itself and take a complex but defined shape-spherical, rod-shaped or any shape in between. Such shapes are referred to as tertiary (3°) structure of protein molecules. The folding and coiling of the polypeptide molecules are so constituted as to conceal the non-polar amino acid chains inwardly and expose the polar side chains. The tertiary structure of a protein positions far away amino acid side chains closer together to create enzymatic protein active sites. Tertiary structure is stabilized by weak bonds like hydrogen, ionic, disulphide and hydrophilic – hydrophobic bonds that are created between a region of a polypeptide and another. This is easily broken down by pH, temperature and chemicals halting protein function.
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.
Ans. 1.
2.
3.
6.
8.
9.
10. 
Fat and many hormones are manufactured by isolation. Pharmaceutical and consumer goods industry can be the major buyers of these products.
5. 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?
Ans. The spatial coordinates of a protein are referred to as the primary structure of a protein. N-terminal amino acid is the amino acid at the beginning of a protein, and C-terminal amino acid is the amino acid at the end of a protein.
Yes, we can relate this information to the purity or homogeneity of a protein. Amino acids are neutral, basic, or acidic based on the carboxyl and amino groups. Proteins may be acidic, basic, or neutral.
6. Find out and make a list of proteins used as therapeutic agents. Find other applications of proteins.
Ans. Proteins that are employed as therapeutic drugs include thrombin, fibrinogen, enkephalins, antigens, antibodies, streptokinase, protein tyrosine kinase, diastase, renin, insulin, oxytocin, vasopressin etc. Proteins find applications in cosmetics, dairy, textile industries, research methods, biological buffers etc.
7. Explain the composition of triglyceride.
Ans. Proteins that are employed as therapeutic drugs include thrombin, fibrinogen, enkephalins, antigens, antibodies, streptokinase, protein tyrosine kinase, diastase, renin, insulin, oxytocin, vasopressin etc. Proteins find applications in cosmetics, dairy, textile industries, research methods, biological buffers etc.
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8. Can you describe what happens when milk is converted into curd or yoghurt from your understanding of proteins.
Ans. Milk is changed into curd or yoghurt by denaturation of proteins. Denaturation involves breaking of bonds that maintains secondary and tertiary structure and, as a result, globular proteins are converted into fibrous proteins. This is a process involving change in physical, chemical and biological characteristics of protein molecules.
9. Can you attempt building models of biomolecules using commercially available atomic models (Ball and Stick models).
Ans. Yes, commercially available atomic models can be utilized to prepare biomolecule models.
Ball and stick models and space filling models are 3D or spatial molecular models that are used to represent the structure of chemical products and substances or biomolecules. In ball and stick models, the centers of the atoms are joined by straight lines representing the covalent bonds. Double and triple bonds are usually represented by springs that make curved connections between the balls. The bond lengths and bond angles portray the true relative positions, with the space actually taken up by the atoms being not at all represented or being represented only schematically by relative sizes of spheres.
10. Attempt titrating an amino acid against a weak base and discover the number of dissociating (ionizable) functional groups in the amino acid.
Ans. Ease with which the various ionic forms of amino acids can be realized by titration curves. In case of basic and neutral amino acids, it is one in number dissociating functional group whereas in case of acidic amino acid, it is two in number dissociating functional group.
11. Draw the structure of the amino acid, alanine.
Ans. 
12. What are gums made of ? Is fevicol different ?
Ans. Gums are hetero-polysaccharides (poly-mers) of many different monosac-charide units. Yes, fevicol is a type of polymer. It is a man-made sticky material named resin which is produced by esteri-fication of organic compounds.
13. Find out a qualitative test for proteins, fats and oils, amino acids and test, any fruit juice, saliva, and urine for them.
Ans. Biuret test for protein : Biuret test is a chemical test to determine the presence of peptide bonds. In a positive test, a copper II ion (Cu2+ ion) is reduced to copper I (Cu+) which combines with the nitrogen and carbon of peptide bonds in an alkaline solution. The presence of proteins is indicated by a violet colour.
Ninhydrin test for amino acid: Ninhydrin (2,2 Dihydroxy indane-l,3-dione) is a reagent which detects ammonia or primary and secondary amines. Upon reacting with such free amines, the production of deep blue or purple color named Ruhemann's purple occurs. Analysis of proteins is also performed for amino acids using ninhydrine. Ninhydrin is hydrolysed and reacted with all amino acids except proline (a secondary amine) for most of them (including a-amino acids). Amino acid having a free amino group and free carboxylic acid group reacts with ninhydrin to give coloured product. When the amino group is secondary, the yellow condensation product is formed.
Solubility test for fats and oils : A good solubility test for fats is that the fat will dissolve in lighter fluid but not in water. For this test, 5 drops of fat or oil are put in two test tubes with 10 drops of lighter fluid and 10 drops cold water respectively.
Fruit juice has sugar in it so it cannot be analyzed by the above tests. Saliva has proteins, mineral salts, amylase etc., so it can be analyzed for protein and amino acids. Urine has proteins in it so it can be analyzed for it.
14. Find out how much cellulose is made by all the plants in the biosphere.
Ans. About 100 billion tonnes of cellulose is prepared per year by the plants of the world.
15. Describe the important properties of enzymes.
Ans. The significant characteristics of enzymes are:
(i) The enzymes are usually proteins which are high molecular weight complex globular proteins. They may bind with non-protein substance for their activity.
(ii) The enzymes do not initiate a chemical reaction but catalyse it only. They bind transiently with the substrate molecules and are not destroyed or altered permanently in the reaction which they catalyse.
(iii) The enzyme regulated reactions are reversible.
(iv) The enzymes are specific in action. An enzyme catalyses only a specific type of reaction or acts on a specific substrate only.
(v) The enzymes are thermolabile i.e., heat sensitive and can work best at a certain optimum temperature. Likewise, enzymes exhibit maximum activity at optimum pH.
(vi) The enzymes get inactivated by poisons and radiation.
