Class 11 Biology


NCERT Solution

Question 1: What are macromolecules? Give examples.

Answer: Biomolecules with molecular weights more than one thousand Dalton are called biomacromolecules. These are found in the acid-insoluble fraction. Examples: Protein, polysaccharides, lipids, etc.

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


glycosidic bond peptide bond phosphodiester bond

Question 3: What is meant by tertiary structure of proteins?

Answer: The overall shape of a protein molecule; and the spatial relationship of the secondary structures to one another; is called tertiary structure of protein. In other words, the various folds which give three dimensional appearances to protein form its tertiary structure.

Question 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.


fatty acid

Fig: Fatty acids


Fig: Phospholipid


Fig: Cholesterol


Fig: Ribose


Fig: Uridine


Fig: Adenosine


Fig: Glycerol


Fig: Uracil



NOTE: All images are taken from Wikipedia

Fat is manufactured by isolation. Many hormones are also manufactured by isolation. Pharmaceutical and consumer goods industry can be the major buyers of these products.

Question 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?

Answer: If the same amino acid is present at both ends of protein, then it is a homopolymer. The protein is not pure in that case. On the other hand, a heteropolymer is a pure protein.

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

Answer: Contraceptive pills are hormones and hence are proteins. Additionally, there are many protein supplements available in the market. Collagen is a protein which is used as an additive in various food and cosmetics.

Question 7: Explain the composition of triglyceride.

Answer: When fatty acids are found esterified with glycerol, they are called glycerides. Presence of three esterified bonds makes them triglycerides.


Fig: An unsaturated fat Triglyceride

In this figure, the left side is composed of glyceride. The right side is composed of palmitic acid, ocleic acid and alpha-linolenic acid; from top to bottom.

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

Answer: Nearly 80% of milk protein is casein. Proteases act on the soluble portion of casein, i.e. K-casein. This leads to coagulation of milk protein and curd is formed.

Question 9: Attempt titrating an amino acid against a weak base and discover the number of dissociating ( ionizable ) functional groups in the amino acid.

Answer: When amino acid is titrated against a weak base, it ionizes into NH2 (amine group) and COOH (carboxylic group).

Question 10: Draw the structure of the amino acid, alanine.



Fig: Alanine

Question 11: What are gums made of? Is Fevicol different?

Answer: Natural gum is a polysaccharide of natural origin. It has high viscosity even at low concentration. Fevicol is a synthetic glue. Synthetic glue is usually made of polymers which are dissolved in a solvent. When the adhesive is exposed, the solvent evaporates; resulting in hardening of the adhesive. Synthetic adhesives come in various strengths and are used accordingly.

Question 12: Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.

Answer: Qualitative tests for proteins, fats and oils are as follows:

Biuret Test: Biuret test is done for protein. Appearance of violet colour in the solution confirms the presence of protein. Biuret (H2NCONHCONH2) reacts with copper ion in a basic solution and gives the violet colour.

Liebermann-Burchard Test: This test is done for cholesterol. The reagent is a mixture of acetic anhydride and sulphuric acid. Appearance of green colour confirms the presence of cholesterol.

Grease Test: This test is done for certain oils. This is a simple test which involves rubbing the given sample on cloth or paper. Appearance of a translucent spot shows the presence of oil.

Question 13: 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: As per a UN report of 2006, about 312 million tons of carbon is stored as biomass of plants. About 10% of the total available cellulose is used in paper making. This appears as a small figure; compared to the total biomass. But when the lost forest cover is replaced by monoculture plantations, it makes the situation grim. Moreover, wood is also cut for many other purposes. Hence, there is a huge loss of vegetation every year.

Question 14: Describe the important properties of enzymes.

Answer: Enzymes are biological catalysts. No metabolic reaction takes place without an enzyme. Enzymes are highly specific to the substrates. Unlike inorganic catalysts, enzymes are susceptible to high temperatures and cease to act after optimum temperature. Enzymes greatly hasten the rate of metabolic reactions.