NCERT Solutions for Class 11 Biology Chapter 9 Biomolecules

Q1. What are macromolecules? Give examples .

Answer:

The large sized complex molecules that get separated in acid-insoluble fraction 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 a phospho-diester bond.

Answer:

Glycosidic bond- This bond is formed between the 1st carbon atom of one monosaccharide with 4 carbon atom of neighbouring monosaccharide unit. 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 neighbouring amino acid. A water molecule is released 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.

3. What is meant by tertiary structure of proteins?

Answer:

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.

Solutions for NCERT class 11 biology chapter 9 biomolecules:

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:

The structures of 10 small molecular weight biomolecules are as follows

These biomolecules are manufactured in biotechnology industries.

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

Answer:

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 triglyceride.

Answer:

A triglyceride is a chemical formed by 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-oleoistearin, dipalmitostearin etc.

CBSE NCERT solutions for class 11 biology chapter 9 biomolecules

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

Answer:

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 of 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).

Answer:

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 bond while balls of different colours 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.

Answer:

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.

Answer:

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.

Answer:

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

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

The qualitative test for amino acids is ninhydrin test.

NCERT solutions for class 11 biology chapter 9 biomolecules:

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:

Paper is made up of pulp of wood which is mainly constituted by cellulose. The 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.

Answer:

Enzymes are proteinaceous substances which are capable of catalysing chemical reactions of biological origin without themselves undergoing any change. They are commonly called as 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 decrease 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 catalyses only a particular substrate. Every enzyme has specific sites called active sites for the binding of substrate.

5. Only a small quantity of enzyme is capable of forming the desired product

6. Enzyme activity is sensitive to certain chemicals called inhibitors or modulators.