NCERT Solutions for Class 11 Science Biology Chapter 9 Biomolecules are provided here with simple step-by-step explanations. These solutions for Biomolecules are extremely popular among Class 11 Science students for Biology Biomolecules Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 11 Science Biology Chapter 9 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 11 Science Biology are prepared by experts and are 100% accurate.
Page No 43:
Question 1:
It is said that elemental composition of living organisms and that of inanimate objects (like earth’s crust) are similar in the sense that all the major elements are present in both. Then what would be the difference between these two groups? Choose a correct answer from among the following:
a. Living organisms have more gold in them than inanimate objects
b. Living organisms have more water in their body than inanimate objects
c. Living organisms have more carbon, oxygen and hydrogen per unit mass than inanimate objects.
d. Living organisms have more calcium in them than inanimate objects.
Answer:
Hence, the correct answer is option c.
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Question 2:
Many elements are found in living organisms either free or in the form of compounds. Which of the following is not found in living organisms?
a. Silicon
b. Magnesium
c. Iron
d. Sodium
Answer:
Silicon is not found in living organisms. Other elements are found in living organisms (the human body).
Hence, the correct answer is option a.
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Question 3:
Aminoacids, have both an amino group and a carboxyl group in their structure. Which one of the following is an amino acid?
a. Formic acid
b. Glycerol
c. Glycolic Acid
d. Glycine
Answer:
Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon i.e., the α-carbon. They are called α-amino acids. Glycine is a simple amino acid with the structure-
Hence, the correct answer is option d.
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Question 4:
An amino acid under certain conditions have both positive and negative charges simultaneously in the same molecule. Such a form of amino acid is called
a. Acidic form
b. Basic form
c. Aromatic form
d. Zwitter ionic form
Answer:
Equation:
Neutral form is the zwitter ionic form.
Hence, the correct answer is option d.
Page No 44:
Question 5:
Sugars are technically called carbohydrates, referring to the fact that their formulae are only multiple of C(H2O). Hexoses therefore have six carbons, twelve hydrogens and six oxygen atoms. Glucose is a hexose. Choose from among the following another hexose.
a. Fructose
b. Erythrose
c. Ribulose
d. Ribose
Answer:
Hexose is a monosaccharide that consists of six carbon atoms. It has a chemical formula . Fructose is a monosaccharide and hexose sugar. Erythrose is a four carbon sugar or tetrose. Ribulose and ribose are five carbon sugars or pentoses.
Hence, the correct answer is option a.
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Question 6:
When you take cells or tissue pieces and grind them with an acid in a mortar and pestle, all the small biomolecules dissolve in the acid. Proteins, polysaccharides and nucleic acids are insoluble in mineral acid and get precipitated. The acid soluble compounds include amino acids, nucleosides, small sugars etc. When one adds a phosphate group to a nucleoside, one gets another acid soluble biomolecule called
a. nitrogen base
b. adenine
c. sugar phosphate
d. nucleotide
Answer:
Hence, the correct answer is option d.
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Question 7:
When we homogenise any tissue in an acid the acid soluble pool represents
a. cytoplasm
b. cell membrane
c. nucleus
d. mitochondria
Answer:
Hence, the correct answer is option a.
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Question 8:
The most abundant component of living organisms is
a. protein
b. water
c. sugar
d. nucleic acid
Answer:
Water is the most abundant chemical component of living organisms.
Hence, the correct answer is option b.
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Question 9:
A homopolymer has only one type of building block called monomer repeated ‘n’ number of times. A heteropolymer has more than one type of monomer. Proteins are heteropolymers usually made of
a. 20 types of monomers
b. 40 types of monomers
c. 30 types of monomers
d. only one type of monomer
Answer:
Hence, the correct answer is option a.
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Question 10:
Proteins perform many physiological functions. For example, some functions as enzymes. Which of the following represents an additional function that some proteins discharge?
a. Antibiotics
b. Pigment conferring colour to skin
c. Pigments making colours of flowers
d. Hormones
Answer:
Hormones regulate several body functions such as growth, vegetative and sexual development, thermal regulation, cellular oxidation, metabolism of biomolecules (carbohydrates, fats, proteins, etc.,). They are required in a small amount to carry out different functions.
Hence, the correct answer is option d.
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Question 11:
Glycogen is a homopolymer made of
a. glucose units
b. galactose units
c. ribose units
d. amino acids
Answer:
Glycogen is a homopolysaccharide and is made of glucose units.
Hence, the correct answer is option a.
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Question 12:
The number of ‘ends’ in a glycogen molecule would be
a. equal to the number of branches plus one
b. equal to the number of branch points
c. one
d. two, one on the left side and another on the right side
Answer:
Glycogen is a homopolysachcharide of glucose which has multiple branches. It has reducing end and non-reducing ends. The number of ‘ends’ in a glycogen molecule would be equal to the number of branches plus one.
Hence, the correct answer is option a.
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Question 13:
The primary structure of a protein molecule has
a. two ends
b. one end
c. three ends
d. no ends
Answer:
Hence, the correct answer is option a.
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Question 14:
Enzymes are biocatalysts. They catalyse biochemical reactions. In general they reduce activation energy of reactions. Many physico-chemical processes are enzyme mediated. Which of the following reactions is not enzyme-mediated in biological system?
a. Dissolving CO2 in water
b. Untwining the two strands of DNA
c. Hydrolysis of sucrose
d. Formation of peptide bond
Answer:
Dissolving carbon dioxide in water is a physical process and this reaction is not enzyme-mediated in the biological system.
Hence, the correct answer is option a.
Page No 46:
Question 1:
Medicines are either man made (i.e., synthetic) or obtained from living organisms like plants, bacteria, animals etc. and hence the latter are called natural products. Sometimes natural products are chemically altered by man to reduce toxicity or side effects. Write against each of the following whether they were initially obtained as a natural product or as a synthetic chemical.
| a. | Penicillin | __________________________ |
| b. | Sulfonamide | __________________________ |
| c. | Vitamin C | __________________________ |
| d. | Growth Hormone | __________________________ |
Answer:
a. Penicillin- Natural product
b. Sulfonamide- Synthetic chemical
c. Vitamin C- Natural product
d. Growth hormone- Natural product
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Question 2:
Select an appropriate chemical bond among ester bond, glycosidic bond, peptide bond and hydrogen bond and write against each of the following.
| a. | Polysaccharide | __________________________ |
| b. | Protein | __________________________ |
| c. | Fat | __________________________ |
| d. | Water | __________________________ |
Answer:
a. Polysaccharide- Glycosidic bond
b. Protein-Peptide bond
c. Fat- Ester bond
d. Water-Hydrogen bond
Page No 46:
Question 3:
Write the name of any one aminoacid, sugar, nucleotide and fatty acid.
Answer:
Amino acid-Alanine
Sugar- Glucose
Nucleotide- Adenylic acid
Fatty acid- Palmitic acid
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Question 4:
Reaction given below is catalysed by oxidoreductase between two substrates A and A’, complete the reaction.
Answer:
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Question 5:
How are prosthetic groups different from co-factors?
Answer:
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Question 6:
Glycine and Alanine are different with respect to one substituent on the α-carbon. What are the other common substituent groups?
Answer:
The R group in glycine amino acid is hydrogen and the methyl group in alanine. The common substituent group in these two amino acids are hydrogen (-H), carboxylic acid (-COOH), and amine (-NH2).
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Question 7:
Starch, Cellulose, Glycogen, Chitin are polysaccharides found among the following. Choose the one appropriate and write against each.
| Cotton fibre | __________________________ |
| Exoskeleton of cockroach | __________________________ |
| Liver | __________________________ |
| Peeled potato | __________________________ |
Answer:
| Cotton fibre | Cellulose |
| Exoskeleton of cockroach | Chitin |
| Liver | Glycogen |
| Peeled potato | Starch |
Page No 47:
Question 1:
Enzymes are proteins. Proteins are long chains of amino acids linked to each other by peptide bonds. Amino acids have many functional groups in their structure. These functional groups are, many of them at least, ionizable. As they are weak acids and bases in chemical nature, this ionization is influenced by the pH of the solution. For many enzymes, activity is influenced by surrounding pH. This is depicted in the curve below, explain briefly.
Answer:
The graph given in the question represents the enzyme activity at different pH values. The enzyme shows its maximum activity at an optimum pH and it is around 7 for enzymes of the human body. The activity of the enzyme decrease when the pH increases or decreases above and below the optimum pH. Changes in pH break the intra- and intermolecular bonds resulting in a change in the shape of the enzyme. This also changes its effectiveness. A bell-shaped curve is observed between the enzyme activity and pH.
Page No 47:
Question 2:
Is rubber a primary metabolite or a secondary metabolite? Write four sentences about rubber.
Answer:
Page No 47:
Question 3:
Schematically represent primary, secondary and tertiary structures of a hypothetical polymer say for example a protein.
Answer:
Primary structure of protein: It is the linear arrangement of amino acids and the amino acids are linked together in a sequence by peptide bonds.
Secondary structure of protein: It is the local folding of amino acid structures that form within a polypeptide chain due to interactions between atoms of the backbone. The most common types of secondary structures are- α helix and the β pleated sheet. Both structures are held in shape by hydrogen bonds, that forms between the carbonyl O- of one amino acid and the amino -H of another.
Alpha-helix
Beta-plated sheet
Tertiary structure of protein: The tertiary structure of protein is formed by the overall three-dimensional structure of a polypeptide chain. The tertiary structure is formed primarily due to the interactions between the R groups of the amino acids that make up the protein. This structure is necessary for the biological activities of proteins. \
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Question 4:
Nucleic acids exhibit secondary structure, justify with example.
Answer:
Nucleic acids exhibit a wide variety of secondary structures. For example, one of the secondary structures that are exhibited by DNA is the famous Watson-Crick model. This model says that DNA exists as a double helix. The two strands of polynucleotides are antiparallel i.e., run in the opposite direction. The backbone is formed by the sugar-phosphate backbone. The nitrogen bases are projected more or less perpendicular to this backbone but face inside. A and G of one strand base pairs with T and C, respectively, on the other strand. There are two hydrogen bonds between A and T and three hydrogen bonds between G and C. Each strand appears like a helical staircase.
Page No 47:
Question 5:
Comment on the statement “living state is a non-equilibrium steady state to be able to perform work”.
Answer:
Page No 47:
Question 1:
Formation of enzyme-substrate complex (ES) is the first step in catalysed reactions. Describe the other steps till the formation of product.
Answer:
Each enzyme molecule has an active site for the specific binding of substrate molecules. The enzyme work by altering the activation energy.
The catalytic site of an enzyme is as follows:
(i) The substrate process to the active site of the enzyme, fitting into it.
(ii) Binding of the substrate induces the enzymes to alter their shape that resulting in the formation of the Enzyme substrate (ES) complex.
(iii) Then the active site of the enzyme is in close proximity with the substrate and breaks its chemical bonds.
(iv) A new enzyme product complex is formed.
(v) The enzyme releases the products of the reaction.
(vi) The enzymatic cycle continue again for binding with another substrate and forms a new product.
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Question 2:
What are different classes of enzymes? Explain any two with the type of reaction they catalyse.
Answer:
There are six classes of enzymes:
(i) Oxidoreductases/dehydrogenases:
Enzymes that catalyze oxidoreduction between two substrates S and S’.
For example S reduced + S’ oxidized → S oxidized + S’ reduced.
(ii) Transferases:
Enzymes catalyze a transfer of a group, G (other than hydrogen) between a pair of substrate S and S’.
For example- S - G + S’ S + S’ - G
(iii) Hydrolases:
Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
(iv) Lyases:
Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.
(v) Isomerases: It involves all enzymes that catalyse inter-conversion of optical, geometric or positional isomers.
(vi) Ligases: Enzymes catalysing the linking together of two compounds.
For example- enzymes that catalyse joining of C-O, C-S, C-N, P-O bonds.
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Question 3:
Nucleic acids exhibit secondary structure. Describe through Watson-Crick Model.
Answer:
- the DNA molecule exists as a double helix. The two strands of polynucleotides are antiparallel i.e., they run in the opposite direction.
- The backbone is formed by the sugar-phosphate-sugar chain.
- The nitrogen bases are projected more or less perpendicular to this backbone but face inside.
- A and G of one strand form base pairs with T and C on the other strand. There are two hydrogen bonds between A and T and three hydrogen bonds between G and C.
- Each strand of DNA appears like a helical staircase.
Page No 48:
Question 4:
What is the difference between a nucleotide and nucleoside? Give two examples of each with their structure.
Answer:
| Nucleotide | Nucleoside |
|
(i) The nucleotide consists of a phosphate group, a sugar (ribose or deoxyribose), and a nitrogenous base. |
(i) A nucleoside consists of a sugar and a nitrogenous base. |
| (ii) Adenosine, guanosine, thymidine, uridine, and cytidine are nucleosides. | (ii) Adenylic acid, thymidylic acid, guanylic acid, uridylic acid and cytidylic acid are nucleotides. |
| (iii) |
(iii) |
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Question 5:
Describe various forms of lipid with a few examples.
Answer:
Simple lipids:
Fatty acid and glycerol are simple lipids. A fatty acid has a carboxyl group that is attached to an R group and the R-group is methyl (–CH3 ), or ethyl (–C2H5 ), or a higher number of –CH2 groups (1 carbon to 19 carbons). As palmitic acid has 16 carbons including carboxyl carbon. Arachidonic acid has 20 carbon atoms including carboxyl carbon.
Fatty acids are of two types- saturated fatty acid- without double bonds or unsaturated fatty acid with one or more C=C double bonds.
Glycerol is trihydroxy propane. A large number of lipids contain both glycerol and fatty acids and the fatty acids are found esterified with glycerols. They are classified as monoglycerides, diglycerides, and triglycerides. These are also called fats and oils based on melting point. Oils have a lower melting point (e.g., gingelly oil) than fats.
Compound lipids:
Some lipids have phosphorus and phosphorylated organic compounds. Such lipids are called phospholipids.
They are found in the cell membrane and Lecithin is an example of phospholipid.
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