CBSE Class 12 Chemistry Biomolecules MCQs Set H

Multiple Choice Questions (MCQs)

Question: Amylopectin is a polymer of
a) β-D-glucose
b) α-D-fructose
c) α-D-glucose
d) β-D-fructose
Answer: c

Question: Distinction between glucose and fructose can be done by
a) Fehling solution
b) Tollen’s reagent
c) Benedict’s solution
d) Selivanoff’s reagent
Answer: d

Question: DNA and RNA differ in
a) Purines
b) Sugar
c) Both sugar and pyrimidines
d) Pyrimidines
Answer: c

Question: Which does not show mutarotation?
a) Maltose
b) Glucose
c) Sucrose
d) Fructose
Answer: c

Question: The sugar present in milk is
a) Glucose
b) Maltose
c) Lactose
d) Sucrose
Answer: c

Question: α-D(+) glucose and β-D(+) glucose are
a) Epimers
b) Anomers
c) Enantiomers
d) Geometrical isomers
Answer: b

Question: The vitamins present in oils and fats are
a) A and C
b) B and C
c) A and D
d) A and B
Answer: c

Question: The disease resulting from intake of amino-acid-deficient diet is
a) Pernicious anaemia
b) PEM
c) Kwashiorkor
d) Haemophilia
Answer: c

Question: Keratin present in hair is an example of
a) Globular protein
b) Conjugated protein
c) Derived protein
d) Fibrous protein
Answer: d

Question: Hydrolysis of sucrose gives
(a) Glucose only
(b) Glucose + fructose
(c) Glucose and galactose
(d) Maltose
Answer: b

Question: The reagent used for obtaining osazone derivative of fructose is
(a) NH₂OH
(b) NH₂—NH₂
(c) NH₂—NHC₆H₅
(d) 2, 4—DNP
Answer: c

Question: The functional group which is found in amino acid is
(a) – COOH
(b) – NH₂
(c) – CH₃
(d) both (a) and (b)
Answer: d

Case Based Questions

Adenosine triphosphate (ATP) is the energycarrying molecule found in the cells of all living things. ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes. ATP is a nucleotide that consists of three main structures: the nitrogenous base, adenine; the sugar, ribose; and a chain of three phosphate groups bound to ribose. The phosphate tail of ATP is the actual power source which the cell taps. Available energy is contained in the bonds between the phosphates and is released when they are broken, which occurs through the addition of a water molecule (a process called hydrolysis). Usually only the outer phosphate is removed from ATP to yield energy; when this occurs ATP is converted to adenosine diphosphate (ADP), the form of the nucleotide having only two phosphates. The importance of ATP (adenosine triphosphate) as the main source of chemical energy in living matter and its involvement in cellular processes has long been recognized. The primary mechanism whereby higher organisms, including humans, generate ATP is through mitochondrial oxidative phosphorylation. For the majority of organs, the main metabolic fuel is glucose, which in the presence of oxygen undergoes complete combustion to CO₂ and H₂O:

C6H₁₂O₆ + 6O₂ → 6O₂ + 6H₂O + energy The free energy (ΔG) liberated in this exergonic (ΔG is negative) reaction is partially trapped as ATP in two consecutive processes: glycolysis (cytosol) and oxidative phosphorylation (mitochondria). The first produces 2 mol of ATP per mol of glucose, and the second 36 mol of ATP per mol of glucose. Thus, oxidative phosphorylation yields 17-18 times as much useful energy in the form of ATP as can be obtained from the same amount of glucose by glycolysis alone The efficiency of glucose metabolism is the ratio of amount of energy produced when 1 mol of glucose oxidised in cell to the enthalpy of combustion of glucose. The energy lost in the process is in the form of heat. This heat is responsible for keeping us warm.

Answer the following MCQs by choosing the most appropriate options:

Question: What is the efficiency of glucose metabolism if 1 mole of glucose gives 38 ATP energy? (Given: Enthalpy of combustion of glucose = 686 kcal, 1 ATP = 7.3 kcal)
a) 100%
b) 38%
c) 62%
d) 80%
Answer: b

Question: Cellular oxidation of glucose is a
a) Spontaneous and endothermic process
b) Non-spontaneous and exothermic process
c) Non-spontaneous and endothermic process
d) Spontaneous and exothermic process
Answer: d

Question: Which of the following statement is true?
a) ATP is a nucleoside made up of nitrogenous base adenine and ribose sugar.
b) ATP consists of the nitrogenous base adenine and the sugar deoxyribose.
c) ATP is a nucleotide which contains a chain of three phosphate groups bound to ribose sugar.
d) The nitrogenous base of ATP is the actual power source.
Answer: c

Question: Which of the following statements is correct?
a) ATP is a nucleotide with three phosphate groups while ADP is a nucleoside with three phosphate groups.
b) ADP contains a nitrogenous base adenine, ribose sugar and two phosphate groups bound to ribose.
c) ADP is the main source of chemical energy in living matter.
d) ATP and ADP are nucleosides which differ in number of phosphate groups.
Answer: b

Question: Nearly 95% of the energy released during cellular respiration is due to
a) Glycolysis occurring in cytosol
b) Oxidative phosphorylation occurring in cytosol
c) Glycolysis occurring in mitochondria
d) Oxidative phosphorylation occurring in mitochondria
Answer: d

Polysaccharides may be very large molecules. Starch, glycogen, cellulose, and chitin are examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of amylose and amylopectin (both polymers of glucose). Amylose is soluble in water and can be hydrolyzed into glucose units breaking glycocidic bonds, by the enzymes α- amylase and β-amylase. It is straight chain polymer. Amylopectin is a branched chain polymer of several D-glucose molecules. 80% of amylopectin is present in starch. Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds. The starch that is consumed by animals is broken down into smaller molecules, such as glucose. The cells can then absorb the glucose.Glycogen is the storage form of glucose in humans and other vertebrates, and is made up of monomers of glucose. It is structurally quite similar to amylopectin. Glycogen is the animal equivalent of starch. It is stored in liver and skeletal muscles. Cellulose is one of the most abundant natural biopolymers. The cell walls of plants are mostly made of cellulose, which provides structural support to the cell. Wood and paper are mostly cellulosic in nature.

Like amylose, cellulose is a linear polymer of glucose. Cellulose is made up of glucose monomers that are linked by bonds between particular carbon atoms in the glucose molecule. Every other glucose monomer in cellulose is flipped over and packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. Cellulose passing through our digestive system is called dietary fiber.

Answer the following MCQs by choosing the most appropriate options:

Question: Amylose is
a) Straight chain, water insoluble component of starch, which constitutes 20% of it
b) Straight chain, water soluble component of starch, which constitutes 20% of it
c) Branched chain, water insoluble component of starch, which constitutes 80% of it
d) Branched chain, water soluble component of starch, which constitutes 80% of it
Answer: b

Question: Cellulose on complete hydrolysis yields
a) Amylose
b) Amylopectin
c) Glucose
d) Amylose and amylopectin
Answer: c

Question: Which biopolymer breaks down to release glucose whenever glucose levels drop in our body?
a) Starch
b) Cellulose
c) Chitin
d) Glycogen
Answer: d

Question: In animals, glycogen is stored in
a) Liver
b) Spleen
c) Lungs
d) Small intestine
Answer: a

Question: The linkages which join monosaccharides to form long-chain polysaccharides are
a) Peptide linkage
b) Disulphide bonds
c) Hydrogen bonds
d) Glycosidic linkage
Answer: d

Very Short Answer Type Questions

Question: Name the only vitamin which can be synthesized in our body. Name the disease caused due to the deficiency of this vitamin. 
Answer. Vitamin which can be synthesized in our body : Vitamin A Its deficiency causes Xerophthalmia.

Question: Define a ‘Peptide linkage’. 
Answer. Peptide linkage : It is an amide linkage formed between – COOH group of one α-amino acid and NH₂ group of the other α-amino acid by loss of a molecule of water. – CO – NH – bond is called Peptide linkage.

Question:Mention one important function of nucleic acids in our body. 
Answer. Function of nucleic acid : Nucleic acids control the transmission of hereditary characters from one generation to another.

Question: Name the products of hydrolysis of sucrose. 
Answer. Glucose and fructose are the products of hydrolysis of sucrose.

Question: Which component of starch is a branched polymer of α-glucose and insoluble in water? 
Answer. Amylopectin.

Short Answer Type Questions-I

Question: What type of linkage holds together the monomers of DNA and RNA?
Answer. Phosphodiester linkage.

Question: Write the main structural difference between DNA and RNA. Of the two bases, thymine and uracil, which one is present in DNA? 
Answer. (i) Difference between DNA and RNA :
(ii) Thymine is present in DNA.

Question:Write such reactions and facts about glucose which cannot be explained by its open chain structure.
Answer. Limitations of the open chain structure of glucose :
(i) Glucose does not form NaHSO₃ addition product. Despite having aldehyde-ammonia group, it does not respond to 2,4-DNP test and does not respond to Schiff’s reagent test.
(ii) Glucose penta acetate does not react with NH₂OH due to absence of aldehydic group.

Question: Write any two reactions of glucose which cannot be explained by the open chain structure of glucose molecule. 
Answer. (i) Despite having the aldehyde group, glucose does not give 2, 4-DNP test or Schiff’s test.
(ii) It does not form the hydrogen sulphite addition product with NaHSO₃.
(iii) The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free – CHO group.

Question: (a) Name the only vitamin which can be synthesized in our body. Name one disease that is caused due to the deficiency of this vitamin.
(b) State two functions of carbohydrates.
Answer. (a) Vitamin that can be synthesized :Vitamin B₁₂ Disease due to the deficiency of Vitamin B₁₂ : Pernicious anaemia.
(b) Two functions of glucose :
(i) Carbohydrates such as glucose, starch, glycogen etc. provide energy for functioning of living organisms.
(ii) Carbohydrates, especially cellulose in the form of wood is used for making furniture, houses etc. by us.

Question:Name the four bases present in DNA. Which one of these is not present in RNA? 
Answer. The four bases present in DNA are :
(i) Adenine (A) (ii) Guanine (G) (iii) Cytosine (C) (iv) Thymine (T)
In RNA, Thymine (T) is absent. It has Uracil (U) in place of Thymine.

Question: Answer the following questions:
(i) Why are vitamin A and vitamin C essential for us?
(ii) What is the difference between a nucleoside and a nucleotide? 
Answer. (i) Because deficiency of vitamin A and vitamin C causes night blindness and scurvy respectively.

Question: Enumerate the reactions of glucose which cannot be explained by its open chain structures.
Answer. Limitations of the open chain structure of glucose :
(i) Glucose does not form NaHSO₃ addition product. Despite having aldehyde-ammonia group, it does not give 2,4-DNP test and does not respond to Schiff’s reagent test.
(ii) Glucose penta acetate does not react with NH₂OH due to absence of aldehydic group.

Question: Name the bases present in RNA. Which one of these is not present in DNA?
Answer. The four bases present in RNA are :
Purines – Adenine (A) and Guanine (G)
Pyrimidines – Uracil (U) and Cytosine (C)
Uracil is not present in DNA.

Question: Describe what you understand by primary structure and secondary structure of proteins. 
Answer. Primary structure of proteins : Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each other in a specific sequence which is known as primary structure of protein.
Secondary structure of proteins : The conformation which the polypeptide chains assume as a result of hydrogen bonding is called the secondary structure of the protein.
Depending upon the size of the R groups, the two different secondary structures are possible which are :
(i) α-Helix structure : Intramolecular H–bonds present between the C = O of one amino acid and N – H of fourth amino acid.
(ii) β-Pleated sheet structure : The two neighbouring polypeptide chains are held together by intermolecular H–bonds.

Short Answer Type Questions-II 

Question: (a) Write the structural and functional differences between DNA and RNA
(b) Name two components of starch.
Answer. Functional difference : DNA’s main function is to control cell activities like telling each organ what to make and what to do. RNA’s main function is to make protein.
(b) Components of starch : Amylose and amylopectin.

Question: Why are carbohydrates generally optically active?
Answer. It is due to the presence of Chiral Carbon atoms in their molecules

Question: Define the following terms :
(i) Glycosidic linkage (ii) Invert sugar (iii) Oligosaccharides
Answer. (i) Glycosidic linkage : The two monosaccharide units are joined together through an etheral or oxide linkage formed by loss of a molecule of water. Such a linkage between two monosaccharide units through oxygen atom is called glycosidic linkage
(ii) Invert sugar : An equimolar mixture of glucose and fructose obtained by hydrolysis of sucrose in presence of an acid such as dil. HCl or the enzyme invertase or sucrase is called invert sugar.
(iii) Oligosaccharides : Those carbohydrates which on hydrolysis give 2-10 molecules of monosaccharides are called oligosaccharides.
Example : sucrose, maltose.

Question: (a) Give two differences between globular and fibrous proteins.
(b) What change occurs in the nature of egg protein on boiling?
Answer.
(b) Because the egg comes in contact with a solution of higher osmotic pressure, the egg will shrink due to going out of water. This shrinking of egg is called plasmolysis.