Important Questions for Class 12 Chemistry Chapter 14 Biomolecules Class 12 Important Questions

Class 12 Biomolecules Important Questions with Answers

Access Important questions with answers for Class 12 Chemistry, Chapter 14: Biomolecules. Aligned with CBSE curriculum, these questions aid in thorough revision for Class 12 exams and entrance tests like NEET and JEE. Students can also access NCERT Solutions for Class 12.

Short Answer Type Questions

Question 1. What is meant by ‘reducing sugars’? (All India 2010)

Answer: Reducing sugar contains aldehydic or ketonic group in the hemiacetal and hemiketal forms and can reduce Tollen’s reagent or Fehlmg’s solution.

Question 2. What are monosaccharides? (All India 2010)

Answer: These are the simplest carbohydrates which cannot be hydrolysed to smaller molecules. Their general formula is (CH₂O)_n where n = 3 – 7

Example : glucose, fructose etc.

Click Here: CBSE Syllabus For Class 12

Question 3. Write the structure of the product obtained when glucose is oxidised with nitric acid. (All India 2012)

Answer:

Question 4. Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain. (All India 2012)

Answer: On prolonged heating with HI, it forms n-hexane, shows that all the six carbon atoms are linked in a straight
chain :

Question 5. What are the expected products of hydrolysis of lactose ? (Comptt. Delhi 2012)

Answer: On hydrolysis, lactose gives P-D-galactose and p-D-glucose.

Question 6. Where does the water present in the egg go after boiling the egg? (Comptt. Delhi 2012)

Answer: Denaturation of proteins is a process that changes the physical and biological properties of proteins without affecting the chemical composition of protein. In an egg, denaturation of protein is the coagulation of albumin present in the white of an egg. When an egg is boiled in water, the globular proteins present in it change to a rubber like insoluble mass which absorbs all the water present in the egg by making hydrogen bond with it.

Question 7. Name a water soluble vitamin which is a powerful antioxidant. Give its one natural source. (Comptt. Delhi 2012)

Answer: Water soluble vitamin : Vitamin C

Natural source : Amla

Question 8. What are three types of RNA molecules which perform different functions? (Delhi 2013)

Answer: m-RNA, t-RNA, r-RNA

Question 9. What is a glycosidic linkage? (Delhi 2013)

Answer: 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.

Question 10. What are the products of hydrolysis of sucrose? (All India 2013)

Answer: Invert sugar: An equimolar mixture of glucose and fructose is obtained by hydrolysis of sucrose in presence of an acid such as dil. HC1 or the enzyme invertase or sucrase and is called invert sugar.

Question 11. Write the name of linkage joining two amino acids. (All India 2013)

Answer: Peptide linkage joins two amino acids.

Question 12. Name the deficiency diseases resulting from lack of Vitamins A and E in the diet. (Comptt. Delhi 2013)

Answer: Deficiency of Vitamin A causes Xerophthalmia and deficiency of Vitamin E causes Sterility.

Question 13. Name one water soluble vitamin which is a powerful antioxidant. Give its one natural source. (Comptt. Delhi 2013)

Answer: Water soluble vitamin : Vitamin C

Natural source : Amla

Question 14. Name one oil soluble vitamin which is a powerful antioxidant and give its one natural source. (Comptt. Delhi 2013)

Answer: Oil soluble Vitamine : Vitamin D

Natural source : Fish liver oil, butter, milk, eggs etc.

Question 15. Name the products of hydrolysis of lactose. (Comptt. All India 2013)

Answer: Lactose on hydrolysis with dilute acids gives an equimolar mixture of D-glucose and D-galactose.

Question 16. Name the only vitamin which can be synthesized in our body. Name the disease caused due to the deficiency of this vitamin. (Comptt. All India 2013)

Answer: Vitamin which can be synthesized in our body : Vitamin A Its deficiency causes Xerophthalmia.

Question 17. Mention one important function of nucleic acids in our body. (Comptt. All India 2013)

Answer: Function of nucleic acid : Nucleic acids control the transmission of hereditary characters from one generation to another.

Question 18. Which of the two components of starch is water soluble? (Delhi 2014)

Answer: Amylose is water soluble component of starch.

Question 19. Name the products of hydrolysis of sucrose. (Delhi 2014)

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

Question 20. Which component of starch is a branched polymer of a-glucose and insoluble in water? (Delhi 2014)

Answer: Amylopectin.

Question 21. What are the products of hydrolysis of sucrose? (All India 2014)

Answer: Glucose and fructose.

Question 22. What are the products of hydrolysis of maltose? (All India 2014)

Answer:

Question 23. Write the products of hydrolysis of lactose. (All India 2014)

Answer: Lactose on hydroloysis with dilute acids gives an equimolar mixture of D-glucose and D-galactose.

Question 24. Define a ‘Peptide linkage’. (Comptt. All India 2014)

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 25. What are enzymes? (Comptt. All India 2014)

Answer: Enzymes are protein molecules which act as catalyst in biochemical reaction.

Short Answer Type

Question 26. Explain what is meant by (Delhi 2009)

(i) a peptide linkage

(ii) a glycosidic linkage.

Answer: (i) Peptide linkage: A peptide linkage is an amide linkage formed between – COOH group of one α-amino acid and NH₂ group of the other a-amino acid by loss of a molecule of water.

(ii) 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.

Question 27. Name two water soluble vitamins, their sources and the diseases caused due to their deficiency in diet. (Delhi 2009)

Answer:

Question 28. Name the four bases present in DNA. Which one of these is not present in RNA? (All India 2009)

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 29. Name two fat soluble vitamins, their sources and the diseases caused due to their deficiency in diet. (All India 2009)

Question 30. Explain the following terms :

(i) Invert sugar

(ii) Polypeptides (Delhi 2009)

Answer:

(i) 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.

(ii) Polypeptides : They are formed when several molecules of a-amino acids are joined together by peptide bonds.

Question 31. Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar? (Delhi, All India 2009)

Answer:

Question 32. What are essential and non-essential amino acids in human food? Give one example of each type.(Delhi 2009)

Answer: Essential amino acids : Amino acids which the body cannot synthesize are called essential amino acids. Example : Valine, leucine etc. Therefore they must be supplied in diet.

Non-essential amino acids : Amino acids which the body can synthesize are called non-essential amino acids. Therefore, they may or may not be present in diet.
Example : Glycine, alanine etc.

More Resources for Class 12

• NCERT Solutions for Class 12 Maths
• NCERT Solutions for Class 12 Physics
• NCERT Solutions for Class 12 Chemistry
• NCERT Solutions for Class 12 Biology
• NCERT Books
• NCERT Books for Class 12

Question 33. State clearly what are known as nucleosides and nucleotides. (Delhi 2009)

Answer: Nucleoside : A nucleoside contains only two basic components of nucleic acids i.e. a pentose sugar and a nitrogenous base. During their formation 1-position of the pyrimidine or 9-position of the purine moitey is linked to C₁ of the sugar (ribose or deoxyribose) by a β-linkage.

Nucleotides : A nucleotide contains all the three basic components of nucleic acids, i.e. a phosphoric acid group, a pentose sugar and a nitrogenous base. These are formed by esterification of C₅‘ – OH of the sugar of the nucleoside with phosphoric acid.

Question 34. What is essentially the difference between a-form of glucose and p-form of glucose? Explain. (Delhi 2009)

Answer: In a-α-glucose, the OH group at C₁ is towards right while in p-D-glucose, the OH group at C₁ is towards left.

Question 35. Describe what you understand by primary structure and secondary structure of proteins. (Delhi 2009)

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 :

1. α-Helix structure : Intramolecular H-bonds present between the C = O of one amino acid and N – H of fourth amino acid.
2. β-Pleated sheet structure : The two neighbouring polypeptide chains are held together by intermolecular H-bonds.

Question 36. Explain what is meant by

(i) a peptide linkage,

(ii) a glycosidic linkage. (Delhi 2009)

Answer: (i) Peptide linkage: A peptide linkage is an amide linkage formed between – COOH group of one α-amino acid and NH₂ group of the other a-amino acid by loss of a molecule of water.

(ii) 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.

Question 37. Name the bases present in RNA. Which one of these is not present in DNA? (Delhi 2009)

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 38. Explain what is meant by the following :

(i) peptide linkage

(ii) pyranose structure of glucose (All India 2009)

Answer:

(i) Peptide linkage: A peptide linkage is an amide linkage formed between – COOH group of one a-amino acid and NH₂ group of the other a-amino acid by loss of a molecule of water.

(ii) Pyranose structure of glucose : The six membered ring containing 5 carbon atoms and one oxygen atom because of its resemblance with pyron is called the pyranose form.

Question 39. Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA. (All India 2009)

Answer:

DNA	RNA
1. The sugar present in DNA is 2-deoxy-(-) ribose.	1. The sugar present in RNA is D-(-) ribose.
2. DNA contains cytosine and thymine as pyrimidine bases.	2. RNA contains cytosine and uracil as pyrimidine bases.
3. DNA has double standard α-helix structure.	3. RNA has single stranded α-helix structure.

The base which are common to both DNA and RNA are :

1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)

Question 40. Write such reactions and facts about glucose which cannot be explained by its open chain structure. (All India 2009)

Answer: Limitations of the open chain structure of glucose :

1. 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.
2. Glucose penta acetate does not react with NH₂OH due to absence of aldehydic group.

Question 41. Write any two reactions of glucose which cannot be explained by the open chain structure of glucose molecule. (Delhi 2012)

Answer:

1. Despite having the aldehyde group, glucose does not give 2, 4-DNP test or Schiff’s test.
2. It does not form the hydrogen sulphite addition product with NaHSO₃.
3. The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free – CHO group.

Question 42. Write the main structural difference between DNA and RNA. Of the two bases, thymine and uracil, which one is present in DNA? (Delhi 2012)

Answer: (i) Difference between DNA and RNA :

The base which are common to both DNA and RNA are :

1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)

(ii) Thymine is present in DNA.

Question 43. Write down the structures and names of the products formed when D-glucose is treated with

(i) Hydroxylamine

(ii) Acetic anhydride. (Comptt. All India 2012)

Answer: (i) D-glucose reacts with hydroxylamine to form oxime.

(ii) D-glucose reacts with acetic anhydride to give penta-acetate.

Question 44.

(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. (Comptt. All India 2012)

Answer:

(a) Vitamin that can be synthesized ‘.Vitamin B₁₂

Disease due to the deficiency of Vitamin B₁₂ : Pernicious anaemia.

(b) Two functions of glucose :

1. Carbohydrates such as glucose, starch, glycogen etc. provide energy for functioning of living organisms.
2. Carbohydrates, especially cellulose in the form of wood is used for making furniture, houses etc. by us.

Question 45. Write down the structures and names of the products formed when D-glucose is treated with

(i) Bromine water

(ii) Hydrogen Iodide (Prolonged heating). (Comptt. All India 2012)

Answer:

Question 46. 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? (Comptt. Delhi 2014)

Answer: (i) Because deficiency of vitamin A and vitamin C causes night blindness and scurvy respectively.

(ii) Nucleoside : A nucleoside contains only two basic components of nucleic acids i.e. a pentose sugar and a nitrogenous base. During their formation 1-position of the pyrimidine or 9-position of the purine moitey is linked to C₁ of the sugar (ribose or deoxyribose) by a β-linkage.

Nucleotides : A nucleotide contains all the three basic components of nucleic acids, i.e. a phosphoric acid group, a pentose sugar and a nitrogenous base. These are formed by esterification of C₅‘ – OH of the sugar of the nucleoside with phosphoric acid.

Question 47. Enumerate the reactions of glucose which cannot be explained by its open chain structures. (Comptt. Delhi 2014)

Answer: Limitations of the open chain structure of glucose :

1. Glucose does not form NaHS03 addition product. Despite having aldehyde-ammonia group, it does not give 2,4-DNP test and does not respond to Schiff’s reagent test.
2. Glucose penta acetate does not react with NH2OH due to absence of aldehydic group.

Question 48. Write the ambident nucleophiles? Give an example. (Comptt. Delhi 2014)

Answer: A group containing two nucleophilic centres. Example : ^–CN (Cyanide) and ^–NC (Isocynide).