Bihar Board - Class 12 Chemistry - Chapter 14: Biomolecules Short Answer Question

                              Short Question Answer

Question.1.  What are the products of hydrolysis of sucrose? 

Answer: 

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

Question.2.  Write the structure of the product obtained when glucose is oxidized with nitric acid. 

Answer: 

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Question.3. What are enzymes?
Answer:  Enzymes are biological catalysts. Each biological reaction requires a different enzyme. Thus, as compared to conventional catalyst enzymes are very specific and efficient in their action. Each type of enzyme has its own specific optimum conditions of concentration, pH and temperature at which it works best.

Question.4. What is the effect of denaturation on the structure of proteins?
Answer:  Denaturation of proteins is done either by change in temperature (upon heating) or by bringing a change in the pH of the medium. As a result, the hydrogen bonding is disturbed and the proteins lose their biological activity i.e., their nature changes. During the denaturation, both the tertiary and secondary structures of proteins are destroyed while the primary structures remain intact.

Question.5. Glucose or sucrose are soluble in water but cyclohexane and benzene (simple six membered ring compounds) are insoluble in water Explain.

Answer:  The solubility of a solute in a given solvent follows the rule ‘ Like dissolves like’.Glucose contains five and sucrose contains eight -OH groups. These -OH groups form H-bonds with water. As a result of this extensive intermolecular H-bonding, glucose and sucrose are soluble in water.On the other hand, benzene and cyclohexane do not contain -OH bonds and hence do not form H-bonds with water. Moreover, they are non-polar molecules and hence do not dissolve in polar water molecules.

Question.6.  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: 

1. Glucose does not form a NaHSO3 additional product. Despite having aldehyde-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 an aldehydic group. 

Question.7. Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.

Answer:  Monosaccharides: Ribose, 2-deoxyribose, galactose and fructose. Disaccharides: Maltose and lactose

Question.8. What do you understand by the term glycosidic linkage?

Answer: The ethereal or oxide linkage through which two monosaccharide units are joined together by the loss of a water molecule to form a molecule of disaccharide is called the glycosidic linkage. The glycosidic linkage in maltose molecule is shown below:

Question .9. What are the hydrolysis products of (i) sucrose, and (ii) lactose?

Answer:  Both sucrose and lactose are disaccharides. Sucrose on hydrolysis gives one molecule each of glucose and fructose but lactose on hydrolysis gives one molecule each of glucose and galactose.

Question.10. How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
Answer:  Vitamins are classified into two groups depending upon their solubility in water or fat: 

(i) Water soluble vitamins: These include vitamin B-complex (B1 , B2 , B5 i.e., nicotinic acid , B6 , B12 , pantothenic acid, biotin, i.e., vitamin H and folic acid) and vitamin C.
(ii) Fat soluble vitamins: These include vitamins A , D , E and K. They are stored in liver and adipose (fat storing) tissues. Vitamin K is responsible for coagulation of blood.

Question.11.  What are essential and non-essential amino acids in human food? Give one example of each type.
Answer:  

1. 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. 

2. 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. 

Question.12. Why are vitamin A and vitamin C essential to us? Give their important sources.
Answer:  Vitamin A is essential for us because its deficiency causes xerophthalmia (hardening of cornea of eye) and night blindness.
Sources: Fish liver oil, carrots, butter, milk, etc. Vitamin C is essential for us because its deficiency causes scurvy (bleeding of gums) and pyorrhea (loosening and bleeding of teeth). Sources: Citrous fruits, amla, green leafy vegetables etc.

Question.13. What is a glycosidic linkage? 

Answer:   The two monosaccharide units are joined together through an ethereal or oxide linkage formed by loss of a molecule of water. Such a linkage between two monosaccharide units through an oxygen atom is called glycosidic linkage. 

Question.14.  (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 anemia.
(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, are used for making furniture, houses etc. by us.

Question.15.  What are monosaccharides? 

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. 

Question.16.  Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain. 

Answer: 

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

Question.17.  Where does the water present in the egg go after boiling the egg? 

Answer: 

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 the egg is called plasmolysis.

Question.18.  Name the products of hydrolysis of lactose. 

Answer: 

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

Question.19.  Define a 'Peptide linkage'. 

Answer: 

Peptide Linkage: It is an amide linkage formed between the -COOH group of one a-amino acid and NH2 group of the other a-amino acid by loss of a molecule of water. CO-NH-the bond is called Peptide linkage. 

Question.20. How are amino acids classified?

Answer:  Amino acids are classified as essential and non – essential amino acids.

The amino acids which can be synthesized in the body are known as non – essential   amino acids e.g. Asparetic acid, Glycine etc.

The amino acids which cannot be synthesized in the body and must be obtained through diet are known as essential amino acids. E.g. Histidine, lysine.

Question.21. What is denaturation of proteins? Explain with examples.

Answer:  Disruption of the native conformation of a protein by changing its environment like PH value, temperature etc. resulting in loss of its biological activity is called denaturation of proteins. During denaturation, secondary and tertiary structures get destroyed while primary structure remains the same e.g., coagulation of egg albumin by boiling.

Question.22. What is glycogen? How is it different from starch?

Answer:  Glycogen is a carbohydrate (polysaccharide). In animals, carbohydrates are stored as glycogen.

Starch is a carbohydrate consisting of two components – amylose (15-20 %) and amylopectin (80-85 %).

However, glycogen consists of only one component whose structure is similar to amylopectin. Also, glycogen is more branched than amylopectin.

Question.23. The two strands in DNA are not identical but are complementary. Explain.

Answer:  In the helical structure of DNA, the two strands are held together by hydrogen bonds between specific pairs of bases. Cytosine forms hydrogen bond with guanine, while adenine forms hydrogen bond with thymine. As a result, the two strands are complementary to each other.

Question.24 . What are the different types of RNA found in the cell?

Answer:  (i) Messenger RNA (m-RNA)

(ii) Ribosomal RNA (r-RNA)

(iii) Transfer RNA (t-RNA)

Question.25. What are essential and non-essential amino acids? Give two examples of each type.

Answer:  Essential amino acids are required by the human body, but they cannot be synthesized in the body. They must be taken through food. For example: valine and leucine

Non-essential amino acids are also required by the human body, but they can be synthesized in the body. For example: glycine, and alanine.