Chemistry Class 12 NCERT Solutions: Chapter 14 Biomolecules Part 1

Download PDF of This Page (Size: 421K)

Q: 1. Glucose or sucrose are soluble in water but cyclohexane or benzene (simple six membered ring compounds) are insoluble in water. Explain.

Answer:

A glucose molecule contains five groups while a sucrose molecule contains eight groups. Thus, glucose and sucrose undergo extensive H-bonding with water.

Hence, these are soluble in water.

But cyclohexane and benzene do not contain groups. Hence, they cannot undergo H-bonding with water and as a result, are insoluble in water.

Q: 2. What are the expected products of hydrolysis of lactose?

Answer:

Lactose is composed of galactose and glucose. Thus, on hydrolysis, it gives galactose and glucose.

Q 2 Lactose Products

Q 2 Lactose Products

Q 2 Lactose Products

Q: 3. How do you explain the absence of aldehyde group in the pentaacetate of D-glucose?

Answer:

D-glucose reacts with hydroxylamine to form an oxime because of the presence of aldehydic group or carbonyl carbon. This happens as the cyclic structure of glucose forms an open chain structure in an aqueous medium, which then reacts with to give an oxime.

But pentaacetate of D-glucose does not react with . This is because pentaacetate does not form an open chain structure.

Q 3 Pentaacetate Of D-glucose

Q 3 Pentaacetate of D-Glucose

Q 3 Pentaacetate Of D-glucose

Q: 4. The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.

Answer:

Both acidic (carboxyl) as well as basic (amino) groups are present in the same molecule of amino acids. In aqueous solutions, the carboxyl group can lose a proton and the amino group can accept a proton, thus giving rise to a dipolar ion known as a zwitter ion.

Due to this dipolar behaviour, they have strong electrostatic interactions within them and with water. But halo-acids do not exhibit such dipolar behaviour. For this reason, the melting points and the solubility of amino acids in water is higher than those of the corresponding halo-acids.

Q: 5. where does the water present in the egg go after boiling the egg?

Answer:

When an egg is boiled, the proteins present inside the egg get denatured and coagulate. After boiling the egg, the water present in it is absorbed by the coagulated protein through H-bonding.

Q: 6. why cannot vitamin C be stored in our body?

Answer:

Vitamin C cannot be stored in our body because it is water soluble. As a result, it is readily excreted in the urine.

Q: 7. What products would be formed when a nucleotide from DNA containing thymine is hydrolysed?

Answer:

When a nucleotide from the DNA containing thymine is hydrolyzed, thymine deoxyribose and phosphoric acid are obtained as products.

Q: 8. When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What does this fact suggest about the structure of RNA?

Answer:

A DNA molecule is double-stranded, in which the pairing of bases occurs. Adenine always pairs with thymine, while cytosine always pairs with guanine. Therefore, on hydrolysis of DNA, the quantity of adenine produced is equal to that of thymine and similarly, the quantity of cytosine is equal to that of guanine.

But when RNA is hydrolyzed, there is no relationship among the quantities of the different bases obtained. Hence, RNA is single-stranded.