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CBSE

Class 12

Chemistry

Chapter 14:

Ncert Books Class 12 Chemistry Chapter 14 Free Download

Q: 1. From an exam perspective, what is the effect of denaturation on the structure of proteins and why is it a frequently asked question?

Denaturation destroys the secondary and tertiary structures of a protein by uncoiling the helices and unfolding the globules. However, the primary structure, which is the sequence of amino acids linked by strong covalent peptide bonds, remains intact. This question is important for exams because it tests the understanding of protein stability and the different types of bonds (weaker hydrogen bonds vs. strong peptide bonds) that hold the protein in its functional shape. Loss of secondary and tertiary structure also leads to the loss of biological activity, such as enzymatic action.

Q: 3. What are essential and non-essential amino acids? Why is this classification important for health and nutrition?

Essential amino acids are those that the human body cannot synthesise and must be obtained through diet. Examples include Valine and Leucine. Non-essential amino acids are those that the body can produce on its own. An example is Glycine. This classification is crucial because a deficiency of essential amino acids in the diet can lead to diseases like Kwashiorkor, highlighting the importance of a protein-rich diet for proper growth and maintenance of the body.

Q: 5. What is a glycosidic linkage, and how does its type (α vs. β) lead to the vastly different properties of starch and cellulose?

A glycosidic linkage is an ether bond that joins two monosaccharide units together to form a disaccharide or polysaccharide. The orientation of this bond is critical. Starch is a polymer of α-glucose and contains α-glycosidic linkages, which result in a helical structure. Human digestive enzymes can break these α-linkages, making starch a key source of energy. In contrast, cellulose is a polymer of β-glucose and contains β-glycosidic linkages, which form straight, rigid chains. Humans lack the enzymes to break β-linkages, making cellulose indigestible for us, where it serves as dietary fibre.

Q: 6. As an expected board question, explain what reducing and non-reducing sugars are, with an example of each.

Reducing sugars are carbohydrates that contain a free aldehyde or ketone group and can reduce Tollens' or Fehling's reagent. In cyclic forms, this corresponds to a free hemiacetal or hemiketal group. Example: Glucose, Fructose, Maltose. Non-reducing sugars do not have a free hemiacetal or hemiketal group, as the anomeric carbons are involved in the glycosidic bond. They cannot reduce Tollens' or Fehling's reagent. Example: Sucrose. In sucrose, the anomeric carbons of both glucose and fructose are linked, so no reducing group is available.

Q: 8. Name the deficiency diseases and two important sources for Vitamin A and Vitamin C, a common 1-mark question topic.

The deficiency diseases and sources are as follows:Vitamin A: Deficiency causes Xerophthalmia (hardening of the cornea) and Night Blindness. Important sources include fish liver oil, carrots, butter, and milk.Vitamin C: Deficiency causes Scurvy (bleeding gums). Important sources include citrus fruits (like oranges, lemons), amla, and green leafy vegetables.

An Overview of Ncert Books Class 12 Chemistry Chapter 14 Free Download

Ever wondered what gives life its sparkle at the deepest level? In Ncert Books Class 12 Chemistry Chapter 14 Free Download, you’ll get to know all about biomolecules, DNA, RNA, proteins, and vitamins in a way that connects science to everyday life. This chapter shows how our bodies work at the tiniest scale, from how food turns into energy to what makes heredity possible.

If you sometimes get confused by terms like "denaturation," "nucleic acids," or "protein synthesis," don’t worry! Everything is explained in simple steps, with plenty of examples. Plus, you can always turn to Vedantu for a free, downloadable NCERT PDF or check the Class 12 Chemistry Syllabus so you never miss what matters for your CBSE board exam.

Practicing these questions will help you solve any tricky problems from the chapter and boost your preparation for exams. Make use of the Class 12 Chemistry Important Questions for more targeted practice!

Class 12 Chemistry Chapter 14 NCERT Books - Biomolecules

Description of Chapter 14 Biomolecules of Class 12 Chemistry:

Chapter 14 of the Biomolecules part of the Class 12 Chemistry textbook talks about DNA and RNA. DNA is a long, spiral-shaped double helix composed of nucleotide subunits, each composed of a sugar molecule called deoxyribose and one of four nitrogenous bases—adenine (A), thymine (T), cytosine (C), or guanine (G). Given the complementary pairing of nucleotides—A with T and C with G—the nucleotide subunits in DNA can pair in two ways to form base pairs. If the bases are oriented so that their hydrogen-bonding sites match up, they form an antiparallel (also called Watson-Crick) base pair. If the bases are inverted so that their sugar-phosphate backbones overlap, the result is a parallel (also called Hoogsteen or anti-Hoogsteen) base pair.

The DNA double helix is held together by weak bonds between the bases. There are hydrogen bonds between single strands of DNA, and there are also intermolecular interactions that take place between two adjacent strands.

DNA contains several types of nucleotide subunits, some of which can combine to form RNA molecules, including the ribonucleotides uridine (U), adenosine (A), guanosine (G), and inosine (I).

The environmental temperature determines the structure of an RNA molecule. The A-form of RNA shows two intertwining base pairs with a single unpaired sugar molecule between them. It is found in hot temperatures or solutions with high salt concentrations. The B-form is found at lower temperatures or in mild solutions.

Ribosomes are cellular organelles that make proteins.

How to prepare For CBSE Class 12 Chemistry Chapter 14

Before you start your preparation for CBSE Class 12 Chemistry Chapter 14, it is important to understand what the CBSE Board wants to test.

CBSE wants you to demonstrate the knowledge of topics like - chemical kinetics, hydrocarbons, diffusion and osmosis, acid-base equilibria.

We know that chemistry can be a tough subject but this blog post will help you prepare for this chapter with concise yet detailed notes on how major concepts are covered in this chapter.

This article is not all-inclusive; it is designed to be a summary of all the topics touched in Chapter 14 of CBSE Text Book, IBSSB Chemistry.

FAQs on Ncert Books Class 12 Chemistry Chapter 14 Free Download

1. From an exam perspective, what is the effect of denaturation on the structure of proteins and why is it a frequently asked question?

Denaturation destroys the secondary and tertiary structures of a protein by uncoiling the helices and unfolding the globules. However, the primary structure, which is the sequence of amino acids linked by strong covalent peptide bonds, remains intact. This question is important for exams because it tests the understanding of protein stability and the different types of bonds (weaker hydrogen bonds vs. strong peptide bonds) that hold the protein in its functional shape. Loss of secondary and tertiary structure also leads to the loss of biological activity, such as enzymatic action.

2. For a 3-mark question in the CBSE 2025-26 board exam, differentiate between DNA and RNA.

The key differences between Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) are:

Sugar: DNA contains Deoxyribose sugar, whereas RNA contains Ribose sugar.
Nitrogenous Bases: DNA has Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). In RNA, Thymine is replaced by Uracil (U).
Structure: DNA is typically a double-stranded helix, while RNA is usually a single-stranded molecule.
Function: The primary function of DNA is the storage and transmission of genetic information, while RNA is mainly involved in protein synthesis.

3. What are essential and non-essential amino acids? Why is this classification important for health and nutrition?

Essential amino acids are those that the human body cannot synthesise and must be obtained through diet. Examples include Valine and Leucine. Non-essential amino acids are those that the body can produce on its own. An example is Glycine. This classification is crucial because a deficiency of essential amino acids in the diet can lead to diseases like Kwashiorkor, highlighting the importance of a protein-rich diet for proper growth and maintenance of the body.

4. Why does the primary structure of a protein remain intact during denaturation?

The primary structure of a protein consists of a specific sequence of amino acids linked by strong covalent peptide bonds. Denaturation is caused by changes in temperature or pH, which disrupt the weaker forces like hydrogen bonds, van der Waals forces, and disulfide bridges that maintain the protein's secondary and tertiary structures. These conditions are not extreme enough to break the strong peptide bonds of the primary structure, which therefore remains unchanged.

5. What is a glycosidic linkage, and how does its type (α vs. β) lead to the vastly different properties of starch and cellulose?

A glycosidic linkage is an ether bond that joins two monosaccharide units together to form a disaccharide or polysaccharide. The orientation of this bond is critical. Starch is a polymer of α-glucose and contains α-glycosidic linkages, which result in a helical structure. Human digestive enzymes can break these α-linkages, making starch a key source of energy. In contrast, cellulose is a polymer of β-glucose and contains β-glycosidic linkages, which form straight, rigid chains. Humans lack the enzymes to break β-linkages, making cellulose indigestible for us, where it serves as dietary fibre.

6. As an expected board question, explain what reducing and non-reducing sugars are, with an example of each.

Reducing sugars are carbohydrates that contain a free aldehyde or ketone group and can reduce Tollens' or Fehling's reagent. In cyclic forms, this corresponds to a free hemiacetal or hemiketal group. Example: Glucose, Fructose, Maltose. Non-reducing sugars do not have a free hemiacetal or hemiketal group, as the anomeric carbons are involved in the glycosidic bond. They cannot reduce Tollens' or Fehling's reagent. Example: Sucrose. In sucrose, the anomeric carbons of both glucose and fructose are linked, so no reducing group is available.

7. Glucose and fructose have the same molecular formula (C₆H₁₂O₆). What is the key structural difference, and what chemical test can distinguish them?

The key structural difference is their functional group. Glucose is an aldohexose (contains an aldehyde group), while fructose is a ketohexose (contains a ketone group). Although both are reducing sugars, they can be distinguished using Bromine water (Br₂ water). Being a mild oxidising agent, bromine water oxidises the aldehyde group of glucose to gluconic acid (and the bromine water is decolourised), but it does not oxidise the ketone group of fructose. This test is a classic example of a distinction question for board exams.

8. Name the deficiency diseases and two important sources for Vitamin A and Vitamin C, a common 1-mark question topic.

The deficiency diseases and sources are as follows:

Vitamin A: Deficiency causes Xerophthalmia (hardening of the cornea) and Night Blindness. Important sources include fish liver oil, carrots, butter, and milk.
Vitamin C: Deficiency causes Scurvy (bleeding gums). Important sources include citrus fruits (like oranges, lemons), amla, and green leafy vegetables.