CBSE Class 12 Chemistry Biomolecules MCQs Set 10

Objective Type Questions

Question 1. Which of the following is a disaccharide?
(a) Glucose
(b) Starch
(c) Cellulose
(d) Lactose
Answer: (d) Lactose
In simple words: Lactose is a double sugar formed by the combination of glucose and galactose.

Exam Tip: Remember that disaccharides are sugars made of two simpler sugar molecules, while starch and cellulose are large polymers.

Question 2. Disaccharides that are reducing in nature are
(a) sucrose and lactose
(b) sucrose and maltose
(c) lactose and maltose
(d) sucrose, lactose and maltose
Answer: (c) lactose and maltose
In simple words: Lactose and maltose can act as reducing agents because they have free aldehyde or ketone groups in their ring structures.

Exam Tip: Sucrose is a non-reducing sugar because its reducing groups are locked in the glycosidic bond, whereas maltose and lactose have free hemiacetal groups.

Question 4. Which one of the following reactions is not explained by the open chain structure of glucose?
(a) Formation of penta-acetate of glucose with acetic anhydride.
(b) Formation of addition product with 2,4-DNP reagent.
(c) Silver mirror formation with Tollen's reagent.
(d) Existence of \( \alpha \)- and \( \beta \)- forms of glucose.
Answer: (d) Existence of \( \alpha \)- and \( \beta \)- forms of glucose.
In simple words: The open chain structure cannot explain why glucose exists in two different crystalline forms, which indicates a cyclic structure.

Exam Tip: The absence of the free aldehyde group reactions (like Schiff's test, 2,4-DNP, and NaHSO3 addition) and mutarotation are primary evidences for the cyclic structure of glucose.

Question 5. Which of the following statements is not true about glucose?
(a) It is an aldohexose.
(b) On heating with HI it forms n-hexane.
(c) It exists in furanose form.
(d) It does not give Schiff's test.
Answer: (c) It exists in furanose form.
In simple words: Glucose actually exists in a six-membered pyranose ring structure rather than a five-membered furanose ring.

Exam Tip: Remember that glucose forms a six-membered ring (pyranose), whereas fructose typically forms a five-membered ring (furanose) in its cyclic forms.

Question 7. \( \alpha \)-D-glucose and \( \beta \)-D-glucose differ from each other with respect to the
(a) number of —OH groups
(b) configuration at the C-1 carbon
(c) size of the hemiacetal ring
(d) configuration at the C-5 carbon
Answer: (b) configuration at the C-1 carbon
In simple words: These two forms of glucose are anomers, which differ only in the arrangement of groups around the first carbon atom (C-1).

Exam Tip: Anomers are a specific class of diastereomers that differ in configuration only at the hemiacetal/acetal carbon (C-1 for aldoses, C-2 for ketoses).

Question 8. One molecule of sucrose on hydrolysis gives
(a) 2 molecules of glucose
(b) 2 molecules of glucose + 1 molecule of fructose
(c) 1 molecule of glucose + 1 molecule of fructose
(d) 2 molecules of fructose
Answer: (c) 1 molecule of glucose + 1 molecule of fructose
In simple words: When sucrose is broken down by water, it splits into equal amounts of glucose and fructose.

Exam Tip: Sucrose is a disaccharide made of \( \alpha \)-D-glucose and \( \beta \)-D-fructose, linked by a \( \text{C1}-\text{C2} \) glycosidic bond.

Question 9. Which one of the following statement is correct about sucrose?
(a) It can reduce Tollen's reagent however cannot reduce Fehling's reagent.
(b) It undergoes mutarotation like glucose and fructose.
(c) It undergoes inversion in the configuration on hydrolysis.
(d) It is laevorotatory in nature.
Answer: (c) It undergoes inversion in the configuration on hydrolysis.
In simple words: Sucrose itself is dextrorotatory, but after hydrolysis, the resulting mixture becomes laevorotatory, which is called inversion.

Exam Tip: This inversion happens because the laevorotatory rotation of fructose (\( -92.4^\circ \)) is stronger than the dextrorotatory rotation of glucose (\( +52.5^\circ \ caravan\)).

Question 10. Hydrolysis of sucrose is called
(a) inversion
(b) hydration
(c) esterification
(d) saponification
Answer: (a) inversion
In simple words: The process of splitting sucrose into glucose and fructose is called inversion because the optical rotation of the solution changes sign from positive to negative.

Exam Tip: The mixture of glucose and fructose produced by hydrolyzing sucrose is commonly referred to as invert sugar.

Question 11. On hydrolysis, which of the following carbohydrates gives only glucose?
(a) Maltose
(b) Sucrose
(c) Lactose
(d) Galactose
Answer: (a) Maltose
In simple words: Maltose is made of two glucose units, so breaking it down with water produces only glucose.

Exam Tip: Be ready to state the hydrolysis products of common disaccharides: Maltose gives glucose + glucose; Lactose gives glucose + galactose; Sucrose gives glucose + fructose.

Question 12. Which of the following is a polysaccharide?
(a) Glucose
(b) Maltose
(c) Glycogen
(d) Lactose
Answer: (c) Glycogen
In simple words: Glycogen is a large polymer made of many glucose units linked together, stored in animals.

Exam Tip: Polysaccharides like starch, glycogen, and cellulose are long chains of monosaccharide units and are non-sugars.

Question 15. The specific sequence in which amino acids are arranged in a protein is called as
(a) primary structure
(b) secondary structure
(c) tertiary structure
(d) quaternary structure
Answer: (a) primary structure
In simple words: The primary structure is simply the linear chain of amino acids linked together in a specific order.

Exam Tip: Any change in the primary sequence of amino acids can completely alter the function of the protein, as seen in sickle cell hemoglobin.

Question 16. An \( \alpha \)-helix is a structural feature of
(a) sucrose
(b) polypeptides
(c) nucleotides
(d) starch
Answer: (b) polypeptides
In simple words: The alpha-helix is a common shape that polypeptide chains fold into, which is part of the secondary structure of proteins.

Exam Tip: The \( \alpha \)-helix structure is stabilized by hydrogen bonding between the amide carbonyl oxygen and the amide nitrogen hydrogen located four residues ahead.

Question 17. Tertiary structure of protein is stabilised by
(a) disulphide bonds
(b) van der Waals' forces
(c) hydrogen bonds
(d) All of the options
Answer: (d) All of the options
In simple words: The overall three-dimensional folding of a protein is held together by several types of chemical bonds and interactions.

Exam Tip: Understand that while primary structure is held by covalent peptide bonds, tertiary structures are maintained by hydrogen bonds, ionic bonds, disulfide links, and hydrophobic forces.

Question 18. Which of the following statements is/are correct?
I. Amongst lysine, histidine and serine, lysine is the most basic in nature.
II. All non-essential amino acids are basic in nature.
III. Adding acids such as lemon juice into meat protein does not denature the primary structure yet tenderize meat.
(a) Only I
(b) Only III
(c) I and III
(d) I, II, and III
Answer: (b) Only III
In simple words: Acid treatment breaks down secondary and tertiary protein structures to tenderize meat, but it leaves the primary sequence of amino acids intact.

Exam Tip: Denaturation affects secondary, tertiary, and quaternary levels of protein structure, but never breaks the covalent peptide bonds of the primary structure.

Question 19. Which of the following statements is/are correct for proteins or enzymes when they are subjected to physical changes as specified?
I. The sequence of amino acids in the peptide changes in a protein when the pH of its environment is changed.
II. Most enzymes stop working above about 50 °C.
III. Albumin, a globular protein found in egg whites, sets into an insoluble white solid when the egg white is heated.
(a) Only III
(b) I and II
(c) II and III
(d) I, II and III
Answer: (c) II and III
In simple words: High heat deactivates enzymes and solidifies egg white proteins, but changing the pH does not alter the primary amino acid order of a protein.

Exam Tip: Remember that physical changes like temperature and pH alter folding and native state but leave the primary structure (amino acid sequence) completely unchanged.

Question 20. Deficiency of which of the following vitamins causes pernicious anaemia?
(a) Vitamin B1
(b) Vitamin B2
(c) Vitamin B6
(d) Vitamin B12
Answer: (d) Vitamin B12
In simple words: Lacking Vitamin B12 in the body prevents proper red blood cell formation, leading to pernicious anaemia.

Exam Tip: Make a table linking each vitamin with its chemical name and the disease caused by its deficiency for quick revision.

Question 21. Which of the following acid represents vitamin C?
(a) Saccharic acid
(b) Gluconic acid
(c) Ascorbic acid
(d) Benzoic acid
Answer: (c) Ascorbic acid
In simple words: Ascorbic acid is the scientific name for Vitamin C.

Exam Tip: Know the chemical names of common vitamins, such as Retinol (A), Thiamine (B1), Ascorbic acid (C), and Calciferol (D).

Question 22. Which of the following acids is a vitamin?
(a) Aspartic acid
(b) Ascorbic acid
(c) Adipic acid
(d) Saccharic acid
Answer: (b) Ascorbic acid
In simple words: Among the options, ascorbic acid is the only one that functions as a vitamin (Vitamin C), while others are basic organic acids.

Exam Tip: Do not confuse amino acids (like aspartic acid) or dicarboxylic acids (like adipic acid) with vitamin acids like ascorbic acid.

Question 23. Nucleotides are composed of a
(a) pentose sugar and phosphoric acid
(b) nitrogenous base and phosphoric acid
(c) nitrogenous base and a pentose sugar
(d) nitrogenous base, a pentose sugar and phosphoric acid
Answer: (d) nitrogenous base, a pentose sugar and phosphoric acid
In simple words: A nucleotide is the complete building block of DNA or RNA, consisting of a base, a sugar, and a phosphate group.

Exam Tip: Sugar + Base = Nucleoside; Sugar + Base + Phosphate = Nucleotide. Memorize this basic relation.

Question 24. Nucleic acids are the polymers of
(a) nucleosides
(b) nucleotides
(c) bases
(d) sugars
Answer: (b) nucleotides
In simple words: DNA and RNA are long chains made of repeating units called nucleotides.

Exam Tip: Nucleotides are linked together by phosphodiester linkages between the 5' and 3' carbon atoms of pentose sugars.

Question 25. Match the following columns.
Column I
A. Amino acids
B. Thymine
C. Insulin
D. Phosphodiester linkage
Column II
1. Protein
2. Nucleic acid
3. DNA
4. Zwitter ion
Codes:
(a) A-1, B-4, C-3, D-2
(b) A-4, B-3, C-1, D-2
(c) A-3, B-4, C-1, D-2
(d) A-1, B-3, C-4, D-2
Answer: (b) A-4, B-3, C-1, D-2
In simple words: Amino acids form zwitterions, thymine is a base in DNA, insulin is a protein, and phosphodiester bonds connect nucleic acids.

Exam Tip: Solve matching questions by pairing up the items you are 100% sure about first, which quickly eliminates wrong options.

Question 26. The bases that are common in both DNA and RNA are
(a) adenine, guanine and cytosine
(b) adenine, guanine and thymine
(c) adenine, uracil and cytosine
(d) guanine, uracil and thymine
Answer: (a) adenine, guanine and cytosine
In simple words: DNA and RNA share three of the same nitrogen bases, while thymine is only in DNA and uracil is only in RNA.

Exam Tip: Remember the base pairing rules: DNA has A, G, C, T, while RNA has A, G, C, U. Cytosine, adenine, and guanine are universal.

Question 27. Helical structure of proteins is stabilised by
(a) ionic bond
(b) covalent bond
(c) hydrogen bond
(d) Van der Waals' forces
Answer: (c) hydrogen bond
In simple words: The spiral shape of a protein chain is kept stable by weak hydrogen bonds between different parts of the chain.

Exam Tip: Be clear that the primary structure is maintained by covalent bonds, while the secondary structure is stabilized strictly by hydrogen bonds.

Assertion-Reason
Directions In the following questions an Assertion (A) is followed by a corresponding Reason (R). Use the following keys to choose the appropriate answer,
(a) Both (A) and (R) are true and (R) is the correct explanation of (A),
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A),
(c) (A) is true but (R) is false,
(d) (A) is false but (R) is true.

Question 29. Assertion: Fructose is a reducing sugar.
Reason (R): Fructose does not reduce Fehling solution and Tollen's reagent.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (c) (A) is true but (R) is false.
In simple words: Fructose is a reducing sugar because it easily reduces both Tollen's and Fehling's reagents due to isomerization in basic solutions.

Exam Tip: Ketoses like fructose act as reducing sugars in alkaline conditions because they undergo tautomerization to form aldoses (glucose and mannose).

Question 30. Assertion (A): Sucrose and fructose can not give positive Tollen's test.
Reason (R): Sucrose and fructose do not contain an aldehyde group.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (d) (A) is false but (R) is true.
In simple words: The assertion is false because fructose actually gives a positive Tollen's test, even though it does not contain an aldehyde group.

Exam Tip: Sucrose is non-reducing and won't react with Tollen's reagent, but fructose is a reducing sugar and gives a positive reaction.

Question 31. Assertion (A): Glucose reacts with hydroxylamine to form an oxime and also adds a molecule of hydrogen cyanide to give cyanohydrin.
Reason (R): The carbonyl group is present in the open chain structure of glucose.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
In simple words: Glucose reacts with hydroxylamine and hydrogen cyanide because it has an active carbonyl group in its open-chain form.

Exam Tip: These addition reactions specifically confirm the presence of a carbonyl group (\( \text{C}=\text{O} \)) in the open-chain structure of glucose.

Question 32. Assertion (A): D-(+)- Glucose is dextrorotatory in nature.
Reason (R): 'D' represents its dextrorotatory nature.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (c) (A) is true but (R) is false.
In simple words: The '+' sign shows that glucose rotates light to the right, whereas the 'D' prefix simply refers to its relative configuration compared to glyceraldehyde.

Exam Tip: Remember that 'D' and 'L' represent relative molecular configuration, while '+' and '-' indicate the actual direction of optical rotation.

Question 33. Assertion (A): \( \beta \)-glycosidic linkage is present in maltose.
Reason (R): Maltose is composed of two glucose units in which C-1 of one glucose unit is linked to C-4 of another glucose unit.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (d) (A) is false but (R) is true.
In simple words: Maltose actually contains an alpha-glycosidic linkage connecting the two glucose molecules together.

Exam Tip: In maltose, the link is \( \alpha \)-1,4-glycosidic, whereas cellophane and cellulose feature \( \beta \)-1,4-glycosidic bonds.

Question 34. Assertion (A): All naturally occurring \( \alpha \)-amino acids except glycine are optically active.
Reason (R): Most naturally occurring amino acids have L-configuration.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
In simple words: Glycine is inactive because it has two identical hydrogen atoms on its alpha-carbon, making it symmetric. This is unrelated to the L-configuration of other amino acids.

Exam Tip: Glycine is the simplest amino acid and is the only one that lacks a chiral carbon, making it optically inactive.

Question 35. Assertion (A): All amino acids are solid at 20°C.
Reason (R): Amino acids can form zwitter ions. The ionic nature of the zwitter ions give amino acids with their relatively strong intermolecular forces of attraction.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
In simple words: Amino acids are crystalline solids because they exist as dipolar ions, which create strong ionic bonds between the molecules.

Exam Tip: Due to their zwitterionic state, amino acids behave like salts, showing high solubility in water and very high melting points.

Question 36. Assertion (A): Proteins are polymers of \( \alpha \)-amino acids connected by peptide bond.
Reason (R): A tetrapeptide contains 4 amino acids linked by 4 peptide bonds.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (c) (A) is true but (R) is false.
In simple words: A tetrapeptide is composed of four amino acid units, but they are held together by only three peptide bonds, not four.

Exam Tip: The number of peptide bonds in a linear peptide chain is always one less than the total number of amino acid residues (\( N - 1 \)).

Question 37. Assertion (A): \( \beta \)-pleated sheet structure of proteins shows maximum extension.
Reason (R): Intermolecular hydrogen bonding is present in them.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
In simple words: In a beta-pleated sheet, the peptide chains are stretched out side-by-side and held together by hydrogen bonds between the chains.

Exam Tip: Unlike the tightly coiled \( \alpha \)-helix, the \( \beta \)-pleated sheet structure features fully extended polypeptide chains.

Question 38. Assertion (A): The coagulation of egg white occurs on boiling.
Reason (R): Denaturation of protein occurs when its native form is subjected to physical change or chemical change.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
In simple words: Boiling an egg causes the proteins to lose their folded shape and clump together, which is a classic example of denaturation.

Exam Tip: Denaturation breaks hydrogen bonds and hydrophobic interactions, leading to unfolding, but does not rupture covalent peptide linkages.

Question 39. Assertion (A): In the presence of an enzyme, substrate molecule can be attacked by the reagent effectively.
Reason (R): Active sites of enzymes hold the substrate molecule in a suitable position.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
In simple words: Enzymes make reactions faster because they hold the reacting molecules in the perfect spot and orientation to react.

Exam Tip: Active sites of enzymes bind substrates through weak interactions (H-bonds, ionic bonds), orienting them to lower the activation energy.

Question 40. Assertion (A): Vitamins A, D, E and K are stored in liver and adipose tissue.
Reason (R): Vitamins A, D, E and K are soluble in fats and oils.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
In simple words: Fat-soluble vitamins are stored in our fatty tissues and liver, which is why we do not need to consume them daily.

Exam Tip: Note that while both statements are correct, the storage of fat-soluble vitamins is due to their hydrophobic nature, which prevents excretion in urine.

Question 41. Assertion (A): The two strands of DNA are complementary to each other.
Reason (R): The hydrogen bonds are formed between specific pairs of bases.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
In simple words: The two DNA strands match each other because adenine always pairs with thymine, and guanine always pairs with cytosine through hydrogen bonds.

Exam Tip: Remember that A forms two hydrogen bonds with T (\( \text{A}=\text{T} \)), while G forms three hydrogen bonds with C (\( \text{G}\equiv\text{C} \)).

Question 42. Assertion (A): In both DNA and RNA, heterocyclic base and phosphodiester linkages are at C-1' and C-5' respectively of the sugar molecule.
Reason (R): Nucleotides and nucleosides mainly differ from each other in presence of phosphate units.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
In simple words: Bases are attached at C-1' and phosphate is at C-5' of the sugar, while nucleotides are nucleosides with a phosphate group attached.

Exam Tip: Sugar carbon numbering uses primed numbers (\( 1', 2', 3', 4', 5' \)) to distinguish sugar carbons from the nitrogenous base ring atoms.

Question 43. Assertion (A): When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained.
Reason (R): RNA molecules are of three types and they perform different functions.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
In simple words: Since RNA is usually a single strand, its base amounts do not have to be equal. Additionally, there are three functional classes of RNA: mRNA, tRNA, and rRNA.

Exam Tip: Chargaff's rule (\( \text{A}=\text{T} \) and \( \text{G}=\text{C} \)) applies strictly to double-stranded DNA, not to single-stranded RNA molecules.

Question 44. Assertion (A): The backbone of DNA and RNA molecule is a chain consisting of heterocyclic base, pentose sugar and phosphate group.
Reason (R): Nucleotides and nucleosides mainly differ from each other in presence of phosphate group.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Answer: (d) (A) is false but (R) is true.
In simple words: The backbone of a nucleic acid actually consists of alternating sugar and phosphate groups, with the bases pointing inward rather than forming the main chain.

Exam Tip: Be clear that the structural backbone of nucleic acids is strictly sugar-phosphate-sugar-phosphate, and bases are attached as side-groups to the sugars.

Case-Study 1

45. Read the given case and answer the following questions.
Organic compounds containing amine as functional group are present in a vivid variety of compounds, namely amino acids, hormones, neurotransmitters, DNA, dyes, etc. Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton giving rise to a dipolar ion known as zwitter ion. In zwitter ionic form, amino acids show amphoteric behaviour.

Question 45. Answer the following questions based on the case study:
(i) Give one point of difference between acidic and basic amino acid.
(ii) Name the linkage formed when carboxyl end of one amino acid condenses with amino end of other amino acid.
(iii) What are essential amino acids and non-essential amino acids?
Or What is meant by zwitter ionic form of amino acids? Why do amino acids show amphoteric behaviour?
Answer:
(i) Acidic amino acids contain a higher number of carboxyl groups (\( -\text{COOH} \)) than amino groups (\( -\text{NH}_2 \)). Conversely, basic amino acids possess more amino groups than carboxyl groups.
(ii) The connection established is called a peptide linkage (or peptide bond).
(iii) Essential amino acids are those that the human body cannot make on its own, meaning they must be obtained through our daily meals, like valine or lysine. Non-essential amino acids can be manufactured by the body internally, such as glycine or alanine.
Or
In a water-based environment, a proton shifts from the acidic carboxyl group to the basic amino group of an amino acid. This transfer creates a dipolar ion known as a zwitterion. Amino acids exhibit amphoteric behavior because this zwitterion structure can react with both acids and bases, acting as either a proton donor or acceptor.
In simple words: Acidic amino acids have extra acid groups, while basic ones have extra base groups. Amino acids link via peptide bonds, and zwitterions allow them to act as both acids and bases.

Exam Tip: Always specify example amino acids when defining essential and non-essential types to score complete marks.

Case-Study 2

46. Read the given case and answer the following questions.
Certain organic compounds are required in small amounts in our diet but their deficiency causes specific disease. These compounds are called vitamins. Most of the vitamins cannot be synthesised in our body but plants can synthesise almost all of them. So, they are considered as essential food factors. However, the bacteria of the gut can produce some of the vitamins required by us. All the vitamins are generally available in our diet. The term 'vitamin' was coined from the words vital + amine, since the earlier identified compounds had amino group. Vitamins are classified into two groups depending upon their solubility in water or fat namely-fat soluble vitamins and water soluble vitamins.

Question 46. Answer the following questions based on the case study:
(i) Why can’t vitamin C be stored in our body? Name the disease caused by the deficiency of this vitamin.
(ii) Which of the following vitamins helps in blood clotting?
(a) Vitamin A
(b) Vitamin C
(c) Vitamin D
(d) Vitamin K
Or Which of the following is a fat-soluble vitamin?
(a) Vitamin B
(b) Vitamin C
(c) Vitamin B12
(d) Vitamin K
(iii) Which vitamin is also known as cobalamin?
(a) Vitamin B11
(b) Vitamin B2
(c) Vitamin B12
(d) Vitamin B6
Answer:
(i) Vitamin C is highly soluble in water and is easily removed from the body through urine. As a result, our tissues cannot store it. A lack of Vitamin C causes scurvy, which is marked by bleeding gums.
(ii) (d) Vitamin K
Or (d) Vitamin K
(iii) (c) Vitamin B12
In simple words: Vitamin C dissolves in water, so our body flushes it out daily, leading to scurvy if we don't get enough. Vitamin K is needed for blood clotting, and Vitamin B12 is also called cobalamin.

Exam Tip: Clearly state that water-soluble vitamins (B and C) are excreted regularly and must be taken daily, unlike fat-soluble ones (A, D, E, K) which are stored in fat tissues.