Part 1 — Basic Concepts & Chemical Constituents, Carbohydrates (Q1–25)

Q1.

Which elements are the most abundant in organic biomolecules of living cells?
A. Carbon, Hydrogen, Oxygen ✅
B. Iron, Calcium, Sodium
C. Nitrogen, Argon, Neon
D. Gold, Silver, Platinum

Explanation:

A. Carbon, Hydrogen, Oxygen (Correct): Carbon forms the backbone of organic molecules; hydrogen and oxygen are abundant in carbohydrates, lipids, proteins and nucleic acids.
B. Iron, Calcium, Sodium: Important biologically (e.g., haem, bones, ions) but not the most abundant constituents of organic biomolecules.
C. Nitrogen, Argon, Neon: Nitrogen is important (proteins, nucleic acids), but argon and neon are inert gases and not components of biomolecules.
D. Gold, Silver, Platinum: Trace or non-biological; not constituents of biomolecules.

Q2.

Which class of biomolecules primarily provides immediate energy for cellular processes?
A. Proteins
B. Carbohydrates ✅
C. Nucleic acids
D. Lipids

Explanation:

A. Proteins: Primarily structural and enzymatic; can be used for energy but not the main immediate source.
B. Carbohydrates (Correct): Simple sugars (e.g., glucose) are rapidly metabolized to yield ATP — the usual immediate energy source.
C. Nucleic acids: Store genetic information, not primary energy source.
D. Lipids: Energy-dense storage molecules used for long-term energy, slower mobilization than carbohydrates.

Q3.

Which of the following is NOT a biological role of lipids?
A. Long-term energy storage
B. Membrane structure
C. Catalyzing biological reactions ✅
D. Insulation and cushioning

Explanation:

A. Long-term energy storage: True — triacylglycerols store energy.
B. Membrane structure: True — phospholipids constitute cellular membranes.
C. Catalyzing biological reactions (Correct): Catalysis is the role of enzymes (proteins or ribozymes), not lipids.
D. Insulation and cushioning: True — lipid layers insulate and protect organs.

Q4.

Which statement about amino acids is TRUE?
A. All amino acids are hydrophobic
B. Each amino acid has an amino group, a carboxyl group and a variable side chain ✅
C. Amino acids contain only carbon and hydrogen
D. Amino acids are not building blocks of proteins

Explanation:

A. All amino acids hydrophobic: False — amino acids vary (polar, nonpolar, acidic, basic).
**B. Correct — the general structure includes an amino group (-NH₂), a carboxyl group (-COOH) and an R (side) group that determines properties.
C. Contain only C and H: False — they include N and often O, S.
D. Not building blocks of proteins: False — amino acids are the monomeric units of proteins.

Q5.

Which carbohydrate is a major structural material in plants?
A. Glycogen
B. Cellulose ✅
C. Starch
D. Sucrose

Explanation:

A. Glycogen: Major storage polysaccharide in animals and fungi.
B. Cellulose (Correct): Structural polysaccharide in plant cell walls providing rigidity.
C. Starch: Storage polysaccharide in plants, not the main structural component.
D. Sucrose: Disaccharide used for transport of sugars, not structural.

Q6.

Which property is characteristic of enzymes?
A. They increase activation energy of reactions
B. They are consumed in the reaction
C. They lower activation energy and increase reaction rate ✅
D. They make non-spontaneous reactions spontaneous

Explanation:

A. Increase activation energy: False — enzymes lower activation energy.
B. Consumed in reaction: False — enzymes are catalysts and are regenerated.
**C. Correct — enzymes accelerate reactions by lowering the activation energy barrier.
D. Make non-spontaneous reactions spontaneous: False — enzymes cannot change the thermodynamic favorability (ΔG) of reactions; they only alter kinetics.

Q7.

Which nucleic acid is typically single-stranded in cells?
A. DNA
B. mRNA ✅
C. tRNA
D. rRNA

Explanation:

A. DNA: Usually double-stranded in cellular chromosomes.
B. mRNA (Correct): Messenger RNA is generally single-stranded and carries genetic code from DNA to ribosomes.
C. tRNA: Although single-stranded, it folds into a cloverleaf secondary structure — but the canonical single-stranded answer intended is mRNA; tRNA has extensive secondary pairing.
D. rRNA: Forms part of ribosomal structure and folds with extensive secondary structure; not typically referenced as “single-stranded” in the simple sense.

(Note: tRNA and rRNA are transcribed as single-stranded molecules but fold into complex structures; mRNA is the clearest single-stranded carrier of genetic code.)

Q8.

Which lipid type is the primary constituent of biological membranes?
A. Triacylglycerols
B. Phospholipids ✅
C. Steroids only
D. Waxes

Explanation:

A. Triacylglycerols: Mainly for energy storage, not membrane structure.
B. Phospholipids (Correct): Amphipathic molecules (hydrophilic head, hydrophobic tails) forming bilayers of membranes.
C. Steroids only: Sterols (e.g., cholesterol) modulate membrane fluidity but are not the main structural class.
D. Waxes: Protective coatings (e.g., on leaves), not primary membrane components.

Q9.

Which of the following best describes an essential amino acid?
A. Can be synthesized by the human body in sufficient amounts
B. Must be obtained from diet because the body cannot synthesize it ✅
C. Lacks an amino group
D. Is never found in proteins

Explanation:

A. Synthesized by body: That’s a non-essential amino acid.
**B. Correct — essential amino acids cannot be synthesized de novo by humans and must be part of the diet.
C. Lacks amino group: Impossible for amino acids; they have an amino group by definition.
D. Never found in proteins: False — essential amino acids are incorporated into proteins.

Q10.

Which sugar is an aldose and a monosaccharide commonly used in cellular respiration?
A. Fructose
B. Glucose ✅
C. Sucrose
D. Cellulose

Explanation:

A. Fructose: A ketose monosaccharide.
B. Glucose (Correct): A six-carbon aldose monosaccharide central to cellular respiration.
C. Sucrose: A disaccharide (glucose + fructose).
D. Cellulose: A polysaccharide of glucose units, not a monosaccharide.

Q11.

Which vitamin is commonly a coenzyme precursor (e.g., NAD⁺ precursor) in redox reactions?
A. Vitamin C
B. Niacin (Vitamin B₃) ✅
C. Vitamin D
D. Vitamin K

Explanation:

A. Vitamin C: Antioxidant, enzyme cofactor in specific hydroxylation reactions but not NAD⁺ precursor.
B. Niacin (Correct): Precursor of NAD⁺ and NADP⁺, essential for oxidation-reduction reactions.
C. Vitamin D: Hormone precursor regulating calcium metabolism.
D. Vitamin K: Important for blood clotting, not NAD⁺ precursor.

Q12.

Which statement about polysaccharides is CORRECT (in context of biological roles)?
A. All polysaccharides are soluble in water
B. Starch acts as an energy reserve in plants ✅
C. Cellulose is easily digestible by humans
D. Glycogen is a structural polymer in plants

Explanation:

A. All soluble: False — many polysaccharides are insoluble (cellulose).
**B. Correct — starch (amylose/amylopectin) is the main plant storage carbohydrate.
C. Cellulose digestible by humans: False — humans lack cellulase to hydrolyze cellulose.
D. Glycogen structural in plants: False — glycogen is animal storage polysaccharide.

Q13.

Which statement about peptide hormones versus steroid hormones is generally TRUE?
A. Peptide hormones are lipid-soluble and pass through membranes easily
B. Steroid hormones bind to intracellular receptors and alter gene expression ✅
C. Both types act only at membrane surface receptors
D. Steroid hormones are proteins

Explanation:

A. Peptide hormones lipid-soluble: False — peptides are water-soluble and bind membrane receptors.
**B. Correct — steroid hormones are lipophilic, cross membranes, and bind intracellular receptors to modulate transcription.
C. Both act only at membrane receptors: False — peptides usually at membrane receptors, steroids often intracellular.
D. Steroid hormones are proteins: False — steroids are derived from cholesterol.

Q14.

Which nitrogenous bases are purines?
A. Adenine and Guanine ✅
B. Cytosine and Thymine
C. Uracil and Cytosine
D. Thymine and Uracil

Explanation:

A. Adenine and Guanine (Correct): Purines have a two-ring structure.
B. Cytosine and Thymine: These are pyrimidines (single ring).
C. Uracil and Cytosine: Both pyrimidines.
D. Thymine and Uracil: Both pyrimidines.

Q15.

Which functional group is present in all nucleotides?
A. Sulfhydryl group
B. Phosphate group ✅
C. Aldehyde group
D. Keto group

Explanation:

A. Sulfhydryl: Found in some amino acids (cysteine), not nucleotides.
B. Phosphate group (Correct): Nucleotides have a phosphate backbone (one or more phosphate groups).
C. Aldehyde: Not a universal nucleotide component.
D. Keto group: Present in some bases but not a universal defining group for nucleotides.

Q16.

Which is TRUE about saturated versus unsaturated fatty acids?
A. Saturated fatty acids contain one or more double bonds
B. Unsaturated fatty acids have no double bonds
C. Unsaturated fatty acids contain one or more double bonds and tend to lower melting point ✅
D. Saturated fatty acids are usually liquid at room temperature

Explanation:

A. Saturated with double bonds: False — saturated have no double bonds.
B. Unsaturated have no double bonds: False — unsaturated have double bonds.
**C. Correct — double bonds create kinks, reducing tight packing and lowering melting points (liquids at room temp).
D. Saturated usually liquid: False — saturated fats (e.g., butter) are typically solid at room temp.

Q17.

Which class of enzymes catalyzes oxidation-reduction reactions?
A. Hydrolases
B. Oxidoreductases ✅
C. Transferases
D. Ligases

Explanation:

A. Hydrolases: Catalyse hydrolysis reactions (e.g., proteases).
B. Oxidoreductases (Correct): Catalyze electron transfer reactions (dehydrogenases, oxidases).
C. Transferases: Transfer functional groups (e.g., kinases).
D. Ligases: Join two molecules often coupled to ATP hydrolysis.

Q18.

Which statement best describes enzyme specificity?
A. Enzymes catalyze any chemical reaction in a cell
B. Each enzyme acts on a particular substrate or class of substrates ✅
C. Enzymes are completely non-specific and random
D. Enzymes are permanently altered after catalysis

Explanation:

A. Any reaction: False — enzymes are specific.
**B. Correct — specificity arises from the match between enzyme active site and substrate(s).
C. Completely non-specific: False.
D. Permanently altered: False — enzymes are regenerated after catalytic cycles (unless irreversibly inhibited).

Q19.

Which of the following nucleotide bases is found in RNA but not in DNA?
A. Thymine
B. Uracil ✅
C. Adenine
D. Guanine

Explanation:

A. Thymine: Found in DNA, replaced by uracil in RNA.
B. Uracil (Correct): Present in RNA instead of thymine.
C. Adenine: Present in both DNA and RNA.
D. Guanine: Present in both.

Q20.

Which type of bond or interaction primarily stabilizes tertiary protein structure?
A. Only peptide bonds
B. Multiple interactions among side chains (hydrogen bonds, ionic interactions, hydrophobic interactions, disulfide bridges) ✅
C. Nuclear bonds
D. Glycosidic bonds

Explanation:

A. Only peptide bonds: Peptide bonds determine primary structure; tertiary folding arises from side-chain interactions.
**B. Correct — tertiary structure is stabilized by various interactions among R-groups (hydrogen bonds, ionic bonds, hydrophobic packing, and sometimes disulfide links).
C. Nuclear bonds: Not a biochemical term.
D. Glycosidic bonds: Link sugars, not relevant to protein tertiary stabilization.

(Note: This question refers to types of interactions rather than the excluded “nature of bond linking monomers”. It doesn’t ask how monomers are linked.)

Q21.

Which of the following is a common property of enzymes?
A. They change the equilibrium of reactions
B. They are active over an infinite pH range
C. They display saturation kinetics at high substrate concentrations ✅
D. They always require cofactors

Explanation:

A. Change equilibrium: False — enzymes do not change equilibrium constants; they only speed attainment of equilibrium.
B. Active over infinite pH: False — enzymes have specific pH optima.
**C. Correct — at high substrate concentrations, enzyme active sites become saturated and reaction rate reaches Vmax.
D. Always require cofactors: False — some enzymes require cofactors/coenzymes, others do not.

Q22.

Which biomolecule class contains long chains of nucleotides?
A. Carbohydrates
B. Lipids
C. Proteins
D. Nucleic acids ✅

Explanation:

A. Carbohydrates: Polysaccharides are sugar polymers.
B. Lipids: Not polymers of nucleotides.
C. Proteins: Polymers of amino acids.
D. Nucleic acids (Correct): DNA and RNA are polymers consisting of nucleotide monomers.

Q23.

Which of the following best describes an apoenzyme?
A. The protein portion of an enzyme without its cofactor ✅
B. The complete active enzyme with cofactor bound
C. A permanently denatured enzyme
D. An enzyme bound to substrate irreversibly

Explanation:

**A. Correct — the apoenzyme is the protein moiety that is inactive until the cofactor/coenzyme (holoenzyme formation) associates.
B. Complete active enzyme: That’s the holoenzyme.
C. Permanently denatured enzyme: Not the definition of apoenzyme.
D. Enzyme irreversibly bound to substrate: This would be an inhibited or covalently modified state, not apoenzyme.

Q24.

Which nucleotide base-pairing is correct in typical DNA double helix?
A. Adenine — Guanine
B. Adenine — Thymine ✅
C. Cytosine — Thymine
D. Guanine — Thymine

Explanation:

A. Adenine — Guanine: Both purines; pairing not correct.
B. Adenine — Thymine (Correct): A pairs with T via two hydrogen bonds in DNA.
C. Cytosine — Thymine: Both pyrimidines; incorrect pairing.
D. Guanine — Thymine: Incorrect — guanine pairs with cytosine.

Q25.

Which of the following statements about enzymes and temperature is generally TRUE?
A. Increasing temperature always increases enzyme activity indefinitely
B. Enzymes have an optimum temperature; activity falls at higher temperatures due to denaturation ✅
C. Temperature has no effect on enzyme activity
D. Enzymes are more active at 0 °C than at physiological temperature

Explanation:

A. Increase indefinitely: False — activity increases up to an optimum, beyond which denaturation reduces activity.
**B. Correct — enzymes show a temperature-activity profile with a peak (optimum); high heat disrupts structure and inactivates them.
C. No effect: False — temperature affects kinetic energy and protein stability.
D. More active at 0 °C: False — cold reduces molecular motion and catalytic rate.

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Part 1 — Basic Concepts & Chemical Constituents, Carbohydrates (Q1–25)