Level 1 — RecognitionEnzymes & Bioenergetics Basics

Enzymes & Bioenergetics Basics

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition

Time limit: 20 minutes | Total marks: 30

Section A — Multiple Choice (1 mark each)

Choose the single best answer.

Q1. The sum of all chemical reactions occurring in a living organism is called: a) catalysis b) metabolism c) respiration d) homeostasis

Q2. ATP releases usable energy mainly by hydrolysis of its: a) ribose sugar b) adenine base c) terminal phosphate bond d) nitrogen atoms

Q3. According to the first law of thermodynamics, energy in a biological system can be: a) created but not destroyed b) neither created nor destroyed, only transformed c) destroyed during respiration d) increased without limit

Q4. An exergonic reaction is characterised by: a) positive $\Delta G$ , energy absorbed b) negative $\Delta G$ , energy released c) $\Delta G = 0$ , at equilibrium d) requires ATP input to proceed

Q5. The minimum energy needed to start a chemical reaction is the: a) free energy b) kinetic energy c) activation energy d) potential energy

Q6. Enzymes speed up reactions by: a) increasing the activation energy b) lowering the activation energy c) changing $\Delta G$ of the reaction d) raising the temperature

Q7. The specific region of an enzyme where the substrate binds is the: a) allosteric site b) active site c) cofactor site d) inhibitor site

Q8. In the induced-fit model, the active site: a) is perfectly rigid b) never changes shape c) changes shape to fit the substrate d) binds any molecule

Q9. A competitive inhibitor typically binds to the: a) allosteric site b) active site c) coenzyme d) product

Q10. A non-protein metallic ion that assists enzyme function is a: a) coenzyme b) cofactor c) substrate d) apoenzyme

Q11. In feedback inhibition, the enzyme is usually inhibited by the: a) initial substrate b) final product of the pathway c) water d) temperature

Section B — Matching (1 mark each; 5 marks)

Q12. Match each term in Column X with its correct description in Column Y.

Column X	Column Y
(i) Allosteric regulation	(A) Non-protein organic helper molecule
(ii) Coenzyme	(B) Reaction that absorbs energy ( $+\Delta G$ )
(iii) Endergonic	(C) Enzyme activity changed by a molecule binding a site other than the active site
(iv) Denaturation	(D) Loss of enzyme shape/function at high temperature
(v) Second law of thermodynamics	(E) Every energy transfer increases entropy (disorder)

Section C — True/False WITH justification (2 marks each; 14 marks)

State True or False (1 mark) AND give a one-line justification (1 mark).

Q13. Raising temperature always increases enzyme activity.

Q14. Non-competitive inhibitors can be overcome by increasing substrate concentration.

Q15. Each enzyme works best at a specific optimum pH.

Q16. Beyond saturation, adding more substrate keeps increasing reaction rate indefinitely.

Q17. In the lock-and-key model, the enzyme and substrate have complementary rigid shapes.

Q18. Enzymes are consumed and used up during the reactions they catalyse.

Q19. A negative $\Delta G$ indicates a spontaneous (exergonic) reaction.

Answer keyMark scheme & solutions

Section A (11 marks)

Q	Ans	Why
1	b	Metabolism = all chemical reactions in an organism.
2	c	Energy is released when the terminal high-energy phosphate bond is hydrolysed (ATP→ADP+Pi).
3	b	1st law: energy is conserved—only transformed, not created/destroyed.
4	b	Exergonic reactions release energy, so $\Delta G < 0$ .
5	c	Activation energy = minimum energy to initiate a reaction.
6	b	Catalysts lower activation energy; they do not alter $\Delta G$ .
7	b	The active site binds substrate.
8	c	Induced fit: active site moulds around the substrate.
9	b	Competitive inhibitors resemble substrate and bind the active site.
10	b	Cofactor = inorganic/metal ion helper; coenzyme is organic.
11	b	End product of a pathway inhibits an earlier enzyme (feedback).

1 mark each correct letter.

Section B (5 marks)

Q12. (i)→C, (ii)→A, (iii)→B, (iv)→D, (v)→E 1 mark per correct pair.

Section C (14 marks)

1 mark True/False + 1 mark justification.

Q13. False — Activity rises to an optimum, then falls as high temperature denatures the enzyme.

Q14. False — Non-competitive inhibitors bind an allosteric site, not the active site; extra substrate cannot displace them (only competitive inhibition is overcome this way).

Q15. True — Each enzyme has an optimum pH; deviations reduce activity by altering charge/shape of the active site.

Q16. False — Rate plateaus at saturation because all active sites are occupied ( $V_{max}$ reached).

Q17. True — Lock-and-key assumes rigid complementary shapes of enzyme and substrate.

Q18. False — Enzymes are catalysts; they are not consumed and are reused.

Q19. True — $\Delta G < 0$ means the reaction is spontaneous/exergonic and releases free energy.

[
  {"claim":"Exergonic reaction has negative delta G (Q4/Q19)","code":"deltaG = -30; exergonic = deltaG < 0; result = (exergonic == True)"},
  {"claim":"Q12 matching mapping is one-to-one and correct","code":"m={'i':'C','ii':'A','iii':'B','iv':'D','v':'E'}; result = (sorted(m.values())==['A','B','C','D','E'] and len(m)==5)"},
  {"claim":"Section A total marks = 11, Section total = 30","code":"secA=11; secB=5; secC=7*2; total=secA+secB+secC; result = (secA==11 and total==30)"},
  {"claim":"Catalysts lower activation energy but do not change delta G (Q6)","code":"Ea_uncat=50; Ea_cat=30; dG_uncat=-20; dG_cat=-20; result = (Ea_cat < Ea_uncat and dG_cat == dG_uncat)"}
]