Biology Enzymes MCQs Chapter 3 Class 11

Enzymes in Biology for Entry Tests and FSC Board Exams

Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed. They are an essential topic for students preparing for MDCAT, NUMS, AKU, NUST, UET, ECAT, and FSC board exams (First Year & Second Year). Understanding enzyme structure, function, and mechanisms, including substrate specificity, active sites, and factors affecting enzyme activity, is crucial for solving both conceptual and MCQ-based questions in exams.

PLS Academy

UNLOCK PREMIUM🔐

7037

Created on March 02, 2022 By Ali Durrani

Biology Ch 3 Class 11 ENZYMES

This is the Free Access to Limited MCQs. Enroll to PLS Boost Premium Bundle to Get More MCQs HERE

1 / 74

Inhibitors which block the enzyme by forming weak bond are called

Competitive inhibitors.

Non-competitive inhibitors

Irreversible inhibitors.

Both a and b

2 / 74

During feedback inhibition, which of the following structural part of enzyme is involved?

NUMS 2020
Biology
Enzymes
Elimination Tool:

A) Active site

B) Binding site

C) Catalytic site

D) Allosteric site

3 / 74

A reaction will proceed faster if the activation energy is?

PMC Sample 1
Biology
Enzymes
Elimination Tool:

A) High

B) Low

C) Remains the same

D) None of these options is correct

4 / 74

Some enzymes require the presence of a non protein molecule to behave catalytically. An enzyme devoid of this molecule is called a(n):

NTS 2013
Biology
Enzymes
Elimination Tool:

A) Holoenzyme

B) Apoenzyme

C) Coenzyme

D) Zymoenzyme

5 / 74

Enzymes work by which of the following?

PMC Practice 1
Biology
Enzymes
Elimination Tool:

A) Increasing the activation energy

B) Reducing the activation energy

C) Making exergonic reactions endergonic

D) Making endergonic reactions exergonic

6 / 74

Extreme change in pH results in:

Change in ionization of amino acids at the active site of the enzyme.

Change in the ionization of the substrate.

Denaturation of the enzyme

IncreaseIncrease in the reaction rate. in the reaction rate.

7 / 74

The inhibitor which closely resembles the substrate in its molecular structure and inhibits the enzyme activity by binding to the active site of the enzyme is called:

NTS 2013
Biology
Enzymes
Elimination Tool:

A) Feedback inhibitor

B) Non-competitive inhibitor

C) Allosteric modulator

D) Competitive inhibitor

8 / 74

In which of the following location enzymes controlling cellular respiration are present?

Nucleus

Chlorophast

Milochondria

Ribosome

9 / 74

Inactive enzyme precursors such as pepsinogen for pepsin are called as:

PMC Practice 1
Biology
Enzymes
Elimination Tool:

A) Holoenzymes

B) Actinases

C) Zymogens

D) Mucopolysaccharides

10 / 74

The optimum pH of catalase is:

NUMS 2018
Biology
Enzymes
Elimination Tool:

A) Slightly alkaline

B) Highly acidic

C) Highly alkaline

D) Slightly acidic

11 / 74

Excessive increase in temperature of medium causes the enzyme molecule to

Activate

Unaffected

Denatured

None of these.

12 / 74

Malonic acid is an example of:

Irreversible inhibitor

Reversible inhibitor

Competitive inhibitor

Non-competitive inhibitor

13 / 74

Which of the following factors affect enzyme activity?

NTS 2011
Biology
Enzymes
Elimination Tool:

A) Temperature

B) pH

C) Concentration of substrate

D) Radiation

E) All of these

14 / 74

A/An _______ is mostly a non-protein chemical compound that is required for the protein’s biological activity.

NTS 2019
Biology
Enzymes
Elimination Tool:

A) Active site

B) Substrate

C) Cofactor

D) Enzyme

15 / 74

A substance which binds at the active site of the enzyme but does not result in the formation of the products is called:

Irreversible inhibitor

Reversible inhibitor

Competitive inhibitor

Non-competitive inhibitor

16 / 74

Restriction endonucleases

PMC Sample 2
Biology
Enzymes
Elimination Tool:

A) are bacterial enzyme

B) convert RNA to DNA

C) hydrolyze protein into amino acids

D) get mutated for DNA repair

17 / 74

The effect of competitive inhibitor on enzyme activity is such that it affects which of the following?

PMC Sample 2
Biology
Enzymes
Elimination Tool:

A) Increases enzyme activity

B) Doesn't change enzyme activity

C) Decreases enzyme activity

D) None of these options is correct

18 / 74

Lock and Key Model for enzyme action propose by Emil Fischer suggests that:

PMC 2020
Biology
Enzymes
Elimination Tool:

A) Enzymes are unbiased for the substrate

B) Enzymes can modify their active sites

C) Enzymes are restricted to one reaction type

D) An enzyme can catalyze variety of reactions

19 / 74

The number of substrate molecules converted into the product by one molecule of enzyme active site per unit time is called?

PMC Practice 2
Biology
Enzymes
Elimination Tool:

A) Turnover number

B) Substrate number

C) Reaction number

D) None of these options is correct

20 / 74

Most enzymes have an optimum temperature of around:

PMC 2020
Biology
Enzymes
Elimination Tool:

A) 30 C

B) 40 C

C) 50 C

D) 20 C

21 / 74

In enzymatic mechanism, the substrate bind to the enzyme active site to produce?

PMC Practice 3
Biology
Enzymes
Elimination Tool:

A) Reactants

B) Enzymes

C) Products

D) All of these

22 / 74

Which of the following statements is incorrect?

PMC Sample 1
Biology
Enzymes
Elimination Tool:

A) The competitive inhibitor affects the rate of breakdown of the enzyme-substrate complex.

B) The presence of the competitive inhibitor decreases the Km of the enzyme for the substrate.

C) A competitive inhibitor reacts reversibly with the enzyme to form an enzyme-inhibitor complex.

D) In competitive inhibition, the inhibitor molecule is not chemically changed by the enzyme.

23 / 74

Due to the similarity of structure, competitive inhibitors may be selected by the _______ site.

NUMS 2019 Reconduct
Biology
Enzymes
Elimination Tool:

A) Catalytic

B) Active

C) Binding

D) Allosteric

24 / 74

Enzymes binds with chemical reactant which is known as?

PMC Sample 3
Biology
Enzymes
Elimination Tool:

A) product

C) substrate

B) reactant

D) all of these

25 / 74

Biological molecules (proteins) which catalyze a biochemical reaction and remain unchanged after completion of reaction are called

Cofactor

Coenzymes

Activator

Enzymes

26 / 74

The structure of an enzyme is altered by:

Irreversible inhibitor

Reversible inhibitor

Competitive inhibitor

Non-competitive inhibitor

27 / 74

The rate of reaction is directly proportional to the concentration of an enzyme which statement is incorrect in this respect:

Increase in enzyme molecule increases the available active sites.

This relation is for unlimited time period with unlimited enzyme concentration

If the concentration is doubled the rate will become two fold.

None of these.

28 / 74

If more substrate to already occurring enzymatic reaction is added and there is no effect on the rate of the reaction what is the form given to this situation:

Saturation

Denaturation

Composition

Inhibition

29 / 74

Which step causes activation of catalytic site of an enzyme?

Change in pH of the surroundings.

Formation of Enzyme Susstrate complex.

Change in the charge of the active site.

Change in temperature

30 / 74

Cyanide for enzymes act as:

NUMS 2018
Biology
Enzymes
Elimination Tool:

A) Substrate

C) Cofactor

B) Prosthetic group

D) Inhibitor

31 / 74

Which type of bonds are never formed when a substrate fits into the active site of an enzyme?

PMC Practice 1
Biology
Enzymes
Elimination Tool:

A) Hydrogen bonds

B) Ionic interactions

C) Hydrophobic interactions

D) Covalent linkages

32 / 74

If more substrate to already occurring enzymatic reaction is added more enzyme activity is seen because:

There is probably more substrate present than there is enzyme.

There is probably more enzayme available than there is substrate.

There is probably more product present than there is either substrate or enzyme.

The enzyme substrate complex is probably failing to form during the reaction.

33 / 74

Which statement about enzyme is incorrect:

Some of them consist solely of protein with no non protein part.

They catalyze a chemical reaction without being utilized.

All enzymes are fibrous Proteins.

They without their cofactor are called apoenzyme.

34 / 74

Optimum temperature for enzymes of human body is:

NUMS 2018
Biology
Enzymes
Elimination Tool:

A) 90 F

B) 95 F

C) 98 F

D) 100 F

35 / 74

The active site of an enzyme:

Never changes

Forms no chemical bond with substrate

Determined by structure and the specificity of the enzyme.

They are non specific in their action.

36 / 74

The cofactor usually acts as “bridge” between:

NUMS 2018
Biology
Enzymes
Elimination Tool:

A) Enzyme & substrate

B) Enzyme & product

C) Coenzyme & substrate

D) Activator & substrate

37 / 74

Upon increasing the temperature the shape of enzyme’s active site?

PMC Sample 2
Biology
Enzymes
Elimination Tool:

A) remains same

B) denatures

C) adopts a geometric conformation

D) dissolves

38 / 74

The lock and key model of enzyme action was proposed by:

PMC Sample 3
Biology
Enzymes
Elimination Tool:

A) Louis Pasteur

B) Emil Fischer

C) Daniel Koshland

D) Urey Miller

39 / 74

Enzymes work by lowering the ______ of the reactions they catalyse:

PMC 2020
Biology
Enzymes
Elimination Tool:

A) Kinetic energy

B) Activation energy

C) Heat energy

D) Potential energy

40 / 74

If another molecule, having a shape very similar to the enzymes substrate, binds to its active site, it would then ____ the enzyme’s function:

NUMS 2020
Biology
Enzymes
Elimination Tool:

A) Fasten

B) Inhibit

C) Reverse

D) Decrease

41 / 74

If we add more substrate to an already occurring enzymatic reaction and it has no affect on the rate of reaction, the process is called?

PMC Practice 2
Biology
Enzymes
Elimination Tool:

A) Denaturation

B) Saturation

C) Composition

D) Inhibition

42 / 74

Which of the following statements about enzymes is false?

PMC Sample 1
Biology
Enzymes
Elimination Tool:

A) The Keq of a reaction remains unchanged in the presence of an enzyme

B) Enzymes speed up the rate of reaction in DNA synthesis

C) Harsh, acidic conditions can completely denature an enzyme

D) An enzyme is completely converted to product during metabolism

43 / 74

Which statement is incorrect about Lock and Key Model?

Specific enzyme can transform only a specific substrate

Active site of an enzyme is a non flexible structure.

Active site does not change before during or even after the reaction.

It explains the mechanism of every chemical reaction.

44 / 74

The Induced fit model was introduced by Koshland in which of the following year?

PMC Sample 1
Biology
Enzymes
Elimination Tool:

A) 1960

B) 1961

C) 1959

D) 1966

45 / 74

The optimum pH for the enzyme arginase is which of the following?

PMC Sample 2
Biology
Enzymes
Elimination Tool:

A) 9.0

B) 9.3

C) 9.7

D) 10

46 / 74

What is not true about the induced fit model:

NUMS 2018
Biology
Enzymes
Elimination Tool:

A) Explains mechanism of enzyme action

B) Enzyme is specific in nature

C) Enzyme is a flexible structure

D) Enzyme doesn’t show change during reaction

47 / 74

Which of the following statements is incorrect?

PMC Practice 1
Biology
Enzymes
Elimination Tool:

A) The competitive inhibitor affects the rate of breakdown of the enzyme-substrate complex

B) The presence of the competitive inhibitor decreases the Km of the enzyme for the substrate

C) A competitive inhibitor reacts reversibly with the enzyme to form an enzyme-inhibitor complex

D) In competitive inhibition, the inhibitor molecule is not chemically changed by the enzyme

48 / 74

Identify the wrong statements.

(a) The substrate binds to active site of enzyme and not fitting into active site

(b) The binding of substrate induces the enzyme to alter its shape

(d) The enzyme releases the products of the reaction and runs through catalytic cycle once again

NUMS 2019 Reconduct
Biology
Enzymes
Elimination Tool:

A) A, C

B) B, D

C) B, C

D) A, D

49 / 74

An activated enzyme made of polypeptide chain and a cofactor is?

PMC Practice 2
Biology
Enzymes
Elimination Tool:

A) Substrate

B) Coenzyme

C) Apoenzyme

D) Holoenzyme

50 / 74

Optimal temperature of enzymes present in human body is

27?C

37?C

47?C

30?C

51 / 74

The type of energy, reduced by the enzymes, for biological reactions to occur is called the:

UHS 2019
Biology
Enzymes
Elimination Tool:

A) Light Energy

B) Heat energy

C) Active energy

D) Activation energy

52 / 74

The enzyme found in saliva responsible for the digestion of carbohydrates is:

NTS 2018
Biology
Enzymes
Elimination Tool:

A) Lysozyme

B) Amylase

C) Pepsin

D) Trypsinogen

53 / 74

An enzyme increases the speed of a reaction:

NTS 2012
Biology
Enzymes
Elimination Tool:

A) by adding activation energy requirements

B) by lowering the activation energy requirements

C) by decreasing the concentration of products

D) by increasing the concentration of products

54 / 74

A cofactor made of inorganic ion which is detachable is called

Prosthetic group

Coenzyme

Activator

Cofactor

55 / 74

If enzyme concentration is low than substrate pH and temperature values are equal to requirement then which of the following will increase rate of reaction.

increase in concentration of enzyme

increase in concentration of substrate

increase in pH

increase in temperature

56 / 74

A three dimensional dcavity bearing a specific charge by which the enzyme reacts with its substrate is called

Active site

Binding site

Catalytic site

Allosteric site

57 / 74

The pH at which the activity of pancreatic lipase enzyme is maximum is:

NUMS 2019 Cancelled
Biology
Enzymes
Elimination Tool:

A) 8.00

B) 9.00

C) 7.40

D) 9.20

58 / 74

A student of chemical engineering mistakenly engulfed the toxic compound “A” which was a potent inhibitor of a certain enzyme. He was immediately brought to a hospital where the doctor injected, intravenously, substrate “B” to minimize the toxic effect of Compound A. His life was saved from serious damage. The treatment method shows that compound A was a ______ inhibitor.

UHS 2019
Biology
Enzymes
Elimination Tool:

A) Non competitive

B) Irreversible

C) Temperature sensitive

D) Competitive reversible

59 / 74

A chemical substance which can react (in place of substrate) with the enzyme but is not transformed into product/s and thus blocks the active site temporarily or permanently is called

Co-enzyme

Blocker

Inhibitor

Cofactor

60 / 74

Enzymes _________ the activation energy of a chemical reaction

Increases

Decreases

Does not effect

Increases or decreases depending upon individual enzyme

61 / 74

The enzyme in breast milk that causes the coagulation of milk or forms precipitates of milk is:

NUMS 2016
Biology
Enzymes
Elimination Tool:

A) Renin

B) Trypsin

C) Amylase

D) Lipase

62 / 74

Which one forms the raw material for coenzymes?

Vitamins

Carbohydrates

Proteins

Metals

63 / 74

If the non-protien part is loosely attached to the protein part in the enzyme, it is known as ______.

PMC Practice 3
Biology
Enzymes
Elimination Tool:

A) Coenzyme

B) Prosthetic group

C) Cofactor

D) Apoenzyme

64 / 74

If the concentration of enzyme is kept constant and amount of substrate is increased a point is reached where increase in substrates concentration does not affect the reaction rate because of

Enzymes get denatured at higher substrate conc.

Rate of reaction is indirectly proportional to substrate concentration at this point.

All the active sites on enzyme molecule are occupied.

None of these.

65 / 74

The following statements are about enzymes:

1. They are globular proteins

2. They can be inhibited by competitive inhibitors

3. They are formed in the smooth endoplasmic reticulum

4. There are only found attached to Plasma membranes in the cell

Which statements are correct for all enzymes?

NTS 2015 DUHS and JSMU
Biology
Enzymes
Elimination Tool:

A) 1 and 4

B) 2 and 4

C) 1 and 2

D) 1,2,3 and 4

66 / 74

The substrate binds to specific region of enzyme called?

PMC Sample 1
Biology
Enzymes
Elimination Tool:

A) key

B) active site

C) hyperactive site

D) none of these

67 / 74

Non-protein but inorganic, detachable co-factors are called ______:

NUMS 2020
Biology
Enzymes
Elimination Tool:

A) Activators

B) Prosthetic groups

C) Coenzymes

D) Apo-enzymes

68 / 74

Lock and Key model was proposed by

Emil Fischer

Koshland

Robin Williams

Rudolph Virchow

69 / 74

Antibodies can be digested by using which of the following types of enzymes?

PMC Sample 3
Biology
Enzymes
Elimination Tool:

A) Lipase

B) Protease

C) Amylase

D) Polymerase

70 / 74

When inhibitor binds to enzyme other than active site and alters its structure, then it is called:

NUMS 2020
Biology
Enzymes
Elimination Tool:

A) Competitive inhibitor

B) Non-competitive inhibitor

C) Reversible inhibitor

D) Irreversible inhibitor

71 / 74

An example of competitive inhibition of an enzyme is the inhibition of;

UHS 2019
Biology
Enzymes
Elimination Tool:

A) Succinic dehydrogenase by malonic acid

B) Cytochrome oxidase by cyanide

C) Hexokinase by glucose

D) Carbonic anhydrase by carbon dioxide

72 / 74

An activated enzyme consisting of polypeptide chain and a cofactor is called:

Apoenzyme

Holoenzyme

Activated enzyme

Both b and c

73 / 74

In 1959, Koshland proposed which of the following?

PMC Practice 1
Biology
Enzymes
Elimination Tool:

A) Unit membrane model

B) Fluid mosaic model

C) Reflective index model

D) Induced fit model

74 / 74

Reversible inhibitors form WEAK linkages with which of the following?

PMC Sample 3
Biology
Enzymes
Elimination Tool:

A) enzyme

B) reactant

C) product

D) substrate

Your score is

The average score is 67%

Importance of Enzyme Concepts and Practice

A clear understanding of enzymes helps students improve problem-solving skills and conceptual clarity. Practicing chapter-wise MCQs on enzyme kinetics, inhibition, coenzymes, and metabolic pathways enables students to identify weak areas and retain key facts. Combining this with mock tests and past papers familiarizes students with exam patterns, question types, and time management, boosting confidence for both entry tests and FSC exams.

PLS Academy Resources for Enzyme MCQs

PLS Academy provides a comprehensive set of Enzymes MCQs, including solved questions, topic-wise exercises, and revision notes for First Year and Second Year students. These resources support systematic practice, concept reinforcement, and performance tracking, helping students maximize understanding and score high in entry tests and FSC board exams.

JazakAllah.

Comments

5 responses to “Biology Enzymes MCQs Chapter 3 Class 11”

M.Ahmad khan

September 29, 2022

thank you sir this is very informative quiz i like your work for the aspirants of Mdcat . May you live long.
Reham Jamal

October 17, 2022

JazakAllah sir for this great effort for MDCAT aspirants
Anonymous

November 4, 2022

Just! awesome ??
Anonymous

January 16, 2023

Kindly share the mcqs explanation
Anonymous

June 7, 2023

What is the characteristic of a non competitive inhibitor