Enzymes: Specificity, Temperature, pH, Denaturation and Industrial Uses

1. In an enzyme-controlled reaction, the substrate concentration is increased while enzyme concentration, temperature and pH are kept constant. At first, the rate increases, but later it becomes constant.
   What is the best explanation?

A substrate molecules have been denatured
B all enzyme active sites are occupied at high substrate concentration
C enzymes are used up during the reaction
D products start acting as competitive inhibitors only at high temperature

2. A protease works fastest at pH 2. The same enzyme is placed at pH 9 for 30 minutes and then returned to pH 2. Its activity remains very low.
   What most likely happened?

A the enzyme was killed because it was alive
B the active site permanently changed shape
C the substrate became permanently smaller
D the enzyme concentration increased too much

3. Which statement best describes enzyme specificity?

A one enzyme can catalyse all reactions if enough substrate is present
B the active site has a shape complementary to only certain substrate molecules
C enzymes change their active sites randomly until a substrate fits
D specificity occurs because enzymes are used up by substrates

4. A student investigates catalase using hydrogen peroxide. At 20 °C, 5 cm³ of oxygen is collected in 80 seconds. At 30 °C, 5 cm³ is collected in 40 seconds.
   What is the best conclusion?

A reaction rate halves when temperature increases by 10 °C
B reaction rate doubles when temperature increases by 10 °C
C oxygen production decreases as temperature increases
D catalase is denatured at 30 °C

5. Which row correctly identifies an enzyme and the molecule it digests?

A amylase: protein
B protease: starch
C lipase: lipid
D maltase: cellulose

6. A reaction has an optimum temperature of 40 °C.
   Which statement is most likely correct?

A at 0 °C, the enzyme is permanently denatured
B at 20 °C, enzyme and substrate molecules collide less often than at 40 °C
C at 60 °C, the enzyme works faster because molecules have more kinetic energy
D at 100 °C, the substrate becomes complementary to the active site

7. An enzyme solution is divided into four tubes.

Tube 1: enzyme + substrate at 10 °C
Tube 2: enzyme + substrate at 35 °C
Tube 3: boiled enzyme + substrate at 35 °C
Tube 4: enzyme only at 35 °C

Which tube should have the fastest product formation?

A tube 1
B tube 2
C tube 3
D tube 4

8. A student adds amylase to starch solution and tests samples every minute with iodine. The colour changes from blue-black to brown.
   What does this show?

A starch is being produced from glucose
B starch is being broken down
C protein is being digested
D reducing sugar is being denatured

9. Which statement about denaturation is correct?

A denaturation always occurs at low temperature
B denaturation changes the shape of the active site
C denaturation increases enzyme specificity
D denaturation means substrate concentration becomes zero

10. A detergent contains protease and lipase.
    Which stains would these enzymes help remove?

A starch and cellulose stains
B blood and fat stains
C salt and water stains
D DNA and mineral ion stains

11. A student uses pectinase to treat apple pulp before filtering.
    What is the industrial advantage?

A it breaks down protein in apples to make juice cloudy
B it increases juice yield by breaking down pectin in cell walls
C it converts glucose to ethanol
D it denatures cellulose to produce amino acids

12. A graph of enzyme activity against temperature rises from 10 °C to 40 °C, then falls sharply from 45 °C to 70 °C.
    Which explanation best fits the fall after 45 °C?

A substrate molecules stop moving
B enzyme active sites lose their specific shape
C enzyme molecules are used up
D product molecules become starch

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Which factor does not directly affect the rate of an enzyme-controlled reaction?

A pH
B temperature
C enzyme concentration
D colour of the test-tube

14. Four tubes contain equal volumes of starch and amylase.

Tube W: pH 2, 37 °C
Tube X: pH 7, 37 °C
Tube Y: pH 9, 37 °C
Tube Z: pH 7, 80 °C

Human salivary amylase is used. Which tube will most likely digest starch fastest?

A W
B X
C Y
D Z

15. Why do enzymes lower activation energy?

A they increase the final amount of product possible
B they provide an alternative reaction pathway
C they increase the pH of the solution
D they permanently combine with the substrate

16. A student says, “Boiling an enzyme and cooling it again restores its activity because the temperature is back to normal.”
    Which response is most accurate?

A correct, because cold temperatures reverse all denaturation
B correct, because enzymes are only inactive above 100 °C
C incorrect, because high temperature may permanently alter the active site
D incorrect, because boiling makes all substrates insoluble

17. In the lock-and-key model, what represents the “lock”?

A substrate
B active site
C product
D pH

18. Which statement best explains why a very low temperature slows enzyme activity?

A enzyme active sites are permanently destroyed
B enzyme and substrate molecules have less kinetic energy and collide less often
C enzyme molecules become smaller than substrate molecules
D the substrate changes into an inhibitor

19. A student measures the time taken for starch to disappear. Which result shows the highest enzyme activity?

A starch disappears in 20 seconds
B starch disappears in 60 seconds
C starch disappears in 120 seconds
D starch does not disappear

20. Which row correctly compares low temperature and high temperature effects on enzymes?

A low temperature denatures enzymes; high temperature slows collisions only
B low temperature slows activity; high temperature may denature enzymes
C low temperature increases active site shape change; high temperature has no effect
D low temperature breaks peptide bonds; high temperature freezes enzymes

21. Lactase is used to produce lactose-free milk.
    Which reaction does lactase catalyse?

A lactose → glucose + galactose
B starch → maltose
C protein → amino acids
D lipid → fatty acids + glycerol

22. Which statement about enzymes in biological washing powders is correct?

A they work best at all temperatures equally
B they are useful because they digest biological stains
C they are used up after one wash reaction
D they only work in strongly acidic conditions

23. A student investigates enzyme activity by measuring gas production. Which change would make the test unfair?

A using the same enzyme concentration each time
B using equal volumes of substrate each time
C changing both pH and temperature at the same time
D measuring gas volume after the same time

24. A particular enzyme works only on substrate X and not substrate Y.
    Which is the best reason?

A substrate Y has a different shape and cannot fit the active site
B substrate Y has less kinetic energy than substrate X
C substrate X is always smaller than substrate Y
D substrate Y has already been converted into product

25. A non-competitive inhibitor binds to a part of the enzyme away from the active site and changes the enzyme’s shape.
    What is the likely effect?

A substrate binds more easily to the active site
B active site shape changes, reducing enzyme activity
C enzyme concentration increases
D product becomes the new substrate

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. A competitive inhibitor affects an enzyme-controlled reaction.
    Which change may reduce the inhibitor’s effect?

A decreasing substrate concentration
B increasing substrate concentration
C boiling the enzyme
D lowering enzyme concentration to zero

27. Which condition would most likely denature a digestive enzyme?

A placing it at its optimum pH
B placing it at its optimum temperature
C exposing it to a very different pH from its optimum
D increasing substrate concentration slightly

28. A student uses amylase to digest starch. Benedict’s test becomes positive after digestion.
    What product caused the positive Benedict’s result?

A amino acids
B fatty acids
C reducing sugar
D starch

29. Which statement correctly describes the active site?

A it is the region of substrate that changes enzyme shape
B it is the part of the enzyme where substrate binds
C it is the product released after digestion
D it is the temperature at which enzyme works fastest

30. Enzyme X has optimum pH 8. Enzyme Y has optimum pH 2.
    Which conclusion is most valid?

A X must be amylase and Y must be catalase
B X and Y have different active site structures suited to different pH conditions
C Y will work faster than X at every temperature
D X is not a protein because it works in alkaline conditions

31. A student wants to compare the effect of temperature on lipase activity.
    Which variable should be measured?

A colour of lipid before adding enzyme only
B time taken for pH to fall by a fixed amount
C mass of test-tube after heating
D volume of water added after reaction stops

32. In an enzyme reaction, the substrate concentration is very high. The enzyme concentration is then doubled.
    What is most likely to happen initially?

A rate decreases because more enzymes compete for substrate
B rate increases because more active sites are available
C rate stays zero because substrate denatures enzymes
D rate decreases because enzymes are used up faster

33. Which industrial process uses enzymes from microorganisms to convert sugars into ethanol?

A pasteurisation
B fermentation
C filtration
D emulsification

34. Biological washing powders may not work well at 90 °C.
    Why?

A stains become enzymes
B enzymes may be denatured
C proteins become carbohydrates
D lipids turn into starch

35. Which row correctly matches industrial enzyme and use?

A lactase: lactose-free milk
B pectinase: leather softening
C protease: starch syrup production
D lipase: DNA copying

36. A student adds enzyme to substrate and records product formed. After some time, product formation stops even though the enzyme is not denatured.
    What is the most likely reason?

A all substrate has been used up
B enzyme has become a carbohydrate
C active sites have disappeared permanently
D product has changed into enzyme

37. Which graph description best shows the effect of pH on most enzymes?

A activity increases continuously as pH increases
B activity decreases continuously as pH increases
C activity is highest at an optimum pH and lower on either side
D activity is zero at the optimum pH

38. A protease in the stomach works best at low pH. If it enters the small intestine, its activity decreases.
    What is the best explanation?

A the higher pH changes the active site shape
B the enzyme becomes a lipid
C the substrate becomes another enzyme
D the enzyme is used up by hydrochloric acid

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Which statement about enzymes and products is correct?

A enzymes are permanently changed into products
B products leave the active site after the reaction
C products remain permanently attached to enzymes
D products denature enzymes at optimum pH

40. A student tests the effect of pH on amylase. Which set-up gives the fairest comparison?

A same temperature, same amylase concentration, different pH buffers
B different temperatures, different starch concentrations, different pH buffers
C same pH, different amylase concentrations, same temperature
D different volumes of iodine, different temperatures, same pH

41. Which statement about enzyme-controlled reactions is correct?

A enzymes increase reaction rate and are not used up
B enzymes decrease reaction rate and are used up
C enzymes only work outside living organisms
D enzymes work by raising activation energy

42. An enzyme-controlled reaction is carried out at 37 °C and pH 7. The enzyme is then placed at 70 °C and pH 7.
    What is most likely to happen?

A enzyme activity increases forever
B enzyme may denature because of high temperature
C substrate becomes denatured but enzyme does not
D pH becomes the only limiting factor

43. In an investigation using catalase and hydrogen peroxide, which result indicates the fastest reaction?

A 10 cm³ oxygen collected in 20 seconds
B 10 cm³ oxygen collected in 50 seconds
C 5 cm³ oxygen collected in 20 seconds
D 2 cm³ oxygen collected in 10 seconds

44. Which enzyme is used to convert starch into sugars in industry?

A amylase
B protease
C lipase
D lactase

45. A student says, “Enzymes are specific because they are all the same shape.”
    Which correction is best?

A enzymes are specific because each type has a particular active site shape
B enzymes are specific because they are all made of glucose
C enzymes are specific because substrates are all identical
D enzymes are specific because products never leave active sites

46. Which factor explains why enzyme activity may rise between 10 °C and 35 °C?

A more frequent successful collisions between enzyme and substrate
B permanent destruction of active sites
C lower kinetic energy of substrate molecules
D complete removal of enzyme from solution

47. A sample of enzyme is heated to 65 °C and loses activity. Extra substrate is added but the reaction still does not speed up.
    What does this suggest?

A substrate concentration was the only limiting factor
B enzyme active sites have been denatured
C the enzyme has become more specific
D all product has turned back into substrate

48. Which statement correctly describes intracellular enzymes?

A enzymes that work inside cells
B enzymes that only work inside test-tubes
C enzymes that are found only in viruses
D enzymes that digest food outside the body only

49. Which statement about immobilised enzymes is correct?

A they are attached to a support and can be reused
B they are boiled before every reaction to increase activity
C they are changed into substrates during the reaction
D they cannot be used in industry

50. Immobilised lactase is used in a column to produce lactose-free milk.
    Which advantage is most likely?

A lactase mixes into the milk and must be replaced each time
B lactase remains in the column and can be reused
C lactase becomes denatured immediately at room temperature
D lactose is converted into starch and cellulose

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. Answer: B
   A is wrong because substrates are not denatured; enzymes can be denatured.
   B is correct because at high substrate concentration, all active sites are occupied, so adding more substrate no longer increases the rate.
   C is wrong because enzymes are not used up in reactions.
   D is wrong because there is no evidence that product molecules are acting as inhibitors.

2. Answer: B
   A is wrong because enzymes are not alive, so they cannot be “killed.”
   B is correct because extreme pH can permanently change the active site shape, so the substrate no longer fits well.
   C is wrong because pH does not permanently make the substrate smaller.
   D is wrong because enzyme concentration did not increase.

3. Answer: B
   A is wrong because one enzyme cannot catalyse all reactions.
   B is correct because enzyme specificity depends on the active site being complementary to a particular substrate.
   C is wrong because active sites do not randomly change until a substrate fits.
   D is wrong because enzymes are not used up by substrates.

4. Answer: B
   At 20 °C, rate = 5 cm³ ÷ 80 s = 0.0625 cm³/s.
   At 30 °C, rate = 5 cm³ ÷ 40 s = 0.125 cm³/s.
   A is wrong because the rate does not halve.
   B is correct because the rate doubles.
   C is wrong because oxygen production is faster at 30 °C.
   D is wrong because catalase is clearly still active at 30 °C.

5. Answer: C
   A is wrong because amylase digests starch, not protein.
   B is wrong because protease digests protein, not starch.
   C is correct because lipase digests lipids.
   D is wrong because maltase digests maltose, not cellulose.

6. Answer: B
   A is wrong because low temperature slows enzyme activity but does not usually denature enzymes.
   B is correct because at 20 °C molecules have less kinetic energy than at 40 °C, so there are fewer successful collisions.
   C is wrong because above the optimum, high temperature may denature the enzyme.
   D is wrong because the substrate does not become complementary at 100 °C.

7. Answer: B
   A is wrong because 10 °C slows the reaction due to fewer collisions.
   B is correct because 35 °C is likely close to a suitable enzyme temperature, with active enzyme and substrate present.
   C is wrong because boiled enzyme is denatured.
   D is wrong because there is no substrate, so product cannot form.

8. Answer: B
   A is wrong because starch is not being produced.
   B is correct because iodine changes from blue-black to brown when starch is broken down.
   C is wrong because amylase digests starch, not protein.
   D is wrong because reducing sugars are not denatured.

9. Answer: B
   A is wrong because denaturation usually happens at high temperature or extreme pH, not always low temperature.
   B is correct because denaturation changes the shape of the active site.
   C is wrong because denaturation reduces or destroys enzyme activity.
   D is wrong because denaturation is not about substrate concentration becoming zero.

10. Answer: B
    A is wrong because starch would need amylase and cellulose would need cellulase.
    B is correct because protease digests protein stains such as blood, and lipase digests fat stains.
    C is wrong because salt and water are not digested by enzymes.
    D is wrong because these enzymes do not mainly remove DNA or mineral ions.

11. Answer: B
    A is wrong because pectinase does not break down protein.
    B is correct because pectinase breaks down pectin in plant cell walls, increasing juice yield and making filtration easier.
    C is wrong because yeast enzymes ferment glucose to ethanol.
    D is wrong because pectinase does not denature cellulose into amino acids.

12. Answer: B
    A is wrong because substrate molecules do not stop moving at high temperature.
    B is correct because high temperature denatures the enzyme by changing the active site shape.
    C is wrong because enzymes are not used up.
    D is wrong because product molecules do not become starch because of temperature.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Answer: D
    A is wrong because pH directly affects enzyme activity and active site shape.
    B is wrong because temperature directly affects collision rate and denaturation.
    C is wrong because enzyme concentration affects the number of active sites available.
    D is correct because the colour of the test-tube does not directly affect enzyme activity.

14. Answer: B
    A is wrong because pH 2 is too acidic for human salivary amylase.
    B is correct because salivary amylase works best around neutral pH and body temperature.
    C is wrong because pH 9 is too alkaline for salivary amylase.
    D is wrong because 80 °C would denature the enzyme.

15. Answer: B
    A is wrong because enzymes do not change the final possible amount of product.
    B is correct because enzymes lower activation energy by providing an alternative reaction pathway.
    C is wrong because enzymes do not work by increasing pH.
    D is wrong because enzymes do not permanently combine with the substrate.

16. Answer: C
    A is wrong because cooling does not reverse denaturation caused by boiling.
    B is wrong because enzymes can lose activity below 100 °C too if the temperature is high enough.
    C is correct because boiling can permanently change the active site shape.
    D is wrong because boiling does not make all substrates insoluble.

17. Answer: B
    A is wrong because the substrate is the “key.”
    B is correct because the active site is the “lock” into which the substrate fits.
    C is wrong because the product is formed after the reaction.
    D is wrong because pH is a condition, not part of the lock-and-key model.

18. Answer: B
    A is wrong because low temperature does not usually permanently destroy active sites.
    B is correct because low temperature gives enzyme and substrate molecules less kinetic energy, causing fewer successful collisions.
    C is wrong because enzyme molecules do not become smaller.
    D is wrong because the substrate does not change into an inhibitor.

19. Answer: A
    A is correct because starch disappearing fastest means enzyme activity is highest.
    B is wrong because 60 seconds is slower than 20 seconds.
    C is wrong because 120 seconds is even slower.
    D is wrong because no disappearance means little or no enzyme activity.

20. Answer: B
    A is wrong because low temperature does not denature enzymes.
    B is correct because low temperature slows activity, while high temperature may denature enzymes.
    C is wrong because low temperature does not increase active site shape change.
    D is wrong because low temperature does not break peptide bonds and high temperature does not freeze enzymes.

21. Answer: A
    A is correct because lactase breaks lactose into glucose and galactose.
    B is wrong because amylase breaks starch into maltose.
    C is wrong because protease breaks protein into amino acids.
    D is wrong because lipase breaks lipid into fatty acids and glycerol.

22. Answer: B
    A is wrong because enzymes have optimum temperatures and do not work equally well at all temperatures.
    B is correct because enzymes in biological washing powders digest biological stains such as protein and fat.
    C is wrong because enzymes are not used up after one reaction.
    D is wrong because washing powder enzymes are designed to work around washing conditions, not only strongly acidic conditions.

23. Answer: C
    A is wrong because keeping enzyme concentration the same makes the test fair.
    B is wrong because equal substrate volumes help control variables.
    C is correct because changing both pH and temperature means you cannot tell which factor caused the change.
    D is wrong because measuring after the same time improves fairness.

24. Answer: A
    A is correct because substrate Y has a different shape and cannot fit into the active site.
    B is wrong because kinetic energy does not explain enzyme specificity.
    C is wrong because substrate size alone is not the key issue; shape matters.
    D is wrong because there is no evidence substrate Y has already become product.

25. Answer: B
    A is wrong because a changed enzyme shape usually makes binding harder, not easier.
    B is correct because a non-competitive inhibitor changes enzyme shape, including the active site, reducing activity.
    C is wrong because inhibitor binding does not increase enzyme concentration.
    D is wrong because the product does not become the new substrate.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. Answer: B
    A is wrong because decreasing substrate concentration gives the inhibitor less competition.
    B is correct because increasing substrate concentration makes it more likely substrate molecules occupy active sites instead of the competitive inhibitor.
    C is wrong because boiling denatures the enzyme.
    D is wrong because lowering enzyme concentration to zero stops the reaction.

27. Answer: C
    A is wrong because optimum pH gives maximum activity.
    B is wrong because optimum temperature gives maximum activity.
    C is correct because a very different pH can change the active site shape and denature the enzyme.
    D is wrong because slightly increasing substrate concentration does not denature an enzyme.

28. Answer: C
    A is wrong because amylase does not produce amino acids.
    B is wrong because amylase does not produce fatty acids.
    C is correct because starch is broken down into maltose, a reducing sugar, which gives a positive Benedict’s test.
    D is wrong because starch itself does not give a positive Benedict’s test.

29. Answer: B
    A is wrong because the active site is part of the enzyme, not the substrate.
    B is correct because the active site is the region of the enzyme where the substrate binds.
    C is wrong because the product is released after the reaction.
    D is wrong because optimum temperature is a condition, not the active site.

30. Answer: B
    A is wrong because the optimum pH alone does not prove the exact enzyme identity.
    B is correct because different enzymes have different active site structures suited to different pH conditions.
    C is wrong because pH optimum does not mean Y is faster than X at every temperature.
    D is wrong because enzymes working in alkaline conditions can still be proteins.

31. Answer: B
    A is wrong because colour of lipid before enzyme is not a good measure of lipase activity.
    B is correct because lipase produces fatty acids, causing pH to fall; time taken for a fixed pH drop measures rate.
    C is wrong because mass of the test-tube is irrelevant.
    D is wrong because water volume after the reaction does not measure lipase activity.

32. Answer: B
    A is wrong because more enzymes do not compete in a way that reduces rate when substrate is high.
    B is correct because doubling enzyme concentration provides more active sites, so rate increases initially.
    C is wrong because high substrate concentration does not denature enzymes.
    D is wrong because enzymes are not used up.

33. Answer: B
    A is wrong because pasteurisation is heat treatment to kill microorganisms.
    B is correct because fermentation uses enzymes from microorganisms such as yeast to convert sugars into ethanol.
    C is wrong because filtration separates solids from liquids.
    D is wrong because emulsification breaks large fat droplets into smaller droplets.

34. Answer: B
    A is wrong because stains do not become enzymes.
    B is correct because high temperature such as 90 °C may denature enzymes in biological washing powders.
    C is wrong because proteins do not become carbohydrates.
    D is wrong because lipids do not turn into starch.

35. Answer: A
    A is correct because lactase is used to make lactose-free milk.
    B is wrong because pectinase is used in fruit juice production, not leather softening.
    C is wrong because protease digests protein, not starch.
    D is wrong because lipase digests lipids and is not used for DNA copying.

36. Answer: A
    A is correct because if the enzyme is not denatured and product formation stops, the substrate has most likely been used up.
    B is wrong because enzymes do not become carbohydrates.
    C is wrong because the question says the enzyme is not denatured.
    D is wrong because products do not change into enzymes.

37. Answer: C
    A is wrong because enzyme activity does not increase continuously with pH.
    B is wrong because it does not simply decrease continuously either.
    C is correct because most enzymes have an optimum pH, with lower activity on either side.
    D is wrong because activity is highest, not zero, at optimum pH.

38. Answer: A
    A is correct because the higher pH in the small intestine can change the active site shape of a stomach protease.
    B is wrong because the enzyme does not become a lipid.
    C is wrong because the substrate does not become another enzyme.
    D is wrong because enzymes are not used up by hydrochloric acid.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Answer: B
    A is wrong because enzymes are not permanently changed into products.
    B is correct because after the reaction, products leave the active site and the enzyme can be reused.
    C is wrong because products do not remain permanently attached.
    D is wrong because products do not normally denature enzymes at optimum pH.

40. Answer: A
    A is correct because only pH is changed while temperature and amylase concentration are controlled.
    B is wrong because too many variables are changed.
    C is wrong because pH is not being changed, so it cannot test the effect of pH.
    D is wrong because different iodine volumes and temperatures make the comparison unfair.

41. Answer: A
    A is correct because enzymes increase reaction rate and are not used up.
    B is wrong because enzymes do not decrease reaction rate and are not used up.
    C is wrong because enzymes work inside and outside living organisms.
    D is wrong because enzymes lower activation energy, not raise it.

42. Answer: B
    A is wrong because enzyme activity does not increase forever.
    B is correct because 70 °C is high enough to denature many enzymes.
    C is wrong because enzymes, not just substrates, can be denatured.
    D is wrong because temperature is clearly a limiting/damaging factor here.

43. Answer: A
    A is correct because rate = 10 cm³ ÷ 20 s = 0.5 cm³/s, the highest rate.
    B is wrong because 10 cm³ ÷ 50 s = 0.2 cm³/s.
    C is wrong because 5 cm³ ÷ 20 s = 0.25 cm³/s.
    D is wrong because 2 cm³ ÷ 10 s = 0.2 cm³/s.

44. Answer: A
    A is correct because amylase converts starch into sugars.
    B is wrong because protease digests protein.
    C is wrong because lipase digests lipids.
    D is wrong because lactase digests lactose.

45. Answer: A
    A is correct because each enzyme type has a specific active site shape.
    B is wrong because enzymes are proteins, not glucose.
    C is wrong because substrates are not all identical.
    D is wrong because products leave the active site after the reaction.

46. Answer: A
    A is correct because increasing temperature up to the optimum increases kinetic energy, causing more frequent successful collisions.
    B is wrong because active sites are not permanently destroyed between 10 °C and 35 °C for most enzymes.
    C is wrong because kinetic energy increases, not decreases.
    D is wrong because enzyme is not removed from the solution.

47. Answer: B
    A is wrong because adding more substrate does not help, so substrate concentration is not the limiting factor.
    B is correct because heating to 65 °C may denature active sites, so extra substrate cannot fit.
    C is wrong because denaturation does not make enzymes more specific.
    D is wrong because product does not turn back into substrate in this situation.

48. Answer: A
    A is correct because intracellular enzymes work inside cells.
    B is wrong because intracellular does not mean only inside test-tubes.
    C is wrong because viruses do not have normal cellular enzymes in the same way.
    D is wrong because enzymes that digest food outside cells are extracellular enzymes.

49. Answer: A
    A is correct because immobilised enzymes are attached to a support and can be reused.
    B is wrong because boiling would denature many enzymes.
    C is wrong because enzymes are not changed into substrates.
    D is wrong because immobilised enzymes are very useful in industry.

50. Answer: B
    A is wrong because immobilised lactase does not mix freely into the milk; that is the point, boss move.
    B is correct because lactase remains in the column and can be reused, reducing cost and contamination.
    C is wrong because lactase does not immediately denature at room temperature.
    D is wrong because lactase converts lactose into glucose and galactose, not starch and cellulose.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.