Question 1 Medium
What is the approximate optimum temperature of a human enzyme in °C?
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Answer: 37
- Human body temperature is about 37.
- Enzymes work best at this.
Enzymes: GCSE Combined Science Biology practice questions
A second set of questions on enzymes. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
Which organ makes hydrochloric acid, giving a low pH for protease?
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Answer: stomach
- The protease there needs pH 2.
- The stomach makes acid.
Question 3 Medium
Starch takes 125 s to break down. Calculate the rate using rate = 1000 ÷ time.
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Answer: 8
- Divide 1000 by 125.
- 1000 ÷ 125 = 8.
Question 4 Medium
When an enzyme is denatured, what changes about its active site?
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Answer: shape
- Bonds in the enzyme break.
- So the active site changes shape.
Question 5 Hard
Name the term for a substance that speeds up a reaction without being used up.
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Answer: catalyst
- The substance is not changed.
- It is a catalyst.
Question 6 Hard
Amylase breaks starch down. Name the product of this reaction.
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Answer: sugar
- Starch is a polymer of glucose.
- It is broken into sugars.
Question 7 Hard
Which variable is changed in the amylase and pH practical?
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Answer: pH
- The independent variable is the one you change.
- In this practical it is pH.
Question 8 Hard
At pH 4, amylase digests starch in 80 s. At pH 7 it takes 20 s. Calculate the rate at pH 7 using rate = 1000 ÷ time.
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Answer: 50
- Rate = 1000 ÷ 20.
- The rate is 50.
Question 9 Medium
At a high substrate concentration the rate of an enzyme reaction stops rising. Why? All the … are in use.
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Answer: active sites
- Each enzyme has a limited number of active sites.
- When all are busy the rate cannot rise.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is a catalyst?
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A substance that speeds up a reaction and is not used up.
Check 2
What is an enzyme?
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A protein that acts as a biological catalyst.
Check 3
What is the active site?
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The region of an enzyme with a special shape where the substrate fits.
Check 4
What is a substrate?
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The molecule that an enzyme acts on.
Check 5
What does the lock and key model say?
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The substrate fits the shape of the active site like a key in a lock.
Check 6
Why are enzymes specific?
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Only one shape of substrate fits the active site.
Check 7
What is the optimum temperature for most human enzymes?
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About 37 °C.
Check 8
What does denatured mean?
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The active site has changed shape so the enzyme no longer works.
Check 9
What can denature an enzyme?
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A temperature that is too high, or a pH that is too high or too low.
Check 10
Can denaturing be reversed?
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No.
Check 11
What is the optimum pH of stomach protease?
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About pH 2.
Check 12
What is the optimum pH of most enzymes?
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About pH 7.
Check 13
Why does a higher temperature increase the rate up to the optimum?
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Enzyme and substrate move faster and collide more often.
Check 14
What colour does iodine turn with starch?
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Blue-black.
Check 15
In the amylase practical, what shows that the starch has been broken down?
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The iodine stays orange-brown and no longer turns blue-black.
Check 16
What equation is used for the rate of an enzyme reaction from a time?
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rate = 1000 ÷ time in seconds.
Check 17
Is an enzyme used up in a reaction?
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No. It is not changed, so it can be used again.
Check 18
What are the products of a reaction?
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The new substances that are made.
Check 19
What does it mean to say an enzyme is specific?
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It works on only one kind of substrate.
Check 20
What happens to the rate above the optimum temperature?
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It falls sharply because the enzyme is denatured.
Check 21
What does a buffer do in the amylase practical?
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It keeps the pH steady at a set value.
Check 22
What does amylase break starch down into?
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Sugar.
Check 23
Why is a water bath used in the amylase practical?
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To keep the temperature constant so the test is fair.
Check 24
Does a shorter time for starch to disappear mean a faster or slower rate?
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A faster rate.
Check 25
What is the optimum pH of enzymes in the small intestine?
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About pH 8 to 9, which is alkaline.
Check 26
Why is denaturing not the same as killing an enzyme?
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Enzymes are not alive. Their shape changes.
Check 27
What happens to the rate of an enzyme reaction as substrate concentration rises?
Show answer
The rate rises, then levels off when all the active sites are in use.
Check 28
Name three types of molecule that enzymes help to build.
Show answer
Carbohydrates, proteins and lipids.
Keep going with Enzymes
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