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5.3Enzymes

Investigating enzyme activity — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 9 parts Lesson 3 of 3 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision
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Lesson summary

5.3 Investigating enzyme activity — IGCSE BIOLOGY notes: Plan and describe investigations of the effect of temperature and pH on amylase and interpret the results.Starch test — Iodine solution stays orange-brown when no starch is present and turns blue-black when starch remains.A…

  • Shorter time
  • Best condition
  • Explaining a low rate
  • Independent variable
  • Controlled variables
  • Control methods

Part 1 of 7Principle

Starch test
  • Iodine solution stays orange-brown when no starch is present and turns blue-black when starch remains.
Amylase
  • It breaks down starch, so the time until iodine stops turning blue-black measures its activity.
Rate
  • The quicker the reaction is completed, the faster the enzyme is working.

Part 2 of 7Effect of temperature on amylase

1
Heat the starch solution to a set temperature.
2
Place iodine solution in the wells of a spotting tile.
3
Add amylase to the starch solution and mix well.
4
Every minute, add a droplet of the mixture to a new well of iodine.
5
Continue until the iodine stops turning blue-black.
6
Record the time taken for the reaction to finish.
7
Repeat at different temperatures.

Part 3 of 7Effect of pH on amylase

1
Place single drops of iodine solution in rows on the tile.
2
Label a test tube with the pH to be tested.
3
Use a syringe to place 2 cm3 of amylase in the tube.
4
Add 1 cm3 of buffer solution with a syringe.
5
Add 2 cm3 of starch solution and start the stopwatch while mixing.
6
After 10 seconds, place one drop of the mixture on the first drop of iodine.
7
Repeat every 10 seconds until the iodine stays orange-brown.
8
Repeat at other pH values.

Part 4 of 7Interpreting results

Shorter time
  • The shorter the time for iodine to stay orange-brown, the faster all the starch was digested.
Best condition
  • The temperature or pH with the shortest time is closest to the optimum.
Explaining a low rate
  • At low temperature there is less kinetic energy and fewer collisions;
    • at high temperature or extreme pH the enzyme is denatured.

Part 5 of 7Fair test

Independent variable
  • Only the temperature or the pH is changed.
Dependent variable
  • The time for the starch to disappear is measured.
Controlled variables
  • Volumes and concentrations of enzyme and starch are kept the same, and pH is fixed when testing temperature.
Control methods
  • A water bath controls the temperature and buffer solutions control the pH.

Part 6 of 7Catalase as an alternative enzyme

Reaction
  • Catalase breaks down hydrogen peroxide into water and oxygen.
Measurement
  • The volume of oxygen collected in a fixed time, or the bubbles per minute, shows the rate.
Control
  • A tube with boiled enzyme shows that the change is caused by active enzyme.

Part 7 of 7More from the specification

More from the specification
Enzymes
  • Enzymes biological catalysts that speed reactions without being used up.
Specificity
  • Specificity the shape of the active site is complementary to its substrate, as in the lock and key model.
Enzyme-substrate complex
  • Enzyme-substrate complex the substrate binds, is converted to products, and the enzyme is released unchanged.
Investigating activity
  • Investigating activity measure rate of product formation as temperature, pH or substrate concentration is changed.
Denaturation
  • Denaturation high temperature or extreme pH alters the active site shape so the enzyme no longer works.
Substrate
  • The molecule that an enzyme acts on and which binds to the active site.
Specificity
  • Each enzyme catalyses only one reaction because only a complementary substrate fits.
Specific
  • Able to act on only one type of substrate.
Complementary
  • Having a matching shape.
Catalyst
  • A substance that increases the rate of a chemical reaction and is not changed by the reaction.
Product
  • The molecule(s) formed from the substrate in an enzyme-catalysed reaction.
Protein
  • A long chain of amino acids containing carbon, hydrogen, oxygen and nitrogen.
Enzyme-substrate complex
  • The temporary structure formed when a substrate binds to an enzyme's active site.

Key terms

TermMeaning
Buffer solutionA solution that holds the pH at a fixed value.
Spotting tileA tile with wells used to test small samples with iodine.
Independent variableThe factor deliberately changed in an investigation.
Dependent variableThe factor measured to see the effect of the change.
Controlled variableA factor kept the same in every trial.
AmylaseAn enzyme that breaks down starch.

Avoid these mistakes

1
Changing temperature and pH together — change only one variable and keep the rest constant.
2
Starting the timer after mixing at the wrong temperature — warm the solutions to the test temperature first.
3
Saying a longer time means a faster enzyme — a shorter time means faster activity.
4
Measuring by eye without a stated end point — use the first drop that stays orange-brown.

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