O LEVEL BIOLOGY/5090 Where passion meets education
3(a) Define catalyst as a substance that speeds up a chemical reaction and is not changed by the
reaction
Properties Enzyme
Proteins that act as Biological catalyst/ speeds up reaction.
Enzymes are specific to their substrate
Work best in a narrow range of pH and Temperature called Optimum
They are not altered at the end of a chemical reactions
Catalyses reversible reactions
Question 1
Question 2
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
3(b) Define enzymes as proteins that function as biological catalysts
Question 21
3(c) Explain enzyme action in terms of the ‘lock and key’ hypothesis
Enzyme Action explained by Lock and Key model
Enzyme has an active site of specific shape. Only a substrate of complementary shape to the active
site can bind into the active site to make a temporary ES-Complexes (enzyme substrate complex).
The substrate is a key and enzyme is a lock according to the lock and key hypothesis. The enzyme
changes the substrate to a product.
Why does a product readily come out of the active site?
The product does not have the shape complementary to the active site so it can not remain bound
in the active site.
Page 2 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Page 3 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Question
Question 22
3(d) Investigate and describe the effects of temperature and pH on enzyme activity
Enzyme Activity
Effect of temperature on the rate of an enzyme action
Investigate
Take three test tubes
Label them A,B and C
Add same volume of Hydrogen peroxide in each
Maintain the pH same
Place them at different temperatures
Tube A at room temperature
Tube B in an Ice cold water
Tube C in boiling water
Add same volume of catalase into each test tube
Record the volume of oxygen released
Repeat the experiment
Describe the effect of temperature on the enzyme activity
Page 4 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Increase of temperature increases rate of enzyme action.
At optimum temperature the rate is maximum
Further increase of temperature decrease the rate of an enzyme action.
Explain
Increasing temperature increase kinetic energy
More enzyme substrate collisions.
More ES complexes formed
More products formed
At higher temperature above optimum
Enzyme denature
Shape of active site changes
Substrate does not fit into the active site
So it is forming less product
Page 5 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Page 6 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Page 7 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Page 8 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Effect of pH on the rate of an enzyme action
Investigate
Take three test tubes
Label them A,B and C
Add same volume of Hydrogen peroxide in each
Maintain the temperature same
Place an acid or alkali to vary the pH
Tube A - low pH
Tube B - neutral
Tube C - high pH
Add same volume of catalase into each test tube
Record the volume of oxygen released
Repeat the experiment
Describe the effect of change of pH on the rate of an enzyme action
Enzymes work best in a narrow range of pH only.
Page 9 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Explain the effect of pH on the rate of an enzyme action
Change of pH changes the shape of enzyme molecule as they are made of proteins. As pH
changes the shape of an active site so a substrate can no longer bind into it and converted into
products, it slows the rate of an enzyme action.
Question 23
Question 24
Page 10 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
O LEVEL BIOLOGY/5090 Where Passion Meets Education, solehri.com
Page 11 of 11
ZAFAR SULEHRI phone; 03218800091 eMail; zafar@solehri.com web; solehri.com
