Biology Paper 3 (Practical), WASSCE (PC), 2020

Question 3


The diagrams below are illustrations of the lock and key theory of enzyme action. Study them and answer questions 3 (a) to 3 (e).

 

  1. (a) (i) Name the parts labeled I and II.                                                               [2 marks]

(ii) Give three reasons why a small amount of a digestive enzyme is required to catalyze a reaction of a large amount of food substance.                                                    [3 marks]

  1. Complete the table below.

Food substrate

Enzyme

Part labeled II

 

Ptyalin

 

 

 

Amino acids

Fats and oil

 

 

 

Pancreatic amylase

 

[8 marks]

  1. (i) Give two reasons why enzymes are specific in action.                              [2 marks]

(ii) List three factors that affect the activities of digestive enzymes.               [3 marks]
(iii) List three uses of enzymes in industries.                                                [3 marks]

  1. Name the major constituents of enzymes.                                                    [1 mark]
  2. Complete the table below on the effect of varying temperature on digestive enzymes.
  3.  

Range of temperature

Effect on digestive enzyme

Reason for the effect

5oC - 10oC

 

 

36oC - 37oC

 

 

40oC - 45oC

 

 

95oC - 100oC

 

 

                                                                                                                        [8 marks]

Observation

 

Majority of candidates could not use the knowledge of the characteristics of enzymes to answer the question. They displayed very little knowledge of the topic.

 

Some candidates could not name the parts labelled I and II, despite food substrate and digestive enzyme were both labelled in the diagram.

 

Many candidates could not give reasons why a small amount of a digestive enzyme is required to catalyze a reaction of a large amount of food substrate.

 

Some candidates were able to complete the table on food substrates and the enzyme that catalyze them. While some could not fill the space for Part labelled II.

The major strength of candidates was in stating the uses of enzymes in industries.

 

Only a few candidates were able to complete the table on the effect of varying temperatures on enzymes.

 

Majority could not use their knowledge of effect of temperature on enzymes to answer the question.

 

The expected answers are:
                                                           
3. (a) (i) Parts labelled
I       -     Active site;                       
II      -     Products.                                  

                                                    
Note: spellings must be correct to score.

 

(ii) Reason a small amount of digestive enzymes is required to catalyse a large amount of food substrate

  • Digestive enzymes are biological catalysts;
  • needed in small amounts to speed up the rate of digestion;
  • and they remain chemically unchanged;
  • hence the enzyme can be used over and over again.                

  (b)      Process of digestion

 

Food substrate

Enzyme

Part labelled II

(Cooked) starch

 

Maltose

Protein

Renin/pepsin/trypsin

 

 

Lipase

Fatty acids and glycerol/carboxylic
acid and glycerol
(both must be written to score)

Starch

 

Maltose

 

  (c)   (i) Reasons enzymes are specific in action

  • Enzymes normally have their active site;
  • which has a shape that fits perfectly into a substrate of the same shape;
  • an enzyme will not fit into a differently shaped substrate/lock and key.                                                                                                                        

         (ii) Factors that affect the activities of enzymes

  • Temperature/heat;
  • pH;
  • concentration of enzyme;
  • concentration of substrate;
  • presence of any inhibitors/activators.                                          

        (iii) Uses of enzymes in industries

  • in brewing/fermentation;
  • in biogas production;
  • in baking;
  • in the production of insulin/renin;
  • in textile industries;
  • in pharmaceuticals/cosmetics;
  • in production of detergents/surfactants;
  • in dairy/cheese-making;
  • in extracting fruit juice;
  • in tanning leather.                                                                        

(d)       Chemical constituents of enzymes
Protein                                                                                                            

(e) Effect of varying temperature on digestive enzymes

 

Range of temperature

Effect on digestive enzymes

Reason for the effect

5oC - 10oC

Very slow rate of reaction

Enzyme is inactivated

36oC - 37oC

Works best/optimum action

Activated/optimum temperature range

40oC - 45oC

Slow rate of reaction/no action/
enzyme is inactive

The enzyme is denatured/enzyme is
destroyed/killed

95oC - 100oC

Enzyme is inactive/no action

The enzyme is denatured/enzyme is
destroyed/killed