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