iGCSE Biology (0610)-5.1 Enzymes – iGCSE Style Questions Paper 4

Question

The enzyme lactase digests lactose into simple sugars.
    (a) Define the term enzyme.

           

   (b) Describe how you could test for the presence of reducing sugars.
           State what you would observe if the result was positive.

         

   (c) Fig. 9.1 shows the results of an investigation into the effect of pH on the activity of the
          enzyme lactase.

     

        (i) Use Fig. 9.1 to determine the optimum pH of lactase.

             

      (ii) Describe the effect of the changes in pH on the activity of lactase.

             

 (d) Enzymes are involved in chemical digestion.
        Explain the role of teeth in physical digestion.

       

Answer/Explanation

Ans:

 

Question

Fig. 7.1 shows the human alimentary canal and some of the organs associated with it.

(a) Use letters from Fig. 7.1 to identify which structure carries out a particular function. Write your answers in Table 7.1.

(b) Name the process which moves food from D to F.
…………………………………………………………………………………………………………………………….

(c) A student investigated the digestion of fats by the enzyme lipase. He found that as lipase digested the fats, the pH of the solution changed from pH 8 to pH 6.

(i) Explain why the digestion of fats changed the pH of the solution.
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(ii) Fig. 7.2 shows three test-tubes that were set up for this experiment.

The time taken for the indicator to change colour after the lipase was added was measured. The results are shown in Table 7.2.

Explain why the indicator in test-tube B changes colour much faster than the indicator in test-tube A.
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(d) Some biological washing powders contain lipase. Instructions on the packet state that biological washing powders should be used in warm water but not in very hot water. Explain why warm water should be used instead of very hot water. Use Fig. 7.2 and Table 7.2 to help with your answer.
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(e) Eating too much fat can be harmful. State one way in which too much fat can be harmful to human health.
…………………………………………………………………………………………………………………………………………………………….

Answer/Explanation

Ans:

(a)

(b) peristalsis;

(c) (i) fat digestion produces fatty acids (and glycerol);
           fatty acids lower pH;

      (ii) (B contains bile) which emulsifies fats;
             increases surface area for enzyme/ lipase action/AW;
             (so) fatty acids are produced more quickly / more rapid fat digestion;
             colour of indicator changes more quickly;

(d) hot water could denature the enzyme;
      changes the shape of active site of enzyme/ enzyme
      inactive;
      tube C shows that boiled enzyme does not digest fats;

(e) obesity;
      (which) leads to joint damage;
      blockage of blood vessels / heart disease/CHD/atherosclerosis / cardiac arrest;
      high blood pressure;
      type 2 diabetes;
      cancer;
      AVP;

Question

(a)     The digestive system produces enzymes.

Define the term enzyme.

(b)     Fig. 8.1 shows how the reaction rates of two different enzymes, L and M, vary when the pH changes.

Fig. 8.1

Use Fig. 8.1 to state the pH at which each of these enzymes work the fastest.

pH for enzyme L: ………………………………
pH for enzyme M: ……………………………..

(c)     Table 8.1 lists the names of three enzymes found in the alimentary canal.

Complete Table 8.1 by writing in the names of the substrate and one end-product for each enzyme.

Choose your answers from the list.

Table 8.1

Answer/Explanation

Ans:

(a)     protein ;

acts as a (biological) catalyst ;

speeds up/ alters rate of (chemical) reaction or is not altered/ used up by reaction ;

(b)      L:  pH 2 ;

M:  pH 8 ;

(c)                         

Question

(a) All organisms depend on enzymes.
            Define the term enzyme and describe the function of enzymes in living organisms.

         

    (b) Samples of an amylase enzyme were incubated with starch at different temperatures.
           The rate of starch digestion in each sample was recorded and points plotted on the
           graph shown in Fig. 8.1.

         

        (i) Complete this line graph to show the effect of temperature on rate of digestion of
               starch by the amylase enzyme by adding the most appropriate line to Fig. 8.1.
                                                                                                               Put your line on Fig. 8.1.                [1]
       (ii) Using your graph estimate the optimum temperature for this enzyme.

                 

       (iii) Suggest the rate of starch digestion at 37 oC.

                 

        (iv) Describe the effect of temperature on the rate of starch digestion.

               

         (v) The enzymes originally incubated at 15oC and 75oC did not digest any starch.
                 These samples were later incubated at the optimum temperature.
                 Predict what results could be expected in each sample and suggest reasons for
                 your predictions.

               

Answer/Explanation

Ans:

 

Question

Biological washing powders contain enzymes that break down food stains.
(a) Complete Table 2.1 by naming the enzymes that break down three substances in food stains
and by stating the product or products.

Some students compared how effective biological and non-biological washing powders are at
removing stains at temperatures between 10 °C and 60 °C.
• Pieces of stained cloth were washed using two different washing powders.
• The degree of stain removal was measured by using a light meter to record the
percentage of light reflected from the cloth.
• A light meter gave a value of 100% when the cloth was completely clean.
• Any stain left on the cloth reduced the percentage of light reflected.
The results of the students’ investigation are shown in Fig. 2.1.

(b) Compare the effectiveness of the two washing powders at removing stains.
Use the information in Fig. 2.1 in your answer.
(c) The students suggested that the enzymes in the biological washing powder were denatured
at high temperatures.
Explain why enzyme molecules do not function when they are denatured.
(d) Forensic scientists often try to find DNA on items of stained clothing. The DNA can be used to
identify individual people.
Suggest why DNA can be used to identify individual people.

Answer/Explanation

Answer:

(a) one mark per row:

(b) any four from:
biological washing powder is more effective, at lower temperatures / between 10 °C and 40 °C / 10 °C and 43 °C ;
comparative data quote for the difference at a stated temperature ;
biological washing powder removes all stain between 30 °C and 40 °C ;
non-biological removes all stain only at 60 °C ;
effectiveness is similar, at high temperatures / between 50 and 60 °C ;
same trend, below 30 °C / at low temperatures / from 50 °C ;
idea of effectiveness of biological washing powder decreases between 40 °C and 44 °C, no such decrease for non-
biological washing powder ;

(c) any two from:
active site changes shape ;
substrate no longer fits into, enzyme / active site ;
no enzyme-substrate complex / no successful collisions ;

(d) any two from:
individual people have, different / unique, DNA ;
DNA has genes or alleles have, sequences of bases ;
AVP ;

Question

Young mammals that are orphaned can be bottle-fed.
     Fig. 6.1 shows a newborn tiger cub sucking on a bottle.

         

(a) (i) Sucking is an example of an involuntary action observed in newborn mammals.
              State the name given to involuntary actions.
              ………………………………………………………………………………………………………………………[1]
      (ii) Describe the advantages of breast-feeding compared with bottle-feeding.
              ………………………………………………………………………………………………………………………….
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             ………………………………………………………………………………………………………………………[4]

(b) The digestive systems of young mammals are not fully developed.
        Enzymes such as amylase, maltase and protease are often added to baby food to aid
        chemical digestion.
       (i) Complete Table 6.1 by stating the substrate and product(s) for each enzyme reaction.

           

                                                                                                                                                                                                                                              [3]
     (ii) Suggest why the temperature of baby food must be controlled when the enzymes are
             added.
               ………………………………………………………………………………………………………………………….
               ………………………………………………………………………………………………………………………….
               ………………………………………………………………………………………………………………………[2]
     (iii) State one other condition that must also be controlled to optimise enzyme activity.
               ………………………………………………………………………………………………………………………[1]

▶️Answer/Explanation

Ans:

Question

(a) (i) Alcohol can be made by the microorganism yeast.
State the balanced chemical equation for the production of alcohol by yeast.
……………………………………………………………………………………………………………………… [2]

(ii) Name the organ that breaks down alcohol in the human body.
………………………………………………………………………………………………………………………  [1]

(b) Fig. 5.1 shows a computer model of the enzyme alcohol dehydrogenase, which is the enzyme responsible for breaking down alcohol.

Enzymes have a specific three dimensional shape.
Explain why the shape of an enzyme is important.
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(c) Table 5.1 shows the enzyme activity of alcohol dehydrogenase at different temperatures.
                                        Table 5.1

(i) The information in Table 5.1 shows that an increase in temperature increases the activity
of alcohol dehydrogenase.
Explain why an increase in temperature causes an increase in enzyme activity.
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(ii) State one factor, other than temperature, that affects enzyme activity.
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(d) A gene is involved in the production of the enzyme alcohol dehydrogenase.
(i) Define the term gene.
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(ii) Describe the role of ribosomes in the synthesis of proteins such as enzymes.
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▶️Answer/Explanation

(a) (i)

$C_6H_{12}O_6$ → $2C_2H_5OH + 2CO_2$ ;;

(a) (ii)

liver ;

(b)

correct ref to active site ;
enzyme must be complementary shape to, substrate / alcohol ;
to make enzyme – substrate complex / to allow substrate to bind to enzyme ;
ref to only fits one substrate / specific to one substrate ;

(c)(i)

ncreased kinetic energy ;
molecules move faster ;
increased frequency of collisions ;
increased number of successful collisions ;

(c)(ii)

pH ;

(d)(i)

ength of DNA ;
that codes for a protein ;

(d)(ii)

mRNA passes through ribosomes ;
ribosomes assemble amino acids into proteins ;
order of amino acids is determined by the sequence of bases in mRNA ;
AVP ;

Question

(a) Complete Table 6.1 to show the names, functions and sites of action of the three different
digestive enzymes.

(b) Enzymes are proteins.
Fig. 6.1 shows the stages involved in protein synthesis.

(i) State the name of the parts represented by the letters A and C in Fig. 6.1.

A ……………………………………………………………………………………………………………………….
C ……………………………………………………………………………………………………………………….

(ii) Describe the events that occur during stage 2 in Fig. 6.1.

………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….

(iii) State what determines the order in which the parts labelled B are assembled.

………………………………………………………………………………………………………………………….
(c) The shape of a protein is very important for its function.
Explain the importance of shape for the function of an enzyme.
…………………………………………………………………………………………………………………………………

Answer/Explanation

Ans

Question

Biological washing powders contain enzymes that break down food stains.
(a) Complete Table 2.1 by naming the enzymes that break down three substances in food stains
and by stating the product or products.

Some students compared how effective biological and non-biological washing powders are at
removing stains at temperatures between 10 °C and 60 °C.
• Pieces of stained cloth were washed using two different washing powders.
• The degree of stain removal was measured by using a light meter to record the
percentage of light reflected from the cloth.
• A light meter gave a value of 100% when the cloth was completely clean.
• Any stain left on the cloth reduced the percentage of light reflected.
The results of the students’ investigation are shown in Fig. 2.1.

(b) Compare the effectiveness of the two washing powders at removing stains.
Use the information in Fig. 2.1 in your answer.
(c) The students suggested that the enzymes in the biological washing powder were denatured
at high temperatures.
Explain why enzyme molecules do not function when they are denatured.
(d) Forensic scientists often try to find DNA on items of stained clothing. The DNA can be used to
identify individual people.
Suggest why DNA can be used to identify individual people.

Answer/Explanation

Answer:

(a) one mark per row:

(b) any four from:
biological washing powder is more effective, at lower temperatures / between 10 °C and 40 °C / 10 °C and 43 °C ;
comparative data quote for the difference at a stated temperature ;
biological washing powder removes all stain between 30 °C and 40 °C ;
non-biological removes all stain only at 60 °C ;
effectiveness is similar, at high temperatures / between 50 and 60 °C ;
same trend, below 30 °C / at low temperatures / from 50 °C ;
idea of effectiveness of biological washing powder decreases between 40 °C and 44 °C, no such decrease for non-
biological washing powder ;

(c) any two from:
active site changes shape ;
substrate no longer fits into, enzyme / active site ;
no enzyme-substrate complex / no successful collisions ;

(d) any two from:
individual people have, different / unique, DNA ;
DNA has genes or alleles have, sequences of bases ;
AVP ;

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