Cambridge IGCSE Combined Science (0653) Practice Paper 6

Cambridge IGCSE Combined and Co-ordinated Sciences

Cambridge IGCSE Combined Science (0653) Practice Paper 6

1 The enzyme amylase digests starch to maltose. Maltose is a reducing sugar. A student set up an experiment to investigate the effect of pH on the rate of activity of amylase.

? She used a measuring cylinder to add 10 cm3 of starch solution to each of five test tubes. ? She added buffer solution at five different pHs to the five tubes. ? She then added 2 cm3 of amylase solution to each test tube. ? Every minute, she tested the contents of each tube for starch. ? She recorded the time it took for the starch to completely disappear from each tube.

These are the results that she wrote down. tube A, pH 2, starch did not disappear tube B, pH 4, took 14 minutes for the starch to disappear tube C, ph 6, took 6 minutes tube D, pH 8, took 3 minutes tube E, pH 10, took 10 minutes

a i State the variable that the student changed in her experiment.

[1]

1

ii State two variables that she kept the same, or should have kept the same.

1

2

[2]

b In the space below, construct a results chart and complete it, to show the student's results.

[3]

Cambridge IGCSE Combined Science (0653) Practice Paper 6

c State one significant source of error that could reduce the reliability of the student's results. (Do not include mistakes that the student may have made.)

2 Fig. 2.1 is a photograph of a centipede.

[1] [Total = 7]

Fig. 2.1

a i Measure the length of the antenna labelled A on Fig. 2.1. length = mm ii The actual length of the antenna is 50 mm. Calculate the magnification of the photograph. Show your working.

2

[1]

magnification =

[2]

Cambridge IGCSE Combined and Co-ordinated Sciences

iii In the space below, make a large drawing of the part of the centipede in

Fig. 2.1 that is enclosed within the box.

[3]

3

3 A student carried out an experiment using the apparatus shown below.

[Total = 6]

Cambridge IGCSE Combined Science (0653) Practice Paper 6

Experiment 1 Dilute sodium hydrogencarbonate solution was added to dilute hydrochloric acid at a temperature of 25 ?C. Readings of the gas syringe were taken every 30 seconds for three minutes and are shown below.

a Use the diagrams of the syringes to enable you to complete the results table.

Time / s

Temperature 25 ?C

4

[3] b Plot your results on the grid provided and complete the graphs with a smooth line.

c Which point on your graph appears to be inaccurate?

d Sketch on the grid the line you would expect if the experiment was repeated using a more concentrated solution of sodium hydrogencarbonate.

e The student noticed that the reading on the thermometer decreased during the experiment. What does this tell you about the reaction?

[3] [1]

[2]

[1] [Total = 10]

Cambridge IGCSE Combined and Co-ordinated Sciences

4 The stomach contains hydrochloric acid of concentration approximately 0.1 mol/dm3. If there is too much acid, acid indigestion results.

Antacids can be used to help cure this problem.

Different antacids contain different compounds.

You are provided with two antacids, X and Y. X contains magnesium carbonate and Y contains magnesium hydroxide.

a Describe an experiment which you could do to show which of the two antacids was the more effective.

[4]

[Total = 4]

5 A student is measuring the volume of a cylindrical piece of wood by immersing it in water. The wood is less dense than water so that it floats.

5

Fig. 5.1

Fig. 5.2

a In Fig. 5.1, a small stone has been submerged in water in a measuring cylinder. The volume of the water + stone V1 as shown by the measuring cylinder is V1 = 60 cm3. In Fig. 5.2, the wood is immersed in the water and is held in position by the stone.

i Record the new level of the water, V2.

V2 =

ii Calculate the volume of the wood VW using the equation VW = V2 ? V1 VW =

iii Assuming that the experiment has been carried out correctly and carefully, suggest two reasons why the value VW may be inaccurate.

Reason 1

Reason 2

[2]

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