0610/63 May/June 2025 Worked Answers (IGCSE Biology 0610 Extended)

19 questions · 40 marks · 60 minutes

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1. Question 1(a)(i)

   4 marksRecording results of an enzyme investigation in a table
   Step 1: A good results table needs clearly headed columns that include the correct units, here the test-tube and the height of foam in mm. Step 2: The maximum foam heights measured are C = 8 mm, R = 15 mm and H = 27 mm. Step 3: Only the option with headed, unit-bearing columns and these correct values records the results properly.
   Method:

   Pick the table that has headed, unit-bearing columns and the correct foam height against each test-tube.
   Examiner tips

   • Headed columns + correct units + values in the right place make a valid results table.

2. Question 1(a)(ii)

   1 marksDrawing a conclusion about temperature and enzyme activity
   Step 1: More foam means more oxygen produced, which shows the catalase is more active. Step 2: The foam was tallest in the hot tube and shortest in the cold tube. Step 3: So over this range, increasing the temperature increases the activity of the catalase.
   Method:

   Compare the foam heights across temperatures and state the trend in enzyme activity.
   Examiner tips

   • Link the size of the response (foam height) to the level of enzyme activity.

3. Question 1(a)(iii)

   2 marksIdentifying independent and dependent variables
   Step 1: The independent variable is the one the student deliberately changes, which is the temperature. Step 2: The dependent variable is the one the student measures as a result, which is the height of the foam. Step 3: So the independent variable is temperature and the dependent variable is the height of the foam.
   Method:

   Decide which variable was changed and which was measured, then label each one.
   Examiner tips

   • "I change" the independent variable; "I measure" the dependent variable.

4. Question 1(a)(iv)

   1 marksAllowing reactants to reach the test temperature
   Step 1: The hydrogen peroxide needs to be at the test temperature before the enzyme is added. Step 2: Standing in the water-bath for five minutes lets the contents warm up or cool down to match the water-bath. Step 3: So the reaction is then carried out at the intended temperature, making the comparison fair.
   Method:

   Recall that reactants must reach the test temperature before the reaction is started.
   Examiner tips

   • Reactants are left to "equilibrate" to the set temperature before the reaction is timed.

5. Question 1(a)(v)

   1 marksValue of repeating an investigation
   Step 1: Carrying out repeats produces several values for each temperature. Step 2: Any odd value that does not fit the pattern can then be identified as anomalous and left out. Step 3: A mean of the remaining values is more reliable, giving more confidence in the results.
   Method:

   Explain that repeats let you identify anomalies and average the rest for reliability.
   Examiner tips

   • Repeats help you find anomalies and calculate a more reliable mean.

6. Question 1(a)(vi)

   1 marksSafety when preparing potato extract
   Step 1: The main hazard is cutting yourself with the knife. Step 2: Cutting on a firm surface with the blade moving away from the body keeps fingers out of the path of the knife. Step 3: So this is a sensible safety precaution for preparing the extract.
   Method:

   Identify the knife as the main hazard and choose the precaution that controls it.
   Examiner tips

   • Most cutting accidents are avoided by cutting away from the body on a firm surface.

7. Question 1(b)(i)

   3 marksCalculating the volume of a cylinder of foam
   Step 1: The radius is half the diameter, so 25 / 2 = 12.5 mm. Step 2: Volume = 3.14 x 12.5 x 12.5 x 29 = 14228.125 mm3. Step 3: There are 1000 mm3 in 1 cm3, so 14228.125 / 1000 = 14.228... which rounds to 14.2 cm3.
   Method:

   Find the radius, compute the cylinder volume in mm3, then convert to cm3 and round.
   Examiner tips

   • radius = diameter / 2, and 1 cm3 = 1000 mm3.

8. Question 1(b)(ii)

   1 marksMeasuring the volume of gas accurately
   Step 1: Oxygen is a gas, so its volume is best measured by collecting the gas itself. Step 2: A gas syringe collects the oxygen and gives a direct reading of its volume on a scale. Step 3: This is far more accurate than estimating from the height of a foam.
   Method:

   Choose the apparatus that collects the gas and reads its volume directly.
   Examiner tips

   • A gas syringe (or measuring cylinder over water) collects a gas and reads its volume directly.

9. Question 1(c)(i)

   1 marksTesting for starch with iodine solution
   Step 1: Iodine solution is orange-brown to start with. Step 2: When starch is present, the iodine turns a blue-black colour. Step 3: So a blue-black colour is the positive result for starch.
   Method:

   Recall the iodine starch test and state the blue-black colour change.
   Examiner tips

   • Iodine + starch = blue-black.

10. Question 1(c)(ii)

    1 marksReagent for testing for vitamin C
    Step 1: Vitamin C is detected using the blue dye DCPIP. Step 2: Vitamin C decolourises blue DCPIP, turning it colourless. Step 3: So DCPIP is the reagent used to test for vitamin C.
    Method:

    Match the vitamin C test to its reagent, DCPIP.
    Examiner tips

    • DCPIP is decolourised by vitamin C.

11. Question 1(d)

    6 marksPlanning an investigation into light intensity and photosynthesis
    Step 1: The independent variable must be the light intensity, set at several different values. Step 2: The rate of photosynthesis is measured as the volume of oxygen produced in a fixed time, while temperature, carbon dioxide supply and the plant are kept constant so the test is fair. Step 3: Repeating at each light intensity makes the results more reliable, so the first plan is the correct one.
    Method:

    Select the plan that varies only light intensity, measures oxygen output, controls other variables and repeats.
    Examiner tips

    • Change one variable (light intensity), measure the oxygen produced, control the rest, and repeat.

12. Question 2(a)(ii)

    3 marksCalculating actual length from magnification
    Step 1: Rearrange the formula: actual length = length of line PQ divided by the magnification. Step 2: actual length = 84 / 3.4 = 24.7 mm. Step 3: To two significant figures this is 25 mm.
    Method:

    Rearrange the magnification formula, divide, then round to two significant figures.
    Examiner tips

    • actual length = measured length / magnification.

13. Question 2(b)(i)

    2 marksIdentifying controlled variables in a germination study
    Step 1: Controlled variables are the conditions kept the same for every group. Step 2: The soil type and the room temperature were the same for all the pots. Step 3: The species and mass are being compared (the independent variable), and the proportion germinated is the measured outcome (the dependent variable), so they are not controlled.
    Method:

    Pick the conditions that were the same for every species, not the ones being compared or measured.
    Examiner tips

    • Controlled variables are kept the same; the independent variable is changed; the dependent variable is measured.

14. Question 2(b)(ii)

    4 marksPlotting a bar chart of two sets of data
    Step 1: A bar chart needs axes that are labelled with units and have a suitable scale for both the mean mass and the proportion germinated. Step 2: All six bars (two per species) should be plotted accurately, with gaps between the different species. Step 3: A key is needed so the reader can tell the two datasets apart, so the first option is correct.
    Method:

    Choose the description that includes labelled scaled axes, all the bars with gaps, and a key.
    Examiner tips

    • Bar charts need labelled, scaled axes, separated bars and a key for two datasets.

15. Question 2(b)(iii)

    1 marksWhy a large sample is measured
    Step 1: Individual acorns vary, so a few of them may not be typical. Step 2: Measuring a large number gives a representative sample and reduces the effect of this natural variation. Step 3: This makes the results more reliable and helps avoid bias.
    Method:

    Explain that a large sample is representative and reduces the effect of variation.
    Examiner tips

    • Large samples are more representative and reduce the effect of variation.

16. Question 2(b)(iv)

    1 marksCalculating percentage water content
    Step 1: The mass of water lost is the initial mass minus the dried mass: 1.96 - 0.74 = 1.22 g. Step 2: Percentage water content = (mass of water / initial mass) x 100 = (1.22 / 1.96) x 100. Step 3: This gives 62.2%.
    Method:

    Subtract the dried mass from the initial mass, divide by the initial mass and multiply by 100.
    Examiner tips

    • % water = (mass lost on drying / initial mass) x 100.

17. Question 2(c)

    1 marksReagent for testing for protein
    Step 1: Protein is detected using biuret solution. Step 2: When protein is present, biuret solution changes from blue to purple. Step 3: So biuret solution is the reagent used to test for protein.
    Method:

    Match the protein test to its reagent, biuret solution.
    Examiner tips

    • Biuret solution turns purple with protein.