October/November 2025 Paper 53 Worked Answers (IGCSE Biology 0610 Core)

17 questions · 40 marks · 75 minutes

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1. Question 1(a)

   1 marksRecording a measured temperature
   Step 1: A measured temperature must be written down as the number read from the thermometer, here about 40. Step 2: It must include the correct unit, which for temperature is degrees Celsius, so it is recorded as a value with its unit such as 40 °C. Step 3: cm³ is a unit of volume and g is a unit of mass, so neither is correct for a temperature.
   Method:

   Give the measured number together with the temperature unit °C.
   Examiner tips

   • Record a temperature as a number followed by the unit °C.

2. Question 1(b)

   4 marksDesigning a results table
   Step 1: A results table needs ruled columns with a header line and headings such as test-tube and colour. Step 2: It must record a colour for all three tubes, A, B and W. Step 3: Tube W has no invertase, so the sucrose is not broken down and Benedict’s stays blue, while tube A has the most invertase, makes the most reducing sugar and turns orange-red, with tube B in between.
   Method:

   Check the table is headed, records all three tubes, and shows W blue with A the strongest positive colour.
   Examiner tips

   • Headed columns, all three tubes recorded, W blue and A orange-red.

3. Question 1(c)

   1 marksDrawing a conclusion
   Step 1: A stronger Benedict’s colour shows more reducing sugar has been produced. Step 2: Tube A had more invertase and gave the stronger colour than tube B. Step 3: So a higher invertase concentration produces more reducing sugar.
   Method:

   Relate the stronger colour in the more concentrated tube to more reducing sugar produced.
   Examiner tips

   • A conclusion links the variable changed (invertase concentration) to the result (reducing sugar produced).

4. Question 1(d)

   2 marksPurpose of a control
   Step 1: Tube W is the same as the others but with water in place of invertase. Step 2: This makes it a control, used for comparison. Step 3: It shows that without invertase the sucrose is not broken down, so any reducing sugar in A and B must be due to the invertase.
   Method:

   Identify tube W as the control and state what it shows about sucrose without invertase.
   Examiner tips

   • A control tube with water shows what happens without the enzyme.

5. Question 1(e)

   1 marksIdentifying the independent variable
   Step 1: The independent variable is the one deliberately changed by the experimenter. Step 2: Tube A gets 100% and tube B gets 10% invertase, so it is the concentration of invertase extract that is changed. Step 3: The colour is the result measured, while the volume of sucrose and the temperature are kept the same.
   Method:

   Pick the factor that is deliberately changed between the tubes.
   Examiner tips

   • The independent variable is the factor changed on purpose: here the invertase concentration.

6. Question 1(f)

   1 marksReason for using a warm waterbath
   Step 1: Invertase is an enzyme, and enzymes work faster at a suitable warm temperature. Step 2: Keeping all the tubes in the same warm waterbath holds them at the same temperature. Step 3: This gives a sufficient rate of reaction so that reducing sugar is produced during the investigation.
   Method:

   Link the warm waterbath to a suitable temperature and a sufficient rate of enzyme reaction.
   Examiner tips

   • A warm temperature lets the enzyme work at a good rate and keeps the tubes the same.

7. Question 1(g)

   1 marksAvoiding contamination
   Step 1: If the same syringe were reused, traces of one liquid would be carried into the next tube. Step 2: Carrying invertase into the water tube, for example, would spoil the results. Step 3: Using a clean syringe each time prevents this contamination so each tube contains only what it should.
   Method:

   Identify that a fresh syringe prevents one liquid contaminating another.
   Examiner tips

   • A clean syringe stops one liquid contaminating the next.

8. Question 2(a)(i)

   2 marksIdentifying control variables
   Step 1: A control variable is anything kept the same so only temperature affects the result. Step 2: The volume of yeast suspension and the time spent counting bubbles must be kept the same at every temperature. Step 3: The temperature is the independent variable and the number of bubbles is the dependent variable, so neither of those is a control variable.
   Method:

   Pick the two factors held the same, not the temperature changed or the bubbles measured.
   Examiner tips

   • Keep the volume of yeast and the counting time the same; change only the temperature.

9. Question 2(a)(ii)

   2 marksSource of error and improvement
   Step 1: Counting bubbles is unreliable because the bubbles can be different sizes or come too fast to count accurately. Step 2: A better measurement is to collect the gas and measure its volume. Step 3: Measuring the volume removes the problem of uneven or fast bubbles, so it is a sensible improvement.
   Method:

   State the unreliable bubble count as the error and measuring gas volume as the improvement.
   Examiner tips

   • Bubbles vary in size and are hard to count; measuring the gas volume is more reliable.

10. Question 2(b)(i)

    2 marksCalculating a rate
    Step 1: The rate is the number of bubbles divided by the time, so 79 ÷ 3 = 26.333 bubbles per minute. Step 2: The data have two significant figures, so the answer should be given to two significant figures. Step 3: Rounding 26.333 to two significant figures gives 26 bubbles per minute.
    Method:

    Divide 79 by 3 and round to two significant figures.
    Examiner tips

    • rate = number of bubbles ÷ time, then round to the right number of significant figures.

11. Question 2(b)(ii)

    4 marksPlotting a graph
    Step 1: Both axes are labelled with their units, here temperature in °C and rate in bubbles per minute. Step 2: A linear scale is chosen so the plotted points fill at least half the grid in each direction. Step 3: Every point is plotted accurately and the points are joined with a smooth best-fit line.
    Method:

    Recall the rules for plotting a graph and choose the approach that meets all of them.
    Examiner tips

    • Labelled axes with units, a linear scale filling the grid, all points plotted, joined by a best-fit line.

12. Question 2(b)(iii)

    2 marksDescribing a trend
    Step 1: From 10 °C to 50 °C the rate rises from 11 to 41 bubbles per minute, so it increases. Step 2: The highest rate, 41, is at 50 °C, which is the peak. Step 3: At 60 °C the rate falls to 12, so after the peak the rate decreases.
    Method:

    Track the rate as temperature rises and identify the peak and the fall.
    Examiner tips

    • Describe the rise to a peak and then the fall, and name the peak temperature.

13. Question 2(c)

    2 marksTesting for carbon dioxide
    Step 1: Carbon dioxide is identified using limewater. Step 2: When carbon dioxide is bubbled through limewater the limewater turns cloudy or milky. Step 3: The glowing-splint and squeaky-pop tests are for oxygen and hydrogen, and Benedict’s tests for reducing sugar, so only the limewater test confirms carbon dioxide.
    Method:

    Recall the limewater test and its cloudy result for carbon dioxide.
    Examiner tips

    • Limewater turns cloudy with carbon dioxide.

14. Question 3(a)(ii)

    3 marksCalculating actual size from magnification
    Step 1: Rearrange magnification = photograph length ÷ actual length to give actual length = photograph length ÷ magnification. Step 2: Actual length = 46 ÷ 0.42 = 109.5238 mm. Step 3: To one decimal place this is 109.5 mm.
    Method:

    Divide 46 by 0.42 and round the answer to one decimal place.
    Examiner tips

    • actual size = photograph size ÷ magnification; then round as asked.

15. Question 3(c)

    6 marksPlanning an investigation into insulation and heat loss
    Step 1: The thickness of one insulating material is the independent variable, so only the thickness is changed while the material, the beaker, the volume of water and the starting temperature are kept the same. Step 2: The temperature fall over a fixed time is measured as the dependent variable. Step 3: Repeating the readings makes the results reliable and handling the hot water safely keeps the method safe, which only the first plan does.
    Method:

    Check the plan changes only thickness, measures the temperature fall, controls the rest, repeats and is safe.
    Examiner tips

    • Vary only the insulation thickness, control the rest, measure the temperature fall, repeat and be safe.