October/November 2025 Paper 63 Worked Answers (IGCSE Biology 0610 Extended)

18 questions · 40 marks · 60 minutes

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1. Question 1(a)

   1 marksNaming the apparatus used to measure temperature
   Step 1: Temperature is measured with a thermometer, which is marked in degrees Celsius. Step 2: A measuring cylinder measures volume, a stop-clock measures time and a balance measures mass. Step 3: So the correct piece of equipment for measuring temperature is a thermometer.
   Method:

   Match the quantity (temperature) to the instrument that measures it.
   Examiner tips

   • A thermometer measures temperature in degrees Celsius.

2. Question 1(b)

   3 marksRecording observations in a results table
   Step 1: A good results table has ruled columns, a header line and clear headings, here test-tube and colour of liquid. Step 2: The recorded colours must match the observations: A is brick-red, B is green and W is blue. Step 3: So the table lists A as brick-red, B as green and W as blue under headed columns.
   Method:

   Recall the features of a good results table, then record each tube’s colour accurately.
   Examiner tips

   • Tables need ruled columns, a header line, clear headings and every recorded value.

3. Question 1(c)

   1 marksConclusion: enzyme concentration and reducing sugar produced
   Step 1: A brick-red colour means more reducing sugar than a green colour. Step 2: Test-tube A had the higher invertase concentration (100%) and gave brick-red, while B had a lower concentration (10%) and gave green. Step 3: So the greater the invertase concentration, the more reducing sugar is produced.
   Method:

   Relate the deeper colour in the higher-concentration tube to the amount of reducing sugar made.
   Examiner tips

   • A conclusion links the measured result (colour) to the variable changed (enzyme concentration).

4. Question 1(d)

   2 marksPurpose of a control tube
   Step 1: Test-tube W has sucrose but no invertase, so it is the control. Step 2: It stays blue, showing that sucrose is not broken down into reducing sugar without invertase. Step 3: This means any reducing sugar found in A and B must be caused by the invertase, making the comparison valid.
   Method:

   Identify tube W as the no-enzyme control and state what its blue result proves.
   Examiner tips

   • A control tube has the variable removed so you can show the result is caused by that variable.

5. Question 1(e)

   1 marksIdentifying the independent variable
   Step 1: The independent variable is the one the student deliberately changes. Step 2: Here the student changes the concentration of invertase extract (100% in one tube and 10% in another). Step 3: So the independent variable is the concentration of the invertase extract; the colour is the dependent variable and the rest are kept constant.
   Method:

   Pick out the factor that differs deliberately between the test-tubes.
   Examiner tips

   • The independent variable is what you choose to change between samples.

6. Question 1(f)

   1 marksReason for using a warm water-bath
   Step 1: Enzymes such as invertase work fastest at a suitable warm temperature. Step 2: Placing all the tubes in the same warm water-bath keeps them at the same temperature and gives a high enough rate of reaction. Step 3: So the warm water-bath ensures a fair comparison and lets the invertase work quickly.
   Method:

   Link the warm water-bath to a suitable, equal temperature for fast enzyme action.
   Examiner tips

   • Enzymes work fastest at a suitable warm temperature, so tubes are kept the same and warm.

7. Question 1(g)

   1 marksWhy a clean syringe is used
   Step 1: A syringe that has measured one solution still has some of it left inside. Step 2: Re-using it would carry that solution into the next tube and change its contents. Step 3: A clean syringe avoids this contamination, keeping each tube’s concentrations accurate.
   Method:

   Recognise that leftover solution would contaminate the next tube, so a clean syringe is needed.
   Examiner tips

   • A clean piece of apparatus avoids carrying one solution into another (contamination).

8. Question 1(h)

   1 marksReagent used to test for protein
   Step 1: The food test for protein uses biuret reagent. Step 2: A positive result is a colour change from blue to purple (lilac). Step 3: So biuret reagent is used to test for protein; the other reagents test for reducing sugar, starch and fat.
   Method:

   Match the protein test to biuret reagent and its purple colour.
   Examiner tips

   • Protein test: add biuret reagent; a positive result is blue to purple.

9. Question 2(a)(i)

   2 marksVariables kept constant in a respiration investigation
   Step 1: Controlled variables are the factors kept the same so they do not affect the result. Step 2: The volume of yeast suspension and the counting time must be kept constant at every temperature. Step 3: Temperature is deliberately changed (independent) and bubble number is measured (dependent), so neither of those can be a controlled variable.
   Method:

   Choose factors that are neither changed nor measured, so the test stays fair.
   Examiner tips

   • Controlled variables are kept the same; the independent and dependent variables are not.

10. Question 2(a)(ii)

    2 marksSource of error and improvement when measuring the dependent variable
    Step 1: Bubbles can vary in size and may be produced too quickly to count exactly, so counting them is not very accurate. Step 2: A better measure of the gas made is to collect it and measure its volume. Step 3: Measuring the volume of gas removes the problem of uneven or fast bubbles, improving the accuracy of the dependent variable.
    Method:

    Identify why counting bubbles is inaccurate, then choose a more reliable measurement.
    Examiner tips

    • Counting variable, fast bubbles is unreliable; measuring the volume of gas is more accurate.

11. Question 2(b)(i)

    2 marksCalculating a rate to an appropriate number of significant figures
    Step 1: Rate of bubble production = number of bubbles ÷ time = 79 ÷ 3 = 26.33 bubbles per minute. Step 2: The other table values are given to two significant figures. Step 3: So 26.33 rounds to 26 bubbles per minute, which matches the rest of the table.
    Method:

    Divide the bubble count by the time and round to the same precision as the table.
    Examiner tips

    • Rate per minute = total count ÷ time in minutes; round to match the data given.

12. Question 2(b)(ii)

    4 marksPlotting a graph of rate against temperature
    Step 1: Both axes must be labelled with units, here temperature / °C and rate of bubble production / bubbles per minute. Step 2: A suitable linear scale should let the points fill at least half the grid, and all six points must be plotted accurately. Step 3: The points are then joined with a smooth curve of best fit, which shows the rate rising to a peak and then falling.
    Method:

    Apply the rules for plotting: labelled axes, sensible scale, accurate points and a best-fit line.
    Examiner tips

    • A good graph has labelled axes with units, a scale filling the grid, accurate points and a best-fit line.

13. Question 2(b)(iii)

    2 marksDescribing the results of a respiration investigation
    Step 1: From 10 °C to 50 °C the rate rises from 11 to 41 bubbles per minute. Step 2: The highest rate (the peak) is at 50 °C. Step 3: After 50 °C the rate falls to 12 at 60 °C, so the rate increases to a peak at 50 °C and then decreases.
    Method:

    State the overall trend and identify the temperature giving the highest rate.
    Examiner tips

    • Describe the trend and name the peak: rate rises, peaks at 50 °C, then falls.

14. Question 2(c)

    2 marksConfirming the gas produced is carbon dioxide
    Step 1: Carbon dioxide is tested for using limewater. Step 2: When carbon dioxide is bubbled through limewater, the limewater turns cloudy (milky) as a white precipitate forms. Step 3: So bubbling the gas through limewater and seeing it turn cloudy confirms the gas is carbon dioxide.
    Method:

    Match the carbon dioxide test to limewater and its cloudy positive result.
    Examiner tips

    • Carbon dioxide turns limewater cloudy (milky).

15. Question 3(a)(ii)

    3 marksMagnification calculation for the beak length
    Step 1: Rearranging the formula, actual length = length of line AB / magnification. Step 2: That is 46 mm / 0.42 = 109.52 mm. Step 3: To one decimal place 109.52 mm rounds to 109.5 mm; because the magnification is less than one, the real beak is larger than its photograph.
    Method:

    Divide the measured line length by the magnification and round to one decimal place.
    Examiner tips

    • Actual size = image size / magnification; a magnification below 1 makes the real object larger.

16. Question 3(c)

    6 marksPlanning an investigation into insulation and heat loss
    Step 1: The independent variable is the thickness of insulation, so only that should change, using at least two different thicknesses of the same material. Step 2: The dependent variable is heat loss, measured as the temperature fall (or the time for a set fall) of the hot water. Step 3: The volume of water, beaker type, starting temperature and surroundings are kept constant, each thickness is repeated for a mean, and a safety precaution is taken with the hot water.
    Method:

    Identify thickness as the only variable to change, choose temperature fall as the measure, control the rest and repeat.
    Examiner tips

    • A good plan changes one variable (thickness), measures a clear outcome (temperature fall), controls the rest and repeats.