October/November 2025 Paper 52 Worked Answers (IGCSE Biology 0610 Core)

17 questions · 40 marks · 75 minutes

Question papers and mark schemes are copyright Cambridge International. We do not reproduce them: the worked answers here are written by The Practice Book. Have the paper open alongside. Get the official paper from Cambridge

1. Question 1(a)(i)

   4 marksDesigning a results table
   Step 1: A results table needs ruled columns with a header line and headings that give the units, here the height in mm. Step 2: It must record the final height of the yeast for both the 1% and the 4% glucose tubes. Step 3: A higher glucose concentration gives more respiration, so the 4% tube shows the greater height.
   Method:

   Check the table has headed columns with units for both tubes, then apply the more-glucose-gives-more trend.
   Examiner tips

   • Ruled columns, a header line, units in the headings, and both glucose tubes recorded.

2. Question 1(a)(ii)

   1 marksDrawing a conclusion
   Step 1: The height measured shows how much the yeast has respired. Step 2: The 4% glucose tube gave a greater height than the 1% glucose tube in the same time. Step 3: So a higher glucose concentration gives a greater rate of respiration in the yeast.
   Method:

   Relate the greater height in the 4% tube to a faster rate of respiration at higher glucose concentration.
   Examiner tips

   • A conclusion links the variable changed (glucose concentration) to the result (rate of respiration).

3. Question 1(a)(iii)

   2 marksIndependent and dependent variables
   Step 1: The independent variable is the one deliberately changed, here the concentration of the glucose solution. Step 2: The dependent variable is the one measured as a result, here the height of the yeast in the large test-tube. Step 3: Temperature, volume of yeast and time are kept the same, so they are control variables.
   Method:

   Pick the quantity deliberately changed as independent and the quantity measured as dependent.
   Examiner tips

   • Independent = changed on purpose; dependent = measured; everything else is controlled.

4. Question 1(a)(iv)

   1 marksMaintaining a constant temperature
   Step 1: Hot water in an open waterbath cools down over time, so the temperature would drift. Step 2: A thermostatically controlled waterbath senses the temperature and heats the water to hold it steady. Step 3: So using a thermostatically controlled waterbath keeps the temperature constant.
   Method:

   Choose the method that automatically holds the water at a fixed temperature.
   Examiner tips

   • A thermostatically controlled waterbath holds a set temperature automatically.

5. Question 1(a)(v)

   1 marksIdentifying a source of error
   Step 1: The height is read off a ruler held against the test-tube. Step 2: If the top of the yeast is uneven or has bubbles, it is hard to decide exactly where to read the height. Step 3: This uncertainty in the reading is a genuine source of error.
   Method:

   Choose the option that genuinely makes the height reading uncertain.
   Examiner tips

   • A source of error is something that makes the measured value uncertain, like an uneven surface.

6. Question 1(b)

   1 marksCalculating volumes for a dilution
   Step 1: The glucose in the final mixture must give 3% in 5 cm³, which is the same amount of glucose as in 3 cm³ of the 5% solution (5 × 3 = 15 = 3 × 5). Step 2: So 3 cm³ of 5% glucose solution is needed. Step 3: The total volume is 5 cm³, so the distilled water is 5 − 3 = 2 cm³.
   Method:

   Match the glucose amount needed, then make up the rest of the 5 cm³ with distilled water.
   Examiner tips

   • Keep the amount of glucose the same, then make the total volume up to 5 cm³ with water.

7. Question 1(c)

   2 marksTest for reducing sugar
   Step 1: Reducing sugars are tested for using Benedict's solution. Step 2: The sample is mixed with Benedict's solution and then heated in a hot waterbath. Step 3: Iodine tests for starch, biuret for protein and ethanol for fats, so only the Benedict's-and-heat method tests for a reducing sugar.
   Method:

   Recall the reagent and the heating step used in the reducing-sugar food test.
   Examiner tips

   • Benedict's solution plus heat tests for reducing sugars.

8. Question 1(d)(i)

   1 marksResult of the ethanol emulsion test
   Step 1: In the emulsion test the food is mixed with ethanol and then added to water. Step 2: If fat is present, it forms tiny droplets that make the mixture look cloudy and white. Step 3: A blue-black colour is the starch result, purple is the protein result and brick-red is the reducing-sugar result, so the fat result is the cloudy white emulsion.
   Method:

   Recall the appearance of a positive emulsion test for fat.
   Examiner tips

   • Fat present gives a cloudy white emulsion in the ethanol test.

9. Question 1(d)(ii)

   1 marksSafety when using ethanol
   Step 1: Ethanol is highly flammable and its vapour can catch fire easily. Step 2: So it must be kept away from any flames, burners or other sources of heat. Step 3: Heating it in a flame or leaving it near the hot waterbath would be dangerous, and saying no precautions are needed is wrong.
   Method:

   Choose the precaution that addresses ethanol being flammable.
   Examiner tips

   • Ethanol is flammable, so keep it away from flames and heat sources.

10. Question 2

    6 marksPlanning an investigation into exercise and heart rate
    Step 1: To test exercise intensity, the intensity is changed while the same person and conditions are kept constant. Step 2: The heart rate is measured after each exercise and allowed to return to resting before the next one. Step 3: Repeating each exercise and including a safety precaution makes the plan reliable and safe, which only the first method does.
    Method:

    Check the plan changes only intensity, measures heart rate, controls the rest, repeats and is safe.
    Examiner tips

    • Vary exercise intensity, control the person and conditions, measure heart rate and repeat.

11. Question 3(a)(ii)

    3 marksCalculating actual size from magnification
    Step 1: Rearrange magnification = photograph length ÷ actual diameter to give actual diameter = photograph length ÷ magnification. Step 2: Actual diameter = 93 ÷ 0.32 = 290.6 mm. Step 3: To two significant figures this is 290 mm.
    Method:

    Divide 93 by 0.32 and round the answer to two significant figures.
    Examiner tips

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

12. Question 3(b)(i)

    2 marksEnsuring results can be compared
    Step 1: To compare counts fairly, the area sampled at each depth must be the same size, here 20 m². Step 2: Taking all the photographs on the same day in July keeps the time of year the same, so seasonal changes do not affect the comparison. Step 3: Different-sized areas, different days or inconsistent counting would all make the comparison unfair.
    Method:

    Choose the two features that keep the sampling the same at every depth.
    Examiner tips

    • Keep the sampled area and the timing the same so counts at different depths can be compared.

13. Question 3(b)(ii)

    4 marksPlotting a histogram
    Step 1: Both axes are labelled with their units, here depth in m and number of starfish, and a linear scale is chosen so the data fill more than half the grid. Step 2: All five counts are plotted accurately. Step 3: The bars are drawn the same width with no gaps between them, which is what makes it a histogram.
    Method:

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

    • Linear scales, labelled axes with units, all bars plotted, equal width and no gaps.

14. Question 3(b)(iii)

    1 marksReading the modal class from data
    Step 1: The depth range with the most starfish is the one with the largest count. Step 2: The counts are 337, 1486, 1243, 241 and 121, and the largest of these is 1486. Step 3: The count of 1486 belongs to the 10.0 to 19.9 m range, so most starfish were found there.
    Method:

    Compare the counts and pick the depth range with the greatest number.
    Examiner tips

    • The modal range is the one with the greatest number counted.

15. Question 3(b)(iv)

    3 marksCalculating a total and a percentage
    Step 1: The total is 337 + 1486 + 1243 + 241 + 121 = 3428 starfish. Step 2: The percentage in the 0.0 to 9.9 m range is (337 ÷ 3428) × 100 = 9.83…%. Step 3: As a whole number this rounds to 10%.
    Method:

    Add the counts for the total, divide 337 by the total, multiply by 100 and round.
    Examiner tips

    • Total = sum of all counts; percentage = (part ÷ total) × 100, then round to a whole number.