0610/62 Oct/Nov 2025 Worked Answers (IGCSE Biology 0610 Extended)

17 questions · 40 marks · 60 minutes

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1. Question 1(a)(i)

   4 marksReading and recording results in a respiration investigation
   Step 1: A good results table has ruled columns, a header line and headings that include the unit, here the height in mm. Step 2: The reading for the 1% glucose tube is 13 mm and the reading for the 4% glucose tube is 23 mm. Step 3: So the table records 13 mm for the 1% tube and 23 mm for the 4% tube, each under a clearly headed column with units.
   Method:

   Recall the features of a good results table, then record each suspension height with its unit.
   Examiner tips

   • Tables need ruled columns, a header line, headings with units, and every measured value.

2. Question 1(a)(ii)

   1 marksConclusion: glucose concentration and rate of respiration in yeast
   Step 1: The 4% glucose tube gave the greater height (23 mm) and the 1% glucose tube gave the smaller height (13 mm). Step 2: A greater height means more gas was released, so more respiration happened with more glucose. Step 3: The conclusion is that the higher the glucose concentration, the greater the rate of respiration in the yeast.
   Method:

   Relate the larger height in the 4% tube to the higher glucose concentration to state the trend.
   Examiner tips

   • A conclusion links the measured result (height) to the variable changed (glucose concentration).

3. Question 1(a)(iii)

   2 marksIndependent and dependent variables
   Step 1: The independent variable is the one the student deliberately changes, here the concentration of the glucose solution (1% and 4%). Step 2: The dependent variable is the one measured as a result, here the height the yeast suspension rises in the large test-tube. Step 3: So glucose concentration is independent and suspension height is dependent.
   Method:

   Identify the variable the student set (concentration) and the one they measured (height).
   Examiner tips

   • Independent = what you change; dependent = what you measure.

4. Question 1(a)(iv)

   1 marksMaintaining a constant water-bath temperature
   Step 1: To keep a temperature constant you need something that adds heat as the water cools. Step 2: A thermostatically controlled water-bath has a heater and a thermostat that switch on and off to hold the set temperature. Step 3: So using a thermostatically controlled water-bath keeps the temperature steady throughout.
   Method:

   Choose equipment that actively holds the water at a fixed temperature rather than letting it drift.
   Examiner tips

   • A thermostatically controlled water-bath holds a set temperature automatically.

5. Question 1(a)(v)

   1 marksWhy a clean syringe is used
   Step 1: The first syringe has been used to measure glucose solution, so some glucose is left inside it. Step 2: Re-using it would carry that glucose into the distilled water, changing the concentration. Step 3: A clean syringe avoids this contamination, keeping the glucose concentrations accurate.
   Method:

   Recognise that leftover glucose would contaminate the water, so a clean syringe is needed.
   Examiner tips

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

6. Question 1(b)

   1 marksCalculating dilution volumes
   Step 1: The amount of glucose must be the same before and after dilution, so volume x 5% = 5 cm3 x 3%, giving volume x 5 = 15. Step 2: So the volume of 5% glucose needed is 15 / 5 = 3 cm3. Step 3: The distilled water makes the total up to 5 cm3, so 5 - 3 = 2 cm3 of water.
   Method:

   Use C1V1 = C2V2 to find the glucose volume, then subtract from 5 cm3 for the water.
   Examiner tips

   • In a dilution the mass of solute stays the same: C1 x V1 = C2 x V2.

7. Question 1(c)

   2 marksTesting for a reducing sugar
   Step 1: The food test for a reducing sugar uses Benedict’s solution. Step 2: The mixture must be heated, usually in a hot water-bath, for the reaction to occur. Step 3: A positive result is a colour change from blue to brick-red (orange), so adding Benedict’s and heating is the correct method.
   Method:

   Match the reducing-sugar test to Benedict’s solution plus heating.
   Examiner tips

   • Reducing sugar: add Benedict’s solution and heat; positive result is blue to brick-red.

8. Question 1(d)(i)

   1 marksResult of a positive fat (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 in the water that scatter light. Step 3: This makes the mixture look cloudy and milky-white, which is the positive result.
   Method:

   Recall that the emulsion test for fat gives a cloudy white result.
   Examiner tips

   • A positive emulsion (fat) test gives a cloudy, milky-white emulsion.

9. Question 1(d)(ii)

   1 marksSafety precaution when using ethanol
   Step 1: Ethanol is highly flammable and its vapour can catch fire easily. Step 2: A naked flame near ethanol could ignite the vapour, so flames must be kept away. Step 3: Keeping the ethanol away from naked flames is therefore a suitable safety precaution.
   Method:

   Identify the fire hazard of ethanol and choose the precaution that removes ignition sources.
   Examiner tips

   • Ethanol is flammable, so keep it away from flames; never taste laboratory chemicals.

10. Question 2

    6 marksPlanning an investigation into exercise intensity and heart rate
    Step 1: The independent variable is exercise intensity, so only the intensity should change, using several levels such as walking, jogging and running for the same time. Step 2: The dependent variable is heart rate, measured after each exercise, letting the heart rate return to resting between tests. Step 3: The same person, duration and surroundings are kept constant and each intensity is repeated at least three times to find a reliable mean, with a sensible safety precaution.
    Method:

    Identify intensity as the only variable to change, choose heart rate as the measure, control the rest and repeat.
    Examiner tips

    • A good plan changes one variable (intensity), measures a clear outcome (heart rate), controls the rest and repeats.

11. Question 3(a)(ii)

    3 marksMagnification calculation for the starfish diameter
    Step 1: Rearranging the formula, actual diameter = length of line PQ / magnification. Step 2: That is 93 mm / 0.32 = 290.6 mm. Step 3: To two significant figures 290.6 mm rounds to 290 mm; because the magnification is less than one, the real starfish is larger than the photograph.
    Method:

    Divide the measured line length by the magnification and round to two significant figures.
    Examiner tips

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

12. Question 3(b)(i)

    2 marksMaking sampling results comparable
    Step 1: To compare counts fairly, the sampling must be the same at every depth. Step 2: Photographing the same 20 m² area each time means the counts are from equal areas, and taking all photographs on the same day in the same region removes day-to-day and place differences. Step 3: So using the same area size and the same day and region makes the counts comparable.
    Method:

    Identify the variables kept constant across depths that make the counts a fair comparison.
    Examiner tips

    • Comparable sampling keeps the area, the timing and the region the same at every depth.

13. Question 3(b)(ii)

    4 marksPlotting a histogram of distribution data
    Step 1: Both axes must be labelled with their units, here depth / m and number of seven-armed starfish. Step 2: A suitable linear scale should let the data fill at least half the grid, and all five depth ranges must be plotted accurately. Step 3: Because the depth is in equal ranges, the bars are drawn equal in width with no gaps between them, which is what a histogram requires.
    Method:

    Apply the rules for a histogram: labelled axes, sensible scale, accurate equal-width bars with no gaps.
    Examiner tips

    • A histogram has labelled axes with units, a scale that fills the grid, accurate bars and equal-width touching bars.

14. Question 3(b)(iii)

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

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

    • The most-populated range is simply the one with the highest count.

15. Question 3(b)(iv)

    3 marksCalculating a total and a percentage
    Step 1: The total is the sum of all five counts: 337 + 1486 + 1243 + 241 + 121 = 3428 starfish. Step 2: The percentage in the 0.0 to 9.9 m range is 337 / 3428 x 100 = 9.83. Step 3: As a whole number this rounds to 10%, so the total is 3428 and 10% were in the 0.0 to 9.9 m range.
    Method:

    Sum all the counts for the total, then express the 0.0 to 9.9 m count as a percentage of that total.
    Examiner tips

    • Percentage = (part / total) x 100; here the part is 337 and the total is 3428.