IGCSE Biology 0610/51 May/June 2025 Past Paper with Answers

Question 1

Cubes of agar containing universal indicator are placed in hydrochloric acid solutions of four different concentrations (0.4, 0.6, 0.8 and 1.0 mol per dm³) and the time for each cube to turn completely red is measured in seconds. Which option describes a correct results table and the expected pattern of the results?

1. a table with ruled columns headed concentration in mol per dm³ and time in s, recording all four concentrations against their times, with the 1.0 mol per dm³ cube turning red in the shortest time
2. a table with ruled columns headed concentration and time but with no units given, recording all four concentrations against their times
3. a table recording only the final colour of each cube, with the 1.0 mol per dm³ cube turning red in the longest time
4. a single column listing the four times only, with the 0.4 mol per dm³ cube turning red in the shortest time

Question 2

In the agar-cube experiment the cubes placed in more concentrated hydrochloric acid turned completely red in a shorter time. What is the correct conclusion about the effect of acid concentration on the rate of diffusion?

1. as the concentration of hydrochloric acid increases, the rate of diffusion increases
2. as the concentration of hydrochloric acid increases, the rate of diffusion decreases
3. the concentration of hydrochloric acid has no effect on the rate of diffusion
4. the rate of diffusion increases only when the acid is very dilute

Question 3

In the agar-cube diffusion experiment the student changes the strength of the acid and measures how long each cube takes to turn completely red. Which option correctly identifies the independent variable and the dependent variable?

1. the independent variable is the concentration of hydrochloric acid and the dependent variable is the time taken for the cube to turn red
2. the independent variable is the time taken for the cube to turn red and the dependent variable is the concentration of hydrochloric acid
3. the independent variable is the size of the agar cube and the dependent variable is the colour of the indicator
4. the independent variable is the temperature of the water-bath and the dependent variable is the volume of acid

Question 4 · Answer A

Step 1: A source of error is a feature of the method that makes the results less reliable. Step 2: If the cubes are not all the same size, the acid has different distances to diffuse, so the times cannot be fairly compared. Step 3: The other options are normal, correct parts of the method, not errors.

Question 5 · Answer A

Step 1: A hazard is something that could cause harm. Step 2: A sharp knife can cut the skin and hydrochloric acid is corrosive and can irritate skin and eyes, so both are hazards. Step 3: The stop-clock, white card, test-tube rack and distilled water are not harmful.

Question 6 · Answer A

Step 1: To test temperature, temperature must be the only variable changed, so the solution concentration, piece size and time are all kept the same. Step 2: Osmosis is detected by the change in mass, so each piece is weighed before and after. Step 3: Using several temperatures and repeating the readings gives reliable results, which only the first method does.

Question 7 · Answer A

Step 1: DCPIP is a blue dye. Step 2: Vitamin C decolourises DCPIP, turning it colourless. Step 3: So before any vitamin C is added the DCPIP solution is blue.

Question 8 · Answer A

Step 1: A fair test keeps everything constant except the variable being investigated, which here is the vitamin C concentration. Step 2: Each test must start with the same volume and the same concentration of DCPIP. Step 3: So the volume of DCPIP and the concentration of DCPIP are the variables kept constant.

Question 9 · Answer A

Step 1: Both axes are labelled with their units and a linear (evenly spaced) scale is chosen so the plotted points fill more than half of the grid. Step 2: Every one of the five points is plotted accurately. Step 3: A single suitable line is then drawn through the points.

Question 10 · Answer A

Step 1: A larger volume needed means a lower vitamin C concentration, so a volume of 1.2 cm³ lies between the 1.1 cm³ result (500 mg per dm³) and the 1.4 cm³ result (250 mg per dm³). Step 2: A volume of 1.2 cm³ is just above 1.1 cm³, so the concentration is a little below 500 mg per dm³. Step 3: This gives an estimate of about 420 mg per dm³.

Question 11 · Answer A

Step 1: The fresh samples are all around 272 to 281 mg per dm³, much higher than the stored samples. Step 2: After storage the values drop to between about 96 and 170 mg per dm³. Step 3: So storing the apple juice decreases its vitamin C concentration.

Question 12 · Answer A

Step 1: Most results in a reliable set follow a clear pattern or trend. Step 2: An anomalous result is one that stands out and does not fit that pattern. Step 3: So an anomalous result is a result that does not fit the trend of the others.

Question 13 · Answer A

Step 1: An anomalous result does not fit the pattern of the others. Step 2: Two of the stored values are close together at 96 and 104 mg per dm³, but 170 mg per dm³ is much higher. Step 3: So 170 mg per dm³ is the anomalous result.

Question 14 · Answer A

Step 1: Percentage change = (final value − initial value) ÷ initial value × 100. Step 2: = (104 − 272) ÷ 272 × 100 = −168 ÷ 272 × 100. Step 3: = −61.76…, which rounds to −61.8 % to one decimal place.

Question 15 · Answer A

Step 1: A biological drawing uses single, clear, continuous lines with no shading or colouring. Step 2: It should be large, using at least half of the available space. Step 3: It must show the structures that were observed, here the stalk, sepals, radiating stripes and seeds.

Question 16 · Answer A

Step 1: Rearrange magnification = image length ÷ actual length to give actual length = image length ÷ magnification. Step 2: Actual diameter = 61 ÷ 1.8 = 33.888… mm. Step 3: To three significant figures this is 33.9 mm.

Question 17 · Answer A

Step 1: Reducing sugars are tested for with Benedict's solution. Step 2: The mixture must be heated, usually in a hot water-bath, and a brick-red colour shows reducing sugar is present. Step 3: Iodine tests for starch, biuret tests for protein and the ethanol emulsion test is for fats, so none of those is used here.