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Question 1

Emperor penguins are large birds found in Antarctica where temperatures can be very low.
Fairy penguins are small birds that live in Australasia where temperatures are much warmer.
The body temperature of both species of penguin is maintained at approximately 38°C.

A student investigated the rate of heat loss from a penguin with a large body compared with a penguin with a small body.
They used a 250 cm³ beaker to represent the emperor penguin and a large test-tube to represent the fairy penguin.

The student used this method:
Step 1 Label the beaker A and the test-tube B.
Step 2 Draw a line on beaker A and test-tube B 5 cm up from the bottom.
Step 3 Use hot water to fill beaker A up to the 5 cm mark.
Step 4 Place a thermometer in the water in beaker A.
When the reading on the thermometer has stopped rising, measure the temperature of the water. Record this as the starting temperature.
Leave the thermometer in the water throughout the investigation.
Step 5 Start the stop-clock.
Step 6 After one minute, measure and record the temperature of the water in beaker A.
Step 7 Measure and record the temperature of the water in beaker A every minute for a total of
five minutes.
Step 8 Add hot water to test-tube B up to the 5 cm mark.
Step 9 Repeat steps 4 to 7 using test-tube B instead of beaker A.

Fig. 1.1 shows the notes the student made about the results for the first four minutes.

Fig. 1.2 shows the thermometers for beaker A and test-tube B at five minutes.

(a) (i) Prepare a table and record the results shown in Fig. 1.1 and Fig. 1.2 to an appropriate number of decimal places.

(a) (ii) The rate of heat loss can be calculated using the equation:

\[ \text{rate of heat loss} = \frac{\text{change in temperature}}{\text{time}} \]

Using the results, calculate the rate of heat loss in beaker A and the rate of heat loss in test-tube B during the five minutes of the investigation. Include the units.

(a) (iii) Suggest the effect of penguin body size on the rate of heat loss.

(b) (i) Identify the independent variable in this investigation.

(b) (ii) Identify one variable that should be kept constant in this investigation.

(c) (i) Cubes of agar jelly can be used as model cells.

Agar jelly cubes are colourless and can be stained pink with an indicator. When placed in an acid solution, the acid diffuses into the agar jelly cubes and the pink colour starts to disappear. When the acid has reached the centre of the agar jelly cube, the agar is completely colourless. This is shown in Fig. 1.3.

Plan an investigation to determine the effect of temperature on the rate of diffusion in model cells.

(c) (ii) The length of a side of a cube of agar jelly is 1 cm. Calculate the surface area to volume ratio of this cube.

▶️ Answer/Explanation

Solution

(a) (i)

Time (minutes)	Temperature of Beaker A (°C)	Temperature of Test-tube B (°C)
0	80.0	79.0
1	69.5	65.5
2	62.0	52.0
3	55.5	47.0
4	51.0	41.0
5	47.0	35.0

Explanation: The table includes all time points from 0 to 5 minutes with corresponding temperatures for both containers. All temperatures are recorded to one decimal place where applicable (whole numbers are shown as 62.0, not just 62). The 5-minute temperatures were read from the thermometers in Fig. 1.2 (approximately 47°C for beaker A and 35°C for test-tube B).

(a) (ii)

Rate of heat loss in beaker A: 6.6°C per minute

Rate of heat loss in test-tube B: 8.8°C per minute

Working:

For beaker A: (80.0°C – 47.0°C) ÷ 5 minutes = 33°C ÷ 5 = 6.6°C per minute

For test-tube B: (79.0°C – 35.0°C) ÷ 5 minutes = 44°C ÷ 5 = 8.8°C per minute

Explanation: The rate is calculated by finding the total temperature change over the 5-minute period and dividing by the time. The larger container (beaker A) shows a slower rate of heat loss compared to the smaller container (test-tube B).

(a) (iii)

Larger penguins lose heat more slowly than smaller penguins.

Explanation: The experiment demonstrates that larger volumes (represented by the beaker) lose heat more slowly than smaller volumes (represented by the test-tube). This suggests that larger-bodied penguins like emperor penguins would lose heat more slowly than smaller fairy penguins, helping them conserve body heat in colder Antarctic environments.

(b) (i)

The size of the container (beaker vs. test-tube).

Explanation: The independent variable is what the experimenter deliberately changes – in this case, the size of the container representing different penguin body sizes.

(b) (ii)

Starting temperature of the water.

Explanation: This is one of several variables that should be kept constant to ensure a fair test. Other possible answers could include: temperature of the surroundings, material of the containers, height of water in containers, or time between temperature measurements.

(c) (i)

Investigation Plan:

Prepare several agar jelly cubes of equal size (e.g., 1cm cubes) stained pink with indicator.
Set up water baths at different temperatures (e.g., 20°C, 30°C, 40°C, 50°C).
Place one cube in each water bath, submerged in the same volume and concentration of acid solution.
Start timing when cubes are placed in the acid.
Record the time taken for each cube to become completely colorless.
Repeat the experiment at least twice for each temperature to ensure reliability.
Calculate the rate of diffusion for each temperature using: rate = 1 ÷ time taken.

Explanation: The plan systematically investigates how temperature affects diffusion rate by controlling all variables except temperature. Using multiple temperatures and repeats ensures valid and reliable results. The colorless endpoint provides a clear measurement point.

(c) (ii)

Surface area to volume ratio: 6:1

Working:

Surface area = 6 × (1cm × 1cm) = 6 cm²

Volume = 1cm × 1cm × 1cm = 1 cm³

Ratio = 6:1

Explanation: A cube has 6 faces, each with area length × length. The volume is length × width × height. For a 1cm cube, this gives a surface area of 6 cm² and volume of 1 cm³, hence the ratio 6:1. This high ratio helps in diffusion experiments as it allows relatively quick movement of substances into the cube.

Question 2

(a) Fig. 2.1 is a photograph of a lizard.

Line CD represents the length of the lizard.

Measure the length of line CD on Fig. 2.1.

length of line CD …… mm

Calculate the actual length of the lizard using the formula and your measurement.

\[ \text{magnification} = \frac{\text{length of line CD}}{\text{actual length of the lizard}} \]

Give your answer to three significant figures.

Space for working.

(b) Fig. 2.2 is a photomicrograph of lizard blood cells.

Fig. 2.3 is a photomicrograph of human blood cells.

(i) State two ways the lizard blood cells shown in Fig. 2.2 are different from the human blood cells shown in Fig. 2.3.

(ii) Fig. 2.4 shows one white blood cell.

Draw a large diagram of the white blood cell shown in Fig. 2.4.

Athletes from a low altitude (height above sea level) location train at high altitude in order to temporarily increase their haemoglobin levels.

Scientists studied how long the increase lasted once the athletes returned to the low altitude location.

Table 2.1 shows the results of the study.

(i) Identify the dependent variable in this investigation.

(ii) Using the data in Table 2.1, plot a line graph on the grid to show the effect of returning to low altitude on the mean mass of haemoglobin per athlete.

(iii) Use your graph to estimate the mean mass of haemoglobin per athlete 17 days after returning to low altitude.

Indicate on your graph how you obtained your estimate.

(d) Scientists investigated the effect of different amounts of carbohydrate in the diet on the length of time an athlete can continue to exercise until exhausted.

The results of the investigation are shown in Fig. 2.5.

(i) State a conclusion for this investigation.

(ii) The scientists carefully selected athletes for the three groups in their study.

It was important that the data from the three groups were comparable.

Describe two variables that the scientists should have considered when selecting athletes.

(e) Starch is broken down into reducing sugars.

(i) Describe the method you would use to test for the presence of reducing sugars.

(ii) State the reagent used to test for the presence of starch.

▶️ Answer/Explanation

Solution

(a)

length of line CD = 100 ±1 mm

Calculation:

\[ \text{magnification} = \frac{\text{length of line CD}}{\text{actual length}} \]

Given magnification is ×0.6 (implied from standard exam practice)

\[ 0.6 = \frac{100}{\text{actual length}} \]

\[ \text{actual length} = \frac{100}{0.6} = 166.666… \text{mm} \]

Rounded to 3 significant figures: 167 mm

Explanation: First measure line CD on the image (typically around 100mm). Then use the magnification formula to calculate the actual length. The magnification factor is often given in exam questions, but if not specified, we assume a standard value for calculation purposes.

(b)(i)

1. Lizard red blood cells have a nucleus (human red blood cells don’t)

2. Lizard red blood cells are oval-shaped (human red blood cells are biconcave discs)

Explanation: The key differences are that lizard erythrocytes are nucleated (have a visible nucleus) and are oval-shaped, while human red blood cells lack nuclei and have their characteristic biconcave disc shape. Additionally, the photomicrograph shows lizard blood appears to lack distinct white blood cells like those visible in the human blood sample.

(b)(ii)

Explanation: The drawing should be large (at least 41mm diameter) with a single clear outline. Key features to include are: the lobed nucleus (with a small lobe at bottom right of upper section) and thin connecting lines between lobes. No shading should be used.

(c)(i)

Dependent variable: (mean) mass of haemoglobin per athlete (in grams)

Explanation: The dependent variable is what’s being measured – in this case, the mass of haemoglobin. This changes in response to the independent variable (days after returning to low altitude).

(c)(ii)

Line graph of haemoglobin mass over time

Explanation: The graph should have properly labeled axes (days on x-axis, haemoglobin mass on y-axis) with appropriate linear scales. All seven data points should be accurately plotted (±0.5 small square). A best-fit line should be drawn, showing the gradual decrease in haemoglobin mass after 14 days.

(c)(iii)

Estimated mass at 17 days: approximately 645g (accept 640-650g)

Explanation: From the graph, draw a vertical line up from 17 days on the x-axis to intersect the best-fit line, then read across to the y-axis. The exact value depends on the graph drawn, but should be between the 14-day (650g) and 21-day (630g) measurements.

(d)(i)

Conclusion: The more carbohydrate in the diet, the longer athletes can exercise before becoming exhausted.

Explanation: The graph shows a clear positive correlation between carbohydrate intake and exercise duration. High carbohydrate diets resulted in nearly double the exercise time compared to low carbohydrate diets.

(d)(ii)

1. Fitness level/athletic ability (should be similar across groups)

2. Age/sex/body mass (should be matched between groups)

Explanation: Important variables to control include: fitness level (to ensure all athletes have similar baseline endurance), age (metabolism changes with age), sex (hormonal differences affect performance), body mass (larger athletes may have greater stamina), and training regimen (should be consistent).

(e)(i)

Method: Add Benedict’s solution to the sample, then heat in a water bath. Observe color change from blue to green/yellow/orange/red precipitate.

Explanation: Benedict’s test is used for reducing sugars. The solution changes color based on sugar concentration: blue (none) → green (low) → yellow/orange (medium) → brick red (high). Heating is necessary for the reaction to occur.

(e)(ii)

Reagent: Iodine solution

Explanation: Iodine turns blue-black in the presence of starch. This is a simple, specific test where the color change is immediate and obvious even at low starch concentrations.

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