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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.

You are going to investigate the rate of heat loss from a penguin with a large body compared with a penguin with a small body.

You will use the beaker to represent the emperor penguin and the test-tube to represent the fairy penguin.

Read all the instructions but DO NOT DO THEM until you have drawn a table for your results in the space provided in 1(a)(i).

You should use the safety equipment provided while you are doing the practical work.
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 Raise your hand when you are ready for hot water to be added to the beaker labelled hot water.
Step 4 Use the hot water to fill beaker A up to your 5 cm mark.
Step 5 Place the thermometer in the water in beaker A.
Once the reading on the thermometer has stopped rising, measure the temperature of the water.
Record this as the starting temperature in your table in 1(a)(i).
Leave the thermometer in the water throughout the investigation.
Step 6 Start the stop-clock and leave it running.
Step 7 After one minute, measure the temperature of the water in beaker A and record it in your table in 1(a)(i).
Step 8 Measure the temperature of the water in beaker A every minute for a total of five minutes.
Record these values in your table in 1(a)(i).
Step 9 Empty the beaker labelled hot water into the container labelled waste. Reset the stop-clock to zero.
Step 10 Raise your hand to get the beaker labelled hot water refilled with hot water.
Step 11 Add hot water to test-tube B up to your 5 cm mark.
Step 12 Repeat steps 5 to 8 using test-tube B instead of beaker A.

(a) (i) Prepare a table for your results.

(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 your 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.

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)

The table should include:

  • Columns for time (minutes) and temperature (°C) for both beaker A and test-tube B
  • Clear headings with units
  • Measurements recorded every minute for 5 minutes
  • Data showing decreasing temperature over time

(a) (ii)

To calculate the rate of heat loss:

  1. Find the temperature difference between start and end (e.g., 80°C to 70°C = 10°C change)
  2. Divide by time (5 minutes)
  3. Example calculation: 10°C ÷ 5 min = 2°C/min
  4. Repeat for both containers
  5. Units should be °C per minute

(a) (iii)

Larger penguins (represented by beaker A) will lose heat more slowly than smaller penguins (test-tube B). This is because larger objects have a smaller surface area to volume ratio, reducing heat loss to the environment.

(b) (i)

The independent variable is the size of the container (beaker vs. test-tube), representing the different penguin body sizes.

(b) (ii)

Variables to keep constant include:

  • Starting temperature of the water
  • Room temperature/environment
  • Material of containers
  • Height of water (5 cm)
  • Time between measurements

(c) (i)

Investigation plan:

  1. Cut equal-sized agar cubes (e.g., 1cm³)
  2. Prepare water baths at different temperatures (e.g., 20°C, 30°C, 40°C)
  3. Place stained cubes in acid solution in each temperature
  4. Measure time until complete decolorization
  5. Control variables: cube size, acid concentration, volume of solution
  6. Repeat for reliability
  7. Wear safety goggles when handling acid

(c) (ii)

Surface area to volume ratio calculation:

  • Surface area = 6 × (1cm × 1cm) = 6 cm²
  • Volume = 1cm × 1cm × 1cm = 1 cm³
  • Ratio = 6:1
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.

(c) Haemoglobin is a protein found in human red blood cells. Haemoglobin carries oxygen.

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

Actual length = length of line CD / magnification = 100 mm / 0.6 ≈ 167 mm (to 3 significant figures)

Explanation: First, measure the length of line CD in the figure (approximately 100 mm). Then use the magnification formula to calculate the actual length. The magnification is given as 0.6×, so we divide the measured length by the magnification factor. The answer should be rounded to three significant figures as requested.

(b)(i)

1. Lizard red blood cells have nuclei (while human red blood cells do not)

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

Explanation: The key differences between lizard and human blood cells visible in the photomicrographs are: lizard red blood cells retain their nuclei (appearing darker in the center) while human red blood cells lack nuclei. Additionally, lizard red blood cells have an oval shape compared to the characteristic biconcave disc shape of human red blood cells.

(b)(ii)

Diagram should show:

  • A single clear outline of the white blood cell (no shading)
  • Size at least 41 mm in diameter
  • Distinct lobes in the nucleus (particularly a small lobe at the bottom right)
  • Thin connections between the lobes

Explanation: When drawing the white blood cell, pay attention to the lobed structure of the nucleus and ensure the proportions are maintained. The drawing should be large and clear, with all visible features accurately represented.

(c)(i)

Mean mass of haemoglobin per athlete (in grams)

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

(c)(ii)

Graph should have:

  • X-axis labeled “Number of days after returning to low altitude”
  • Y-axis labeled “Mean mass of haemoglobin per athlete (g)”
  • Appropriate linear scale (e.g., x-axis: 0-40 days, y-axis: 600-650g)
  • All seven data points accurately plotted
  • A smooth line connecting the points

Explanation: When plotting the graph, ensure both axes are properly labeled with units. Choose scales that make good use of the graph paper and show the trend clearly. Plot each point carefully and connect them with a smooth line to show the relationship.

(c)(iii)

Approximately 640g (accept 635-645g)

Explanation: From the graph, at 17 days on the x-axis, draw a vertical line up to the curve, then horizontally to the y-axis to read the value. The exact value will depend on how the graph was drawn, but should be in the range of 635-645g based on the data points.

(d)(i)

Athletes with higher carbohydrate diets can exercise for longer before becoming exhausted.

Explanation: The conclusion directly relates the independent variable (amount of carbohydrate in diet) to the dependent variable (exercise duration). The data shows a clear positive correlation between carbohydrate intake and exercise endurance.

(d)(ii)

1. Age of the athletes (should be similar across groups)

2. Fitness level/training regimen (should be comparable)

Explanation: To ensure valid comparisons, the scientists needed to control variables that could affect exercise performance. Age is important as metabolic rates change with age. Fitness level is crucial as trained athletes respond differently to exercise than untrained individuals. Other acceptable answers could include sex, body mass index, or baseline haemoglobin levels.

(e)(i)

Add Benedict’s solution to the food sample, heat the mixture in a water bath, and observe color change from blue to green/yellow/orange/red.

Explanation: The Benedict’s test for reducing sugars involves mixing the reagent with the sample and heating. A positive result is indicated by a color change through green, yellow, orange to brick red, depending on the concentration of reducing sugars present.

(e)(ii)

Iodine solution

Explanation: Iodine solution (yellow-brown) turns blue-black in the presence of starch. This is a simple and reliable test that can be done at room temperature.

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