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Question 1

Some animals live in cold places. They sometimes huddle together as shown in Fig. 1.1.

A student investigated the effect of huddling on heat loss from model animals.
Test-tubes containing hot water represented the animals.
The student used the method described in step 1 to step 10.

Step 1 Place a test-tube in an empty beaker and put a thermometer into the test-tube.

Step 2 Approximately half-fill the test-tube with hot water and start the stop-clock.

Step 3 After one minute record the temperature of the hot water in the test-tube.

Fig. 1.2 is a diagram of part of the thermometer from step 3.

(a) (i) Record the temperature shown in Fig. 1.2.

Step 4 Record the temperature of the hot water in the test-tube every minute for a total of five minutes.
Step 5 Put three identical test-tubes together and keep them in place with an elastic band, as shown in Fig. 1.3. Place the group of three test-tubes in an empty beaker.

Step 6 Half-fill all three test-tubes with hot water and put a thermometer into one of the test-tubes.
Step 7 Record the temperature in the test-tube at one minute intervals for a total of five minutes.
Step 8 Put seven identical test-tubes together and keep them in place with an elastic band, as shown in Fig. 1.4. Place the group of seven test-tubes in an empty beaker.

Step 9 Half-fill all seven test-tubes with hot water and put a thermometer into the central test-tube.
Step 10 Record the temperature in the test-tube at one minute intervals for a total of five minutes.

Fig. 1.5 shows the results the student recorded in their notebook.

(ii) Prepare a table and record the results shown in Fig. 1.5 and your answer to 1(a)(i).

(iii) Plot a line graph on the grid of temperature against time. Include all three sets of data from your table in 1(a)(ii) and a key.

(iv) State two conclusions for this investigation.

(v) State two variables that were kept constant during this investigation.

(vi) Suggest two possible sources of error in this investigation.

(vii) Suggest one improvement to the method that was used in this investigation.

(viii) Identify one hazard for this investigation.

(b) In mammals, respiration releases heat energy to maintain an optimum temperature for enzyme activity in the body.
Amylase is an enzyme that catalyses the breakdown of starch into reducing sugars.
Plan an investigation to identify the temperature at which the enzyme amylase is most active.

▶️ Answer/Explanation
Solution

(a)(i) 68.5 °C

Explanation: The thermometer in Fig. 1.2 shows the mercury level between 68 and 69, so the precise reading is 68.5 °C.

(a)(ii)

Time (minutes)One test-tube (°C)Three test-tubes (°C)Seven test-tubes (°C)
068.5––
1686773
2656473
3616273
4586172
5556072

Explanation: The table includes all the data from Fig. 1.5 and the initial temperature from part (a)(i). The headers clearly indicate the variables and units.

(a)(iii)

Graph requirements:

  • Axes labeled with “Temperature (°C)” and “Time (minutes)”
  • Suitable linear scale covering the range of data
  • Three lines plotted for one, three, and seven test-tubes
  • Key identifying each line

Explanation: The graph should show that as the number of test-tubes increases, the temperature decreases more slowly, demonstrating reduced heat loss in huddles.

(a)(iv)

  1. Huddling reduces heat loss (more test-tubes lose heat more slowly).
  2. Temperature decreases over time in all setups, but at different rates.

Explanation: The data shows that groups of test-tubes (representing huddling animals) retain heat better than single test-tubes, and larger groups retain heat even more effectively.

(a)(v)

  1. Size/type of test-tubes
  2. Volume of water in each test-tube

Explanation: These variables were controlled to ensure that only the number of test-tubes (the independent variable) affected the results.

(a)(vi)

  1. Inconsistent starting temperatures
  2. Variations in room temperature during the experiment

Explanation: If the initial water temperature wasn’t exactly the same for all trials, or if the room temperature fluctuated, this could affect the rate of cooling and introduce errors.

(a)(vii) Repeat the experiment multiple times and calculate mean temperatures.

Explanation: Repeating the experiment would help identify and reduce the impact of random errors, making the results more reliable.

(a)(viii) Risk of burns from hot water or broken glass.

Explanation: Handling hot test-tubes poses a burn hazard, and glass breakage could cause cuts. Safety precautions like using tongs and goggles would be important.

(b)

Investigation plan:

  1. Set up water baths at different temperatures (e.g., 20°C, 30°C, 40°C, 50°C, 60°C)
  2. Add equal volumes of starch solution and amylase solution to test tubes
  3. Place tubes in water baths and start timer
  4. At regular intervals, test samples with iodine solution (starch test) or Benedict’s solution (sugar test)
  5. Record time taken for starch to disappear or for reducing sugars to appear
  6. Repeat each temperature to ensure reliability
  7. Plot graph of enzyme activity (1/time) against temperature
  8. Identify temperature with fastest reaction as optimum

Explanation: This method systematically tests amylase activity across a range of temperatures. The optimum temperature will be where the reaction occurs fastest, indicating maximum enzyme activity. Controls would include using the same concentrations and volumes of solutions, and maintaining pH constant.

Question 2

(a) Some plants lose their leaves in the winter and grow new leaves in the spring.

A scientist measured the total leaf area of the leaves on one grapevine plant. They repeated this on 100 grapevine plants and found the mean total leaf area per plant.

This procedure was done every two months for one year. The results are shown in Fig. 2.1.

 

(i) Suggest why a large number of plants were sampled.

(ii) Estimate the mean total leaf area per plant for month 7.

Show on Fig. 2.1 how you estimated this value.

(iii) Using the information in Fig. 2.1, calculate the percentage increase in the mean total leaf area per plant from month 4 to month 6.

Give your answer to two significant figures.

(b) Fig. 2.2 shows a leaf from a grapevine plant.

 

Use the grid to determine the area of the grapevine leaf shown in Fig. 2.2 by counting the squares containing the leaf.

Only count squares that are more than half-filled by the leaf.

Include the unit.

(c) Grapevines produce fruits called grapes. A large leaf area is important when growing grapes because the leaves supply reducing sugars to the grapes.

Describe the method for testing for reducing sugars. Include the result for a positive test.

(d) Fig. 2.3 is a photograph of a leaf from a fig plant.

 

Make a large drawing of the leaf in Fig. 2.3.

(e) State one similarity and one difference between the grapevine leaf in Fig. 2.2 and the fig leaf in Fig. 2.3.

▶️ Answer/Explanation
Solution

(a)(i) To get a representative sample / to avoid bias / to identify or exclude anomalies / to increase confidence in results.

Explanation: Sampling a large number of plants (100 in this case) helps ensure that the data collected is representative of the entire population. This reduces the impact of individual variations and increases the reliability of the mean value calculated. It also helps identify and exclude any unusual or outlier plants that might skew the results.

(a)(ii) 3.3 m²

Explanation: To estimate the value for month 7, you would locate month 7 on the x-axis of Fig. 2.1, draw a vertical line up to the curve, then draw a horizontal line to the y-axis to read the value. The exact method would involve showing these construction lines on the graph itself.

(a)(iii) 57%

Explanation: First, read the values from the graph: at month 4 the mean area is approximately 1.4 m², and at month 6 it’s approximately 2.2 m². The increase is 2.2 – 1.4 = 0.8 m². The percentage increase is calculated as (0.8/1.4) × 100 = 57.14%, which rounds to 57% to two significant figures.

(b) 59 cm²

Explanation: To determine the area, count all grid squares that are more than half-covered by the leaf. The exact count may vary slightly depending on interpretation, but values between 55-66 cm² would be acceptable. The unit (cm²) is crucial as it indicates we’re measuring area.

(c) Method: Add Benedict’s reagent and heat. Positive test: green/yellow/orange/red/brown color.

Explanation: To test for reducing sugars, you would first prepare a liquid sample from the grapes. Then add Benedict’s reagent (a blue solution) to the sample and heat it in a water bath. If reducing sugars are present, the solution will change color from blue through green, yellow, and orange to brick red, depending on the concentration of reducing sugars. The color change occurs because the copper(II) ions in Benedict’s solution are reduced to copper(I) oxide.

(d) Drawing should show: outline with single clear unbroken line, size at least 65mm wide, five distinct lobes, and one main vein in each lobe.

Explanation: The drawing should accurately represent the shape and features of the fig leaf shown in Fig. 2.3. Key features to include are the overall lobed shape (typically with 5 main lobes), the pattern of veins radiating from the base of the leaf, and the size proportion. The drawing should be large enough to show details clearly (at least 65mm wide).

(e) Similarity: Both leaves are lobed/have veins/have uneven edges.
Difference: Grapevine leaf has serrated edges while fig leaf has smooth edges.

Explanation: The main similarity is that both leaves have a lobed structure (multiple protruding sections). A key difference is that the grapevine leaf typically has jagged, serrated edges, while the fig leaf has smoother, more rounded edges. Other possible differences include the number of lobes or the pattern of veins.

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