Biology 5090/32 — October/November 2014
Cambridge O-Level · Practical Test · worked solutions for every part, with the mark scheme
Topics Observations and Measurements · Experimental Contexts · Analysis, Conclusions and Evaluation · Planning Experiments and Investigations · Microscopy and Biological Drawing · Use of Techniques, Apparatus and Materials
You will carry out an investigation to find the effect of the shape of an animal's body on heat loss from the body. Heat loss will be measured as a decrease in temperature in .
You will use two containers, A and B, to represent two differently shaped bodies of an equal volume. Container A is taller and narrower than container B.
You are provided with a thermometer supported in a block or piece of card. Do not remove the thermometer from this.
The two containers will each be filled with of hot water. You will need to use the thermometer immediately to measure and record this temperature. This is the reading at the start time, 0 minutes.
Every two minutes, up to a total of eight minutes, you will measure the water temperature in containers A and B, and record them in Table 1.1.
Table 1.1 is an incomplete results table for this investigation.
Complete the headings and missing figures in the shaded parts of Table 1.1.
Table 1.1
| temperature / | temperature / | |
|---|---|---|
| ______ | A | ______ |
| 0 | ||
| 2 | ||
| 4 | ||
| ______ | ||
| ______ |
Answer
| time / minutes | temperature / container A | temperature / container B |
|---|---|---|
| time / minutes | B | |
| 0 | ||
| 2 | ||
| 4 | ||
| 6 | ||
| 8 |
The shaded blanks are completed as: first column heading = time / minutes, second column heading = B, and the missing times = 6 and 8.
time / minutes; B; 6 and 8
Walkthrough
Table 1.1 records how water temperature changes over time in two containers. The first column is clearly the independent variable — the times at which readings are taken — so its heading must be 'time' with the unit '/ minutes'. The two temperature columns must be distinguished by container, so the blank beside column A is filled with 'B'. Readings were taken every two minutes up to eight minutes total, so after 0, 2 and 4 come 6 and 8.
Key Takeaways
Every results-table heading needs the quantity AND its unit (time / minutes). Column headings identify what is being compared. Time values follow the stated sampling interval.
Common Mistakes
Writing just 'time' without '/ minutes' loses the unit mark. Writing 'temperature' instead of 'B' for the column label confuses the variable with the sample. Missing one of the two missing times (6 or 8) costs a mark.
Things to Be Careful About
The mark scheme awards one mark each for B, 'time / minutes', and '6 and 8' — all three blanks must be filled. Use the slash form exactly as printed: 'time / minutes'.
Raise your hand to indicate that you are ready for a supply of hot water to fill each container A and B to the level.
Care is required.
Carry out the investigation and complete Table 1.1 as follows:
- Immediately place the thermometer into container A.
- Record the temperature of the water in Table 1.1.
- Immediately place the thermometer into container B.
- Record the temperature of the water in Table 1.1.
These will be the recordings for the start time, 0 minutes.
- At two minute intervals, up to a total of 8 minutes, repeat your temperature measurements and record each one in Table 1.1 until it is completed.
Answer
Record temperatures for both containers at 0, 2, 4, 6 and 8 minutes in Table 1.1. To score:
- the two starting temperatures (0 minutes) should differ by less than ;
- five temperature readings recorded for container A;
- five temperature readings recorded for container B;
- the general trend of the readings is a decrease in temperature with time.
Candidate-dependent: five readings per container, start temperatures within of each other, showing a decreasing trend.
Walkthrough
This part is marked on your actual data. The examiner checks four things: (1) both containers started within of each other — if one started much hotter, the comparison would be unfair; (2) you took all five readings (0, 2, 4, 6, 8 min) for A; (3) the same five for B; (4) the numbers go down over time, which is what cooling water does. Reading the thermometer immediately on filling matters because hot water cools fastest at the start, so any delay distorts the 0-minute reading.
Key Takeaways
A fair comparison needs similar starting conditions. Complete data sets (all planned readings) earn marks. The expected physical trend here is monotonic cooling.
Common Mistakes
Leaving gaps in the table if a reading was missed. Starting temperatures differing by more than . Recording an increasing value by misreading the thermometer scale.
Things to Be Careful About
Do not remove the thermometer from its support block. Take the 0-minute readings immediately — the scheme explicitly says so. Record every reading even if it looks odd; anomalous points can still be plotted and discussed later.
Calculate and record the total decrease in temperature of the water for each container and record these two values below.
Show your working.
A = ______
B = ______
Working
For each container:
Using example readings: A = ; B = .
Answer
A = 18
B = 13
(Use your own Table 1.1 values; the working above shows the required subtraction.)
Start temperature minus final (8-minute) temperature for each container, with working shown
Walkthrough
'Total decrease in temperature' means how many degrees the water cooled over the whole eight minutes. That is simply the 0-minute reading minus the 8-minute reading for each container. Show the subtraction explicitly because the question demands working — the mark scheme gives one mark for the drop in A and one for the drop in B.
Key Takeaways
A 'decrease' or 'change' is always final minus initial in magnitude; state it as a positive number of degrees here since the question asks for the decrease.
Common Mistakes
Subtracting the wrong way round and writing a negative number without explanation. Using the 6-minute reading instead of the 8-minute one. Forgetting to show working when it is explicitly requested.
Things to Be Careful About
Use your own measured values — there is no single correct number, but the arithmetic must be consistent with your table. Include the unit on both answers.
Construct a graph to show the decrease in temperature of the water with time, in containers A and B, using the results in Table 1.1. Use the same axes for both sets of data.
Answer
Draw the graph on the printed grid following these credited conventions:
- time on the x-axis, temperature on the y-axis, both axes fully labelled with units (time / minutes; temperature / );
- one linear scale on each axis, each scale using at least half the grid;
- all ten points plotted accurately (within half a small square);
- two continuous ruled lines joining the points (or two smooth curves);
- a key or labels distinguishing line A from line B.
Line graph of temperature against time with two labelled lines (A and B), correctly scaled axes and all points plotted
Walkthrough
Time is the independent variable, so it goes on the x-axis; temperature (the dependent variable) goes on the y-axis. Both axes need full labels WITH units — 'time / minutes' and 'temperature / '. Choose scales that spread across at least half the grid in each direction and keep them linear (equal steps per small square). Plot each of your ten readings carefully; tolerance is half a small square. Join the points of each container with a continuous ruled line — 5090 accepts either neatly joined straight lines or smooth curves, but never a jagged dot-to-dot with breaks. Finally, distinguish the two containers with a key or direct labels, otherwise the examiner cannot tell which line is which.
Key Takeaways
Independent variable on x, dependent on y; full axis labels with units; linear scales filling at least half the grid; accurate plotting; joined lines or smooth curve; key for multiple data sets.
Common Mistakes
Swapping the axes. Omitting units on the axis labels. Using a non-linear scale (e.g. 0, 2, 5, 10 equally spaced). Plotting points more than half a small square out. Leaving the two lines unlabelled. Extrapolating lines beyond the last plotted point.
Things to Be Careful About
The mark scheme notes tolerance of small square on plots. Do not draw a bar chart — this is continuous data over time. Use a sharp pencil and a ruler for the lines.
Describe these results.
______
Answer
- The temperature drops in both containers over the eight minutes.
- The drop is greater in container A than in container B (the temperature falls most quickly in the first two minutes in both).
Temperature decreases in both containers; the decrease is greater (faster) in A than in B, with the steepest fall in the first two minutes
Walkthrough
'Describe' means say what the graph shows, not why. Two creditable statements: (1) both sets of data show a fall in temperature — the overall trend; (2) a comparison — container A's temperature falls further/faster than B's, and in both cases the steepest fall is in the first two minutes when the water is hottest. Check your own data before writing: the scheme allows the reverse comparison if your results came out the other way.
Key Takeaways
A good description states the overall trend plus a specific comparison or detail about rate (e.g. fastest change early).
Common Mistakes
Explaining heat loss mechanisms — that belongs in (c)(iii), not here. Writing only about one container. Saying 'temperature changed' without saying it decreased.
Things to Be Careful About
Refer to YOUR results — the scheme says it will check against the candidate's data. Keep this purely descriptive; save explanations for the next part.
In another investigation it was found that the shape of a container does affect the heat loss from the container.
Suggest an explanation for this.
______
Answer
Container A has a larger surface area than container B (for the same volume). A larger surface area loses heat faster, e.g. by radiation/convection/evaporation/conduction.
A has the larger surface area for the same volume, so it loses more heat by a named process such as radiation or convection
Walkthrough
Both containers hold the same volume (), but tall narrow A exposes more of its surface to the air than squat wide B. Heat escapes through the surfaces in contact with the surroundings, so the larger surface area of A means more heat is lost per minute — which matches the bigger temperature drop you recorded for A. Name a mechanism: radiation from the warm surfaces, convection currents in the surrounding air, evaporation from the open top, or conduction through the walls. This is really an argument about surface area : volume ratio — the same principle behind small mammals losing heat faster than large ones.
Key Takeaways
Shape affects surface area : volume ratio; greater surface area for the same volume means faster heat loss. Always name the heat-transfer process.
Common Mistakes
Saying 'A is taller so it holds more water' — volumes are equal. Giving 'loses more heat' without linking it to surface area. Naming no mechanism of heat loss.
Things to Be Careful About
The scheme checks this against your data — if your results showed B losing more, argue the reverse consistently. Acceptable named processes: radiation, convection, conduction, evaporation.
State three factors that were kept constant in your investigation.
- ______
- ______
- ______
Answer
Any three of:
- volume of water in each container ()
- starting temperature of the water
- room/environmental temperature
- times at which temperatures were measured (every two minutes)
- material of the containers
- type of liquid used (water)
Volume of water, starting temperature, room temperature, timing intervals, container material, or type of liquid — any three
Walkthrough
Controlled variables are everything except the shape (the independent variable) that could affect heat loss and must therefore be kept the same. From the method: equal volumes of , similar starting temperatures, measurements at the same two-minute intervals, same room conditions, same container material, same liquid. Any three score.
Key Takeaways
To identify controlled variables ask: what else, if it varied, would change the rate of heat loss?
Common Mistakes
Naming 'shape of container' — that is the independent variable, not controlled. Naming 'temperature decrease' — that is the dependent variable. Vague answers like 'same conditions' without naming a factor.
Things to Be Careful About
Give exactly three factors. State specifics where possible ('volume of water = ', 'readings every two minutes') — the scheme credits stated volumes and temperatures.
Suggest and explain two possible improvements to the method used in your investigation.
improvement 1 = ______
explanation = ______
improvement 2 = ______
explanation = ______
Answer
Improvement 1 = use a data logger / digital thermometer with automatic recording
Explanation = removes human error in reading and timing, giving more precise readings taken exactly on time
Improvement 2 = use two thermometers, one left in each container throughout
Explanation = allows simultaneous readings in both containers, avoiding the time delay caused by moving one thermometer between them
See working — two improvements each paired with its explanation
Walkthrough
The mark scheme lists several acceptable pairs; improvement and explanation must be LINKED — the explanation must say what limitation the improvement fixes. Good pairs include: a data logger/digital thermometer (removes human error, increases precision); two thermometers left in place (simultaneous readings, no delay moving one thermometer, avoids re-equilibration); screening the containers or turning off air conditioning (prevents draughts causing uneven heat loss); shorter time intervals (a clearer, more detailed curve); repeats with a mean (improves reliability, removes the effect of anomalies). Note the scheme rejects the bare phrase 'more accurate' as an explanation — you must say HOW the limitation is addressed.
Key Takeaways
An improvement is only credited with a reason tied to a specific weakness of the method. Precision (how finely you measure) and reliability (repeatability) are different ideas.
Common Mistakes
Writing 'be more careful' or 'avoid human error' as the whole answer — vague and rejected. Pairing an improvement with an unrelated explanation. Giving two improvements but only one explanation.
Things to Be Careful About
The structure demanded is improvement + explanation twice, four marks total. Quote the link explicitly: 'so that…', 'this prevents…'. Avoid the rejected wording 'more accurate' on its own.
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1 more questions- Q2Experimental Contexts · Microscopy and Biological Drawing · Observations and Measurements · Analysis, Conclusions and Evaluation · Use of Techniques, Apparatus and Materials15M