Practical papers: Paper 5 and Paper 6

📚The two papers

Everyone takes one practical paper; both are worth 20%, test only AO3 (experimental skills and investigations) and cover grades A*–G, so Core and Extended candidates sit the same one.

Both need the same skills and the same experimental contexts: measuring volumes, masses, temperatures, times and lengths; diffusion and osmosis; food tests; enzyme rates (including judging an end-point from a colour change); pH with hydrogencarbonate indicator, litmus and universal indicator; photosynthesis; transpiration; heart and breathing rate; respiration; tropic responses; seeds and flowers; germination; variation; sampling; and drawing specimens. Paper 6 candidates should still do these experiments in class — the paper rewards people who have.

Readings and precision

• Thermometers in the syllabus list have 1 °C graduations: record whole degrees (24 °C), not 24.35 °C.
• Rulers are graduated in mm: measure to the nearest mm. Stop-clocks read to 1 s. Balances to at least 0.1 g.
• Measuring cylinders and syringes: read the bottom of the meniscus at eye level; choose the smallest one that holds the volume.
• Keep the same number of decimal places down a column, matching the instrument.

Results tables

Graphs

• Independent variable on the x-axis, dependent on the y-axis, each labelled like the table heading (distance of lamp / cm).
• Scales must use more than half the grid in both directions, with sensible steps (2 cm = 1, 2 or 5 units). The axes need not start at 0.
• Plot to within half a small square, with a sharp pencil. Draw a best-fit line only if intermediate values can be predicted; ignore clearly anomalous points.
• Use a bar chart (bars not touching) for categories, a histogram (bars touching) for continuous data, and a pie chart for proportions.

Biological drawings

• Sharp pencil, clear continuous lines, no shading or colour; use most of the space provided.
• Show the features you can see, in the right proportions; include structures inside the outline if they are visible.
• Label lines ruled, not crossing each other, touching the feature, with no arrowheads.

Magnification

Both lengths must be in the same units. Magnification has no units; write it as ×4. To find the actual size, rearrange: actual size = image size ÷ magnification.

Planning an investigation

1. State the independent variable (what you change) and how you change it, with at least five values over a sensible range.
2. State the dependent variable (what you measure) and how: the apparatus and the units.
3. List the controlled variables and how each is kept constant (a water bath for temperature, a buffer for pH, a measuring cylinder for volume).
4. Describe a control where needed (boiled enzyme, no leaf, distilled water) to show the effect is caused by the independent variable.
5. Do repeats (at least three) and calculate a mean, to make the results more reliable and show up anomalies.
6. Identify risks and precautions: eye protection with chemicals, care with hot water baths and scalpels (cut away from you, on a tile).
7. Say how you will record (a table) and process the results (mean, rate, graph), and what result would support the prediction.

Food tests (topic 4)

Evaluating

Sources of error should be specific to the experiment: “the end-point colour was hard to judge”, “the temperature was not controlled”, “bubbles differ in size”, “only one leaf was used”. Each improvement should answer one of them: compare with a colour standard, use a water bath, collect the gas in a syringe and measure its volume, use more leaves and calculate a mean. “Human error” and “be more careful” score nothing.