Paper 3 Practical Trends

What recurs in Paper 3

Paper 3 has a 5-minute planning session followed by 40 minutes of answering, and it is applied to the compulsory experiments set out in the DSKP, which span both Form 4 and Form 5. From one paper to the next, the specific experiment, organism or manipulated variable can differ, but the underlying package of science process skills being assessed stays the same.

This is why past papers are useful less for their exact experiment and more for the recurring skill demands behind it.

The skills tested every time

How the compulsory experiments recur

Paper 3 draws on the fixed list of compulsory experiments in the DSKP rather than an open-ended set of topics. The same experiment can reappear with a different manipulated variable, a different organism, or a different set of given data from one year to the next, so a candidate who only memorises one version of an experiment can be caught out by a small change in context.

Practising the underlying skills across several different experiments is more reliable than rehearsing a single fixed version.

Preparing without needing a laboratory

How Paper 3 marks are awarded

Paper 3 is worth 15 marks and is timed as 5 minutes planning followed by 40 minutes answering. The marks are spread across the science process skills rather than concentrated in one long answer, so a candidate who writes a strong hypothesis but a weak table still loses the table marks.

Reading past papers, no single skill dominates; the reliable strategy is to be competent at all of them.

The planning time is short, so it is best used to decide the manipulated, responding and fixed variables and to sketch the shape of the results table before writing. Because the marks are analytic, each correctly completed element, a clear hypothesis, a fully labelled table, an accurate graph, a data-based conclusion, is scored on its own terms.

Writing a hypothesis and identifying variables well

The hypothesis is one of the most consistently examined elements. A strong hypothesis names both the manipulated and the responding variable and states a clear direction, for example, that as the manipulated variable increases, the responding variable increases or decreases.

A hypothesis that only says the two are related, with no direction, is marked as incomplete.

Variables must be separated cleanly. The manipulated variable is the one you deliberately change, the responding variable is the one you measure, and the fixed variables are everything kept constant so the test is fair.

Past papers repeatedly award marks for naming a specific fixed variable, such as temperature or volume of solution, rather than a vague phrase like the conditions.

A worked Paper 3-style item

Scenario. A student investigates how temperature affects the rate at which the enzyme amylase breaks down starch. Starch solution and amylase are mixed at 20, 30, 40, 50 and 60 degrees Celsius, and the time taken for the mixture to stop giving a blue-black colour with iodine is recorded.

(a) State a suitable hypothesis. (b) Identify the manipulated, responding and one fixed variable.

(c) The reaction was fastest at 40 degrees and very slow at 60 degrees. Draw a conclusion and explain it.

Model answer. (a) As temperature increases up to an optimum, the rate of starch breakdown by amylase increases; above the optimum the rate decreases. (b) Manipulated: temperature; responding: time taken for the blue-black colour to disappear (rate of reaction); fixed: volume and concentration of starch (or of amylase), or pH.

(c) Amylase works fastest near 40 degrees, its optimum temperature; at 60 degrees the high temperature has denatured the enzyme, changing the shape of its active site so the substrate no longer fits, which is why the reaction is very slow.

Source:SRC-FORMAT, SRC-DSKP-EN

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