SPM Biology Paper 3 (4551/3)

What Paper 3 tests

Paper 3 assesses the science process skills used to plan and analyse an experiment: making a hypothesis, identifying and controlling variables, recording results in a table, drawing a graph and reaching a valid conclusion. These are marks you earn on paper, so they can be practised fully even without a laboratory.

The format at a glance

The skills that earn marks

1. A clear, directional hypothesis linking the manipulated and responding variables.
2. Correctly named manipulated, responding and fixed (controlled) variables.
3. A neat results table with headings and units.
4. A well-drawn graph with labelled axes and a sensible scale.
5. A conclusion that refers to the data and states whether the hypothesis is supported.

Common mistakes

How the practical session is organised

Paper 3 is a single practical task applied to one of the compulsory experiments in the syllabus. It runs as a short planning session of 5 minutes planning, in which you read the question and plan your approach, followed by 40 minutes answering in which you carry out the task and write your answers.

Because the marks reward your scientific thinking on paper, you can rehearse the whole task with worksheets before exam day.

The question is built around a real procedure, but what earns marks is how you frame the hypothesis, control the variables, record and present the data, and reason from it, not the tidiness of your apparatus.

The practical work Paper 3 draws on

The science process skills in Paper 3 are applied to the practical work set out in the KSSM Biology syllabus across Form 4 and Form 5. Knowing the standard experiments means the procedure is familiar, so your time goes into the analysis rather than into working out what to do.

These commonly include:

• The effect of temperature and pH on enzyme activity.
• Osmosis and diffusion in living tissue, such as potato strips or Visking tubing.
• The effect of light intensity or carbon dioxide on the rate of photosynthesis.
• The rate of respiration in germinating seeds or yeast.
• Food tests for starch, reducing sugar, protein and fat.
• Transport in plants, such as the movement of water through a shoot.
• The effect of exercise on pulse rate or breathing rate.
• Population sampling of plants using a quadrat.

Worked planning example

Question stem. Plan an experiment to investigate how the concentration of a sucrose solution affects the change in mass of potato strips.

Hypothesis. As the concentration of the sucrose solution increases, the change in mass of the potato strips decreases, becoming a loss of mass at high concentrations. Variables. Manipulated: concentration of the sucrose solution; responding: change in mass of the potato strips; fixed: length or initial mass of the strips, volume of solution, temperature, and the time left in the solution.

Table headings. A first column headed 'Concentration of sucrose / mol dm⁻³', then columns for initial mass / g, final mass / g and change in mass / g. Conclusion. The strips gain mass in dilute solutions because water enters the cells by osmosis, and lose mass in concentrated solutions because water leaves; the concentration at which there is no change in mass is isotonic with the cell sap.

Making the most of the marks

Before you hand in your answers

• Check that the hypothesis names both variables and gives a direction.
• Check that you have listed the manipulated, responding and at least two fixed variables.
• Check that every table heading has a unit and that the readings share the same number of decimal places.
• Check that the graph axes are labelled with units and the points are plotted accurately.
• Check that the conclusion uses your own data and states whether the hypothesis is supported.
• Check that any suggested improvement is specific and could actually be carried out.
• Check that units are consistent throughout, for example, all volumes in cm³ and all masses in g.
• Check that the number of readings matches the range of values you planned to test.

Source:SRC-FORMAT

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