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Learn5090Paper 3 · Practical TestPractical skillsPractical skills in biology
Practical skills · Subtopic 1 of 1

Practical Skills in Biology

A good investigation changes one independent variable, measures the dependent variable, and keeps other variables controlled (e.g. temperature with a water bath). A control experiment (e.g. boiled enzyme) shows the effect is caused by the factor tested. Repeats improve reliability. The CORMS plan: Change, Organisms (same species, age, size), Repeat, Measure (what and how), Same (control variables). Biological drawings use clear single lines, no shading, labelled with ruled lines. Evaluate by identifying anomalies and suggesting specific improvements.

Cambridge 5090 Paper 3Cambridge 5090 Paper 4Cambridge 0610 Papers 5, 6Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 40 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Plan investigations using CORMS.
  • Explain the use of controls and repeats.
  • Record data, draw graphs and make biological drawings.
  • Evaluate reliability and validity.
Pause and think

To show that yeast causes dough to rise, why should you also set up dough without yeast?

Section 2 of 14

Core idea

Start hereThinking like a scientist

Every fact in your textbook came from an experiment someone planned, controlled and repeated. Practical skills are how biology knows what it knows.

The big idea

Change one variable, measure another, control the rest, include a control, and repeat. Present data clearly and evaluate honestly.

1. Planning with CORMS

CORMS

Five things every plan needs.

Worked examplePlanning an enzyme investigation

Plan how to investigate the effect of temperature on amylase.

Goal
A CORMS plan.
Strategy
Address each letter.
  1. C: 20, 30, 40, 50, 60 °C\text{C: 20, 30, 40, 50, 60 °C}
    Water baths.
  2. R: three repeats each\text{R: three repeats each}
    Calculate means.
  3. M: time for starch to disappear (iodine test every 30 s)\text{M: time for starch to disappear (iodine test every 30 s)}
    Dependent variable.
  4. S: same volumes, concentrations, pH buffer\text{S: same volumes, concentrations, pH buffer}
    Controls.
AnswerA fair, repeatable plan.
✓ CheckAdd a control with boiled amylase ✓.
Exam tipBiological drawings Large, clear continuous lines, no shading, ruled label lines that don't cross, and a magnification or scale.
Pause and think

Why might a student's results be precise but not accurate?

Summary

  • CORMS planning.
  • Controls and repeats.
  • Clear tables, graphs, drawings.
Key words
Control experiment
A version without the factor being tested.
Reliability
How consistent repeated results are.
Validity
Whether the experiment tests what it intends to.
HistoryControlled trials. The first controlled clinical trial in medicine, James Lind's scurvy study in 1747, compared six treatments with sailors kept on the same diet otherwise.
Fun factThe placebo effect. In medical trials, some patients given a sugar pill improve just because they expect to. That's why drug trials need a control group.
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