Scientific Method and Laboratory Skills
The cycle of inquiry
Science is a structured way of asking questions. A typical investigation moves from observation to a question, then to a hypothesis - a testable, falsifiable prediction, not a guess. You then design a controlled experiment, collect data, analyse it, and draw a conclusion that may revise the hypothesis. Know the vocabulary: the independent variable is what the investigator deliberately changes; the dependent variable is what is measured in response; controlled variables are kept constant so the comparison is fair. A control group receives no treatment (or a placebo) and anchors the comparison.
Laboratory craft
Candidates must recognise common apparatus and its purpose: beakers for holding and rough mixing, measuring cylinders and pipettes for volume, Bunsen burner with the air hole closed for a yellow safety flame and open for a hot blue flame, tripods, gauze, filter funnels, and test-tube racks. Safety rules are examinable content: goggles on, hair tied, never point a test tube at anyone, heat test tubes at an angle and move them through the flame, waft vapours toward the nose rather than sniffing directly, and report spills and breakages immediately.
Traps to watch
- Confusing the independent variable with the controlled variables when a question describes a table of results.
- Claiming a hypothesis is "proved"; results support or fail to support a hypothesis.
- Describing a conclusion that goes beyond the data (e.g. extrapolating one trial to all conditions).
- Forgetting that repeat trials reduce the effect of random error, while better instruments reduce systematic error.
Worked example
A student tests whether fertiliser affects plant height: five plants get fertiliser, five get water only, all in identical pots by the same window for four weeks. Independent variable = fertiliser amount; dependent variable = height; controlled variables = pot size, light, water volume, soil type; control group = water-only plants. Measuring all ten plants with the same ruler and averaging each group reduces random error.