Steps of a scientific investigation
A scientific investigation follows an orderly method so results are reliable. The usual steps are:
- Observation — noticing something and asking a question.
- Hypothesis — a testable, tentative statement that predicts an answer.
- Planning and experimenting — designing a fair test and collecting data.
- Analysing data — organising results in tables and graphs.
- Conclusion — deciding whether the hypothesis is supported.
Understanding variables
An experiment must be a fair test, so variables are controlled:
- Manipulated (independent) variable — the one you change on purpose.
- Responding (dependent) variable — the one you measure as the result.
- Fixed (controlled) variables — everything else kept the same so it does not affect the result.
Example
To test how light affects photosynthesis in pondweed, the manipulated variable is light intensity, the responding variable is the number of bubbles produced per minute, and fixed variables include temperature and the type of plant.
Why control variables?
If more than one thing changes at a time, you cannot tell which factor caused the result. Keeping the fixed variables constant makes the test fair and the conclusion trustworthy.
Key idea
Change one variable, measure one variable, keep the rest constant — that is a fair test.
Making results reliable
Even a well-planned experiment can give scattered readings, so biologists repeat each measurement several times and take an average. Repeating reduces the effect of random error and shows whether a result can be trusted. A well-designed investigation may also include a control — a set-up with no treatment — so the effect of the manipulated variable can be seen against a fair comparison.
After the experiment, the data are studied for a pattern. If the results support the hypothesis, it is accepted for now; if they do not, the hypothesis is rejected or improved and tested again. This honest cycle of testing and re-testing is what makes science trustworthy, because any other person can repeat the same method and check the findings for themselves.