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Biological Investigation

12 min read

Scientific investigation

A biological investigation answers a question by collecting evidence. It follows the steps of the scientific method.

The scientific methodFive boxes in a row joined by arrows: observe, ask a question, make a hypothesis, test with an experiment, and conclude. A curved arrow returns from the conclusion to a new question.1Observe2Ask aquestion3Make ahypothesis4Test with anexperiment5ConcludeIf the results do not fit, change the hypothesis and test again.

Variables and controls

Type of variableMeaningExample
IndependentThe one you changeTemperature
DependentThe one you measureNumber of seeds germinated
ControlledKept the sameSeed type, water, time
Control experimentA set-up with no change in the independent variable, for comparisonSeeds kept at room temperature

Measuring and recording

Take repeated readings and calculate the mean to reduce the effect of random error. Record results in a table with clear headings and units. Draw graphs with the independent variable on the x-axis. Be accurate with instruments, and note any safety precautions and ethical rules, such as treating animals with care.

The mean of repeated measurements.
Worked exampleMean number of seeds

Four trays gave germination counts of 18, 20, 19 and 23. Find the mean.

  1. Add the counts.
  2. Divide by 4.

Answer: The mean is 20 seeds per tray.

Writing the report

A report has a title, aim, hypothesis, materials and method, results (tables and graphs), discussion and conclusion. Write in the past tense and give sources of error and ways to improve the experiment.

Use the microscope
Practise skills of observation and drawing with the virtual microscope.
Try itRepeated readings

A single reading can be off by chance. Choose how many repeats you take; the uncertainty of the mean falls.

The uncertainty of the mean falls as the number of repeats rises.
Check yourself In a germination experiment on temperature, the independent variable is...
Check yourself What is the purpose of a control experiment?
Check yourself Why repeat readings?

Key terms

Hypothesis
A testable prediction.
Independent variable
The variable that is changed.
Dependent variable
The variable that is measured.
Control
A comparison set-up.

Summary

  • An investigation follows the scientific method from question to conclusion.
  • Change one variable, measure the effect and keep others constant.
  • Repeat readings and use the mean.
  • A report states the aim, method, results, discussion and conclusion.
Classification and Taxonomy