Overview
This lecture explains how to properly design a scientific experiment by identifying independent, dependent, and control variables, as well as distinguishing between experimental and control groups.
Designing an Experiment
- Test only one variable at a time to isolate its effects.
- Use a control group and an experimental group to compare results.
- In the example, 20 plants are used: 10 receive fertilizer (experimental group) and 10 do not (control group).
- All other conditions (temperature, sunlight, water) must be kept constant for all plants.
Variables in an Experiment
- The independent variable is what you change or control (in this case, the presence or amount of fertilizer).
- The dependent variable is what you measure (e.g., plant height, biomass, number of leaves).
- Control variables are factors kept the same for all groups (e.g., temperature, sunlight, water).
Control Group vs. Control Variable
- The control group is the group that does not receive the independent variable (no fertilizer).
- Control variables are all the conditions kept constant to ensure a fair test.
Measuring Results
- Common dependent variables in plant studies include height, width, biomass, number of leaves, and stem thickness.
- Data from both qualitative (descriptive) and quantitative (numeric) observations can be collected.
Key Terms & Definitions
- Independent Variable — The factor intentionally changed or tested in an experiment.
- Dependent Variable — The factor measured to assess the effect of the independent variable.
- Control Variable — Conditions kept the same for all groups to ensure a fair test.
- Control Group — The group not exposed to the independent variable, used for comparison.
- Experimental Group — The group that receives the independent variable.
Action Items / Next Steps
- Review how to identify independent, dependent, and control variables in sample experiments.
- Prepare examples of control and experimental groups for class discussion.