Experimental Skills and Scientific Reasoning
What this domain tests
Experimental Skills and Scientific Reasoning tests whether you can design, interpret, and critique investigations. Expect variables, controls, sampling, measurement quality, graphs, simple statistics, microscopy, and dilution calculations.
Core rules and concepts
- Identify the independent variable changed by the investigator, the dependent variable measured, and controlled variables kept constant. A control group receives no treatment or a standard treatment for comparison.
- Replication reduces the effect of random variation. Random sampling reduces bias. Precision means repeated measurements agree; accuracy means they are close to the true value.
- A conclusion should be limited to the evidence. Statistical significance indicates that a result is unlikely under the null hypothesis, not that it is biologically important.
- When drawing graphs, put the independent variable on the x-axis and the dependent variable on the y-axis. Use units and appropriate scales.
Worked example
Make 50 mL of 0.10 M solution from a 2.0 M stock. Use C1V1 = C2V2: 2.0 × V1 = 0.10 × 50, so V1 = 2.5 mL. Add 2.5 mL stock to about 40 mL water, mix, then make up to 50 mL. Reasoning: dilution conserves solute amount, and the final volume determines the new concentration.
Traps
Do not confuse a control with a controlled variable. Do not claim causation from a correlation. Do not report more significant figures than the measurement supports. In microscopy, magnification enlarges the image, but resolution determines the smallest detail that can be distinguished.