What the exam asks
- Identify the independent variable, dependent variable, or standardized (controlled) variables from an experimental description, data table, or graph.
- Identify and justify a negative or positive control group.
- State the null hypothesis () for an investigation (and know how it differs from an alternative hypothesis, ).
- Pose a testable scientific question or propose a new investigation (or modification) to test an alternative claim.
- Predict experimental outcomes when a procedure or variable is altered.
Core ideas
Testable questions and variables
A scientific investigation begins with an observation or model that leads to a testable question—one that asks how a specific, measurable change in one factor affects a measurable biological outcome.
| Component | Definition | How to spot it in an energetics lab |
|---|---|---|
| Independent variable (IV) | The factor deliberately manipulated by the researcher. | Plotted on the -axis or listed in the first column of a table (e.g., , substrate concentration, light wavelength). |
| Dependent variable (DV) | The measured response that depends on the IV. | Plotted on the -axis (e.g., rate of production in , absorbance at ). |
Experimental controls
Do not confuse controlled variables (constants kept the same across all tubes) with a control group (a separate experimental treatment used as a baseline for comparison).
- Negative control: A group where no phenomenon or response is expected. It verifies that the response is caused by the independent variable and not by contamination or background reaction.
- Energetics examples: A tube with boiled (denatured) enzyme, distilled water instead of enzyme, or leaf disks kept in the dark.
- How to justify: “It provides a baseline for comparison to confirm that any observed reaction is due to the active enzyme/treatment and not spontaneous substrate breakdown.”
- Positive control: A group using a treatment known to produce the expected effect. It verifies that the assay, reagents, and equipment are functioning properly.
- Energetics example: Testing a new, unknown amylase extract alongside a tube containing a proven, commercial amylase solution.
Hypotheses and predictions
- Null hypothesis (): A precise, testable statement that the independent variable has no statistically significant effect on the dependent variable (or that there is no statistically significant difference between treatment groups). Any observed difference is due to random chance alone.
- Alternative hypothesis (): A statement that the independent variable does have a significant effect on the dependent variable.
- Prediction: An “If... then...” or direct forecast of the specific data trend expected if a hypothesis is supported (e.g., “Adding the competitive inhibitor will decrease the initial reaction rate at low substrate concentrations”).