6.3 Scientific Method, Hypotheses & Variable Identification

6.3 Scientific Method, Hypotheses & Variable Identification

Scientific reasoning constitutes roughly 30% of the entire GED Science assessment. Rather than requiring rote memorization of factual trivia, the test evaluates your ability to evaluate experimental setups, critique hypotheses, isolate variables, and distinguish between valid and invalid scientific conclusions.

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1. The Structure of Scientific Inquiry

Scientific inquiry is a systematic process used to investigate natural phenomena, acquire new knowledge, and correct previous understandings.

 Observation --> Question --> Hypothesis --> Experiment --> Data Analysis --> Conclusion

1. Observation: Gathering qualitative or quantitative information using senses or instrumentation.
2. Question: Formulating a specific, answerable inquiry based on observations.
3. Hypothesis: Developing a tentative, testable explanation.
4. Experimentation: Conducting controlled tests to gather empirical evidence.
5. Data Analysis: Processing raw data using graphs, tables, and statistics.
6. Conclusion: Determining whether data supports or refutes the hypothesis.

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2. Formulating Testable & Falsifiable Hypotheses

A valid scientific hypothesis must meet two strict criteria:

1. Testable: Must be capable of being evaluated through physical experimentation or observational studies.
2. Falsifiable: There must exist a possible outcome or observation that could prove the hypothesis false.

Non-Example (Untestable): "Plants grow better when played classical music because they enjoy peaceful melodies." (Cannot objectively measure plant emotion or musical preference).

Scientific Example (Testable & Falsifiable): "If tomato plants are exposed to 12 hours of red light daily, then their fruit yield (mass in kg) will increase compared to plants exposed to white light, because red wavelengths maximize chlorophyll absorption during photosynthesis."

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3. Variable Identification: Independent, Dependent, and Controlled

In any controlled experiment, variables must be rigorously defined and isolated.

Variable Identification Memory Hack:

Use the DRY MIX acronym:

• Dependent / Responding / Y-axis
• Manipulated / Independent / X-axis

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4. Experimental Groups vs. Control Groups

To ensure results are caused solely by the independent variable, an experiment must compare two types of groups:

• Experimental Group: Receives the treatment or independent variable being tested (e.g., plants given a new fertilizer).
• Control Group: Does not receive the independent variable treatment, or receives a baseline standard. It provides a benchmark to compare results against.
  • Negative Control: Receives no treatment (e.g., plants watered with pure distilled water).
  • Positive Control: Receives a treatment known to produce a positive result (ensures test equipment functions correctly).
  • Placebo Control: Used in medical trials where human subjects receive an inactive substance (sugar pill) to account for psychological bias.

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5. Distinguishing Hypotheses, Theories, and Laws

A common misunderstanding on the GED exam is confusing everyday language with scientific terminology.

• Hypothesis: A proposed, testable explanation for a narrow set of observations. Has not yet been broadly validated.
• Scientific Theory: An extensively tested, highly supported, comprehensive explanation of why natural phenomena occur (e.g., Cell Theory, Theory of Plate Tectonics, Theory of General Relativity). A theory never turns into a law upon receiving more proof.
• Scientific Law: Concise mathematical statements or descriptions of what occurs consistently under specific conditions (e.g., Law of Universal Gravitation, Law of Conservation of Energy, Ohm's Law). Laws state what happens; theories explain why.

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6. GED Science Application & Worked Example

Scenario:

A marine biologist tests the impact of ocean acidification on clam shell degradation. She sets up five 50-gallon aquariums filled with artificial seawater.

• Tank 1: pH 8.2 (normal ocean pH)
• Tank 2: pH 7.8
• Tank 3: pH 7.4
• Tank 4: pH 7.0
• Tank 5: pH 6.6

She places 20 adult clams of the same species into each tank. Water temperature in all tanks is maintained at 20°C, and all clams are fed 5 grams of algae daily. After 30 days, she measures the change in shell mass (in grams) for each clam.

Analysis of Setup:

1. Independent Variable: The water pH level (intentionally varied across Tanks 1–5).
2. Dependent Variable: The change in shell mass (grams) (measured outcome).
3. Control Group: Tank 1 (pH 8.2), representing baseline normal seawater.
4. Controlled Variables (Constants): Water volume (50 gal), water temperature (20°C), initial clam count (20), clam species, algae food mass (5g daily), and test duration (30 days).