Investigation Lab
Learn
Scientific investigation is the systematic process of asking questions, designing experiments, collecting data, and drawing conclusions. In this lesson, you will learn how to design and conduct rigorous scientific investigations.
The Scientific Method in Practice
While the scientific method is often presented as a linear sequence, real scientific inquiry is iterative and flexible. Key components include:
- Observation: Noticing patterns or phenomena that spark curiosity
- Question formulation: Developing testable questions based on observations
- Hypothesis development: Creating falsifiable predictions
- Experimental design: Planning controlled tests of hypotheses
- Data collection: Gathering quantitative and qualitative information
- Analysis: Interpreting results using statistical methods
- Conclusion: Drawing evidence-based conclusions
Variables in Experiments
Understanding variable types is essential for experimental design:
- Independent variable: The factor you deliberately change or manipulate
- Dependent variable: The factor you measure as a response
- Controlled variables: Factors kept constant to ensure fair testing
- Confounding variables: Uncontrolled factors that may affect results
Controls and Replication
Valid experiments require:
- Control group: A baseline for comparison that receives no treatment
- Experimental group: The group receiving the treatment or manipulation
- Replication: Multiple trials to ensure results are reproducible
- Sample size: Sufficient subjects to achieve statistical significance
Examples
Example 1: Plant Growth Investigation
Research Question: How does the amount of light affect plant growth?
Hypothesis: Plants exposed to more hours of light per day will grow taller than plants with less light exposure.
Variables:
- Independent: Hours of light per day (0, 4, 8, 12, 16 hours)
- Dependent: Plant height (measured in cm)
- Controlled: Soil type, water amount, temperature, plant species, pot size
Design: 5 groups of 10 plants each, measured weekly for 6 weeks
Example 2: Enzyme Activity Investigation
Research Question: How does pH affect the rate of enzyme activity?
Hypothesis: Amylase enzyme will show maximum activity at pH 7 and decreased activity at extreme pH values.
Variables:
- Independent: pH level (2, 4, 6, 7, 8, 10, 12)
- Dependent: Time for starch breakdown (measured by iodine test)
- Controlled: Temperature, enzyme concentration, substrate concentration, volume
Practice
Complete these practice problems to strengthen your investigation design skills.
1. A student wants to test whether caffeine affects reaction time. Identify the independent and dependent variables.
2. In an experiment testing fertilizer effects on crop yield, what variables should be controlled?
3. Why is it important to have a control group when testing the effectiveness of a new medication?
4. A researcher conducts an experiment with only 3 subjects per group. What is the main limitation of this design?
5. Design a hypothesis for testing whether music affects concentration during studying.
6. What is the difference between a hypothesis and a prediction? Provide an example of each.
7. Explain why randomization is important when assigning subjects to experimental groups.
8. A scientist claims that a new drug cures a disease based on one successful trial with 5 patients. Evaluate this claim.
9. Design an experiment to test whether salt concentration affects the freezing point of water. Include all variables and controls.
10. What is a confounding variable? Give an example from a study on exercise and weight loss.
Check Your Understanding
Question 1: Which of the following is NOT a characteristic of a well-designed experiment?
- A) Multiple trials for replication
- B) A single large sample instead of a control group
- C) Controlled variables kept constant
- D) Random assignment to groups
Question 2: In an experiment testing how temperature affects bacterial growth, what is the dependent variable?
- A) Temperature
- B) Type of bacteria
- C) Amount of bacterial growth
- D) Time of incubation
Next Steps
- Review the scientific method and variable identification
- Practice designing experiments for various research questions
- Continue to the next lesson on Data and Graphs