Investigation Lab
Learn
Laboratory investigations are the backbone of scientific research. In this lesson, you will learn how to design, conduct, and document controlled experiments that yield reliable, reproducible results.
Key Components of a Lab Investigation
- Research Question: A focused, testable question that guides your investigation
- Hypothesis: A prediction based on prior knowledge that can be tested experimentally
- Variables: Independent (what you change), dependent (what you measure), and controlled (what stays constant)
- Procedure: Step-by-step instructions that another scientist could replicate
- Materials List: All equipment, chemicals, and supplies needed
- Safety Considerations: Hazards identified and precautions planned
Experimental Controls
A well-designed experiment includes:
- Control Group: A baseline for comparison that does not receive the experimental treatment
- Experimental Group: The group that receives the treatment or change being tested
- Replication: Multiple trials to ensure results are consistent and not due to chance
Data Collection Standards
Professional-quality data collection requires:
- Quantitative measurements with appropriate precision and units
- Qualitative observations recorded systematically
- Organized data tables prepared before the experiment begins
- Documentation of any unexpected observations or deviations from procedure
Examples
Example 1: Identifying Variables
Research Question: How does fertilizer concentration affect tomato plant height?
- Independent Variable: Fertilizer concentration (0%, 25%, 50%, 100%)
- Dependent Variable: Plant height (measured in cm)
- Controlled Variables: Soil type, water amount, light exposure, pot size, plant variety, temperature
Example 2: Writing a Testable Hypothesis
Weak: Plants need sunlight to grow.
Strong: If tomato plants are exposed to 12 hours of direct sunlight daily versus 6 hours, then the plants receiving 12 hours will grow 30% taller over a 4-week period because increased light provides more energy for photosynthesis.
Example 3: Sample Data Table Design
| Trial | Treatment | Day 0 Height (cm) | Day 14 Height (cm) | Day 28 Height (cm) |
|---|---|---|---|---|
| 1 | Control (0%) | 5.2 | 8.7 | 12.1 |
| 2 | 50% fertilizer | 5.0 | 11.3 | 18.6 |
Practice
Complete these exercises to strengthen your lab investigation skills.
1. A student wants to test whether water temperature affects the rate at which sugar dissolves. Identify the independent, dependent, and three controlled variables for this experiment.
2. Rewrite the following hypothesis to make it testable: "Exercise is good for health."
3. An experiment has 5 trials in the control group and 5 trials in the experimental group. Why is this better than having only 1 trial in each group?
4. Design a data table for an experiment testing how different soil pH levels (5.0, 6.0, 7.0, 8.0) affect bean seed germination rate over 10 days.
5. A researcher finds that their experimental results vary widely between trials. List three possible sources of error and suggest how to minimize each.
6. What is the purpose of a control group in an experiment? Give an example of an experiment without a proper control and explain why the results would be unreliable.
7. A student measures plant height "to the nearest centimeter." Another student measures "to the nearest millimeter." Which measurement is more precise? When would each level of precision be appropriate?
8. Write a complete materials list and safety considerations for an experiment testing the effect of acid rain (simulated with dilute vinegar solutions) on limestone rock samples.
9. Critique the following procedure: "Put salt in water and stir until dissolved. Measure how long it takes." What details are missing that would prevent replication?
10. Design a controlled experiment to test whether background music affects student performance on math problems. Include: research question, hypothesis, all variable types, and a brief procedure outline.
Check Your Understanding
Q1: What distinguishes a hypothesis from a prediction?
Q2: Why must controlled variables be kept constant throughout an experiment?
Q3: How does replication improve the reliability of experimental results?
Q4: What information should be recorded if something unexpected happens during an experiment?
Next Steps
- Review the components of experimental design until you can identify them in any study
- Practice writing testable hypotheses for everyday questions
- Continue to the next lesson on Data and Graphs to learn how to analyze your results