Grade: Grade 11 Subject: Science Unit: Advanced Science SAT: ProblemSolving+DataAnalysis ACT: Science

Investigation Lab

Learn

Scientific investigation is the systematic process of asking questions, designing experiments, collecting data, and drawing conclusions based on evidence. This lesson focuses on developing your skills in experimental design and the scientific inquiry method.

The Scientific Method

The scientific method provides a structured approach to investigating natural phenomena:

  1. Observation: Notice something interesting or puzzling in the natural world
  2. Question: Formulate a testable question about your observation
  3. Hypothesis: Propose a tentative explanation that can be tested
  4. Experiment: Design and conduct a controlled experiment
  5. Analysis: Collect and analyze data from your experiment
  6. Conclusion: Determine whether your hypothesis was supported

Variables in Experiments

Understanding variables is crucial for designing valid experiments:

  • Independent Variable: The factor you deliberately change or manipulate
  • Dependent Variable: The factor you measure in response to changes
  • Controlled Variables: Factors kept constant to ensure a fair test

Experimental Controls

A control group receives no treatment or the standard treatment, providing a baseline for comparison. This allows you to determine whether observed effects are due to your independent variable rather than other factors.

Sample Size and Trials

Repeating experiments multiple times (trials) and using adequate sample sizes increases the reliability of your results. More data points reduce the impact of random errors and outliers.

Examples

Example 1: Identifying Variables

Scenario: A student wants to test whether the amount of fertilizer affects plant growth.

  • Independent Variable: Amount of fertilizer (0g, 5g, 10g, 15g)
  • Dependent Variable: Plant height after 4 weeks
  • Controlled Variables: Type of plant, soil type, water amount, sunlight exposure, pot size
  • Control Group: Plants receiving 0g fertilizer

Example 2: Designing a Valid Experiment

Research Question: Does temperature affect the rate of enzyme activity?

Hypothesis: Enzyme activity will increase with temperature up to an optimal point, then decrease at higher temperatures.

Procedure:

  1. Prepare enzyme solution at constant concentration
  2. Set up water baths at 10C, 25C, 37C, 50C, and 65C
  3. Add substrate to enzyme solution at each temperature
  4. Measure reaction rate by timing product formation
  5. Repeat each trial 3 times and calculate averages

Example 3: Evaluating Experimental Design

Flawed Design: "I tested whether music helps plants grow by playing classical music to one plant and rock music to another plant for a week."

Problems:

  • Sample size too small (only 1 plant per group)
  • No control group (no-music condition)
  • Duration may be too short to observe growth differences
  • No quantitative measurement specified

Practice

Work through these problems to strengthen your experimental design skills.

1. A researcher wants to test whether caffeine improves reaction time in students. Identify the independent variable, dependent variable, and at least three controlled variables.

2. Design an experiment to test whether salt concentration affects the germination rate of seeds. Include your hypothesis, materials, procedure, and how you would analyze results.

3. A student claims: "I proved that studying with background noise is better because I got a higher grade on a test when I studied with music playing." What are the flaws in this reasoning?

4. Why is it important to have a control group in an experiment testing a new medication?

5. An experiment tests how light intensity affects photosynthesis rate in aquatic plants. The student measures oxygen bubble production. What variables should be controlled?

6. A study finds that students who eat breakfast score higher on tests. Can we conclude that eating breakfast causes better test performance? Explain why or why not.

7. Design an experiment to determine the optimal pH for amylase enzyme activity. Specify at least 5 different pH levels to test.

8. A researcher conducts only one trial of an experiment and gets unexpected results. What should they do, and why?

9. Explain the difference between qualitative and quantitative observations. Provide an example of each from a biology experiment.

10. An experiment with 50 subjects in each group finds that the treatment group showed improvement. The control group also showed some improvement. What might explain the control group's improvement?

Check Your Understanding

Q1: What distinguishes a hypothesis from a prediction?

Show Answer

A hypothesis is a testable explanation for an observation, while a prediction is a specific, measurable outcome you expect to observe if the hypothesis is correct. For example, a hypothesis might be "Plants need light for photosynthesis," while a prediction would be "Plants kept in darkness will produce less oxygen than plants in light."

Q2: Why should experiments be repeated multiple times?

Show Answer

Repetition increases reliability by reducing the impact of random errors and anomalies. Multiple trials allow you to calculate averages, identify outliers, and determine whether results are consistent and reproducible.

Q3: What is the purpose of controlled variables?

Show Answer

Controlled variables are kept constant to ensure that any observed changes in the dependent variable are due solely to the independent variable, not other factors. This makes the experiment a fair test.

Next Steps

  • Practice identifying variables in published research studies
  • Design your own investigation on a topic that interests you
  • Move on to the next lesson: Data and Graphs