Biology is the study of living systems, so biologists need a careful way to test ideas about organisms, cells, ecosystems, and behavior. The scientific method helps turn observations into testable questions, fair experiments, and evidence-based conclusions. It matters because living things are complex, and careful experimental design helps separate real patterns from coincidence.
A plant-growth experiment is a clear example because growth can be measured and conditions such as light, water, and soil can be controlled.
Key Facts
- A hypothesis is a testable explanation, such as: If light exposure increases, then plant height will increase.
- Independent variable = the factor the scientist changes, such as hours of light per day.
- Dependent variable = the factor measured in response, such as plant height in cm.
- Controlled variables = factors kept the same, such as plant species, soil type, pot size, and water amount.
- Average growth = total growth of all plants in a group / number of plants in the group.
- A conclusion should state whether the data support the hypothesis, using evidence from measurements.
Vocabulary
- Hypothesis
- A hypothesis is a testable explanation or prediction based on observations and prior knowledge.
- Independent Variable
- The independent variable is the factor deliberately changed by the experimenter.
- Dependent Variable
- The dependent variable is the measured result that may change because of the independent variable.
- Control Group
- A control group is a comparison group kept under standard conditions to help identify the effect of the tested variable.
- Data
- Data are observations or measurements collected during an investigation and used as evidence.
Common Mistakes to Avoid
- Changing more than one variable at a time makes the experiment unfair because you cannot tell which factor caused the result.
- Forgetting a control group weakens the conclusion because there is no baseline for comparison.
- Using only one plant per treatment is unreliable because individual differences or random events could affect the result.
- Claiming the hypothesis is proven is too strong because experiments support or do not support a hypothesis rather than proving it with absolute certainty.
Practice Questions
- 1 A student grows three bean plants with 4 hours of light per day. Their height increases are 5 cm, 7 cm, and 6 cm. What is the average growth for this group?
- 2 In a plant-light experiment, Group A receives 2 hours of light, Group B receives 6 hours, and Group C receives 10 hours. All plants receive 50 mL of water daily. Identify the independent variable, dependent variable, and one controlled variable.
- 3 A plant experiment finds that plants under 10 hours of light grow taller than plants under 2 hours of light, but the 10-hour group also received more water. Explain why this design makes the conclusion uncertain and how to fix it.