Scientific Method

Scientific Theory Theories can be disproven. A theory is an explanation of a set of related observations or events, supported by experiments, and verified multiple times by many independent scientists. Theories can be disproven.

How Does a Theory differ from a Law? A Law is an accepted fact.

Observation vs. Inference Information gathered by one or more of the senses –sight, hearing, touch, smell, taste

Observation vs. Inference A logical interpretation or explanation based on prior knowledge and experience

Steps in the Scientific Method Observation State the Problem Hypothesis Experiment Data Collection Conclusion Retest

Observation How would you explain what you see? Plants grow differently in differently colored light.

1. State the Problem What problem are you trying to solve? Always write it as a question beginning with DOES or WILL….? Ex. Does red light affect the growth of a plant?

2. State Your Hypothesis Hypothesis = an educated guess. Written as --- If….Then.. statement. Hypothesis must be testable. Ex. If the red light is used, then the plant will grow bigger.

Example situations – Using Temperature and Breathing Rate Problem: Does the water temperature affect the breathing rate of the fish?

Here are some possible hypotheses. Hypothesis: If the water temperature is increased, then the fish’s breathing rate will increase.

Formulate a hypothesis on the following topics: Smoking Global Warming Steroids Sleep

3. Perform An Experiment

Set up a Controlled Experiment There are always two groups in an experiment: Control Group – does not receive the treatment; used for comparison or as a reference point Experimental Group – receives the treatment, the “variable”

A factor in the experiment that is being changed or changes Variable

The independent variable is the one factor that is being changed by experimenter The Experimental Group receives the Independent Variable, the control group does not.

A Controlled Experiment should have ONLY ONE variable. Independent Variable

What is the dependent variable then? The variable that is measured in the experiment. Ex. --- growth of a plant, breathing rate of the fish Remember to always include a unit of measurement.

conditions that are kept the same between the two groups. All of the other conditions that are kept the same between the two groups. Ex. location, age, gender, size Constants

Let’s Practice Hypothesis: If the water temperature Problem: Does the water temperature affect the breathing rate of the fish? Hypothesis: If the water temperature is increased, then the fish’s breathing rate will increase. Control group: Experimental Group: Independent variable: Dependent variable: Constants:

4. Collect Data Utilize a chart, table or graph to organize data. Makes data easier to compare.

Graphing Basics Line Graphs Independent Variable: - always plotted on the x-axis - factor in the experiment that the experimenter changes -you know the values before you begin the experiment Dependent Variable: - always plotted on the y-axis - factor that is measured as the experiment proceeds

Data Tables pH Plant Growth after 1 hour Plant Growth after 2 hours 10 cm. 15 cm. 22 cm. 4 6 cm. 12 cm. 6 5 cm. 8 4 cm. 9 cm. 10 8 cm.

Practice Problem A scientist is conducting an experiment to determine the number of oxygen bubbles produced by plants at varying levels below the surface of water. What is the independent variable? What is the dependent variable? What is the title of the graph? What will you label the x-axis? What will you label the y-axis?

5. Draw A Conclusion Draw a conclusion based on the data. (you should reference your data, use #’s) Determine if your hypothesis was supported or refuted (rejected).

GOOD Experiment- To Improve Validity Qualities of a GOOD Experiment- To Improve Validity Repeated trials - do the experiment many times for valid results. Large sample size – use many subjects for valid results. Controlled experiments

What are the Qualities of a BAD Experiment Too Few Subjects: not a large enough sampling to draw a valid conclusion from. More than one variable – more than one thing is being changed in the experiment.

Question # 1 A new concept that is tested in a scientific investigation is known as A theory The hypothesis An inference An observation

Question # 2 Which procedure must be followed for the results of an experiment to be considered valid? The experiment must be repeated a number of times and yield similar results. After one trial, the results of the experiment must be published. The results must be expressed in the form of a graph or table. The data must include metric measurements.

Question # 3 An investigation was designed to determine the effect of sunlight on mold growth. Two groups of mold were grown under identical conditions except that one group was exposed only to sunlight, while the other was grown in total darkness. In this investigation, the group of mold grown without receiving sunlight is known as the Experimental variable Dependent variable Control Experimental group

Question # 4 A biologist in a laboratory reports a new discovery based on experimental results. If the results are valid, biologists in other laboratories should be able to Repeat the same experiment with a different variable and get the same results. Perform the same experiment and obtain different results. Repeat the same experiment and obtain the same results. Perform the same experiment under different environmental conditions and obtain the same results.

Question # 5 To test the effect of hormones (auxins) on plant growth, 6 plant seedlings of the same species were measured and then sprayed with auxin (growth hormone). After 4 weeks of growth under ideal conditions, the plants were measured again. To set up a proper control for this experiment, the investigator should Spray the same plants with different amounts of auxin. Spray auxin on 6 plant seedlings of the same species and grow them in the dark. Wash the auxin off 3 of the plants after 2 weeks. Grow another 6 plant seedlings of the same species under the same conditions, spraying them with water.