Scientific Method

Scientific Theory A theory is an explanation of a set of related

observations or events supported by proven experiments and verified multiple times by many independent scientists.

Theories can be disproven

How Does a Theory differ for a Law

A Law is accepted fact

Observation vs. Inference

• Observation:

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

Observation vs. Inference

• Inference:

A logical interpretation or explanation based on prior knowledge and experience

Steps in the Scientific Steps in the Scientific MethodMethod

ObservationObservation State the State the

ProblemProblem HypothesisHypothesis ExperimentExperiment Data CollectionData Collection ConclusionConclusion RetestRetest

Observation• How would you explain what you see? • Plants grow differently in different color

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?

Example situations – Using Temperature and Breathing Rate

• Does the water temperature effect the breathing rate of the fish?

2. State Your Hypothesis

• Hypothesis = an educated guess.• Written as --- If….then statements.• Hypothesis must be testable.• Ex. If the red light is used, then the

plant will grow bigger.

Here are some possible hypotheses.

Hypothesis: If the water temperature is increased, then the fish breathing rates will increase.

Formulate a hypothesis on the following topics:

1. Global Warming2. Smoking3. Sleep4. Steroids

3. Perform A Experiment

Set up a Controlled Experiment

• Performing a procedure to scientifically solve a problem.

• There are always two groups in an experiment:

• Experimental Group – receives the treatment, the “variable”

• Control Group – does not receive the treatment; used for comparison or as a reference point

•A factor in the experiment that is being changed

•A controlled experiment may have ONLY ONE 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.

What is the dependent variable then?

• The variable that is measured in the experiment.

Ex. --- growth of a plant, breathing rate of the fishRemember to always include a unit of measurement

All of the other conditions that are kept the same

between the two groups.Ex. location, age, gender, size

Let’s Practice

Control group:

Experimental Group: Independent variable: Dependent variable:

Constants:

Problem: Does the water temperature effect the respiration rate of the fish?

Hypothesis: If the water temperature is increased, then the fish breathing rate will increase.

4. Collect Data

•Utilize a chart, table or graph to organize data.•Makes data easier to compare.

Graphing Basics

• Independent Variable: - always plotted on the x-axis- factor in the experiment that the experimenter changes

• Dependent Variable:- always plotted on the y-axis- factor that is measured as the experiment proceeds

Line Graphs

pHpH Plant Plant Growth Growth after 1 after 1 hourhour

Plant Plant Growth Growth after 2 after 2 hourshours

Plant Plant Growth Growth after 3 after 3 hourshours

22 10 cm.10 cm. 15 cm.15 cm. 22 cm.22 cm.

44 6 cm. 6 cm. 12 cm. 12 cm. 15 cm.15 cm.

66 5 cm.5 cm. 10 cm. 10 cm. 12 cm.12 cm.

88 4 cm.4 cm. 9 cm.9 cm. 10 cm.10 cm.

1010 4 cm.4 cm. 8 cm. 8 cm. 8 cm. 8 cm.

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 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).

• Repeated trials - do the experiment many times for valid results.

• Large sample size – use many subjects for valid results.

• Controlled experiments

• 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

1. A theory2. The hypothesis3. An inference4. An observation

Question # 2

• Which procedure must be followed for the results of an experiment to be considered valid?

1. The experiment must be repeated a number of times and yield similar results.

2. After one trial, the results of the experiment must be published.

3. The results must be expressed in the form of a graph or table.

4. 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 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

1. Experimental variable2. Dependent variable3. Control4. 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

1. Repeat the same experiment with a different variable and get the same results.

2. Perform the same experiment and obtain different results.

3. Repeat the same experiment and obtain the same results.

4. Perform the same experiment under different environmental conditions and obtain the same results.

Question # 5• To test the effect of hormones 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

1. Spray the same plants with different amounts of auxin.2. Spray auxin on 6 plant seedlings of the same species

and grow them in the dark.3. Wash the auxin off 3 of the plants after 2 weeks.4. Grow another 6 plant seedlings of the same species

under the same conditions, spraying them with water.