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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
Method
 Observation
 State the Problem
 Hypothesis
 Experiment
 Data Collection
 Conclusion
 Retest
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.
2.
3.
4.
Global Warming
Smoking
Sleep
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 fish
Remember 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
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.
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
• Dependent Variable:
- always plotted on the y-axis
- factor that is measured as the
experiment proceeds
pH
Plant Growth Plant Growth Plant Growth
after 1 hour after 2 hours after 3 hours
2
10 cm.
15 cm.
22 cm.
4
6 cm.
12 cm.
15 cm.
6
5 cm.
10 cm.
12 cm.
8
4 cm.
9 cm.
10 cm.
10
4 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.
2.
3.
4.
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?
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.
2.
3.
4.
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
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.