Scientific Method

Imagine yourself as a scientist
Science is an
organized way of
using evidence to
learn about the
natural world.
3 Goals of Science:
1. Find Explanations
2. Identify Patterns
3. Make Predictions
Scientific Method
In the 17th century most people believed in
spontaneous generation:
the idea that living
things could arise from
nonliving substances.
For example, people
believed that if you left
meat out to rot it would
produce maggots.
Scientific Method
Step 1: Observing
and Questioning
• Example Observation:
Flies frequently land
on the meat a few
days before the
maggots appear.
• Example Question:
Are the maggots
produced by flies?
Scientific Method
Step 2: Forming a
• Hypothesis: a possible
explanation for
• It must be testable to
continue the scientific
• Example: The maggots
come from the flies not
the rotting meat.
Scientific Method
Step 3: Experiment
• Independent variable: the variable that the
experimenter changes.
• Dependent variable:
changes in response
to the independent
Identify the
dependent and
Scientific Method
Step 3: Experiment
• Experimental Group: the independent variable has been
• Control Group –
exactly the same as the
experimental group
except the
independent variable
has not been changed.
What is the control
group in the
Scientific Method
Step 4: Collecting and Analyzing Data
• Data: Information gathered from
• Two types of data
– Quantitative – involves numbers,
counting or measuring
– Qualitative – involves
characteristics that cannot easily
be measured or counted.
• Inference – a logical interpretation
of data based on prior knowledge
Scientific Method
Step 5: Drawing Conclusions
– Researchers use data as
evidence to determine if
the hypothesis needs to be
supported or refuted.
– Do the results of the
experiment support the
idea of spontaneous
generation? Explain.
Scientific Method
Scientists record and publish their work so
that they can review, evaluate and
criticize each other’s work.
• After reviewing Redi’s experiment,
scientist John Needham, thought that he
could show that bacteria grow through
spontaneous generation.
– He boiled broth in an open flask to kill
all bacteria. After several days more
bacteria grew in the flask.
– What is the problem with this
Scientific Method
• Scientist, Lazzaro Spallanzani, reveiwed
Needham’s experiment and
hypothesized that the bacteria could
have come from the air.
– He repeated Needham’s experiment
but he sealed the flasks.
– Showed that bacteria did not grow
from spontaneous generation.
– After review, scientists did not accept
Spallanzani’s conclusions. Why not?
Scientific Method
• Louis Pasteur repeated the experiment but this time he
used a flask that would let air in but keep out bacteria.
– Because previous scientists’ published their work
Pasteur was able to improve on their experimental
– Did Pasteur’s results support spontaneous generation?
Scientific Method
Scientific Terms
• Hypothesis: a possible
explanation for observations.
• Theory: a well-tested
explanation for a broad range
of observations based on
– Ex: Theory of Biogenesis: all
living thing come from other
living things.
– Theories can be supported or
disproven but never proven
Scientific Method
Scientific Terms
• Law: A statement or
equation that summarizes
observations without
explaining them.
– Law of conservation of matter
– Laws of inheritance