Transcript You Light Up My Life

Concepts & Methods in
Biology
Chapter 1
Scientific Method
• Observe phenomenon
• Develop hypotheses
• Make predictions
• Devise test of predictions
• Carry out test and analyze results
Inductive Logic
• Using observations and facts to arrive at
generalizations or hypotheses
• Observation: Eagles, swallows, and
robins have feathers
• Hypothesis: All birds have feathers
Deductive Logic
• Drawing a specific conclusion based on
a generalization
– Generalization - Birds have feathers
– Example - Eagles are birds
– Conclusion - Eagles have feathers
Role of Experiments
• Procedures used to study a
phenomenon under known conditions
• Allows you to predict what will happen if
a hypothesis is not wrong
• Can never prove a hypothesis 100%
correct
Experimental Design
• Control group
– A standard for comparison
– Identical to experimental group except for
variable being studied
• Sampling error
– Non-representative sample skews results
– Minimize by using large samples
Draw samples from some aspect of nature
CONTROL GROUP
The variable being
tested is absent
EXPERIMENTAL GROUP
The variable being
tested is present
Compile results
Compile results
Compare and analyze the test results
Report on experimental design, test results,
and conclusions drawn from results
Fig. 1.10, p. 12
Scientific Theory
• A hypothesis that has been tested for its
predictive power many times and has
not yet been found incorrect
• Has wide-ranging explanatory power
– Darwin’s Theory of Evolution by Natural
Selection
Biological Therapy
Experiments
Can we use viruses that attack bacteria
(bacteriophages) to fight infections?
Experiment 1
• Hypothesis - Bacteriophages can
protect mice against infectious bacteria
• Prediction - Mice injected with
bacteriophages will not die as a result of
bacterial injection
Experiment 1 - Test
• Experimental group
Inject with bacteria and
bacteriophage
• Control group
Inject with bacteria and saline
Experiment 1 Results & Conclusion
• Experimental group
All mice lived
• Control group
All mice died
• Conclusion - Bacteriophage injections
protect mice against bacterial infections
Experiment 2
• Prediction - Bacteriophage injections
will be more effective treatment than
single dose of the antibiotic
streptomycin
• Test - Mice injected with bacteria, then
with saline, streptomycin, or
bacteriophage
Experiment 2 - Results
• When 2nd injection was:
– Bacteriophage - 11 of 12 mice lived
– 60mg/gm streptomycin - 5 of 12 lived
– 100mg/gm streptomycin - 3 of 12 lived
– Saline - all mice died
• Conclusion - Bacteriophage treatment can be
as good or better than antibiotics
Minimizing Variables
• All mice were same age and sex, reared
under same conditions
• Each mouse in each test group received
exact same treatment
• All mice in control group received same
amount of saline
• Variable tested was antibiotic treatment
versus bacteriophage treatment
Limits of Science
• Scientific approach cannot provide
answers to subjective questions
• Cannot provide moral, aesthetic, or
philosophical standards
Science and the Supernatural
• Science has run up against religious
belief systems
– Copernicus suggested that sun, not the
Earth, was center of universe
– Darwin suggested that life was shaped by
evolution, not a single creation event
Asking Questions
• Scientists still ask questions that
challenge widely held beliefs
• The external world, not internal
conviction, is the testing ground for
scientific beliefs