the scientific method i. the scientific method is an orderly way to solve problems five steps: –1....
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The Scientific Method
I. The scientific method is an orderly way to solve problems
• Five steps:– 1. Observations/Asking a question– 2. hypothesis– 3. Experiment– 4. Recording results– 5. Discussion & Conclusion
A. Asking a question- Based on identification of a problem
- Scientists make OBJECTIVE observations of the natural world in order to identify the problem.
- Observations are followed by inferences, logical interpretation based on prior knowledge and experience.
B. Hypothesis – possible explanation for a set of observations
• Making an “educated guess” that is testable.
• Deductive hypothesis: “if”…”then” statement.
• Inductive hypothesis: most common type; gut feeling.
C. Designing an Experiment:• Controlled experiment – only one
variable, or factor, is changed at a time.
• All other factors are called constants and are exactly the same for all test groups.
• Independent variable – the thing that is changed or manipulated.
• Dependent variable – the response to the change that was made. (What you measure)
Controlled experiment• Based on a comparison of a control
group and an experimental group.
• Control group – the “norm” – you don’t do anything to this group. It should represent the normal situation, and be a standard of comparison.
• Experimental Groups – these are the groups that you change or manipulate to test a certain variable.
• Example: You are testing a certain drug was effective in lowering blood pressure:
• All participants in the study should be similar in age/gender/condition to eliminate these factors from affecting the results. You only want to test ONE FACTOR or VARIABLE at a time.
• Control group: People who receive a PLACEBO (or a pill that doesn’t do anything). These people have not received treatment and can be compared to the ones who do.
• Experimental Group: People who receive the blood pressure medicine.
D. Recording data
– Qualitative data – descriptive info, such as color, texture, etc.
– Quantitative data – numerical info
– In the recording section of a scientific paper, the scientist simply RECORDS the data, they do not attempt to analyze or explain it.
– Create graphs and tables to illustrate your data
E. Discussion & Conclusion
*Explain the graphs and tables in paragraph form. – Refer back to your graphs in your
written description. • Ex. As seen in figure 1.1, the amount of
oxygen…….
*This is where you interpret your data, and tell us what it means.
Drawing Conclusions
• -explain your findings – whether you “support” or “reject” your hypothesis
F. Ideal Experiments
• Should be repeatable.
• Scientists publish at the end of the process, so that others may share their knowledge and verify their results.
G. Theories vs. Laws• Theory
– Attempts to explain WHY something happens
– Applies to a well-tested explanation– Unifies a broad range of observations– Is subject to change - Ex.: atomic
theory
• Law– Always true– Explains WHAT happens– Ex. Law of gravity
II. Real-life example:
• 1976 – outbreak of disease in Zaire, Africa
• Disease was very contagious and deadly
• Victims had severe headaches, fever, bloody diarrhea, and vomiting.
In the last stages of the disease:
• Victim’s internal organs bled uncontrolably and blood leaked through the nose, ears, and even skin.
• Death from shock and cardiovascular shock followed rapidly.
What happened?
• Teams of scientists from the Centers for Disease Control were sent to Zaire to investigate what seemed to be a new disease.
Centers for Disease Control (CDC)
• Agency for the United States government responsible for monitoring diseases.
• The CDC is also the agency in charge of dealing with bioterrorism.
A. OBSERVATION
• All scientific understanding of the world starts with an observation or question about something unusual or unexplained.
• For example: People are dying from
a disease that no one has seen before.
Here are some of the initial data/observations the CDC recorded:• Outbreak had caused nearly 300 deaths
• Death followed within a week of 1st symptom
• 80 to 90% of people who become infected died.
• Photographed a virus in the blood of victims
• Observations always lead to the formation of a question:
• What is this new disease?
• How is it transmitted?
• What is the disease causing agent???
(I.e. – is it a bacteria, virus, parasite…)
B. CDC hypothesis:
• CDC scientists believed that a virus they had photographed in the blood of victims was the organism that caused the disease.
To test a hypothesis, scientists make a prediction that logically follows from the hypothesis:
• For example: If the virus were the true disease-causing agent, then introducing the virus into healthy tissue would cause cell death like that found in victims of the disease.
C. EBOLA EXPERIMENT• Liver cells from a monkey were placed
in a test tube (monkeys are genetically similar to humans)
• Test tubes in the control group (the
group that mimics NORMAL environment) were left alone.
• Blood containing the virus was placed in the experimental test tubes.
• Independent variable – the addition of blood to the monkey cells.
• Dependent variable – the health of the cells.
D. Collecting data:
• 11 days after addition of virus blood – the experimental group cells were dead.
• Control group was fine.
• Liquid from the experimental group could be passed to healthy cells, resulting in rapid death.
E. Conclusion:
• The virus photographed was the infectious agent. (caused the disease)
• In a conclusion you admit the failings of your experiment: – for example: scientists still don’t
know the animal that harbors the virus in the wild – or how the virus is spread to humans.
• Scientists also don’t know how EBOLA virus is spread –
– They know it requires close contact
– Don’t know if the person has to have a break in the skin to get the virus.
Hemorrhagic = bleeding
The scientific method is a cycle:
Observation
question hypothesis
prediction
experiment
Collect data
Analyze dataconclude
(revise hypothesis if necessary.)