1. Scientific Method
How Scientists Work

2. Objectives Understand how scientific work within Biology
Review the definition of the scientific method
Understand the process for the scientific method through the lens of Biology

3. Experimenting
Let’s look at the Scientific Method using Redi’s Experiment on Spontaneous Generation
He was trying to disprove the idea of Spontaneous Generation (or actually that flies came from maggots, which came from flies)
Francesco Redi (1668)

4. Stating the Problem Example: How do new living things come into being?
Spontaneous generation once commonly accepted
Redi wanted to show what caused the appearance of maggots (and then flies) on meat

5. Belief based on prior observations
If leaf lands on water it becomes a fish
If bale of hay left in barn it produces mice
Muddy soil gives rise to frogs
Meat hung out in the market is the source of flies

6. Belief based on prior observations
Redi observed that maggots appeared on meat a few days after flies were on meat
No microscope = no way to see eggs
But Redi believed that maggots came from eggs that were laid by flies

7. Forming a Hypothesis Redi’s Hypothesis: Flies produce maggots.
How could he test this?
Through a controlled experiment

8. Redi’s Controlled Experiment
Redi used two groups of jars
Jars that contained meat and no cover
Jars that contained meat and gauze cover
Jars with meat
Uncovered jars
Covered jars

9. Control and Experimental Groups
used as a standard of comparison
the group containing the factor (variable) that has been changed
Control group:
Experimental group:
(manipulated or independent variable)
Two groups of jars
Uncovered jars
Covered jars

10. Variables in an Experiment
Variables - Factors that can be changed
Controlled Variables - all the variables that remain constant
Manipulated Variable - (also called the Independent Variable) - factor in an experiment that a scientist purposely changes
Responding Variable- (also called the Dependent Variable) - the outcome or results, factor in an experiment that may change because of the manipulated variable…. what a scientist wants to observe

11. Setting up a Controlled Experiment
In a controlled experiment, only one factor is changed at a time.
Independent variable: the factor that is deliberately changed
Dependent variable:
the factor that the scientist wants to observe; it changes in response to the independent variable

12. Variables in Redi’s Experiment
Controlled Variables: jars, type of meat, location, temperature, time
Manipulated Variables: gauze covering that keeps flies away from meat

13. Let’s think about this.…
Which is the control group?
Which is the experimental group?
Uncovered jars
Covered jars
Two groups of Jars with meat
Uncovered jars
Covered jars

14. Redi’s Experiment on Spontaneous Generation
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.
PROCEDURE
Manipulated Variables:
gauze covering that
keeps flies away from
meat
Uncovered jars
Covered jars
Several
days pass
Maggots appear
No maggots appear
Responding Variable:
whether maggots
appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.
Controlled Variables:
jars, type of meat,
location, temperature,
time

15. 6. Collect and Record Data
observations and measurements made in an experiment
Types of Recorded Data
Quantitative - observations that involve measurements/numbers; i.e. 3 days, 12 maggots, 4 g, 13 sec, 8 liters
Qualitative - observations that do not involve numbers, are of a descriptive nature i.e. white maggots covered the meat, leaves were all wilting

16. 7. Analyze the Data Examine data tables, charts, and graphs
Examine experimental notes
Look for trends, patterns, and averages
What does the data show
Put your data into words

17. 8. Draw Conclusions Restate the hypothesis:
Example: Flies produce maggots.
Accept or reject the hypothesis.
Support your conclusion with specific, numerical data.
What was Redi’s conclusion?
Flies lay eggs too small to be seen.
Maggots found on rotting meat are produced
from the eggs laid by flies.
Maggots are not appearing due to spontaneous generation!

18. 9. Determine Limitations
Scientists look for possible flaws in their research
They look for faulty (inaccurate) data
They look for experimental error or bias's
They decide on the validity of their results
They make suggestions for improvement or raise new questions

19. 10. Publish Results Communication is an essential part of science
Scientists report their results in journals, on the internet, or at conferences
This allows their experiments to be evaluated and repeated
Scientists can build on previous work of other scientists
Redi’s experiment
on insects generation

20. Repeating the Investigation
Sometimes results are unexpected.
John Needham challenged Redi’s experiment and designed his own to show that spontaneous generation CAN occur under certain circumstances.
Lazzaro Spallanzini designed a slightly different experiment to improve on Needham’s work
Repeat the experiment!

21. Repeating the Experiment (continued)
Louis Pasteur further modified the experiment.

22. S C I E N T I F I C M E T H R E O V D I W

23. Can you put these steps in order?
Define the Problem 2
Analyze Data 7 10 8 6
Report Results
Make an Observation
State the Hypothesis 5 1 4
the Problem 9 3
Determine Limitations

24. Steps of Scientific Method in order1
State the Hypothesis
Make an Observation
Define the Problem 2
the Problem 3 4 5 6
Analyze Data 7 8 9 10
Report Results
Determine Limitations