Scientific Method; Levels of Organization
I. The Nature of Science and the Scientific Method
1. Observation and inductive reasoning
Observe nature and pose a general (universal) principle. Universal principles must be testable using the scientific method and applicable in all cases.
observation: apples fall to the earth
General principle:
-all objects fall toward the center of the earth
-Law of Universal Gravitation
2. Observation and deductive reasoning
Make observations
Ask questions (RQ's)
Pose hypotheses
Predict outcomes using deductive reasoning
Research Questions (RQ's):
Will heavier objects fall to the center of the earth faster than lighter objects?
Do differences in shape and density influence objects as they fall to earth?
Hypotheses
establishes a possible cause and effect relationship
-used in detective work
-example hypothesis:
"The killer will have the victim's blood on his clothes"
(What is H1? H0?)
"Larger, heavier balls will fall faster than smaller, lighter balls when dropped from a tall building."
A good idea for beginners
-"if...then..."
-Prediction or predictive hypothesis:
"If a bowling ball and a golf ball are dropped from the top of a building, then the bowling ball will hit the street first".
if (cause), then (effect)
-Experimental Design
-Data Gathering and Analysis
-Conclusion: accept or reject your hypothesis (no partial decisions allowed!)
3. Science in Action: A Case Study of Ozone Depletion in the Antarctic
Scientific Process
a. Observations
Farman et al.
satellite view: the "Ozone Hole"
Where is the ozone layer?
from http://www.al.noaa.gov/WWWHD/Pubdocs/Assessment02/images/Fig01-2high.jpg
What is the benefit of having ozone in the upper atmosphere?
Ozone is continually formed and broken down by UV light
formation:
O2 + UV --> 2O
O + O2 --> O3
breakdown:
O3 + UV --> O2 + O
O + O3 --> 2O2
The amount of ozone present at any given time is the result of a balance between formation and breakdown.
Rowland, Molina, Crutzen
What happens when CFC's react with ozone?
from http://www.nobel.se/chemistry/educational/poster/1995/2.html
RQ's:
Are CFC's present in the upper atmosphere?
Are CFC's breaking down the ozone layer?
Are CFC's in the upper atmosphere long enough to break down large amounts of ozone?
Is the thinning of the ozone layer caused by natural (not man-made) processes? (e.g. sunlight, microbial action, etc.)
b. Predictive hypotheses
If CFC's are responsible for producing the ozone hole, then it should be possible to detect CFC's (as well as the chlorine produced from it) in the upper atmosphere.
If CFC's are responsible for producing the ozone hole, then a correlative relationship should be observed between rising CFC levels in the upper atmosphere and declining ozone.
If natural (not man-made) cycles are thinning the ozone, then evidence (correlative or cause and effect) should be found.
c. Experimental Design
-stratospheric sampling
d. Results
Problem??
e. Conclusion
Accept or reject hypothesis?
Flaws?
4. How to Design a Controlled Experiment: Ozone Studies in the Lab
a. Predictive Hypothesis:
If CFC's are introduced into conditions similar to the upper atmosphere, then ozone levels should fall.
What are experimental variables? (what are the conditions in the upper atmosphere?)
What is the purpose of a control?
b. Experimental Design:
Experiments with atmospheric chambers:
photo from: http://www.cert.ucr.edu/news/spring00.asp
What is in the control chamber? What is in the experimental chamber?
c. Results and Conclusions
Ozone levels fall in the experimental chamber, not in the control
Hypothesis is supported by the data
Is this issue settled? Are CFC's the definitive cause of ozone depletion?
Not yet!!!
NO (nitrogen oxide) also destroys ozone:
NO + O3 --> NO2 + O2
(NO indirectly produced by microbes)
Does the scientific method lead to the absolute truth?
What is a theory? How strongly are theories supported by scientific data?
II. Levels of Organization in Biology
1. levels: (chemical, cellular, tissue, organ, body system, organism, population, community, ecosystem, biosphere)
2. Importance of Integration
-hormonal control of behavior
3. Emergent Properties
With each step upward in the hierarchy of biological order, novel properties emerge that were not present at the simpler levels of organization.
Any level is greater than the sum of its parts.
4. Reductionism
-different types of biologists
