Scientific Method/ Background

OBJECTIVES: List and describe/ explain the 5 steps in the scientific method in the correct sequence. Apply/ use steps in the scientific method in a given problem. Analyze a scientific problem and be able to identify specific examples of a hypothesis, experiment, data, etc. Contrast a hypothesis and a theory. List the 2 functions of a good theory. Discuss the limitations of science. Differentiate between a control group from an experimental group and an independent variable from a dependent variable. Explain the work of Aristotle, Redi, Spallanzani, Needham, and Pasteur concerning the origin of new living organisms--- relate their work to the scientific method. Compare and contrast 3 kinds of microscopes used in biology--- gives some advantages and disadvantages for each. Identify and sequence the various levels of organization for the study of life. Describe common metric units used in science for length, mass, volume, and temperature.

Correct observation is most difficult- due to unsuspected bias Scientific Method 1. Observation Must be repeatable Correct observation is most difficult- due to unsuspected bias People see what they want to see; difficult to explain unconscious prejudice Several scientists repeating it independently give observation more validity  

2. Statement of Problem To be valuable scientifically, a question must be relevant as well as testable and specific Proper testing techniques must be available In general, science does best with “how” or “what” questions “Why” questions are more difficult/ Ex: “ Why does the universe exist?”  untestable

3. Formulation of Hypothesis Not a random guess Hypothesis a tentative answer or postulation based on numerous observations Scientist does not know if his “guess” was correct or incorrect until he has completed experimentation

4. Experimentation Provides enough evidence to explain hypothesis Most difficult step must be a controlled experiment Requires at least 2 parallel sets of tests, identical in all respects except one Control Series provides a standard or reference for assessing results of the Experimental Series

Cont. Experimentation Ex: In drug experiments on people, up to 100,000 to 200,000 test, 2 of them controls and 2 experimental groups Control Series Experimental Group a. All conditions same as Experimental group a. All conditions same as Control group b. No drug taken b. Drug taken-specific dose

Redi’s Experiment on Spontaneous Generation Section 1-2 OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Cont. Experimentation e) Large samples (#) of organisms must be used f) Even after careful execution, etc. results may not be clear g) Results of any experiment represents EVIDENCE the original guess about the answer is confirmed as correct or incorrect (invalid) h) If invalid, a new hypothesis and new experiments must be designed - Process must be repeated until a hypothesis is found that can be supported with experimental evidence i) Results of experiments cannot be called “proof” or “fact”, merely evidence for a hypothesis (some hypothesis have more evidence than others)

Cont. Scientific Method 5. Formulation of Conclusion: Theory Based on evidence produce by experimentation Theory a hypothesis that has withstood repeated testing by many scientists doing independent work Good theory has predictive value forecasts certain results based on substantial evidence - Scientific forecast does not guarantee something will happen-- indicates that it is likely to happen with a stated degree of probability d) Natural Laws theories that have proved so universally valid to a high degree of probability - Ex: Apple falls from tree no exception even observed Law of Gravity e) Most theories are valid for a time, but with time, exceptions are found f) Science is a steady progression, not revolution - Ex: Isolation and synthesis of a gene took 5 years

Microscopes Used in Biology Light Microscope  tissues, whole cells 2. Transmission Electron Microscope (TEM) slices of cells 3. Scanning Electron Microscope (SEM) surfaces of cells

Transmission Electron Microscope

SCOPE ADVANTAGES DISADVANTAGES LIGHT Living cells Color Movement Processes Low magnification (up to 1000x) No fine detail TEM Very high magnification Extremely fine details- view internal structures No living cells No color No movement No processes Special technique ( fix, slice, stain, freeze, vacuum) SEM Surface details “3D” image/ realistic Same as TEM (no slicing)

Light Microscope Staph aureus (100x) Onion Cells

Transmission Electron Microscope E. coli Striated muscle

Scanning Electron Microscope Mascara brush covered w/ dried mascara & flakes of skin Cat flea flattened from side to side along with the spines on its head (have either simple eyes or no eyes at all)

Guess What?!?

The dentist drill is covered with tiny diamond chips The dentist drill is covered with tiny diamond chips. Diamonds are the hardest substance known and will easily wear away tooth particles as the drill spins at high speeds.

Redi’s Experiment on Spontaneous Generation Section 1-2 OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Spallanzani’s Experiment Section 1-2 Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. Flask is sealed. Gravy is free of microorganisms. Gravy is boiled.