AP Biology

1. AP Biology Lecture #4

2. Scientific Method ObservationsQuestions HypothesisPrediction Test/ExperimentConclusion Uses controlled experiments with only one experimental variable

3. Observation 1. Scientists believe nature is orderly and measurable. 2. Science also considers that natural laws do not change with time.3. Phenomena can therefore be understood from observations.4. Actual science research may also involve chance (e.g., Alexander Fleming’s discovery of penicillin). *This principle of science is known as NATURAL CAUSALITY, by its nature it excludes supernatural phenomenon*

4. Hypothesis Examples of hypotheses, check those that are valid and can be tested: ____Bluebirds sing to attract mates. ____Bluebird songs are beautiful. ____Only male bluebirds sing. ____Sparrows will leave territories where they hear bluebirds sing. ____Bluebirds hate sparrows. Ahypothesis is a possible explanation for a natural event - must be testable.

5. Inductive vs. Deduction Reasoning • Inductive: Reasoning from a set of specific observations to reach a generalized conclusion. A generalization that summarizes observations • Deductive: scientific method: Reasoning flows from general to specific. Predictions about what outcomes of experiments or observations we should expect if a particular hypothesis is correct.

6. Experiments/Further Observations 1. Testing a hypothesis involves either further observations or conducting an experiment. 2. Deductive reasoning involves “if, then” logic that predicts what will happen based on the hypothesis. 3. An experimental design is proposed that tests the hypothesis. 4. Scientists may use a model (global warming, but models are not always valid)  5. If a model cannot be tested, it always will remain a hypothesis.

7. Data You roll two dice, they both turn up ONEs.  This does not fit your prediction that you will only roll a ONE  1 out of 6 times.  Is the data significant enough to change your prediction? 1. Data are the results of experiments, and are observable and objective.2. Data are often displayed in a graph or table.3. Often the data must be inspected for the probability the data could show a relationship by chance; this is a measure of “significance.”

8. Conclusion 1. Whether the data support or reject the hypothesis is the basis for the “conclusion.” - avoid the word "prove"  2. The conclusion of one experiment can lead to the hypothesis for another experiment. 3. Science findings are reported in scientific journals so results are available to the research community (peer review). 4. The experiments and observations must be repeatable or the research is suspect. The Scientific Method http://www.youtube.com/watch?v=zcavPAFiG14&feature=player_embedded

9. Scientific Theory 1. The ultimate goal is to understand the natural world in scientific theories, conceptual schemes supported by a broad range of data. 2. The terms “principle” and “law” are also used for generally accepted theories. Basic theories of biology are:a. Cell theory: all organisms are made of cells.b. Biogenesis theory: life only comes from life.c. Evolution theory: living things have a common ancestor and are adapted.d. Gene theory: Organisms contain coded information that determines their form, function, and  behavior.

10. Other Theories e. Germ Theory - proposes that microorganisms are the causes of many diseasesf. Heliocentric Theory - the sun is the center of the solar system, planets revolve around the sung. Law of Gravity - masses attract each other

11. A Controlled Study 1. Some investigations are managed where conditions can be kept constant a. A variable is a factor that can cause an observable change b. The experimental variable is the step that is deliberately manipulated (ex.  nitrogen fertilizer). c. A dependent variable is component of an experiment that changes due to the experimental variable (growth).

12. Study I a. The hypothesis that pigeon peas will increase winter wheat production, compared to nitrogen fertilizer, is tested in clay pots using both treatments and a control group without treatment. b. Although both treatments exceed the control in wheat growth, the fertilizer-only treatment exceed the use of pigeon peas.

13. Study II a. To test the hypothesis that pigeon pea residues will build up over time and will increase winter wheat production, compared to nitrogen fertilizer, the test is continued. b. The fertilizer-only treatment no longer exceeded biomass production with the use of pigeon peas.c. All results and conclusions were then reported in a science journal.

15. Study III Observation: Babies are born with severe birth defects, mothers of these babies report taking the drug thalidomide during pregnancy for morning sickness. Question: Does thalidomide cause birth defects? Hypothesis: Thalidomide causes birth defects.

16. Experiment: Control group: Mice not given thalidomide during pregnancy Variable: Mice given thalidomide during pregnancy In this experiment, mice born from both the control and variable group will not have birth defects. This experiment was performed long before thalidomide was marketed and prescribed to pregnant women. Does these mean that the hypothesis is not supported?

17. Quick Review:  What is a Theory? Theories must explain a wide range of observations Theories must be falsifiable Theories can be changed if new evidence presents itself Generally, a THEORY explains the phenomenon  (WHY)  A LAW defines it, or establishes a pattern  (WHAT) A Theory is an explanation for natural events that is based on a large number of observations. Can also be referred to as a PRINCIPLE or a LAW. Scientific Theories join together well supported and related hypotheses

18. What is Occam's Razor? Ockham's Razor (Occam is the latinized and more common spelling) is a principle proposed by William Ockahm in the 15th century. The original principle stated "Pluralitas non estponenda sine neccesitate" which translates as "entities should not be multiplied unnecessarily" Simply put:  The simplest explanation is usually the correct one.