The Scientific Method

PHEOC

Problem

Identify the question

- a problem to solve– Do background research to prepare

Hypothesis

An educated guess that can be testedIndependent Variable: the one change that is madeDependent Variable: result that occurs due to the IV. Written: If Independent Variable, then Dependent Variable.Ex: If music is played to plants, then they will grow taller.

Experiment

Procedure that tests a hypothesis by collecting info under controlled conditions.Control: the group with conditions that are kept the same or “normal”Experimental: The part of the experiment where one factor or variable is changed.Constants: Parts of the experiment that stay the same in the control & experimental groups.

Observation

Collecting and organizing data/information from the experiment.

Conclusion

Reporting results (graphs, reports)

True scientific studies do repeated trials

Form a theory when repeated trials give the same results

If results are not what was expected, scientists still report results and may try again or adjust their hypothesis first

Law vs Theory

Law: fact of nature known to be true• Law of gravity

Theory: explanation of a phenomenon or behavior that is supported by a large body of evidence – Theories can be changed based on new evidence– They are never proven to be 100% true

Germ Theory - timeline

7000 b.c. – drilling holes in people’s heads to release evil spirits “causing disease”377 bc – Hippocrates – body fluids cause disease1300s - incense tried to cure the Black Death1800s - people still believe illness is due to supernatural causes.1857 - Louis Pasteur proposed that microorganisms cause disease

Germ Theory (cont.)1865 - antiseptic technique reduces surgery infections

1883 – Koch’s postulates prove pathogens cause disease

1900s – drinking water treated with chlorine to reduce cases of cholera

1928 - Penicillin was used to treat infections

1955 - Vaccine against polio is made

2002 - New diseases are springing up, SARS

Cell Theory

1665 - Hooke identifies cells through use of a microscope.

1674 - Leeuwenhoek made a better lens to observe cells in greater detail.

1838 - Schleiden studies plant structures- finds they are made of cells

Cell Theory (cont.)

1839 - Schwann studied animal structures -concluded from Schleiden’s work and his - all living things are made of cells. (although Schwann thought cells spontaneously formed)1855 Virchow proposed that all cells come from other pre-existing cells Cell Theory Principles:– All organisms are made of cells– cells are produced by other existing living cells– The cell is the most basic unit of life

Theory of Natural Selection

1749 - Buffon – recognizing there are variations among species1794 – E. Darwin (Charles Darwin’s grandfather) begins considering how organisms could evolve through mechanisms such as competition.1809 - Lamarck - evolution due to environmental changes over time.

Theory of N.Selection (cont.)

1830s - Charles Darwin - influenced by Lamarck’s ideas and his species variation studies; continues his research on evolution

Theory of Natural Selection now states:– Individuals with inherited beneficial

adaptations will produce more offspring.

Research

Quantitative vs. Qualitative

Quantitative

Results in numerical data

Involves counts or measurements

Qualitative

Descriptive

Results purely observational data

Useful because in some cases descriptions are more important than measurements.

Resources:

- Holt McDougal, “Biology” 2010