Introduction to Scientific Theories, Reasoning, and Discovery

Scientific theories differ in definition from everyday usage.
Scientific theories are extensively and reproducibly tested and function similarly to a principle or natural law (e.g., atomic, gravitational, and cell theories).
Theories can be modified if strong enough evidence emerges (e.g., Prions).
A central tenet of science is that "Nothing is ever proven".
Misunderstanding scientific terminology can have practical consequences (e.g., in 2002, a Georgia school board voted to place stickers in textbooks stating "evolution is a theory, not a fact").

Induction: Uses specific observations to form general principles (e.g., concluding all organisms are made of cells based on all previous observations).
Deduction: Applies general principles to specific situations (e.g., if all organisms are made of cells and humans are organisms, then humans are made of cells).

Bacteria can be grown in a pattern created by streaking on solid growth medium in a petri dish.
A substance from a colony of Penicillium mold inhibits the growth of bacteria.
Fleming hypothesized that mold produced an antibacterial substance.
Scientific tests using broth from pure Penicillium cultures led to the discovery of penicillin, the first antibiotic.
Fleming continued his investigation beyond a lucky accident, illustrating Louis Pasteur's phrase: "Chance favors the prepared mind".