Scientific Method Notes (using Mendel’s pea plant experiment for examples)
***Scientists begin with a testable question or statement/claim. The question must be answerable with
objective, repeatable observations and experiments.
~Gregor Mendel was a monk in what is now the Czech Republic, and he raised pea plants (as
part of an experiment). The testable questions Mendel asked were about how traits are passed from
one generation to the next.
***Hypothesis: a prediction backed up or supported by a logical rational reason.
~ Mendel tested several specific hypotheses: his over-arching prediction was that physical
characteristics are passed from parent to offspring in predictable ways.
*** Variables:
* Manipulated (independent) Variable (on the x-axis): only one, changed intentionally by the
observers/experimenters; it is changed (or manipulated) on purpose.
* Responding (dependent) Variable (y-axis): this variable is measured; the one you count,
measure, or observe.
* Controlled Variable: kept the same on purpose; experimenters control as many aspects as
possible for the best, most accurate results.
~Gregor experimented very carefully, controlling many variables: how the plants were
pollinated, how much sunlight and water, the species of plant…
~ Gregor manipulated which parent plants he bred together.
~ Traits he examined and measured (responding variables) included: flower color (purple or
white), pod color (yellow or green), wrinkled or smooth peas, etc.
*** Procedure: The specific, logical, step-by-step plan or instructions for an experiment or set of
observations. MUST be repeatable (must be repeated ), MUST give data that will help answer the
testable question.
~ Mendel set up his plant-breeding experiment by: breeding strains of peas for one specific trait
for several generations; manipulated which strains produced offspring; raised strains with traits that
“bred true”; selectively bred plants with different traits (a plant with green pods crossed with a plant
with yellow pods); counted how many individual plants had each trait; repeated his process with many
crosses, collecting data about patterns of inheritance.
*** Data: (singular “datum”) Information or evidence.
quantitative data are about amounts: how much, how many; numerical data. Root word
“Quantity”
qualitative data are descriptive: what something is like.
Data must be recorded in pen. You must report data honestly and accurately.
~ Mendel collected quantitative and qualitative data. For each generation of plants, he
described the traits he saw, and he measured and counted how many offspring showed each trait.