Biology basics & diversity of life · Topic 1 of 17

Biology Basics & the Scientific Method

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Biology · basics & scientific method

Living things share key traits and build up from atom to biosphere; experiments test a hypothesis by changing one variable against a control.

01 · LevelsCell → tissue → organ → organ system

02 · MethodObserve → hypothesis → experiment → conclude

03 · VariablesIndependent = changed; dependent = measured

8 traits of life: order, response, reproduce, grow, homeostasis, energy, adapt, evolve must know

Hypothesis = a testable explanation that results could prove wrong must know

Independent variable = what you change; dependent variable = what you measure must know

Cell = the smallest unit of life; organisms have one cell or many

Homeostasis = keeping internal conditions stable while the outside changes

Negative feedback reverses a change back to the set point

Reproduction passes on DNA; genes guide growth and development

Tissue = similar cells; organ = tissues together; organ system = organs together

Population (one species) → community (all species) → ecosystem (+ nonliving) → biosphere

Hypothesis not supported → revise it and test again

Control group = same setup, minus the change being tested

Controlled variables (constants) are kept the same in every group

Atom → molecule → organelle → cell → tissue → organ → organ system → organism

Observe → ask a question → hypothesis → experiment → analyze data → conclude

Fertilizer test: dose = independent, height = dependent, 0 mL plants = control

Theory = a well-tested, well-supported explanation, not a guess

Commonly confused

	Independent variable	Dependent variable
Role	The cause being tested	The effect being measured
Who sets it	The experimenter changes it on purpose	It responds; the experimenter records it
Fertilizer example	mL of fertilizer	Seedling height
Statistics name	Explanatory variable	Response variable

Viruses are not alive: no cells, and they copy only inside a host cell

Results support or reject a hypothesis — they never "prove" it

Show 6 more facts

Response to stimuli: a houseplant bends toward the light

Energy processing: capture sunlight (plants) or eat food (animals)

A prediction is written "If … then …"

Inductive: observations → general rule; deductive: rule → specific prediction

Results must be repeatable; peer review checks work before publication

Explanatory variable = independent; response variable = dependent

Pearl

Change the independent variable, measure the dependent one, and compare against a control group that never got the change.

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