Learn how biologists test explanations, design experiments, and connect evidence to theories.
Part of the free Knowledge Mountain biology library. Read an explanation, try a question, and use a memory cue to check what you can recall.
A hypothesis is a testable explanation. A prediction says what you expect to observe if that explanation is correct. Evidence can support an explanation without proving it forever.
“Plants grow toward a window because of light” suggests a test: change the light direction while keeping other conditions similar, then measure the growth direction.
You give one plant fertilizer and more sunlight than another. The first grows taller. Can you conclude that fertilizer caused the difference?
No. Fertilizer and sunlight both changed, so their effects are mixed together.
To test fertilizer, keep light, water, plant type, starting size, and other relevant conditions as similar as possible. Use several plants per group to reduce the influence of unusual individuals.
An emergent property appears when parts interact. One heart cell can contract; an organized heart pumps blood. A molecule is not alive, but interacting molecules build living cells.
The cell is the smallest unit that carries out all basic functions of life. Biological organization runs from molecules to cells, organisms, populations, communities, and ecosystems.
In science, does calling evolution a “theory” mean it has little supporting evidence?
No. A scientific theory is a broad explanation supported by extensive evidence.
A hypothesis is a specific testable proposal. A theory connects many observations and successful tests. Scientific explanations remain open to revision when good evidence requires it.