From the atoms in a molecule up to the whole biosphere, life is built in levels — each one made of the level beneath it. ▶ Play to climb from cell to ecosystem.
A cell is the smallest living unit; similar cells form a tissue; tissues form an organ; organs form a system; systems form an organism — and organisms build populations, communities and ecosystems.
Biology runs on evidence. The scientific method cycles through observation → hypothesis → experiment → results → conclusion, then refines and repeats. ▶ Play to step round the cycle.
A good experiment changes one variable (independent), measures the effect (dependent), holds everything else constant, and includes a control — so any change must be due to the one thing you changed.