IB Biology · Theme D

Continuity
and Change

DNA copies itself; cells divide; populations evolve. The mechanisms that keep life going — and the ones that let it become something new.

12Topics
152Sub-topics
316Key terms
4Levels of organisation
D
Theme D · Four levels of organisation

From molecules to ecosystems.

IB Biology organises each theme across four scales — molecules, cells, organisms, ecosystems. Browse below.

D1Molecules

3 topics

D2Cells

3 topics

D3Organisms

3 topics

D4Ecosystems

3 topics