IB Biology · Theme C

Interaction
and Interdependence

Nothing alive is alone. From the chemistry of enzymes to the architecture of ecosystems, life is made of conversations.

9Topics
155Sub-topics
154Key terms
4Levels of organisation
C
Theme C · Four levels of organisation

From molecules to ecosystems.

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

C1Molecules

3 topics
C1.1

Enzymes and Metabolism

17 sub-topics · 16 key terms

C1.1Theme C
C1.2

Cell Respiration

17 sub-topics · 17 key terms

C1.2Theme C
C1.3

Photosynthesis

19 sub-topics · 15 key terms

C1.3Theme C

C2Cells

2 topics
HL only

Chemical Signalling

14 sub-topics · 0 key terms

C2.1Theme C
C2.2

Neural Signalling

16 sub-topics · 24 key terms

C2.2Theme C

C3Organisms

2 topics
C3.1

Integration of Body Systems

23 sub-topics · 44 key terms

C3.1Theme C
C3.2

Defence Against Disease

18 sub-topics · 38 key terms

C3.2Theme C

C4Ecosystems

2 topics
C4.1

Populations and Communities

18 sub-topics · 0 key terms

C4.1Theme C
C4.2

Transfers of Energy and Matter

13 sub-topics · 0 key terms

C4.2Theme C