Diagram Note — Mitochondrial Structure and Respiration Sites — Notes

Mitochondrial Structure Image: Mitochondrion ultrastructure showing cristae, matrix, and membranes — Wikimedia Commons (public domain)

Label #	Structure	Respiratory Function
1	Outer mitochondrial membrane	Permeable to small molecules; no direct role in ATP synthesis
2	Intermembrane space	Site of $H^{+}$ accumulation during ETS; low pH, high $H^{+}$ concentration
3	Inner mitochondrial membrane (cristae)	Site of ETS Complexes I–IV + ATP synthase ( $F_{0}$ - $F_{1}$ ); highly folded to increase surface area
4	Mitochondrial matrix	Site of TCA cycle (8 steps) and oxidative decarboxylation; contains TCA enzymes, mtDNA
5	$F_{0}$ - $F_{1}$ ATP synthase	$H^{+}$ flows from intermembrane space → matrix through $F_{0}$ ; $F_{1}$ synthesises ATP
6	Complex I (NADH dehydrogenase)	Accepts electrons from NADH; pumps $H^{+}$ into intermembrane space
7	Complex II (succinate dehydrogenase)	Accepts electrons from $FADH_{2}$ ; does NOT pump $H^{+}$
8	Ubiquinone (CoQ)	Mobile, lipid-soluble carrier; shuttles electrons from CI/CII to CIII
9	Complex III (cytochrome bc1)	Accepts electrons from CoQ; pumps $H^{+}$
10	Cytochrome c	Mobile, water-soluble carrier; shuttles electrons from CIII to CIV
11	Complex IV (cytochrome c oxidase)	Accepts electrons from cyt c; pumps $H^{+}$ ; final step — transfers electrons to $O_{2}$ → $H_{2}O$