Mitochondria are the cell organelle where the bulk of aerobic respiration occurs.

Mitochondria have 2 bilayer membranes with the inner membrane (cristae) folded.

Cristae: Folded inner membranes increases surface area. Electron transport & oxidative phosphorylation occur here.

Matrix: Fluid-filled inner compartment of mito.. Contains enzymes for the Krebs cycle.

Outer Compartment: Space between inner & outer membranes. Protons pumped here to create a high proton concentration (used to power creation of ATP - Chemiosmosis).

The 1st step of respiration, Glycolysis, occurs just outside the mitochondria in the cytoplasm.