Figure 1.

Schematic representation of the energy flux from the sun to heterotrophic eukaryotic cells.⁹ As indicated in the scheme, chloroplasts fix carbon from CO₂ and convert this carbon into high-energy organic molecules that constitute the basis of the global food chain. Mitochondria convert the energy of the chemical bonds of these compounds into adenosine triphosphate.⁷ The scheme indicates also the two internal milieux within a cell: the classical internal milieu and a protected embedded milieu belonging to the mitochondrial colony.