Figure 1. The carbon cycle. Driven by photosynthesis, biomass is formed from CO ₂ and minerals. As a result of various food chains, CO ₂ and minerals are regenerated in respiratory processes and fermentations. A more detailed cycle is depicted in Figure 1. (Diagram: Petra Ehrenreich, Goettingen, Germany.)

Figure 2. Salt works on the island of Lanzarote, in the foreground a salt evaporation pond with reddish haloarchaea. (Photograph: Dieter Oesterhelt, Munich, Germany.)

Figure 3. The path of protons through the bacteriorhodopsin (BR) pump, from the inside (CP) to the exterior (EC). The seven helices of BR span the membrane. The critical amino acids of the light-mediated vectorial catalysis are aspartic acid 85 (D 85) as proton acceptor and aspartic acid 96 (D 96) as proton donor. The key steps of proton movement are: (1) proton release, (2) proton transfer following rearrangement of retinal, caused by a light impulse, (3) backfolding of retinal and proton uptake, (4) reprotonization, that is, proton uptake by aspartic acid 96 after it has provided the proton to the retinal in step (3). (Model: Dieter Oesterhelt, Munich, Germany.)

Figure 4. Composition of the ATP synthase and arrangement in the cytoplasmic membrane. Subunits c are the rotor blades; subunits γ and ε form the central shaft. The “orange slices” mentioned in the text are the three α (alpha) and the three β (beta) subunits. The peripheral shaft consists of subunits b and δ. (Model: Volker Mueller, Frankfurt/Main, Germany.)