Biodiversity: the richness of living systems as reflected in genetic variability within and among species, the number of species living on earth and the variety of communities and ecosystems. Biosphere: all regions of earth"s crust, waters and atmosphere that sustain life. One way to organize organisms is according to how they obtain carbon; either autotrophs or heterotrophs. Autotrophs: an organism that produces its own food using carbon dioxide and other inorganic compounds from its environment and energy from the sun or from oxidation of inorganic substances. (oxides containing carbon are considered an organic molecule). Inorganic molecule: a molecule without carbon atoms in its structure. Organisms can also be divided according to their energy source; chemotrophs, which obtain energy by oxidizing inorganic or organic substances or phototrophs which obtain energy from light. Chemoautotroph: found in some bacteria and archeans, not found in eukaryotes. Chemoheterotroph: found in some bacteria and archeans and also in protists, fungi, animals and plants.