-C4 is the alternative pathway of Calvin cycle (C3 cycle) taking place during the dark phase (light-independent stage) of photosynthesis. In the C4 cycle the first stable compound is 4 carbon compound, namely oxaloacetic acid. Hence it is called C4 cycle. It is a process of carbon dioxide fixation.
-C3 plants have the disadvantage that in hot dry conditions their photosynthetic efficiency suffers because of a process called photorespiration. When the CO2 concentration in the chloroplasts drops below about 50 ppm, the catalyst rubisco that helps to fix carbon begins to fix oxygen instead.
-The problem of photorespiration is overcome in C4 plants by a two-stage strategy that keeps CO2 high and oxygen low in the chloroplast where the Calvin cycle operates.
Organisms decompose more quickly when they are in contact with oxygen. ... When an organism is buried quickly, there is less decay and the better the chance for it to be preserved. The hard parts of organisms, such as bones, shells, and teeth have a better chance of becoming fossils than do softer parts.
