Some plants have a supplementary mechanism that temporarily fixes carbon dioxide, thus producing a sugar with four carbon atoms, and these plants are known as C 4 plants . For a variety of biochemical reason, the C 4 photosynthetic pathway is most advantageous under conditions of high light intensity and high temperatures , but disadvantageous at low light and low temperature conditions. Equal amounts of carbon gain by the C 3 and C 4 pathways are found at 45 N. Above that latitude, C 3 plants are superior, while below that C 4 plants are superior. A larger proportion of C 4 plants would indicate warmer conditions in the past. Dragonflies are a good example.
Some organisms stay with a pressure gradient.
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