In some plants, the first product of photosynthesis is sugar that contains three carbons, and these plants are known as C 3 plants . 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. All rights reserved. Last updated 30.Jan.2000.