Photosynthesis160-page19

Photosynthesis160-page19 - In the daytime, the accumulated...

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Photosynthesis - 19 C 3 Leaf Structure C 4 Leaf Structure C 4 photosynthesis is highly productive in hot and dry environments. The world's most productive plants, sugar cane and corn, are C 4 plants, as is crab or quack grass, a weedy grass that stays healthy when lawns dry in summer months. However, regenerating PEP requires ATP, so C 4 photosynthesis is not always more productive than the C 3 pathway. Unfortunately, the pathway is genetic, so plants can't choose. CAM - Another Conservation Mechanism Some plants can minimize water loss by reversing the time of day when stomates are open. Plants that have reverse stomatal opening can also store CO 2 in 4- carbon acids. They do not, however, have photosynthesis separated into two different cells.
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Unformatted text preview: In the daytime, the accumulated acids release CO 2 for "normal" mesophyll cell light reactions and Calvin cycle, while the stomata can remain closed to prevent excessive water loss. They do not reduce photorespiration. The name, CAM (for Crassulacean Acid Metabolism) is derived from the types of plants in which it was first discovered, Crassuleans, a plant family of succulents, and for the fact the CO 2 trapped forms acids. Some CAM plants can even fix CO 2 into acids during prolonged droughts when stomata can't even open at night using the CO 2 produced during aerobic respiration. This is minimal, but sufficient to sustain life. A mature saguaro cactus can survive about 18 months of drought....
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