How Does the Photosynthesis Process Change During a Full Day?
Many important processes in plant cells are timed to coincide with the 24-hour daytime cycle. Photosynthesis is one of these. The rate of photosynthesis varies over the course of a 24-hour cycle. Does this Spark an idea?
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Stomata
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Plants need to take in carbon dioxide for photosynthesis through pores in the underside of their leaves; these pores are called stomata. At night, little or no light is available for photosynthesis, so photosynthetic activity ceases. Consequently, most plants close their stomata at night and open them during the day, since the rate of photosynthesis decreases at night and increases during the day. Curiously enough, this daily opening and closing of the stomatal pores continues even if the plants are kept in dark locations, indicating that it's regulated by an internal clock.
Function
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All else being equal, the rate of photosynthesis will increase with an increase in light availability -- at least up to a point. During the daytime, plants increase production of enzymes needed for photosynthesis and the rate of photosynthesis increases towards midday, falling again as nightfall approaches.
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Considerations
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To maximize the efficiency of photosynthesis and minimize water loss, some plants in hot or dry climates have evolved alternate modes of photosynthesis. In certain plants like sugarcane, cells closer to the outside of the leaf fix carbon in the form of an organic acid and shunt this compound to cells nearer the center of the leaf, where photosynthesis takes place. Some other plants like cacti, known as CAM plants, fix carbon at night and then photosynthesis takes place during the day. Unlike most plants, CAM plants close their stomata during the day and open them at night.
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References
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