Explain the phenomenon of photorespiration, including why it is thought to occur (evolutionarily speaking), and why plants have evolved to minimize its occurrence.

Photorespiration limits casualty products of light reactions that build up in the absence of the Calvin cycle. In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle.  The closing of stomata reduces access to CO2 and causes O2 to build up. These conditions favor a seemingly not useful process called photorespiration.  In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound.  In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle. Photorespiration eats up O2 and organic fuel and releases CO2 without producing ATP or sugar. Photorespiration can evolve relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2. 

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."    

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