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Photorespiration
- plants absorb CO2 through the stomata
- when weather becomes hot and dry, guard cells decrease the size of the stomata to conserve water; resulting in the decrease of carbon dioxide in the leaf
- cellular respiration still goes on, so oxygen levels increase
- oxygen competes with carbon dioxide for the enzyme rubsico’s active site
- rubsico may either catalyze the addition of carbon dioxide to RuBP or the addition of oxygen to RuBP
- when oxygen levels are greater than that of carbon dioxide, oxygen binds with rubisco more often, causing the oxidation of RuBP more often then the carboxylation of PGA (in presence of carbon dioxide)
- this process is called photorespiration because it happens in light
- photorespiration decreases the sugar production by photosynthesis because it decreases the amount of PGA in the Calvin Cycle
- one 3-C PGA molecule and one 2-C glycolate molecule are formed from one 5-C RuBP instead of the 2 PGA when carbon dioxide reacts
- glycolate is partially converted to carbon dioxide
- ¾ of carbons in 2 glycolate molecules return to the Calvin Cycle as G3P; C3 plants lose one quarter to half of the carbon they fix to photorespiration
- under normal conditions the rate of carbon fixation is 4 times than that of oxidation
- the optimum temperature for photorespiration is higher than that for photosynthesis
C4 Plants
- C4 plants (i.
Approximate Word count = 442
Approximate Pages = 1.8
(250 words per page double spaced)
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