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Photosynthesis

Topic 2
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9

Biology SL

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Takes place in the chloroplasts

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ATP and hydrogen are used as forms of chemical energy to convert carbon
dioxide and water into useful organic molecules for the plant

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Glucose is an organic molecule made out of 6 inorganic carbon dioxide
molecules
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The conversion of an inorganic form of any element to an organic
form is known as fixation
6CO2 + 6H2O ⇒ C6H12O6 + 6O2

Rate of photosynthesis
➢ Photosynthesis is the reverse reaction of cell respiration
➢ A plant has a fairly consistent and low rate of cell respiration at any given time, day
and night
➢ Low need of ATP
➢ The photosynthetic rate is highly dependent on many environmental factors
➢ The glucose and some of the oxygen produced in photosynthesis is used by the
plant itself
➢ When no light is available, the plant must rely on produced glucose and take in
oxygen through the stomata from the air
➢ Measuring the oxygen production or carbon dioxide intake is a direct measurement
of photosynthetic rate
➢ We can also keep track of the change in biomass of experimental plants
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Indirect reflection of photosynthetic rate, as biomass can be affected by
other factors

Environmental limiting factors
➢ Rate of photosynthesis will increase, as the light intensity increases
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Until enzymes start working at maximum rate

➢ Rate of photosynthesis will increase, as the temperature increases
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Until enzymes and proteins become denatured

➢ Rate of photosynthesis will increase, as carbon dioxide increases
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Rate reaches a plateau unless light and temperature also increase

➢ Light and temperature are limiting factors

2



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