Photosynthesis light phase and dark phase balanced

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Photosynthesis reactions


1. LIGHT DEPENDENT REACTION
Photolysis: H2O --- H+  + O2  + e-
Light is absorbed by the pigments found in the chloroplasts: clorophyll a, b and carotenoids

The light absorbed is used to break down the water molecule (photolysis). Water is broken down into O2, protons and electrons. The H+ and e- are needed for next reaction, but O2 is released into atmosphere.
Light absorbed results in formation of ATP

2. LIGHT INDEPENDENT REACTION
NADPH --- is a donor/aceptor of H+ and e-. It carries the H+ and e- obtained in the first reaction to be used in the second phase of photosyntesis. ATP produced in the first reaction is used here to produce carbon copunds
H2O ---- O2 + e- + H+  + ATP

CHANGES TO EARTH DUE TO PHOTOSYNTHESIS

Oceans - oceans initially had high levels of dissolved iron (released from the crust by underwater volcanic events)

Atmosphere- for the first 2 billion years after the earth was formed, its atmosphere was anoxic (oxygen free)

Rock dposition - The reaction between dissolved iron and oxygen gas created oceanic deposits called bonded iron formations (BIFs)

Biological life - free oxygen is toxic to obligate anaerobes and increase in O2 levels many have wiped out many of these species

LIMITING FACTORS ON RATE OF PHOTOSYNTHESIS
- temperature
- light intensity
- CO2 concentration

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