Everything about Light-independent Reaction totally explained
In
photosynthesis, the
light-independent reactions, also somewhat misleadingly called the
dark reactions (they don't require darkness, but they require the
products of the
light reactions), are
chemical reactions that convert
carbon dioxide and other
compounds into
glucose. It occurs in the stroma, the fluid filled area of a chloroplast outside of the thylakoid membranes. These reactions, unlike the
light-dependent reactions, don't need
light to occur; hence the term
dark reactions. These reactions take the products of the light-dependent reactions and perform further chemical processes on them. There are three phases to the light-independent reactions, collectively called the
Calvin Cycle: Carbon Fixation, Reduction reactions, and ribulose 1,5-biphosphate (RuBP) regeneration.
However in
CAM (Crassulacean acid metabolism) plants, carbon fixation actually
does take place at night.
Carbon fixation
Main article:
carbon fixation
The
carbon fixation reaction is the first step of the light-independent reactions.
Carbon from
carbon dioxide is "fixed" into a larger
carbohydrate causing three
pathways to occur:
C3 carbon fixation (the most common),
C4 carbon fixation, and CAM (Crassulacean Acid Metabolism). C3 fixation occurs as the first step of the Calvin-Benson cycle in all plants. C4 plants first fix carbon dioxide into
oxaloacetate, a 4C acid, and then into
malate, which is transported to the bundle sheath cells, where it's decarboxylated to supply carbon dioxide to the Calvin-Benson cycle. CAM plants perform a similar process, but in stead of spatial separation of carbon dioxide fixation and the Calvin-Benson cycle, they separate the processes in time: at night they open their stomata and fix
carbon dioxide into
oxaloacetate which is converted to
malate. During the day malate is decarboxylated and the thus released
carbon dioxide enters the Calvin-Benson cycle.
Calvin cycle
The
Calvin-Benson cycle takes
carbon dioxide and shares it with
glucose, which the plant uses for food.
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