NADPH produced earlier in photosynthesis. The ”food” made by photosynthesis is formed
from the 3-carbon carbohydrate. Two 3-carbon carbohydrates combine to form glucose, a
6-carbon carbohydrate. Next, the 6-carbon RuBP must be reproduced so the Calvin Cycle
can start again (Figure4.11).
Figure 4.11: The Calvin Cycle begins with carbon fixation, or carbon dioxide attaching to
the 5-carbon molecule RuBP, forming a 6-carbon molecule and splitting immediately in to
two 3-carbon molecules. This is shown at the top of the figure. This carbon molecule is
then reduced to a 3-carbon carbohydrate, shown at the bottom of the figure. The energy
and reducing power needed for this process are provided by the ATP and NADPH produced
from the light reactions. Next, RuBP must be reproduced so the Calvin Cycle can continue.
The carbons are the small black circles. You can keep track of the number of carbons at each
stage by counting these circles.( 10 )
The 3-carbon product of the Calvin Cycle can be converted into many types of organic
molecules. Glucose, the energy source of plants and animals, is only one possible product of
photosynthesis. Glucose is formed by two turns of the Calvin Cycle. Glucose can be formed
into long chains as cellulose, a structural carbohydrate, orstarch, a long-term storage
carbohydrate. The product of the Calvin Cycle can also be used as the backbone of fatty
acids, or amino acids, which make up proteins.