Photosynthesis has four stages:

Glycolysis.
The Link Reaction.

3. The Krebs Cycle.

Oxidative Phosphorylation.

Photosynthesis converts glucose from food into energy that the body can use called ATP. In the first three steps, glucose is converted into a series of byproducts and molecules of reduced FAD and reduced NAD are released. The reduced FAD and reducd NAD are then used to drive ATP synthesis in step 4.

Initially in the Krebs cycle, oxaloacetate (4 carbons) from the previous cycle combines with acetyl CoA (2 carbons) from the link reaction forming citrate (6 carbons.) For every glucose, the link reaction produces two moleucles of Acetyl CoA and so the Krebs cycle will occur twice. The steps then follow DeNa DeNa A Fa Na:

DeNa is the decarboxylation of citrate and production of reduced NAD and a 5 carbon compound and carbon dioxide.
The next DeNa is further decarboxylation, producing reduced NAD, regenerating oxaloacetate and making carbon dioxide.
A is the production of ATP from ADP and a phosphate ion.
Fa is the production of reduced FAD and Na is the production of reduced NAD.

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