Overview:

Photosynthesis occurs in algae, green plants and photosynthetic bacteria. Its role is to catch solar energy and use this to drive the synthesis of carbohydrate from water and carbon dioxide. While using (CH₂O) to represent carbohydrate, the whole reaction is:

Light

H₂O+CO₂→ (CH₂O) +O₂

Photosynthesis reactions occur in two distinct phases that are:

-  the light reactions: that use light energy to synthesize ATP and NADPH;

-  the dark reactions: which use the ATP and NADPH to synthesize carbohydrate from CO₂ and H₂O.  In fact, the word 'dark reactions' is a misnomer; this carbon-fixation reaction should actually be known as light-independent reactions.