Biochemistry of Photosynthesis

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Biochemistry of Photosynthesis

Overall Word Equation:

Water+ Carbon Dioxide( Carbohydrates+ Oxygen ((: light + chlorophyll)

1. Light Dependent Stage/ photochemical reaction/ light reactions:

Word Equation:

Water ( Hydrogen ions + Oxygen ((: light + chlorophyll)

Site: On the Thylakoid membrane of the chloroplast

Major events:

• Light absorption

o Chlorophyll in the thylakoids absorbs light. The energy absorbed is used for photolysis (splitting of water molecules).

• Photolysis of water (Photodissociation)

o The light energy absorbed split H2O molecules into H+ ions and O2

▪ 2H2O(4H+ +4e- + O2

▪ O2 is released as a gas to the atmosphere (as a by-product)

▪ H+ ions is accepted by NADP to form NADPH2

• NADPH2 acts as a reducing agent by donating H+ ions in Calvin Cycle.

• Generation of ATP (Adenosine triphosphate)

o The light energy absorbed is used to form ATP (photophosphorylation)

o In this way, light energy is converted to chemical energy stored in ATP

▪ Used to drive the reactions in Calvin Cycle

Products formed in this stage:

• Photolysis of water molecules to give H+ ions and O2

• ATP molecules: as energy source for subsequent synthesis of carbohydrates in light dependent reactions.

The flow of electrons in Photosynthesis


Photosystem: Consists of chlorophyll molecules & accessory pigments e.g. carotenoid accessory pigments trap light energy and pass to the chlorophyll.

Results of chromatography:

2. Light independent stage/ carbon fixation/ dark reactions

Word Equation:

Carbon dioxide + Hydrogen ions ( Carbohydrates + Water ((enzymes)

• Site: In the stroma of chloroplast with the presence of enzymes for dark...
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