Photosynthesis

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Two Parts of Photosynthesis

Two reactions make up photosynthesis:

1.Light Reaction or Light Dependent Reaction -

Produces energy from solar power (photons) in the form of ATP and NADPH.

SUN

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Two Parts of Photosynthesis

2. Calvin Cycle or Light Independent Reaction

Also called Carbon Fixation or C3 Fixation

Uses energy (ATP and NADPH) from light reaction to make sugar (glucose).

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Light Reaction (Electron Flow)

Occurs in the Thylakoid membranes

During the light reaction, there are two possible routes for electron flow:

A. Cyclic Electron Flow

B. Noncyclic Electron Flow

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Cyclic Electron Flow

Occurs in the thylakoid membrane.

Uses Photosystem I only

P700 reaction center- chlorophyll a

Uses Electron Transport Chain (ETC)

Generates ATP only

ADP + ATP

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Cyclic Electron Flow

Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP

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Noncyclic Electron Flow

Occurs in the thylakoid membrane

Uses Photosystem II and Photosystem I

P680 reaction center (PSII) - chlorophyll a

P700 reaction center (PS I) - chlorophyll a

Uses Electron Transport Chain (ETC)

Generates O2, ATP and NADPH

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Noncyclic Electron Flow

H2O is split in PSII & ATP is made, while the energy carrier NADPH is made in PSI

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Noncyclic Electron Flow

ADP +  ATP

NADP+ + H  NADPH

Oxygen comes from the splitting of H2O, not CO2

H2O  1/2 O2 + 2H+

P

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Chemiosmosis

Powers ATP synthesis

Takes place across the thylakoid membrane

Uses ETC and ATP synthase (enzyme)

H+ move down their concentration gradient through channels of ATP synthase forming ATP from ADP

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Chemiosmosis

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Calvin Cycle

Carbon Fixation (light independent reaction)

C3 plants (80% of plants on earth)

Occurs in the stroma