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Module 4.5

In photosynthesis light energy is transferred to ATP in the light dependent reactions and used to
make carbohydrate in the light independent reactions.

Know photosynthesis has both light dependent and light independent reactions.
Know that in the light dependent reactions light energy excites electrons, the energy they contain…

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Limiting factor: a variable that limits the rate of a chemical reaction.

Light dependent reaction:

o To add an inorganic phosphate molecule to ADP to make ATP
o To split water into H+ ions (protons) and OH- ions. As the splitting is caused by light ­
The making…

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o The loss of electrons when light strikes a chlorophyll molecule leaves it short of
o If the chlorophyll molecule is to continue absorbing light energy it needs a
replacement of electrons.
o They are provided from water molecules.
o Photolysis also yields H+ ions.
o 2H2O 4H+ +…

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The light-independent reaction

o Products from the light dependent
reaction ­ ATP + reduced NADP are used
to reduce carbon dioxide.
o Takes place in the stroma of
o The Calvin cycle.

1. Carbon dioxide from the
atmosphere diffuses into the leaf through
the stomata and dissolves in water…

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7. Most TP molecules are used to regenerate ribulose bisphosphate using ATP from the light
dependent reaction.

Site of the light-dependent reaction

Takes place in the stroma of chloroplasts.
The fluid of the stroma contains all the enzymes needed to carry out the light-independent
reaction (reduction of carbon dioxide)

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In the light-dependent reaction of photosynthesis, light energy generates ATP. Describe how:

Light energy excites/raises energy level of electrons in chlorophyll.
Electrons pass down electron transfer chain;
Electrons reduce carriers/passage involves redox reactions
Electron transfer chain/role of chain associated with chloroplast membranes/in
Energy released/ carriers at decreasing energy levels;…


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