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The light dependent stage takes place in the thylakoids.
There are two types of photophosphorylation- cyclic and non-cyclic.
Cyclic: uses only photosystem I where the excited e- pass continuously around the electron transport
chain producing ATP from ADP and Pi *on thylakoid membrane.
Non-Cyclic: uses both photosystems and continues to produce reduced NADP/NADPH/NADPH2 using
the 2e- and the 2H+ from photolysis in photosystem II while the 1/2 O2 is a waste product and the 2e-
replace those lost by master pigment (P680) to primary acceptor. The protons (H+) are pumped into
thylakoid space where a proton gradient or proton motive force is formed.
Photolysis is when water is broken down using light (H2O is split).
1. The light energy is converted into chemical energy in photosystem II where electrons (e-) are
lost by master pigment as the energy from accessory pigments is transferred to the master
pigment (P680) in order to utilize all wavelengths of light.
2. These electrons then move to the primary electron acceptor before travelling down the
electron transport chain along cytochromes/ the cytochrome complex via redox reactions.
During this process ATP is produced.
3. The electrons then move to photosystem I where electrons are then released by the master
pigment (P700) to the final electron acceptor (usually O2).
4. These electrons are then added to NADP using NADP reductase alongside 2H+ from the
photolysis of H2O. This produces NADPH/NADPH2/reduced NADP.
5. NADPH2 and ATP are then transported to Calvin's Cycle (Light Independent Stage) in the
The light independent stage takes place in the stroma and is also called Calvin's cycle.
At any one time 6 turns of Calvin's Cycle take place 1/6 carries out 3. Food syntheses, while 5/6
continue the cycle.
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Faults of measuring the uptake of CO2 to give an indication of photosynthetic activity:
× Only presents Calvin's Cycle
× CO2 produced may be used up for Calvin's Cycle
Faults of measuring oxygen production to give an indication of photosynthetic activity:
× Some may be used up for respiration
× Only shows activity of light dependent stage
Light intensity and how it affects results:
If other substances bind to electrons in photosystem I:
× It will prevent non- cyclic photophosphorylation
× Both cyclic and…read more