Biology A2 Unit 4 - Photosynthesis

My photosynthesis condensed notes

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  • Created on: 14-12-13 16:27
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Photosynthesis stores energy in glucose
o Light energy used to make glucose from H2O and CO2 (light energy chemical energy)
o Light Energy + 6CO2 + 6H2O C6H12O6 (glucose) + 6O2
Key Terms
o Metabolic Pathway ­ series of reactions controlled by enzymes e.g respiration &
o Phosphorylation ­ adding a phosphate to a molecule e.g ADP ATP.
o Photophosphorylation ­ adding a phosphate to a molecule using light.
o Photolysis ­ splitting (lysis) of a molecule using light (photo)
o Hydrolysis ­ splitting of a molecule using water.
o Decarboxylation ­ removal of CO2 from a molecule.
o Dehydrogenation ­ Removal of hydrogen from a molecule.
o Redox Reactions ­ Involve oxidation & reduction ­ (OxidationIsLossReductionIsGain)
Coenzymes are involved in photosynthesis
o Coenzyme ­ molecule that aids function of an enzyme.
o Transfer a chemical group from one molecule to another.
o NADP is used in photosynthesis. It transfers hydrogen from one molecule to another. It can
reduce (give H to) or oxidise (take H from) a molecule. Electrons are transferred too.
Photosynthesis takes place in chloroplasts
o Have a double membrane (chloroplast envelope)
o Thylakoids are stacked up to form grana. Grana are linked by lamellae
o Chloroplasts contain photosynthetic pigments (e.g chlorophyll) that absorb the light energy
for photosynthesis. These attach to thylakoid membranes. Protein & pigment=photosystem.
o Photosystems used ­ PS1 absorbs light best at wavelength 700nm and PS2 at 680nm
o Stroma (inside inner membrane) contains enzymes, sugars and organic acids. Carbohydrates
produced by photosynthesis and not used immediately are stored as starch in the stroma.
The Light-Dependent Reaction
o Needs light energy
o Takes place in thylakoid membranes of the chloroplasts.
o Light energy absorbed by photosynthetic pigments in the photosystems and
converted to chemical energy.
o Light energy is used to add a phosphate group to ADP to form ATP.
o And to reduce NADP to form reduced NADP.
o ATP transfers energy and reduced NADP transfers hydrogen to light independent r.
o H2O is oxidised to O2 during the reaction.
The Light-Independent Reaction (Calvin Cycle)
o Doesn't use light energy directly, but relies on the products of the light-dependant r.
o Takes place in the stroma of the chloroplast.
o ATP and reduced NADP from the light-dependent r. supply energy and hydrogen to
make glucose from CO2

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The Light-Dependent Reaction
Photophosphorylation ­ When ATP is made in the light dependent r.
o Light energy absorbed by photosystems used to:
o Make ATP from ADP and an inorganic phosphate (Pi) (photophosphorylation).
o Make reduced NADP from NADP.
o Split water into protons (H+), electrons and oxygen (photolysis)
Non-Cyclic Photophosphorylation
o Produces ATP, Reduced NADP and O2.
o Photosystems linked by electron carriers (proteins).
o Photosystems + electron carriers = electron transport chain.
1.…read more

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The Light-Independent Reaction (Calvin Cycle)
o In the stroma of chloroplasts.
o Makes triose phosphate (TP) from CO2 and ribulose bisphosphate (5C compound)
o TP can be used to make glucose & other useful organic substances.
o Calvin Cycle requires ATP and H+ for energy.
o The starting compound, ribulose bisphosphate (RuBP), is regenerated.
1. CO2 combined with RuBP to form 2x glycerate-3 phosphate(GP)
o CO2 leaf through stomata and diffuses into chloroplast stroma.…read more


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