Unit 4: Photosynethesis

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ATP in a cell and Where does Photosynthesis Take P

6CO2 + 6H20 +Energy   =   C6H12O6 + 6O2     <------ Photosynthsis

Respiration is reversed

ATP is synthesised from ADP and Inorganic Phosphate

Energy Stored as chemical energy in phosphate bond

ATP diffuses into parts of cells that need energy

Broken back down into ADP and Pi

Chemical energy from phosphate bond is used by cell

ATPase catalyses reaction

ADP and Pi recycled again

Photosynthesis takes place in Chloroplasts

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Important Words Photosynthesis

Phosphorylation- Adding phosphate to a molecule

Photophosphorylation- Adding phosphate to a molecule using light

Photolysis- The splitting of a molecule using light

Hydrolysis- The splitting of a molecule using water

Oxidation-Loss of electrons

Reduction- Gain of electrons

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Light Dependent Reaction

Takes Place in thylakoid membrane of chloroplasts

Photosynthetic pigments are converted to chemical energy from the light energy

Light energy is used to add phosphate group to ADP to form ATP

Also reduces NADP to form Reduced NADP

H20 is oxidised to 02

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Light Independent Reaction (Calvin Cycle)

Takes place in the stroma of chloroplasts

ATP and reduced NADP supply energy and hydrogen to make glucose from CO2

CO2 enters leaf and diffuses into stroma of chloroplast where it combines with RuBP (Rubisco)

Breaks down into two GP molecules where ATP from LDR, H+ ions from rNADP reduce the GP into GALP

rNADP is recycled back to NADP

GALP is converted into glucose, proteins, lipids, carbohydrates, nucleic acids, amino acids

5 of 6 GALP are used to regenerate RuBP

6 turns of cycle make a glucose molecule as glucose required 6 carbon molecules

Therefore it requires 18 ATP and 12 rNADP molecules 

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Electron Transport Chain

PSII absorbs light energy and excites electrons in chlorophyll where they move to a higher energy lvl

They move to PSI 

Light energy splits water into protons,electrons and oxygen  H20----> 2H+  +  1/2 O2

Excited electrons lose energy to PS1, and energy is used to transport protons into thylakoid

Concentration gradient formed between thylakoid and stroma and forms protein gradient

Protons move down gradient into stroma with ATP Synthase

The energy from the movement combines ADP and Pi to form ATP

PSI absorbs light energy and re-excites electrons to an even higher energy level

Electrons are transferred to NADP with a proton from the stroma to form rNADP

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Cyclic Photo-phosphorylation

Only uses PSI

Electrons from cholorphyll are not passed onto NADP

They go back to PSI via electron carriers

Electrons are recycled back into system

Doesnt produce rNADP or O2

Only small amounts of ATP

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Cholorplast envelope keeps reactants for photosynthesis close to reaction sites increasing efficiency

Thylakoids have a large surface area to maximise light energy intake

Lots of ATP synthase in thylakoid to produce a lot of ATP in LDR

Stroma contains enzymes, sugars and organic acids for LIR

Learn how to draw a Chloroplast


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