5.2 Photosynthesis Flashcards
Thylakoids
Discs containing chlorophyll
Grana
Stacks of thylakoids
Lamellae
Join thylakoids in other grana
Light Dependant stage takes place here
Stroma
Fluid filled matrix
Light Independant stage take place here
Light Dependant Reaction
Occurs in thylakoid membranes
Provides ATP, Hydrogen + Oxygen
Reaction captures light which is used to form ATP
LDR - Making ATP
1) A photon of light is absorbed by chlorophyll a, boosting the energy levels of a pair of e-
2) Excited e- leave the chlorophyll molecule
3) Chlorophyll molecule is ionised
LDR - ETC and Photosystems
1) Excited e- are taken up by an e- carrier
2) The carrier molecules are a series of proteins found in the thylakoid membrane
3) Excited e- move along the ETC from PS2
4) Each carrier has a slightly lower energy level than the last one
e- lose energy at each stage
5) This energy is used to synthesise ATP
LDR - Photolysis
1) Water molecules are split using light energy absorbed by chlorophyll a
2) When chlorophyll a absorbs light it loses e- + becomes +vely charged
3) Chlorophyll is now oxidised + needs e- to react again
Photolysis Products
e- which are used up to reduce the chlorophyll
O2 - which is a by product
H+ are taken up by NADP which is the final acceptor of e-
Cyclic Phosphorylation
1) A photon of light hits a chlorophyll molecule
2) e- are excited
3) e- are taken up by an e- acceptor
4) e- passed along an ETC
Energy is released + ATP is synthesised
5) e- returns to PS1 chlorophyll
Non-cyclic Phosphorylation
1) Photon hits chlorophyll in PS2
2) e- are excited
3) e- are taken up by an e- acceptor, passed along an ETC to PS1
Energy is released + ATP is synthesised
4) Photon hits chlorphyll in PS1
5) Photolysis occurs
6) e- are excited
7) e- are taken up by an e- acceptor, passed along an ETC chin to NADP
8) NADP takes a H+ ion to form NADPH
9) OH- ions react together to form H2O + O2
Chemiosmotic Theory
1) Protons are actively transported from the stroma into the thylakoid
2) The proton pump is driven by the energy released from the excited e- as they pass along the ETC
3) Protons accumulate inside the thylakoid + forms a CG
4) Protons diffuse back across the membrane into the stroma
5) Can only go through chemiosmotic channels
6) Channels are formed by ATP synthase
7) Channels form small granules on membrane surface called stalked granules
8) Protons pass through ATPase which causes changes to the structure of the enzyme
9) Enzyme catalyses ADP + Pi to form ATP
Light Independent Reaction
1) RuBP combines with CO2 catalysed by RUBISCO (6C)
this is called carbon fixation
2) Compound is unstable
broken down into 2x GP
3) NADPH reduces 2x GP into 2x GALP using ATP
4) NAPD is reformed + returns to LDR
5) GALP has 2 uses
5 out of 6 carbons regenerate RuBP using ATP
1 carbon helps form glucose
Absorption Spectrum
The amount of light absorbed by each pigment at different wavelengths
Action Spectra
Rate of photosynthesis at each wavelength
