5.1 Photosynthesis - Light Dependent Reaction Flashcards
what are photosystems?
functional units for photosynthesis, defined by a particular pigment, whose work is the absorption and transfer of light energy which implies the transfer of electrons
describe redox in terms of electrons
oxidation = loss of electrons, reduction = gain of electrons
describe redox in terms of hydrogen
oxidation = loss of hydrogen, reduction = gain of hydrogen
describe redox in terms of oxygen
oxidation = gain of oxygen, reduction = loss of oxygen
describe redox in terms of energy
oxidation = energy given out, reduction = energy taken in
where does the light dependent reaction occur?
in the thykaloid membranes of a granum in a chloroplast
what are the products of the light dependent reaction?
reduced NADP (NADPH,) ATP and oxygen
name the 6 main processes involved in the light dependent reaction
1) photoionisation
2) photolysis
3) electron transport chain
4) reduction of NADP to NADPH
5) proton pumps
6) chemiosmosis and synthesis of ATP (photophosphorylation)
describe the process of photoionisation
chlorophyll molecules absorb light energy, which excites electrons to a state where they are lost from the molecule altogether.
the chlorophyll molecule that loses e- is oxidised and the electron carrier which gains e- is reduced.
describe the process of photolysis and state what each of the products is used for
light energy splits water molecules into hydrogen, oxygen and electrons.
the electrons produced replace those lost through the transport chain.
the protons produced are used to reduce NADP into NADPH.
the oxygen produced is either used in respiration or diffuses out of the plant as a waste product
describe the process of the electron transport chain
electron carrier proteins receive electrons from photolysis of chlorophyll molecules.
the electrons are passes down the transfer chain in a series of redox reactions.
energy PSII > C > PSI > FD, so electrons lose energy at each step.
this energy is used to combine ADP to Pi to form ATP during photophosphorylation
describe the process of the reduction of NADP to NADPH
the NADP co-enzyme is reduced to NADPH as it accepts an electron from the transfer chain and a proton from the stroma produced during photolysis
describe the process of proton pumps
protons are pumped from the stroma into the thylakoid lumen using a proton pump.
this is an active process and the energy to do so comes from the splitting of water molecules during photolysis
how is the concentration gradient created and maintained for chemiosmosis?
H+ pumped from the stroma and into the thylakoid membrane.
Photolysis also produces H+ which further increases the concentration
define chemiosmosis
the movement of ions (e.g. H+) across a semipermeable membrane, down their electrochemical gradient.