Photosynthesis Flashcards
What reactions take place in photosynthesis?
Light dependent reaction
Light independent reaction
Define photo ionisation
The oxidation of chlorophyll when hit by light
Define photolysis of water
H2O –> 2H+ + 2e- + 1/2O2
Define photophosphorylation
Making ATP (from ADP + Pi) using energy from light
What is the light dependent reaction?
Chlorophyll absorbs light energy via photo ionisation
This excites electrons and electrons are removed from chlorophyll (chlorophyll is oxidised)
Electrons move along electron transport chain releasing energy
Energy released by the electrons is used to form proton gradient
H+ ions diffuse through ATP synthase (photophosphorylation) providing energy to join ADP and Pi to form ATP
Photolysis of water produces 2 protons, 2 electrons and 1/2 oxygen
The electrons produced from the photolysis of water replace the electrons lost from chlorophyll during photo ionisation
NADP reduced by electrons
Where does the light dependent reaction take place?
In the granum of chloroplasts
How are the H+ ions pumped into the thylakoid space during the light dependent reaction?
Using the energy released from the electrons
Where does the photolysis of water occur?
In the thylakoid space
Why can a photosynthesising organism fluoresce when an electron transport chain is not available for the excited electron?
This is because the excited electron cannot lose energy via the electron transport chain so releases the energy as light
In plants, ATP is produced in the light dependant reaction. Suggest why this is not a plants only source of ATP (4)
Plants don’t photosynthesise in the dark
Not all the parts of a plant photosynthesise (root)
Plants require more ATP than is produced in the light dependent reaction
ATP is used in active transport
Describe the effect of introducing herbicide on the electron transport chain (4)
Reduced transfer of protons across thylakoid membrane
So less ATP produced
So less reduced NADP produced
So light-independent reaction slows/stops
Less reduction of GP to triose phosphate
Where does the light independent reaction take place?
In the stroma
Describe the light independent reaction
Carbon dioxide combines with RuBP using the enzyme Rubisco
Produces two GP molecules
2 GP reduced to 2 x triose phosphate
Using reduced NADP
Using energy from ATP
Some triose phosphate converted to glucose and some is regenerated to form RuBP using phosphate from ATP
Describe Carbon Fixation in the Calvin Cycle
RuBP acts as a carbon dioxide acceptor. Reaction is catalysed by the enzyme rubisco. The CO2 reacts with RuBP to form two molecules of GP
Describe reduction in the Calvin Cycle
The GP is reduced to triose phosphate. This required NADPH from the light dependent stage which provides the reducing power and ATP. Some of the triose phosphate is converted into useful organic compounds such as amino acids
