5.1 photosynthesis Flashcards
Light dependent reaction
Chlorophyll absorbs light energy which excites electrons to a higher energy level, releasing them from chlorophyll (photoionisation)
Some electrons released during photoionisation is conserved in production of ATP and reduced NADP
Production of ATP
Electrons passed down electron transfer chain from PSII to PSI via redox reactions, losing energy at each step
Energy used to actively transport protons from stroma into thylakoid
Creates electrochemical gradient across thylakoid membrane
Protons move by facilitated diffusion down electrochemical gradient into stroma via enzyme ATP synthase embedded into thylakoid membrane
Energy from this allows ADP + Pi > ATP (photophosphorylation). Chemiosmotic theory
Production of reduced NADP
In PSI electrons are excited and transferred to NADP (with a proton from photolysis) to reduce NADP to form reduced NADP
Photolysis
Splitting of water using light energy
Produces protons, electrons and oxygen
Photolysis equation
2H2O > O2 + 4e- + 4H+
Electrons replace those lost from chlorophyll
Products of light dependent reaction
ATP > LIR
Reduced NADP > LIR
O2 - leaves cell as by-product or used in respiration
Light-independent reaction
CO2 reacts with RuBP (5C), catalysed by enzyme rubisco
produces 2 molecules of GP (3c)
GP reduced to triose phosphate (TP) using products from LDP
- energy from hydrolysis of ATP and H+ from reduced NADP
some TP converted into useful organic substances e.g. glucose
(5/6) TP used to regenerate RuBP (using rest of ATP)
temperature
rate of photosynthesis increases as temperature increases, up to an optimum, decreases after
limits LIR as its enzyme controlled (rubisco)
increasing temp up to the optimum:
- more kinetic energy, more E-S complexes (rubisco)
above optimum:
- H bonds in tertiary structure break > active site changes shape/enzyme denatured, fewer E-S complexes
light intensity
rate of photosynthesis increases as light intensity increases (then plateaus)
if light intensity was reduced :
levels of ATP and reduced NADP would fall due to
- LDR limited as less photoionisation of chlorophyll (less photolysis)
so, LIR would also slow/stop as
- GP cant be reduced to TP (requires ATP and reduced NADP)
- TP cant regenerate RuBP (requires ATP)
CO2 concentration
rate of photosynthesis increases as CO2 concentration increases (then plateaus)
if CO2 conc reduced:
- limits LIR
- less CO2 to combine with RuBP to form GP
- less GP reduced to TP
- less TP (and GP) converted to organic substances e.g. hexose an to regenerate RuBP
agricultural practices to overcome limiting factors
e.g. growing under artificial lighting to maximise light intensity
heating a greenhouse to increase temperature
burning fuel, paraffin burners, to release more CO2
if limiting factors are minimal
rate of photosynthesis increases
faster production of glucose allowing faster respiration
more ATP to provide energy for growth e.g. cell division, protein synthesis
higher yield so more profit
