photosynthesis Flashcards
where does the LDR take place
on thylakoid membrane
in chloroplast
where does LIR take place
in stroma
in chloroplast
describe LDR - absorption of light
• Chlorophyll (in photosystem II) absorbs light energy (photon) which excites electrons to a higher
energy level, releasing them from chlorophyll = photoionisation
• Some energy from electrons released during photoionisation is conserved in the production of ATP and
reduced NADP:
describe LDR atp production
- Electrons pass down electron transfer chain (electron carriers) from PSII to PSI via redox
reactions, losing energy at each step - This energy is used to actively transport protons from stroma into thylakoid
- Creating a proton / electrochemical gradient across the thylakoid membrane (higher in
thylakoid than stroma) - Protons move by facilitated diffusion down the electrochemical gradient into the stroma via
the enzyme ATP synthase embedded in the thylakoid membrane - Energy from this allows ADP + Pi ATP (photophosphorylation)
This is called the chemiosmotic theory
describe LDR NADPH production
- In PSI electrons are excited and transferred to NADP (with a proton from photolysis) to
reduce NADP to form NADPH
• Photolysis (splitting of water using light energy) produces protons, electrons and oxygen (2H2O O2 +
4e- + 4H+)
• Electrons replace those lost from chlorophyll
products of LDR and what happens to them
ATP - LIR
NAPH- LIR
O2- by product/respiration
desribe LIR
carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP).
reaction is catalysed by the enzyme rubisco
ATP and reduced NADP from the light-dependent reaction used to reduce GP to triose phosphate
some of the triose phosphate is used to regenerate RuBP in the Calvin cycle
some of the triose phosphate is converted to useful organic substances.
define limiting factor of photosyntheise
- limiting factor = more favourable value, rate of photosynthesis increases
- till photosynthesis limited by diff factor
how does increasing temp affect rate of photosynthesis
- r of photosynthesis increases as temp increases, up to optimum,
- then decreases and LIR is enzyme controlled (rubisco)
Up to optimum
- more KE
- more E-S complexes
Above optimum
- H bonds in tertiary structure break = active site changes shape
- enzyme denatured
- fewer E-S complexes
explain how light intensity affects rate of photosynthesis
Rate of P increases as light intensity increases then plateaus
Light intensity reduced
- levels of ATP and NADP reduced
- LDR limited as less photoionisation of chlorophyll + photoslysis
- LIR also stops/ slows
- GP not reduced to TP ( ATP + NADPH needed)
- TP can’t regenerate RUBP ( ATP needed)
explain how CO2 conc affects rate of photosynthesis
- as co2 conc increases, r o p increases
CO2 dramatically decreased
- limits LIR reaction
- less CO2 combines with RuBP to form GP
- less Gp reduced to TP
- less TP converted to organic substances + to regenerate RuBP
agricultural practices to overcome effect of limiting factors + benefits to the farmer
- artifical lighting - maximises intensity
- heating greenhouse - increase temp
- burning fuels - increase CO2
benefits
benefits of agricultural practices to overcome effect of limiting factors
- faster production of glucose = faster r o p
- more ATP for growth
- higher yield = more profit
what is the compensation point
rate of photosynthesis = rate of respiration
why does the apparatus need to be airtigt
- escaping/ entering air decreases/increases vol of air measured
- so unreliable result
