Topic 5 - Energy transfers Flashcards
state the two stages of photosynthesis
LDR (light dependent reaction)
LIDR (light independent reaction) - also known as the dark reaction
where does LDR occur
thylakoid membrane of chloroplast
where does LIDR occur
stroma of chloroplast
describe the structure of chloroplasts
did you mention:
double membrane (envelope), stoma containing thylakoid membrane, 70s ribosomes, circular DNA, starch granules, lamella, grana
describe photoionisation in the LDR
- chlorophyll absorbs light energy which exites its electrons (higher energy levels)
- so electrons are released from chlorophyll (chlorophyll becomes positively charged)
describes what happens after photoionisation in the LDR
some energy from electrons released in photoionisation is conserved in the production of ATP./reduced NADP:
- electrons move along electron transfer chain (electron carriers), releasing energy
- energy is used to actively pump pprotons from stroma into thylakoid
- protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase
- energy used to join ADP and Pi to form ATP (photophosphorylation
- NADP accepts a proton and an electron to become reduced NADP
state 3 products of LDR
ATP, reduced NADP, half an O2 molecule
describe photolysis of water in the LDR
water splits to produce protons, electrons and oxygen (H2O –. 0.5 O2 + 2e- + 2H+)
electrons replace those lost from chlorophyll
what is the light independent reaction known as (2 names)
the dark reaction or the calvin cycle
where does the LIDR occur
stroma of the chloroplast
what 2 products of the LDR is used in the LIDR
reduced NADP and ATP
why are reduced NADP and ATP used in the LIDR
to reduce CO2
describe the LIDR
- CO2 reacts with ribulose bisphosphate (RuBP) and is catalysed by the enzyme rubisco
- this forms 2 glycerate 3-phosphate (GP) molecules [3C]
- GP is then reduced to triose phosphate (TP) [3C]. this uses reduced NADP oxidised into NADP and ATP reduced into ADP + Pi
- some TP is converted into useful organic substances e.g. glucose (6C)
- some TP is used to regenerate RuBP (5C) in the calvin cycle using energy from ATP (ATP is reduced into ADP + Pi)
does LIDR require light?
not directly
describe how temperature affects rate of photosynthesis
temperature increases = rate increases
above optimun temperature, rate decreases = fewer sucessful collisions and fewer ES complexes form
explain how temperature affects rate of photosynthesis
temp increases because enzymes like rubisco gain kinetic energy
enzymes will denature above optimun temperature. H bonds in tertiary structure break = fewer ES complexes form
describe how light intensity affects rate of photosynthesis
light intensity increases as rate increases but above a certain light intensity, rate stops increasing
explain how light intensity affects rate of photosynthesis
light increases as rate increases
LDR increases so more ATP and reduced NADP -produced so LIDR increases as more GP reduced to TP and more TP regenerates RuBP
above certain light intensity, rate stops increasing
another factor is limiting when light intensity rate stops increasing e.g. tmeperature or Co2 concentration
describe how CO2 conc affects rate of photosynthesis
as CO2 conc increases, rate increases
above certain CO2 conc, rate stops increasing
explain why CO2 conc affects rate of photosynthesis
rate increases as CO2 increases
LIDR increases as more CO2 combines w RuBP to form GP so more GP reduced to TP so more TP converted to organic substances and more RuBP regenerated
rate stopping after certain CO2 conc
another factor is limiting e.g. temp or light intensity
what is the law of limiting factors
when a process depends on two or more factors, the rate of that process if limited by the factor which is in shortest supply
what three factorrs can the rate of photosynthesis in a plant can be limited by
light intensity, conc of CO2, temperature
what happens to rate of photosynthesis when temeprature is too low
lower kinetic energy so fewer sucessful collision and fewer ES complexes form and a slower rate of reaction = lower rate of electron transport chain/lower rate of carboxylation by rubisco
what happen to rate of photosynthesis when temperature is high
high kinetic energy breaks the hydrogen bonds in the tertiary structure of enzymes and proteins involved in the LDR and calvin cycle. enzymes + proteins lose their tertiary structure and change shape [denature] so cannot perform role in LDR or calvin cycle
lower rate of electron transport chain/lower rate of carboxylation by rubisco