PHOTOSYNTHESIS Flashcards
what are autotrophs
things that produce organic molecules from CO2 – make their own food
what are heterotrophs
live off organic compounds produced by other things
what is photosynthesis
Process that feeds the biosphere
what are chloroplasts
- sights of photosynthesis
- capture light energy from the sun – convert it into chemical energy
- About 500,000 per mm2 of a leaf
- Found mostly in mesophyll – interior of leaf
- Each chloroplast has 2 membranes around a dense fluid called stroma
- Stacks of grana (thylakoids = single) are suspended within the stroma – series of membrane sacs
where are chloroplasts found
mesophyll
what are stomata
microscopic pores in the leaf where co2 + o2 enter and exit
what is chlorophyll
green pigment in chloroplasts (in thylakoid membranes) - absorbes specific wavelength
what is photosynthesis
reduction of CO2 using electrons from H2O
what do chloroplasts split water into
H + O - incorporating the electrons of H into sugar
2 parts of photosynthesis
light reactions / cycles (get some electrons)
Calvin cycle (use the electrons to reduce co2 to sugar)
what happens in light reactions
- water is split
- reduction of NADP -> NADPH
- generate ATP from ADP by photophosphorylation
how does energy get transfer through photosystems (light cycle)
- light energy excites chlorophyll in PSII - brings to higher energy shell
- when the energy is lowered, passes to neighbouring chlorophyll until reaches P680
- sends electrons in P680 (which are there due to splitting of water) to primary acceptor
- electrons passed down a chain (makes ATPs)
- ends up in P700
- chlorophyll in PSI gets exited - passes electrons in P700 to primary acceptor
- electrons end up in NADP reductase
major products and byproducts of light cycle
major products:
ATP
NADPH
byproducts:
O2
main source of electrons for the light cycle
water - pulled from soil by roots of plant
2 kinds of light cycles
linear
cyclic
whats the cyclic cycle of the light cycle
- uses only PSI - goes continually from primary acceptor to ETC
- produces ATP but not NADPH
- generates surplus ATP - not efficient
- evolved before linear flow
- could have a role in protecting cells from light damage
whats the Calvin cycle
- uses ATP + NADPH to reduce CO2 to sugar (CH2O)
- carbon enters the cycle as CO2 and leaves as glyceroldehyde 3 phosphate (G3P - 3C sugar)
- for net synthesis of 1G3P the cycle must fix 3CO2 molecules - 3C plants
- 3 stages:
1. carbon fixation
2. reduction
3. regeneration
what happen in carbon fixation
- RuBisco - fixes CO2 to 6C molecule - broken into 2X 3C molecules
what happen in reduction
3C molecules get reduced using the electrons from NADPH
what happen in regeneration
regenerate all materials so cycle can happen again
how does hot air climates relate to rubisco
rubisco can combine O2 with catalytic efficiency
- hot climates - lots of O2 inside the cell that can’t get out through stomata (closes to prevent water loss) - photorespiration happens (wasteful process)
- no CO2 can combine with Rubisco if its surrounded by O2
what happens in photorespiration
rubisco adds an O2 rather than CO2 in Calvin cycle - consumes o2 + organic fuels (RuBP) - destroying 50% carbon mass of planet
strategies plants use to make photorespiration not happen
- change place of carbon fixation - C4 plants
- change time of carbon fixation- CAM plants
what happens in change place of carbon fixation
C4 plants change the location of carbon fixation
- incorporates Co2 INTO 4C compounds in mesophyll cells
- need PEP carboxylase to do this - has higher affinity to CO2 than rubisco
- 4C compounds are transported to bundle-sheath cells - release CO2 then used in Calvin cycle
what happens in change time of carbon fixation
CAM plants
- open their stomata at night - incorporating CO2 into organic acids
- Stomata close during the day - CO2 is released from organic acids and used in the Calvin cycle
what kind of reaction is photosynthesis
anabolic
