photosynthesis Flashcards
1
Q
Why do plants need both chloroplasts and mitochondria?
A
- photosynthesis takes place in tissues containing the green pigment chlorophyll
- these are the chroloplasts; highly structured, membrane rish organelles
- 40 to 50 chroloplasts per cell
- chloroplasts convert light energy into chemical energy, and mitochondria consume the chemical energy to produce ATP
2
Q
What is the purpose of photosynthesis?
A
- the process of using sunligh to produce carbohydrates
- requires sunlight, co1, and h20 and produces o2 as a by product
- usually glucose is produced, but several carbohydrates can be made
3
Q
What are the two main reaction pathways in photosynthesis and the purpose of each?
A
- light dependant reactions which produce o2 from h20
- light independant reactions (cavin cycle) which produce sugar from co2
- two sets of reactions are linked by electrons: electrons are released in the light-dependant reactions when water is split to form oxygen gas; electrons are transferred to NADP= forming NADPH
- calvin cycle uses this NADPH to reduce co2: ATP made by the light dependant reactions is also used in the calvin cycle
4
Q
Would human impacts on the environment affect C3, C4 or CAM plants differently? Why?
A
- more equipped to survived these conditions
- global warming causing more hard and dry envionments
- c4 would thrive
cam
- less sunlight due to co2 and urbanizaition
- cam is temporal
-
5
Q
summary of photosynthesis
A
- energy from the sun must be transformed into chemical energy for use by organisms
- autotrophs are organisms that use sunlight to produce carbohydrates (heterotrophs must meet their needs for nutrients from other oragnisms…. no heterotrophs without autotrophs)
- electrons carried by NADPH (battery molecule) and the potential energy of ATP link light reactions with co2 reduction to carbohydrates
6
Q
stsructure of the chloroplast
A
- the inernal membranes of chloroplasts form flattened, vesicle-like structures called thylakoids, some of which form stacks called grana
- the fluid-filled space between the thylakoids and the inner memebrane is the stroma
- light dependant reactions happen in the chloroplasts
7
Q
light dependant reactions
A
- starts with chlorophyll
- chlorophyll molecules work together in groups, foring a complex called a photosystem
- photosystem 2 feed and ETC that pumps protons to ATP synthases in a process called photorespiration
- in ps 2 excited eelctrons feed an ETC.
- plastoquinone carries protons to inside of thylakoids creating a proton motive force. this is analogous to etc in cr, but with diff molecules. similar/same processes
- protons diffuse down their electrochemical gradient. flow of protons through atp synthase drives the phosphorylation of ADP
- capture of light energy by photosystem 2 to produce atp is photophosrylation
8
Q
what is chlorphyll
A
- chlorophylls are pigments
- the chlorophylls (a and b) absorb red and blue lght and transmit green light
- diff pigments absorb diff wavelength of light
- pigments that absorb blue and red photons are the most effective at triggering photosynthesis
9
Q
what are photosystems
A
- two types: 1 and 2 (named after the order in wich they were found)
- photosystems work together to produdce and enhancement effect in which photosynthesis more than doubles when cells are exposed to both red and far red ligh
- some organisms only have 1 photosystem, but in organsms with both, photosynthesis is more enchance
10
Q
how does ps 2 work
A
- photon hits chlorophyll in ps, a high-energy electron is donated to phenophytin, and chorophyll is oxidized
- pheophytin is sim to chlorophyll, but is electron acceptor, not donor
- electron from reduced pheophytin passed to etc in thylakoid membrane
- etc include plastquinone which shuttles electrons from pheophytin across the thylakoid membrane to a cytochrome complex
- electrons in etc parpicate in redox rxns. redox rxns result in proons being pumped from one side of membrane to other
- proton transport increases proton concentration inside the thylakoid 1000 fold
11
Q
how does ps 2 recharge
A
- ps 2 splits water to replace its lost electrons and in the process produces oxygen
- this is oxygenic photosythesis
- ps2 is the only known protein complex able to oxidize water in this way
12
Q
how does ps1 work
A
- reduces nadp+ to nadph
- excited electrons are passed down an etc of iron and sulfer containing proteins to ferredoxin
- the enzyme nadp+ reductase transfer a proton and two electrons from ferredoxin to nadp+, forming nadph
- nadph functions as an electron carrier to reduce other compounds
13
Q
how does ps1 recharge
A
-ps 2 recharges ps1
14
Q
what is the z scheme
A
- model of how ps 1 and 2 interact
- a photon excites an electron in the P680 chlorophyll of ps2 and passes the eelctron to pheophytin
- pot energy of the electron is gradually stepped down through redox rxns in an etc
- PQ uses released energy to transport protons across the thylakoid membrane, builing proton motive force. atp synthase uses this force to make atp
15
Q
how does z scheme link ps 1 and ps
A
- at end of ps2 etc, cytochrome complex passes an electron to a protein, plastocyanin
- pc carries e back to thylakoid membrane and donates it to ps1, linking the two ps
- e from pc replace e from p700 chlorophyll in ps1. these e enter an etc, passed to ferredoxin and used to reduce nadp+ to nadph
- e in ps2 are replced by e stripped from water, producing o2
- explains enhancement effect; most efficeint whn both p680 and p700 avalible
16
Q
what is the calvin cycle
A
- common to all photosynthetic eukaryotes (algea to angiosperms)
- occurs in the chloroplast stroma ( in the cytosol)
- is a cycle, it spins
- has three phases: fixation, reduction and regeneration
- co2 is reduced in the calvin cycle
- needs three turns of the cycle to generate one G3P
17
Q
fixation
A
- co2 reacts with ribulose bisphospahe (RuBP), producing two 3-phosphoglycerate molecules
- the attachement of co2 to an organic compound is called carbon fixation
18
Q
reduction
A
- the 3-phosophoglycerta molecules are phosphorlate by atp and reduced by nadph to produce glyceraldhyde 3-phosphate (g3p)
- the 6 g3P produced are used to turn the cycle again
19
Q
regeneration
A
the remaining G3P is used in reactions that regenerate RuBP
- get glucose from regeneration
20
Q
what is rubisco
A
- ribulose 1,5 bisphosphate carboxylase/oxygenase, or rubisco catalyzes the reaction
- 10^7 tons of enzyme required globally comprises 40-50% of total solubale lear protin, aka it is very abundant
- in all photosyntheic organisms
- worlds most abudant “fixing: protein (fixes approx 200 billiontons o co2 annually)
- it is the best battle againt the co2 we produce
21
Q
what is the problem with rubisco
A
- sluggish catalysis enzyme
- onlt 3 reactions/sec compared to other enzymes which can do thousands/sec
- it evolved early when the planet had negligable o2 in atmopshere
- uses o2 as a substrate bu with net loss of c fixes
d, this is PHOTORESPIRATION - cycle used to salvage this carbon uses atp and loses another molecule of co2
22
Q
photorespiration vs calvin cycle
A
- depends on what molecule is present and what goes to rubisco
- when o2 is present, co2 is produced = PHOTORESPIRATION. also uses atp
- calcvin cycle is when co2 is produced
23
Q
what is stomata
A
- leaf structures where gas exchange occurs
- open pores bounded by guard cells in plant leaves
- usually on the underside of leaves because the pore wont get clogged
- co2 diffuses ino plants through pores of stomata and is fixed by rubisco in mesophyll cells of leaves
- under dry conditions when plans need to reduce water loss, they close stomatasince co2 and h2o share the same pathway. this also stops plants from fixing co2
- when co2 conc low during photosynthesis, stomata opens and co2 diffuses in
- open during day and close at night (open bc water loss)
- in hot and dry conditions, many plants close stomata toprevent water loss, prvents photosynthesis
24
Q
how can plants get around photorespiration
A
- plangs in different places have evolved to combat photorespiration in different ways
c4 plants - cam plants
- c3 plants
25
c4 plants
- carbon fixation and calvin cycle occur in seperate types of cells
- SPATIAL seperation
- during C fixation, c4 plants incorperate co2 into 4-c organic acis instead of g3p
- the acids prodced travel to bundle sheath cells and release a co2 molecule, which rubisco uses to form 3-phosphoglycerate and initates the calvin cycel
- occurs mostly in plants from hot, dry habitats, limits the damaging effects of photorepiration
- reduced water loss where water loss if more likely
- splits up photosynthesis
- least efficeint
26
cam plants
- in super hot climates
- cuctus, succulant, etc
- most effecient compared to c3 and c4
- reduced water loss if achieved by opening stomata during cool nights and closing thm during the day when temps ar ehigh
- co2 only enters at night which requires plant to release co2 from stored c4 acids during the day for fixation by rubisco
- with stomata closed, there is litle o2 present do phororespiration is suppressed
- uses same spatial as c4. so they run the same thing but it temporally divided
- SPATIAL and TEMPORAL seperation
- some cam do both, some only do time
27
c3 plants
redular plants
28
Differentiate C3, C4 and CAM plants. Where would you typically find examples of each?
