photosynthesis and translocation Flashcards
what is photosynthesis
a process that converts light energy into biochemical energy whihc is then used to drive the assimilation of low energy inorganic carbon into high energy organic biochemicals
what are some photoautotrophic organics
prokaryotes= some bacteria e.g cyanobacteria
eukaryotes = alage, bryophytes, vascular plants
what are the characteristics of photosynthesis in green plants
1) chloroplasts containing grana and stroma
2) primary pigment chlorophyll a
3) accessory pigments such as chlorophyll b and carotenoids
how does chlorophyll a make photosynthesis possible
it passes its energised electron on to molecules which manufacture sugars
what are accessory pigments
pigments which cant transfer energy directly to the photosynthetic pathway so must pass absorbed energy to chlorophylla
what does the light phase of photosynthesis take place
photosystems embedded in the thylakoid membranes
what does the light phase of photosynthesis take place
photosystems embedded in the thylakoid membranes
where does the dark phase of photosynthesis take place
the soluble matrix of the stroma
what are photons
particles of light each containing quantum enegry which are absorbed by pigments causing them to become energised
what is photosynthetically active radiation (PAR)
the part of the spectrum which drives photosynthesis which is measured in a flux of photons
what is PFD
photon flux density which is the measure of a flux of protons which measures the part of the spectrum which drives photosynthesis
what are xanthophylls
yellow pigments which form one of two major division in the carotenoid group, the other being carotenes
what are anthocyanins
water soluable vacvuolour pigments which appear red, purple or blue depending on PH
what is formed in the light phase
1) light energy is absorbed by accessory pigments and funnelled to the reaction centre of an antenna complex
2) this drives the production of ATP and NADPH
3) oxygen is also formed during this phase
what occurs in the dark phase
the use of ATP and NADPH formed during the light phase is used in a series of enyzme catalysed reactions to assimilate carbon dioxide into a high energy organic form
what are the 4 protein complexes which contorl electron and proton transfer in the thylakoid membrane
1) PSI
2) PSII
3) cytochrome b6f
4) ATP synthase
what is water used for in the thylakoid membrane
it is oxidised producing oxygen and hydrogen ions
outline the movement of electrons through PSI and PSII
1) electron flow from reaction centrein PSII though the Z scheme via the PQ electron carrier
2) flows through the cytochrome complex to plastocyanin electron carrier to PSI
3) movement through the z scheme generates ATP enegry and NADPH reducing power
what is PQ and PC
electron carriers
what is non-cyclic photophosphorylation
When ATP is generated in an open electron transfer system linked with oxygen evolution in PSII (from photolysis), electron transfer to PSI resulting in NADPH formation
what is cyclic photophosphorylation
ATP is generated in a closed system as electrons are cycled from ferredoixn to PQ (plastoquinol) and then back to PSI via the cytochrom complex
what is the cytochrome complex
an enyzme found in the thylakoid membrane which catalyses the transfer of electrons from plastoquinol to plastocyanin
what are the three different types of photosynthesis in plants and how do they differ
1) C3 = most plants
2) C4= mostly plants of arid climates
3) crassulacean acid metabolism= mostly cacti and succulents
all differ in terms of carbon dioxide fixation biochemistry
all three involve the calvin cycle
outline the calvin cycle phases
1) fixation= carboxylation where co2 is linked to a carbon skeleton using RUBISCO forming 6c moleucle
2) reduction- 6c reduced using ATP and NADPH forming 6 3c GP moleucle
3) regeneration = 5 of the GP moleuccles used to regenrrated RuBP
what is photorespiration
when rubp has oxygen added instead of co2 by the enzyme RUBISCO which reduces efficiency of photosynthesis
outline c4 photosynthesis
1) the first stable organic compound formed is c4 acids such as oxaloacetic acid
2) the initial carboxylation is catalysed by phosphoenol pyruvate carboylase and takes place in cytoplasm of mesophyll cells
3) requires 2 additional ATP to regenerated PEP
outline the carbon cycle in c4 plants
1) the fixed co2 as a c4 acid is imported into the bundle sheath chloroplasts from mesophyll where they are decarboxylated enriching chloroplasts with co2 and forming a pyruvate which is used to trgenerate PEP
2) the co2 is fixed by RUBSICO to give 2 PGA whcih enter the calvin cycle
what are some characteristics of c4 plants
1) kranz anatomy
2) no photorespiration
3) high productivities at warm temp
4) low co2 compensation point
5) high water use efficiency
what is CAM photosynthesis
1) plants open stomata at night and close during the day
2) co2 enters and is fixed into organic acids by the PEP carboxylase in cytoplasm
3) malic acid (c4) is stored in the vacuole
4) during the day the malic acid is released and decarboxylated to liberate co2 which is used in calvin cycle
give some examples of CAM plants
pineapples
crassulaceae
cataceae
what is the difference between C4 and CAM plants
1) spatial
- c4 carbon fixation and calvin cycle occur in different cells
2) temporal
- in CAM carbon fixation and calvin occur in same cells at different times
what factors limit photosynthesis
1) light
2) co2
3) temo
4) mineral
5) herbicides
6) pollutants
what occurs at low PAR
photosynthesis is masked by respiration
what is the compensation point
when co2 upatke = co2 output
what is photoinhibition
a decrease in photosynthesis induced by high fluxes of PAR
what causes high fluxes of PAR
1) excess irridiance
2) chlling under normal irridiance
3) exposure to condtions which decrease co2 fixation
where is startch synthesised and stored
leaves, stems and roots and seeds
outline some features of translocation
- ## bidirectional from sources to sinks
what are companion and transfer cells
companion= provide metabolic support for sieve elements
transfer= involved in solute exchanhe between sieve elements and leaf mesophyll
what is p protien
protiens arranged in tubular filaments in sieve tubes obsevred in pluggin sieve pores
involved in protecting and sealing plates therefore maintaining hydrostatic pressure after damage
what is callose
a glucan which becomes depositied on the surface of sieve plates
involved in protecting and sealing plates therefore maintaining hydrostatic pressure after damage
what is the mass flow mechanism
phloem translocation from source to sinks
1) sugar enters tubes causing water to follow by osmosis increasing turgour pressure
2) sugar leaves tuves so water moves into xylem into the transpiration stream
