photosynthesis and translocation

Question 1

what is photosynthesis

Answer 1

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

Question 2

what are some photoautotrophic organics

Answer 2

prokaryotes= some bacteria e.g cyanobacteria
eukaryotes = alage, bryophytes, vascular plants

Question 3

what are the characteristics of photosynthesis in green plants

Answer 3

1) chloroplasts containing grana and stroma
2) primary pigment chlorophyll a
3) accessory pigments such as chlorophyll b and carotenoids

Question 4

how does chlorophyll a make photosynthesis possible

Answer 4

it passes its energised electron on to molecules which manufacture sugars

Question 5

what are accessory pigments

Answer 5

pigments which cant transfer energy directly to the photosynthetic pathway so must pass absorbed energy to chlorophylla

Question 6

what does the light phase of photosynthesis take place

Answer 6

photosystems embedded in the thylakoid membranes

Question 6

what does the light phase of photosynthesis take place

Answer 6

photosystems embedded in the thylakoid membranes

Question 7

where does the dark phase of photosynthesis take place

Answer 7

the soluble matrix of the stroma

Question 8

what are photons

Answer 8

particles of light each containing quantum enegry which are absorbed by pigments causing them to become energised

Question 9

what is photosynthetically active radiation (PAR)

Answer 9

the part of the spectrum which drives photosynthesis which is measured in a flux of photons

Question 10

what is PFD

Answer 10

photon flux density which is the measure of a flux of protons which measures the part of the spectrum which drives photosynthesis

Question 11

what are xanthophylls

Answer 11

yellow pigments which form one of two major division in the carotenoid group, the other being carotenes

Question 12

what are anthocyanins

Answer 12

water soluable vacvuolour pigments which appear red, purple or blue depending on PH

Question 13

what is formed in the light phase

Answer 13

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

Question 14

what occurs in the dark phase

Answer 14

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

Question 15

what are the 4 protein complexes which contorl electron and proton transfer in the thylakoid membrane

Answer 15

1) PSI
2) PSII
3) cytochrome b6f
4) ATP synthase

Question 16

what is water used for in the thylakoid membrane

Answer 16

it is oxidised producing oxygen and hydrogen ions

Question 17

outline the movement of electrons through PSI and PSII

Answer 17

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

Question 18

what is PQ and PC

Answer 18

electron carriers

Question 19

what is non-cyclic photophosphorylation

Answer 19

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

Question 20

what is cyclic photophosphorylation

Answer 20

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

Question 21

what is the cytochrome complex

Answer 21

an enyzme found in the thylakoid membrane which catalyses the transfer of electrons from plastoquinol to plastocyanin

Question 22

what are the three different types of photosynthesis in plants and how do they differ

Answer 22

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

Question 23

outline the calvin cycle phases

Answer 23

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

Question 24

what is photorespiration

Answer 24

when rubp has oxygen added instead of co2 by the enzyme RUBISCO which reduces efficiency of photosynthesis

Question 25

outline c4 photosynthesis

Answer 25

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

Question 26

outline the carbon cycle in c4 plants

Answer 26

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

Question 27

what are some characteristics of c4 plants

Answer 27

1) kranz anatomy
2) no photorespiration
3) high productivities at warm temp
4) low co2 compensation point
5) high water use efficiency

Question 28

what is CAM photosynthesis

Answer 28

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

Question 29

give some examples of CAM plants

Answer 29

pineapples
crassulaceae
cataceae

Question 30

what is the difference between C4 and CAM plants

Answer 30

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

Question 31

what factors limit photosynthesis

Answer 31

1) light
2) co2
3) temo
4) mineral
5) herbicides
6) pollutants

Question 32

what occurs at low PAR

Answer 32

photosynthesis is masked by respiration

Question 33

what is the compensation point

Answer 33

when co2 upatke = co2 output

Question 34

what is photoinhibition

Answer 34

a decrease in photosynthesis induced by high fluxes of PAR

Question 35

what causes high fluxes of PAR

Answer 35

1) excess irridiance
2) chlling under normal irridiance
3) exposure to condtions which decrease co2 fixation

Question 36

where is startch synthesised and stored

Answer 36

leaves, stems and roots and seeds

Question 37

outline some features of translocation

Answer 37

• ## bidirectional from sources to sinks

Question 38

what are companion and transfer cells

Answer 38

companion= provide metabolic support for sieve elements

transfer= involved in solute exchanhe between sieve elements and leaf mesophyll

Question 39

what is p protien

Answer 39

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

Question 40

what is callose

Answer 40

a glucan which becomes depositied on the surface of sieve plates

involved in protecting and sealing plates therefore maintaining hydrostatic pressure after damage

Question 41

what is the mass flow mechanism

Answer 41

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