3.3 Translocation Flashcards
what is translocation?
the movement of sugars throughout the plant in the phloem from source to sink
in which direction can translocation occur?
both directions (bidirectional)
is translocation an active or passive process?
both
what are the products being transported called?
assimilates
what are the main SOURCES of a plant?
green leaves and stems
storage organs that are unloading (tubers)
food stores in seeds when they germinate
what do sources do?
store sugars
what do sinks do?
need and use the sugars
what are the main SINKS of a plant?
growing roots
meristems actively dividing
parts laying down food stores - fruits, seeds
translocation is the movement of organic solutes e.g.
sucrose
what is the process by which organic solutes move from source to sink through the phloem?
mass flow
in the symplastic route phloem loading occurs as the sucrose moves through what?
cytoplasm mesophyll cells
(phloem loading) in the symplastic route, sucrose moves from mesophyll cells onto where, and how?
sieve tubes by diffusion through plasmodesmata
(phloem loading) is the symplast route mainly passive or active?
passive
what is the plasmodesmata?
gaps between cells through which cytoplasm can move
(phloem loading) in the apoplast route sucrose travels through cell walls to where?
companion cells and sieve tube elements
(phloem loading) in the apoplast route what is the process by which sucrose travels to companion cells and sieve tube elements?
diffusion
(phloem loading) in the apoplast route, sucrose then moves across the cell membrane where and by what process?
cytoplasm
by active transport
(phloem loading) in the symplastic route sucrose ends up where and what flows in?
sieve elements and water flows in by osmosis
(phloem loading) in the symplastic route water flowing into the sieve elements where the sucrose is creates what?
pressure of water moving the sucrose through the phloem by mass flow
(phloem loading) in the apoplast route sucrose moves by diffusion along a concentration gradient maintained by what?
removal of sucrose into phloem vessels
(phloem loading) in the apoplast route, hydrogen ions are actively pumped out of where and using what?
companion cells into surrounding tissue using ATP
(phloem loading) in the apoplast route hydrogen ions return to the companion cell down a what and via what?
concentration gradient via co transport protein
(phloem loading) in the apoplast route, what is co transported with the hydrogen ions?
sucrose
(phloem loading) in the apoplast route, as sucrose is co transported what does it increase?
sucrose concentration in companion cells and sieve tube elements
companion cells have infoldings in their cell membrane to give what?
increased surface area for active transport of sucrose into cytoplasm
companion cells also have many mitochondria for what?
supplying ATP needed for transport pumps
a build up of sucrose means water moves in by osmosis, building up what?
turgor pressure due to rigid cell walls
solute accumulation in the source leads to increase in what?
turgor pressure
increased turgor pressure forces what to where?
sap to regions of low pressure in sinks
(phloem unloading) sucrose can be unloaded at which point and to where?
at any point to cells needing it
(phloem unloading) sucrose diffuses from phloem to where?
surrounding cells
(phloem unloading) sucrose moves into other cells by what process?
diffusion
(phloem unloading) sucrose can also move into other cells by being what?
converted into other substances
(phloem unloading) give an example of when sucrose is converted into another substance:
glucose for respiration
starch for storage
(phloem unloading) what effect does loss of solutes from phloem have on water potential?
increases water potential
(phloem unloading) increase of water potential in phloem means water does what?
moves into surrounding cells by osmosis
(phloem unloading) of water carried from solute to sink some is drawn into where?
transpiration stream in the xylem
