3.1.3 f translocation Flashcards
what is translocation?
transporting of organic compounds from sources to sinks
what process is translocation?
an active process
what are the products transported called?
assimilates
what is the main assimilate transported around the plant?
sucrose
what are the main sources in the plant?
green leaves and stems
storage organs like tubers and tap roots
food stores in seeds when they germinate
what are the main sinks in plants?
roots that are growing or actively absorbing mineral ions
meristems that are actively dividing
any parts of plants that are laying down food stores
what happens during passive phloem loading?
sucrose moves from the source cell through the plasmodesmata to the companion cell through diffusion
what happens during active loading of sucrose?
H+ ions are pumped from the companion cells to the surrounding tissue using ATP
the H+ ions want to move down the concentration gradient into the companion cells but in order to do that they need to have a sucrose molecule with it otherwise the co-transporter protein won’t let it through
this is repeated to actively load sucrose into the companion cells
what happens during phloem unloading?
sucrose is diffused from the phloem to surrounding cells
the loss of solutes leads to a rise in the water potential of the phloem so water moves from the phloem to the xylem
in the sink cells the sucrose is made into starch with means there is a low concentration of sucrose so it can continually diffuse into the sink cells
what happen with water when phloem loading occurs?
water moves into the phloem because there is a high concentration of solutes giving it a low water potential
the water moving in increases the hydrostatic pressure of the phloem
the water moves the assimilates up or down the plants
pressure is reduced as assimilates are carried around the plant
evidence for the details of translocation
if mitochondria is poisoned, translocation stops meaning energy is needed for the process to occur
the flow of sugars in the phloem is 10,000 times faster than it would be with only diffusion
aphids can be used
what is the evidence aphids provide for the details of translocation?
when aphids insert their stylus into the phloem, if their heads are snapped off from their bodies, the sugars will come out of the stylus showing it is under pressure
different parts of the phloem have different pressures
