Translocation - sources and sinks

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  • Created by: EClou
  • Created on: 07-04-15 18:37
what is the hydrostatic pressure gradient?
gradient created by flow of water from source to sink in phloem
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what is mass flow?
flow of water along the phloem created by the movement of water entering the phloem at a source, travelling down the hydrostatic pressure gradient carrying assimilates, and leaving at the sink.
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can mass flow move up or down the phloem?
both up and down depending on where the sugars are needed
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can it go up and down in different tubes at the same time?
yes
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how does sucrose get into the phloem in the first place?
active transport of H+ ions into surrounding cells from CC using ATP, causes diffusion gradient so the H+ diffuse back to the CC through cotransporter proteins with the sucrose molecules which then diffuse into the STE through plasmodesmata
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give 2 examples of uses for the sucrose once it gets to the sink
1. used in respiration, 2. converted to starch for storage
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give 2 examples of sources:
1. leaves - in late spring - early autumn when sugars are made during photosynthesis and converted to sucrose, 2. roots - in spring when other parts of the plants need energy for growth
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give 2 examples of sinks::
1. leaves - early spring when the leaves are growing and need energy, 2. roots - when growing
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why is the pH of the companion cells higher than in the surrounding cells?
as the H+ ions are pumped out of the CC there are fewer H+ ions in the cells and therefore theres a higher pH
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what could the sieve plates be used for?
block the flow of sugars if phloem is cut and sugars are being lost.
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give 2 examples of how we know the phloem is used:
1. Ringing a tree as the phloem is in the bark whilst the xylem is in the wood and therefore the sugars build up, 2. Aphids feeding from the phloem - when fluid is collected it contains many sugars/aphid cut off from stylet and sugars flow out
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how do we know translocation requires metabolic energy (ATP)? - (2)
1. many mitochondria in the companion cells, 2. translocation can be stopped by using a metabolic poison that inhibits the formation of ATP
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How do we know that translocation uses this mechanism? (2)
1. pH of companion cells is higher than the other cells, 2. concentration os sucrose is higher at the source than at the sink
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give two pieces of evidence against this mechanism:
1. not all the solutes in the phloem sap move at the same rate, 2. sucrose is moved to all parts of the plant at the same rate, rather than going more quickly to areas with a low concentration.
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Other cards in this set

Card 2

Front

what is mass flow?

Back

flow of water along the phloem created by the movement of water entering the phloem at a source, travelling down the hydrostatic pressure gradient carrying assimilates, and leaving at the sink.

Card 3

Front

can mass flow move up or down the phloem?

Back

Preview of the front of card 3

Card 4

Front

can it go up and down in different tubes at the same time?

Back

Preview of the front of card 4

Card 5

Front

how does sucrose get into the phloem in the first place?

Back

Preview of the front of card 5
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