Translocation

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  • Created by: Louisa
  • Created on: 16-05-13 13:19
What is translocation?
The transport of assimilates throughout the plant in the phloem tissue
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What is meant by source and sink?
Source is where the assimilates are loaded into the phloem, Sink is where the assimilates are unloaded from the phloem
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Is translocation a passive or active process?
active as it needs energy eg. active transport of hydrogen ions into the surrounding tissues of the companion cell
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How is sucrose loaded into the phloem?
ATP used to actively transport hydrogen ions out cytoplasm into surrounding tissues.Diffusion gradient created so hydrogen ions diffuse back into companion cells +sucrose(by cotransporter proteins)High concen sucrose=diffuse into sieve tube elements
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How do assimilates move from source to sink?
Sucrose into SieveTube Element lowers Ψ.So water moves into phloem(osmosis) This increases Hydrostatic Pressure. HP is low at sink so travels down. Sucrose unloaded at sink by surrounding cells and increaseΨ in SieveTube + decreases HP. MASS FLOW
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Give an example of a source and a sink
Source= Leaves Sink= Meristem or Roots
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What evidence is there to support this theory?
PHLOEM USED:Ringing a tree to remove the phloem results in sugars collecting above the ring. An aphid feeding on a plant stem shows the mouth parts taking food from the phloem. NEEDS ATP: Companion cells many mitochondria
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What evidence is there against this mechanism?
Not all solutes in phloem sap move at same rate. The role of sieve plates is unclear
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Other cards in this set

Card 2

Front

What is meant by source and sink?

Back

Source is where the assimilates are loaded into the phloem, Sink is where the assimilates are unloaded from the phloem

Card 3

Front

Is translocation a passive or active process?

Back

Preview of the front of card 3

Card 4

Front

How is sucrose loaded into the phloem?

Back

Preview of the front of card 4

Card 5

Front

How do assimilates move from source to sink?

Back

Preview of the front of card 5
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