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26 Cards in this Set
- Front
- Back
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What is translocation? |
It is the movement of dissolved substances to where they're needed (up and down the plant) |
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What are dissolved substances called? |
Assimilates |
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Is translocation passive? |
No, it requires energy so is active |
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Where does translocation occur? |
In the Phloem |
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What is a source? |
Releases assimilates into the phloem |
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What are sink? |
Removes assimilates from the phloem |
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What is the form in which sugars are transported around the plant? Why? |
Sucrose because it's soluble and metablically inactive so isn't used up |
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Example of a sources: |
Leaves |
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Example of sinks: |
Flowers Growing areas Food storage organs Roots Stems Meri stem cells (area of growth) |
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Give an example of something which can be a sink and a source: |
Roots; they are sinks because sucrose can be stored in them
They are sources because in growing seasons, sucrose is transported from roots to leaves for growth. |
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How is the concentration gradient maintained in the plants and why? |
With the help of enzymes. They change the dissolved substance at the sink (breaking down). This ensures that there is always a lower concentration at the sink than at the source maintaining a concentration gradient |
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What happens in potatoes? |
Sucrose in converted to starch in sink areas = always a lower concentration of sucrose at the sink than in the Phloem. Constant supply of sucrose from phloem to sink. |
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How to tell if an area uses active transportation? |
Many mitochondria ATP involved |
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What is the definition of mass flow and where can it occur in a plant? |
Flow of water and assimilates
It can occur anywhere in the plant |
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How do substances enter the phloem at the source? |
By active loading |
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What is active loading? |
Active loading is used to move assimilates into companion cells into sieve tube cells... against the concentration gradient since the conc of sucrose is higher in the seive cells than the companion cells than the surrounding tissue cells |
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What two process does active loading consist of? |
Active transportation Co-transporter proteins |
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How is sucrose transported into the phloem? |
•H+ initially pumped out of the companion cells (actively using a hydrogen pump, against the conc gradient) •Once out, the membrane is impermeable to H+ so it must move back into cell through a protein co-transporter •For that it must have a sucrose • H+ with sucrose moves back in the cc down the conc gradient •Sucrose enters the seive tube elements via the plasmodesmata from the cc via diffusion (passive) |
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How are assimilates transported through the plant? |
*Assimilates are actively loaded into the seive tubes of the phloem at the source *This lowered wp inside the seive tubes so water enter them via osmosis from the xylem and companion cells *This creates high hydrostatic pressure inside the seive tubes at the source end |
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How are assimilates unloaded from the phloem? |
*The assimilates are removed at the sink. *This increases the wp inside the seive tubes so water leaves to a lower region via osmosis *This lowers the hydrostatic pressure inside the seive tubes |
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What overall causes the flow of water from source to sink? |
The hydrostatic pressure gradient; this pushes solutes along the seive tubes to the sinks. |
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Leaf: source and sink? |
Depends of time of year
Summer: source, creating and loading assimilates in phloem
Spring: sink, removing assimilates from phloem for growth |
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What 2 forms are assimilates transported in in the phloemn? |
Sucrose Amino acids |
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How do H+ ions move back into the companion cell with the sucrose? |
Co-transporter proteins via Faciliatted diffusion |
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How does the sucrose move into the phloemn from the companion cells? |
Diffusion |
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Why may increasung the temperature increase phloemn activity? |
Greater Resp More Konetic Energy More ATP More Active Transport |
