9.4 Translocation Flashcards Preview

A level Biology OCR A > 9.4 Translocation > Flashcards

Flashcards in 9.4 Translocation Deck (9)
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1
Q

What is a source?

A

region of plant PRODUCING ASSIMILATES by PHOTOSYNTHESIS

/STORAGE

2
Q

What is a sink?

A

region of plant REQUIRING ASSIMILATES UNLOADED

to supply METABOLIC needs

3
Q

What are examples of sources?

A

mature leaf/stem, storage organs, seeds

4
Q

What are examples of sinks?

A

fruits, meristem, roots

5
Q

What is translocation?

A

movement of ORGANIC SOLUTES around a plant

in PHLOEM vessels from source to sink

6
Q

What occurs to transport sucrose from source to sink?

A
  1. H+ ions ACTIVELY TRANSPORTED from COMPANION cells ⟶ surrounding tissue
    • proton gradient
  2. Sucrose + H+ ⟶ companion cell by FACILITATED diffusion using COTRANSPORT protein
  3. Sucrose diffuses into SIEVE TUBE ELEMENT via PLASMODESMATA.
    • decreases Ψ of sieve tube element.
  4. Water enters sieve tube element by OSMOSIS
    • increases HYDROSTATIC pressure
  5. Assimilates transported by MASS FLOW ⟶ low pressure.
  6. Sucrose diffuses/actively transported out of sieve tube element into surrounding tissue via plasmodesmata.
    • increases Ψ of sieve tube element.
  7. Water moves out of sieve tube element by OSMOSIS.
    • decreases hydrostatic pressure
    • area of low pressure @ sink.
7
Q

Is a growing leaf a sink or a source?

A

sink

still growing&raquo_space; REQUIRES assimilates unloaded to supply metabolic processes

8
Q

If a mature leaf a sink or a source?

A

source

photosynthesises to PRODUCE assimilates

9
Q

What is the evidence for active transport in translocation?

A

advances in MICROSCOPY - can see adaptation (↑ mitochondria) of companion cells

POISONED MITOCHONDRIA = no translocation - indicates active process

FLOW is 1000x faster than DIFFUSION - active process drives mass flow

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