Mass Transport- Phloem Flashcards

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1
Q

What does phloem tissue transport?

A

Solutes- dissolved substances

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2
Q

What are sieve tube elements?

A

Living cells that form the tube for transporting solutes

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3
Q

What is the role of companion cells?

A

Carry out living functions for sieve cells

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4
Q

What is translocation?

A

The movement of solutes to where they’re needed in a plant

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5
Q

What kind of process is translocation?

A

Energy-requiring

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6
Q

What way does translocation move solutes?

A

From sources (where solutes are made) to sinks (wher solutes are used up)

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7
Q

What is the role of enzymes in translocation?

A

Maintain a concentration gradient from source to sink by changing solutes at the sink

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8
Q

What happens at the source? (step 1 of mass flow hypothesis)

A
  • Active transport is used to actively load solutes from companion cells into sieve tubes of phloem at the source
  • Lowers water potential inside sieve tubes, so water enters tubes by osmosis from xylem and companion cells
  • Creates high pressure inside sieve tubes at source end
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9
Q

What happens at the sink? (stage 2 of mass flow hypothesis)

A
  • Solutes removed from the phloem to be used up
  • Increases water potential inside sieve tubes, so water also leaves tubes by osmosis
  • Lowers pressure inside sieve tubes
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10
Q

What is the result of translocation? (stage 3 of mass flow hypothesis)

A
  • Pressure gradient from source to sink
  • Gradient pushes solutes along sieve tubes towards sink
  • Solutes will be used or stored at sink
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11
Q

How does ringing provide evidence for mass flow?

A

If a ring of bark is removed from a tree then a bulge forms above the ring that has a higher concentration of sugars than fluid below the ring which shows there’s downwards flow of sugars

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12
Q

How do radioactive tracers provide evidence for mass flow?

A

Can track movement of organic substances in a plant

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13
Q

How do aphids provide evidence for mass flow?

A

Pierce the phloem then bodys are removed leaving mouthparts behind, allows sap to flow out and sap flows quicker nearer the leaves so evidence of a pressure gradient

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