3.4.2 Mass Transport in Plants Flashcards

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1
Q

What enviromental factors INCREASE the rate of transpiration

A
  • Increasing temperature
  • Decreasing humidity
  • Increasing light intensity
  • Increasing wind speed
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2
Q

What enviromental factors DECREASE the rate of transpiration

A
  • Decreasing temperature
  • Increasing humidity
  • Decreasing light intensity
  • Decreasing wind speed
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3
Q

Why does the rate of transpiration increase with increasing light intensity

A

Causes stomata to open

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4
Q

Why does the diameter of the xylem decrease as the rate of transpiration increases

A
  • Water lost from the leaf in transpiration
  • Creates more tension and pulling force on water molecules in xylem
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5
Q

What does water lost from the leaf in transpiration creating more tension and pulling force on water molecules in xylem create

A

The diameter of the xylem to decrease

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6
Q

What device is used to measure the rate of transpiration

A

Potometers

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7
Q

What are the vital procedures to setting up a potometer

A
  • Cut stem underwater, and at a slant
  • Ensure no air bubbles are present
  • Seal joints with vasaline to ensure airtight
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8
Q

Why do potometers not truly measure the rate of transpiration

A
  • Water used for support
  • Water used in photosynthesis
  • Water produced in aerobic respiration
  • Apparatus not fully sealed
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9
Q

What is the benefit of xylem cells being dead, and therefore empty with no cytoplasm contents

A

Allows water to flow easier

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10
Q

What xylem specialisation allows water to flow easier

A

Cells are dead, and therefore empty with no cytoplasm contents

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11
Q

What is the benefit of xylem cells being long, forming tubes, with no end walls, meaning it’s hollow

A

Allows for continuous columns of water

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12
Q

What xylem specialisation allows continuous columns of water to flow

A

Cells are long, forming tubes, with no end walls meaning thay are hollow

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13
Q

What is the benefit of xylem cells having a thickened cell wall with cellulose and lignin

A

Support, and waterproofing

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14
Q

What xylem specialisation allows for support, and waterproofing

A

Thickened cell walls with cellulose and lignin

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15
Q

What is the benefit of xylem cells have pits in walls

A

Allows lateral movement of water

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16
Q

What xylem specialisation allows for lateral movement of water

A

Pits in walls

17
Q

Describe and explain the cohesion-tension theory

A
  • Water lost from the leaves by evaporation, due to transpiration
  • Lowers the water potential of mesophyll cells, so water drawn out of xylem
  • Water pulled up xylem creating tension
  • Due to cohesive forces between water molecules, caused by hydrogen bonding
  • Allows a continous column of water to be pulled
  • Water molecules adhere to the xylem walls
18
Q

In the cohesion-tension theory how is water lost from the leaves

A

By evaporation, due to transpiration

19
Q

In the cohesion-tension theory why is water drawn out of the xylem

A

The water potential of mesophyll cells has been lowered

20
Q

In the cohesion-tension theory what creates tension

A

Water being pulled up xylem

21
Q

In the cohesion-tension theory what causes cohesive forces between water molecules

A

Hydrogen bonding

22
Q

In the cohesion-tension theory what allows a continous column of water to be pulled

A

Cohesive forces between water molecules, due to hydrogen bonding

23
Q

In the cohesion-tension theory what do water molecules adhere to

A

Xylem walls

24
Q

In the phloem solution, what key molecules are transported

A

Sucrose and amino-acids

25
Q

What key component are within the sieve tube element of the phloem

A

Sieve plates

26
Q

What is the specialisation of companion cells in the phloem

A

Have lots of mitochondria, to actively transport sucrose into phloem from source

27
Q

What is the most general way of describing route of mass-flow hypothesis

A

From source to sink

28
Q

Describe and explain the Mass-Flow Hypothesis

A
  • Sucrose actively transported into sieve tube element, from source, by companion cells
  • This lowers the water potential in the sieve tube element, so** water moves in by osmosis** from the xylem
  • Produces a high hydrostatic pressure
  • Mass flow of sucrose from source to sink
  • At sink, sucrose is unloaded and used or converted to starch for storage
29
Q

In the Mass-Flow Hypothesis what actively transports sucrose into sieve tube element from source

A

Companion cells

30
Q

In the Mass-Flow Hypothesis what does a low water potential in the sieve tube element allow

A

Water to move in by osmosis from the xylem

31
Q

In the Mass-Flow Hypothesis what does the movement of water into the sieve tube element by osmosis from the xylem create

A

High hydrostatic pressure

32
Q

In the Mass-Flow Hypothesis where is the mass flow

A

From source to sink

33
Q

In the Mass-Flow Hypothesis what happens at the sink

A

Sucrose is unloaded and used or converted to starch for storage

34
Q

Explain how the following provides evidence for the Mass-Flow Hypothesis: Translocation slows if respiration inhibitors used

A

No active transport of sucrose from companion cells at source

35
Q

Explain how the following provides evidence for the Mass-Flow Hypothesis: If phloem punctured, contents flows out

A

Occuring at high pressure

36
Q

Explain how the following provides evidence for the Mass-Flow Hypothesis: Plants can be supplied with radioactive CO2 and traced

A

Sucrose moves from source, up and down stem, to sinks

37
Q

Explain how the following provides evidence for the Mass-Flow Hypothesis: ring of bark removed, so that xylem remains, but phloem removed

A
  • Bulging above ring due to build-up of fluid in phloem
  • Tissues die below, as no sucrose for respiration