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Biology > Mass transport in plants > Flashcards

Mass transport in plants Flashcards

1
Q

What does xylem transport

A

Water in stems and leaves

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2
Q

theory associated with xylem

A

Cohesion-tension theory

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3
Q

What does the phloem do

A

Transports organic substances

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4
Q

Theory associated with phloem

A

Mass flow hypothesis for the mechanism of translocation in plants

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5
Q

What process is the uptake of water

A

Passive via osmosis

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6
Q

Uptake of minerals is

A

Passive or active
Diffusion or active transport

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7
Q

Two pathways that water can take to move across the cortex

A

Apoplast
Symplast

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8
Q

What pathway is the apoplast that water travels through

A

Spaces though cellulose walls, dead cells and hollow tubes in xylem

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9
Q

Which pathway is faster

A

Apoplast

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10
Q

What is the casparin strip

A

Impassible barrier

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11
Q

What happens when water reqaches the endodermis

A

Casparian strip blocks pathway of apoplast

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12
Q

What does symplast pathway involve

A

Cytoplasm
Plasmodemata
Vacuole of cells

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13
Q

What does the water move by in symplast and apoplast pathway

A

Apoplast = diffusion
Symplast = osmosis

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14
Q

How does the water move in the symplast

A

Water moves via osmosis across the partially permeable cell membrane into vacuole and between cells through plasmodesmata

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15
Q

How does water move in the plant in transpiration

A

Water potential gradient from soil (high water potential) to the atmosphere (low)

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16
Q

Where do plants lose water

A

Stomata

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17
Q

What is transpiration

A

Loss of water via stomata by diffusion

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18
Q

Why is transpiration important

A

Cool plant via exporative cooling

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19
Q

What is cohesion

A

water molecules form h2 bonds between one another and stick together

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20
Q

Whats the transpiration pull

A

Column of water is pulled up xylem as a result of transpiration

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21
Q

What is the surface area in plants

A

total area of the organism exposed to external environment

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22
Q

What is the volume of a plant

A

total internal volume of the organism (space inside an organism)

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23
Q

Interaction between surface area and volume

A

surface increases volume decreases

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24
Q

why do they interact this way

A

volume increases more rapidly than surface does

25
Q

What happens to the water potential of mesophyll cells

A

when evaporation occurs in their air spaces, they have a lower water potential
so water enters by osmosis from neighbouring cells

26
Q

Process of how water moves up the stem of the xylem

A

1) transpiration of mesophyll cells
2) H2 bonds form between water molecules, known as cohesion
3) Water forms unbroken column across mesophyll cells down the xylem
4) Water evaporates from mesophyll cells, drawing water up behind stomata
5) Transpiration pull occurs
6) Transpiration pull puts xylem under tension, cohesion-tension theory

27
Q

Why is transpiration important

A

Provides cooling = evaporative cooling
Uptake of mineral ions
Turgor pressure of cells supports leaves and stem (of non-woody plants)

28
Q

What can cause a water potential gradient and what results in this change

A

Environmental conditions -> low humidity, high temp
Causes water potential gradient between air inside leaves (high) and air outside (low)
So water vapour diffuses out of the leaves through stomata (transpiration)

29
Q

Transpiration pull formation

A

Water vapour lost by transpiration lowers water potential in air spaces around mesophyll cells
As water evaporates out mesophyll cell walls into air spaces a transpiration pull is formed

30
Q

What does the transpiration pull result in

A

Water moving out of mesophyll cytoplasm/ walls
Pulls water to leave xylem vessels through pits causing water to be constantly moving up xylem vessels to replace water lost forming a transpiration stream

31
Q

What pathways move water in which areas

A

Movement of water through cell walls = apoplast
Movement of water through cytoplasm = sympoplast

32
Q

What occurs when the rate of transpiration is high

A

Walls of xylem pulled inwards by faster flow of water

33
Q

How is transpiration controlled

A

Guard cells around stomata
Guard cells open when stomata are turgid and close when stomata lose water
Stomata open = greater rate of transpiration and gaseous exchange

34
Q

Describe the process of transpiration

A

1) Water vapour diffuses from air spaces through stomata via transpiration, lowering water potential
2) Water evaporates from mesophyll cell walls into air spaces, creating a transpiration pull
3) Water moves through the mesophyll cell (apoplastic pathway) or out of the mesophyll cytoplasm into the cell wall symplastic pathway)
4) Water leaves a xylem vessel to replace the water lost from the leaf

35
Q

What is the water potential gradient

A

Loss of water results in potential gradient between leaves (low) and roots high)

36
Q

What is transpiration

A

The loss of water vapour from the leaves or stem

37
Q

What is the transpiration stream

A

Movement of water through the xylem tissue and mesophyll cells

38
Q

How does water enter a plant

A

Not through the leaves, through the roots
Travel through xylem vessels using the transpiration stream where it ends up being released through mesophyll cells via transpiration

39
Q

Method of potometer experiment (detailed)

A

1) Cut shoot underwater
2) Place shoot in tube
3) Set up apparatus
4) Make sure it’s airtight using vaseline to seal gaps
5) Dry leaves of shoot
6) Remove capillary tube from water beaker to allow a single air bubble to form and place tube back in water
7) Set up environment investigating
8) Allow plant to adapt to new env
9) Record starting location and end location of air bubble
10) Change intensity of factor being investigated
11) Reset bubble

40
Q

Potometer exp short of process

A

1) Record distance of air bubble at start of exp
2) Leave for set period of time
3) Record end location of bubble and calculate distance travelled
4) Reset air bubble using tap of resevoir if neccessary
5) Repeat and change factor being investigated

41
Q

What does the phloem transport

A

Phloem sap containing sucrose and water dissolved with substances such as amino acids, hormones and minerals

42
Q

Source of assimilates (substances transported into tissue that will become tissue)

A

Green leaves that photosynthesis (glucsoe)
Storage organs (unload substances)
Food stores in seeds (which germinate)

43
Q

Where are assimilates required

A

Tissues and sinks

44
Q

What are some examples of sinks that require assimilates

A

Meristems that are actively dividing
Roots that are growing or absorbing mineral ions
Parts where assimilates are stores -> developing seeds, fruits, storage organs

45
Q

Where do assimilates move

A

Upwards or downwards in the phloem sieve tubes as they move from source to sink

46
Q

How do assimilates move by

A

Symplastic (passive process by diffusion through cytoplasm)
apoplastic pathway (active process through cell walls)

47
Q

How do sucrose molecules move via the apoplastic pathway (loading mechanism)

A

1) Companion cells pump H+ out of the cytoplasm using proton pumps in their cell walls (requires ATP)
2) H+ move down concentration gradient back to the cytoplasm of the companion cell through a cotransporter protein
3) H+ carries sucrose molecules into companion cells against the concentration gradient
4) Sucrose molecules move into the sieve tubes via the plasmodesmata from the companion cells
5) Allows plants to build up sucrose in the phloem
6) High concentration of sucrose decreases the water potential in the phloem and water enters by osmosis
7) Water enters at a high pressure which enables mass flow of sugars towards sink tissues where sugars are unloaded

48
Q

Where does the unloading of assimilates occur

A

Sinks

49
Q

What type of reaction unloads sucrose

A

Active transport

50
Q

How are assimilates unloaded

A

1) Sucrose actively transported out of companion cells and move out of the phloem tissue via apoplast or symlpastic pathway
2) To maintain the concentration gradient in the sink tissue, sucrose is converted to storage molecules using enzymes

51
Q

How is the unloading mechanism adapted

A

-The intercellular space has very few organelles so phloem sap can flow easily by moving through open corridor that has low resistance
-Sieve cells have thick cell walls to help them withstand pressure exerted by the mass flow of sugars

52
Q

How does phloem sap move

A

By mass flow up and down the plant

53
Q

Why are carbohydrates transported in the form of sucrose

A

Efficient energy transfer and increased energy storage
Less reactive than glucose (because it’s a non-reducing sugar) no immediate reactions occur as it is being transported

54
Q

What is the advantage of mass flow

A

Moves organic solutes faster

55
Q

Mass flow in the xylem

A

Xylem tissue has a pressure differences that causes mass flow to occur because of a water potential gradient between soil and leaf

56
Q

When is ATP required in mass flow

A

In phloem tissue NOT the xylem

57
Q

How is a pressure difference generated during mass flow in the phloem

A

Pressure difference generated by actively loading sucrose into the sieve elements at the source which lowers the water potential in the sap
This allows water to move into the sievve elements as it travels down the water potential gradient by osmosis

58
Q

Overall how mass flow works

A

1) Sucrose is loaded into the phloem through companion cells (at the leaf)
2) Water flows into the phloem from the xylem vessel (using the transpiration stream)
3) Sucrose moves via translocation through sieve tubes in the water moving down the hydrostatic pressure gradient
4) Sucrose is unloaded from the phloem into the sink (at the root cell)
5) Water moves back into the xylem by osmosis

https://cdn.savemyexams.com/cdn-cgi/image/w=1280,f=auto/uploads/2021/01/Phloem_-Mass-flow-from-source-to-sink.png

Biology (53 decks)

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