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Biology > Adaptations for transport in plants > Flashcards

Adaptations for transport in plants Flashcards

1
Q

What are the 2 functions of the xylem?

A

Transporting water and dissolved minerals.
Providing mechanical strength and support

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2
Q

What does the phloem transport?

A

Sucrose and amino acids from the leaves to the rest of the plant

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3
Q

Where is the xylem and phloem located in roots?

A

Xylem is star shaped and central with phloem between the xylem cells.
It resists pull and anchors the plant in soil

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4
Q

What does the vascular bundle consist of?

A

The phloem and xylem

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5
Q

Where is the xylem and phloem located in the stem?

A

Located in a ring shape with the xylem towards the centre and the phloem towards the outside.

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6
Q

What direction does the xylem transport water and dissolved minerals in?

A

Upwards

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7
Q

What direction does the phloem transport sucrose and amino acids in?

A

Bidirectional (up and down)

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8
Q

What is the structure of the phloem?

A

It is plant tissue containing sieve tube elements and companion cells.

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9
Q

Describe how the xylem is formed

A

Lignin builds up in cell walls causing the contents to die. This leaves an empty space called the lumen.
As tissue develops the end walls of the cells break down leaving a hollow tube through which water moves up the plant.

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10
Q

What plants do vessels of xylem occur in?

A

Angiosperms ONLY

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11
Q

Why is movement in xylem of angiosperms more efficient than in plants like ferns with tracheids?

A

Water can move straight upwards in vessels of the xylem in angiosperms.
Tracheids of the xylem are spindle-shaped so water takes a twisting pathway up the plant which is less efficient.

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12
Q

How is water taken up by roots?

A

Water moves from the soil which has a high water potential into the root hair cell by osmosis down its gradient.

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13
Q

Why does water move into the root hair cell?

A

Because the cytoplasm and vacuole of the root hair cell contains a more conc solution of ions/sugars (cell sap) so has a more neg water potential

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14
Q

Why are the roots the greatest region of water uptake and why do they have a large SA?

A

They have root hairs which increase SA
They have thin cell walls for short diffusion

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15
Q

What is the apoplast pathway?

A

Water moving through the root in spaces between separated cellulose fibres in the cell wall.

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16
Q

What is the symplast pathway?

A

Water moving through the root via the cytoplasm and plasmodesmata.

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17
Q

What is plasmodesmata?

A

Strands of cytoplasm which go through pits in the cell wall joining adjacent cells.

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18
Q

What is the vacuolar pathway?

A

Water moving through the root vacuole to vacuole

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19
Q

What pathway is fastest?

A

The apoplast pathway

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20
Q

Where is the water potential greatest in the root, where is it lowest and which way does water move?

A

The root hair cells is highest, lowest in the xylem so water moves down its gradient across the root

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21
Q

What is the endodermis and describe its structure.

A

A single layer of cells surrounding the pericyle.
Its cells wall have a waxy material called suberin which forms a band called the casparian strip.

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22
Q

What pathways can water only pass into the xylem from and what does it mean?

A

The symplast and vacuolar pathway which means water travelling in the apoplast pathway must leave it.

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23
Q

What does the casparian strip do?

A

The casparian strip is made from suberin which is hydrophobic.
This prevents water moving further in the apoplast so water leaves to the cytoplasm to be moved further in the root.

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24
Q

How are minerals taken up by the plant?

A

Minerals like potassium and nitrogen will move via active transport against their conc gradient into root hair cells.

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25
Q

Why does water move from the roots to the leaves of plants?

A

Because air has a very low water potential and soil water has a very high water potential, the water will want to move upwards and out the plant into air

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26
Q

What is the cohesion-tension theory?

A

the movement of water up the xylem by the adhesion of water molecules and cohesion

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27
Q

What is the cohesion of water?

A

The attraction of water molecules for each other due to hydrogen bonding

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28
Q

What is the adhesion of water?

A

Charges on water are attracted to hydrophilic molecules in the cell wall of the xylem

29
Q

What is capillarity?

A

The movement of water up narrow tubes/xylem by capillary action.

30
Q

How does water actually move by adhesion and cohesion?

A

Cohesion between water molecules produces surface tension, this combined with adhesion draws water up the xylem

31
Q

What is root pressure?

A

The upwards force of water due to the osmotic movement of water from endothermal cells into the xylem

32
Q

What are the three mechanisms by which water moves up the xylem?

A

The pull of transpiration
Capillarity
Push of root pressure

33
Q

What is the transpiration stream?

A

The continual flow of water in at the roots, up the stem to the roots and out to the atmosphere

34
Q

In the transpiration stream how is water drawn upwards?

A

The cohesion forces between water molecules
The adhesion forces between water molecules and hydrophilic molecules of the lining of xylem vessel

35
Q

What are the factors that affect the transpiration stream?

A

Temp
Humidity
Wind speed
Light intensity
Genetic factors

36
Q

What is the transpiration rate?

A

The rate at which water is lost from a plant

37
Q

How could genetic factors affect the transpiration rate?

A

Genetic factors control the number, size and distribution of stomata which can increase water loss

38
Q

How can temperature affect the transpiration rate?

A

Increased temps lowers WP in the atmosphere, it also increases the kinetic energy of water molecules so evaporation from mesophyll walls is faster.
If stomata are open the speed of diffusion is faster.
Higher temps therefore = higher transpiration rate

39
Q

How can humidity affect the transpiration rate?

A

Air inside the leaf is saturated with water vapour so it has a high humidity.
The higher the humidity the higher the WP, so water vapour will want to diffuse out of the leaf to an area with lower WP.

40
Q

How can wind speed affect the transpiration rate?

A

Movement of surrounding air will blow away the humid air that has diffused out of the leaf.
This causes the WP gradient between the inside and outside of the leaf to increase, so more water vapour will diffuse out increasing the transpiration rate.
The faster the wind the faster the transpiration rate

41
Q

How does light intensity affect the transpiration rate?

A

Stomata open wider when light intensity is higher increasing the rate of transpiration.

42
Q

What does a potometer measure?

A

Indirectly measures the rate of water loss during transpiration by actually measuring the rate of water uptake

43
Q

If cells in a plant are fully turgid what is the rate of uptake equal to?

A

The rate of transpiration

44
Q

How are mesophytes adapted to conserve water?

A

Shed their leaves before winter, so that they do not lose water by transpiration.
Aerial parts of plants die off so that they are not exposed to the conditions of winter, their bulbs underground survive
Survive winter by becoming dormant seeds, low metabolic rate so little water is needed

45
Q

What are mesophytes?

A

Plants which are adapted to both wet and dry conditions.
Evolved in temperate regions with good water supply.

46
Q

Why do leaves droop/wilt when there is a low water supply?

A

To reduce the SA of leaf absorbing light so that less photosynthesis occurs which means less water is used.

47
Q

How are xerophytes adapted to conserve water?

A

Rolled leaves to reduce the area exposed to wind reducing transpiration
Sunken stomata reduces water loss by trapping humid air outside the stomata reducing the WP gradient so less diffusion
Hairs to trap water vapour and reduce the WP gradient
Waxy cuticle which is waterproof reduced water loss

48
Q

What are xerophyes?

A

Extremophiles

49
Q

What is the adaxial surface of a leaf?

A

The upper surface of a leaf

50
Q

How are hydrophytes adapted to conserve water?

A

No lignified support tissues as water is the support medium
Poorly developed xylem because they are surrounded by water
No waxy cuticle
Stomata are on the upper surface because the under surface is submerged
Stems and leaves have large air spaces forming a reservoir of O2 and CO2, providing buoyancy

51
Q

What is translocation?

A

Movement of soluble products of photosynthesis/amino acids and sucrose through the phloem from sources to sinks

52
Q

Where is the source?

A

The leaves, this is where amino acids and sucrose are produced

53
Q

Where are the sinks?

A

Parts of the plant that are growing or are being used for storage

54
Q

What is the structure of the phloem?

A

Has companion cells surrounding the sieve tube elements.
Sieve tube elements where the cellulose cell end walls are perforated producing sieve plates.
Sieve tube elements lose nucleus and other organelles to allow space for transport.

55
Q

Draw the structure of the phloem

A

PG 220

56
Q

What is the structure of the companion cells?

A

They are very metabolically active so have a large nucleus, RER and many mitochondria.

57
Q

How are companion cells and sieve tube elements connected?

A

By plasmodesmata

58
Q

How did ringing experiments work?

A

Outer bark was removed all the way around a woody stem, removing the phloem.
The plant was left to photosynthesis, contents in the phloem above and below the ring were analysed.
Above the ring showed alot of sucrose indicating it has been translocated in the pholem
Below the ring there was no sucrose, indicating it had been used by the plant and not replaced as the ring prevented sucrose from being translocated.
The bark above the ring was also swollen due to the accumulation of solutes.

59
Q

Why is glucose produced in photosynthesis converted to sucrose?

A

Because sucrose is less chemically reactive.
Sucrose is less osmotically active,.

60
Q

What might sucrose be used for in the sinks?

A

Respiration during division
Stored as starch
Converted to cellulose for the cell wall
Stored in nectaries

61
Q

What does the mass flow hypothesis suggest?

A

The passive flow of sucrose from phloem of the leaf to the sink

62
Q

What are the limitations of the mass flow hypothesis?

A

Translocation in the phloem is faster than diffusion
Phloem transports sucrose to the tops of trees but mass flow hypothesis does not produce enough pressure to do this
Sucrose and amino acids move in different directions and at different rates in the same tissues

63
Q

What is the disadvantage of transpiration?

A

Water loss

64
Q

Describe how mass flow works

A

At the source/leaves sucrose is made during photosynthesis, sucrose makes the WP of water negative so water moves in via osmosis.
The movement of water increases hydrostatic pressure in the leaves, this forces sucrose in solution into the phloem to a low pressure.
The pressure pushes solution down phloem into the sink/roots with a lower hydrostatic pressure, this movement is mass flow.
In the sink sucrose is converted to insoluble starch, this increases WP.
Water moves out of the sink into endodermal cells then into the xylem by osmosis and back to the source to a lower WP.

65
Q

READ PAGE 221 ON APHIDS AND AUTORADIOGRAPHY

A

PG 221

66
Q

What is the pericycle?

A

The layer located between the endodermis and vascular tissue

67
Q

What is the endodermis?

A

A layer which surrounds the vascular tissue in the roots

68
Q

Why is the vacuolar route slower than symplast?

A

Vacuolar route: water crosses more membranes than the symplast as it moves in and out of the vacuole
•Symplast route: water moves through the cytoplasm and cell membrane so only crosses one membrane

69
Q

Describe the role of the endodermis in the uptake of water into the xylem and how it generates root pressure

A

Suberin which is waterproof forms the casparian strip which diverts the apoplast pathway into the symplast pathway.
Endodermal cells/pericycle actively transports ions into the xylem vessels producing a low WP therefore water moves from the symplast pathway into the xylem via osmosis.
This movement produces hydrostatic pressure which increases uptake of water.

Biology (26 decks)

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