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A-level Biology > 9 - Transport In Plants 🌵 > Flashcards

9 - Transport In Plants 🌵 Flashcards

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1
Q

What are the main 3 reasons why multicellular plants need transport systems?

A
  • metabolic demands
  • size
  • SA:V
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2
Q

Why is a transport system needed for metabolic demand?

A
  • need oxygen and glucose transported for photosynthesis
  • absorb mineral ions
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3
Q

Why is a transport system needed for size?

A

to move substances across the cell from roots to leaves

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4
Q

Why is a transport system needed for SA:V?

A
  • leaves have large SA:V
  • whole plant has small SA:V
  • means they can’t rely on diffusion alone so need system
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5
Q

What do dicotyledonous (dicots) plants do?

A

make seeds that contain 2 cotyledons

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6
Q

What are cotyledons?

A

organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates

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7
Q

What are herbaceous dicots?

A

have soft tissues and a relatively short life cycle (leaves and stem die down at end of growing season to soil)

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8
Q

What are arborescent (woody) dicots?

A

have hard lignified tissues and a long life cycle (hundreds of years)

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9
Q

What is the series of transport vessels running through dicots called?

A

vascular system

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10
Q

In herbaceous dicots, what is the vascular system made up of?

A

xylem and phloem, arranged in vascular bundles

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11
Q

Summarise the function of the xylem

A

non-living tissue used in the transport of water and mineral ions, and for support

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12
Q

Which way do materials flow in the xylem?

A

up from the roots to the shoots and leaves

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13
Q

What are xylem vessels made of?

A

hollow structures made by several columns of cells fusing together end to end

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14
Q

What cells pack around xylem vessels in herbaceous dicots, storing food and containing tannin deposits?

A

the thick-walled xylem parenchyma

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15
Q

What is tannin?

A

a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores

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16
Q

What are xylem fibres?

A

long cells with lignified secondary walls that provide extra mechanical strength

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17
Q

What do xylem fibres not do?

A

transport water

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18
Q

How can lignin be laid down in the walls of xylem vessels?

A
  • rings
  • spirals
  • solid tubes with small unlignified areas called bordered pits
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19
Q

In xylem vessels, what do bordered pits do?

A

where water leaves thee xylem and moves to other cells of the plant

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20
Q

Summarise the function of phloem

A

a living tissue that transports food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis

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21
Q

What does the phloem supply cells with to help with cellular respiration and synthesis?

A

sugars and amino acids

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22
Q

Which way does the flow in phloem go?

A

both up or down

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23
Q

What is the main transporting vessel of the phloem?

A

sieve tubes

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24
Q

What makes up sieve tubes?

A

many cells joined end to end to form a long, hollow structure, unlignified

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25
Q

In areas between cells in phloem, what happens to the walls?

A

the walls become perforated to form sieve plates, which look like sieves and let the phloem contents flow through

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26
Q

What organelles begin to break down as the large sieve plates appear?

A

tonoplast and nucleus

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27
Q

What happens as a phloem tube matures after sieve plates are formed?

A

phloem becomes a tube filled with phloem sap, and the mature phloem cells have no nucleus

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28
Q

What forms with sieve tubes?

A

companion cells

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29
Q

How are companion cells and sieve tubes linked?

A

by many plasmodesmata

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30
Q

What are plasmodesmata?

A

microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells

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31
Q

What do plasmodesmata function as for sieve tube cells and why?

A

a life support system, as the sieve tubes have lost most normal cell functions

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32
Q

What supporting tissues do phloem cells contain?

A

fibres and sclereids (cells with extremely thick cell walls)

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33
Q

How does turgor pressure help plants?

A
  • Provides a hydrostatic skeleton to support the stems and leaves
  • drives cell expansion
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34
Q

What does the loss of water by evaporation help a plant to do?

A

Stay cool

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35
Q

What does water transport in plants?

A

Mineral ions and the products of photosynthesis

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36
Q

What is a root hair cell?

A

The exchange surface in plants where water is taken into the body

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37
Q

What adaptations to root hair cells have?

A
  • large SA:V for diffusion
  • thin surface layer shortens diffusion pathway
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38
Q

Why do root hair cells have a conc of solutes in their cytoplasm?

A

To maintain a water potential gradient between soil water (higher wp) and the cell (lower wp)

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39
Q

What is the concentration/wp of soil water of mineral ions?

A

Low conc = high water potential

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40
Q

What are the 3 pathways water can travel along to get from the root to the xylem?

A

Symplast
Vacuolar
Apoplast

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41
Q

Where does water move in symplast pathway?

A

Through the living spaces of the cell = cytoplasm

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42
Q

How does water move from cell to cell in the symplast and vacuolar pathway?

A

Through plasmodesmata

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43
Q

How is water drawn up the plant as water moves away from the roots?

A

Cells away from roots have a lower w.p. so water is drawn up the plant to replace it

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44
Q

What is the slowest pathway for water movement?

A

Vacuolar pathway

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45
Q

What makes the Vacuolar pathway different to the symplast?

A

Water moves into cytoplasm, then into vacuole, then into cytoplasm and to next cell by plasmodesmata

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46
Q

How does water move in the apoplast pathway?

A

Through cell walls and intracellular spaces

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47
Q

Why is the apoplast pathway the fastest?

A

Water doesn’t have to go through membranes

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48
Q

What pulls water through the cell walls in the apoplast pathway?

A

Cohesive and tension forces

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49
Q

Water moves through the pathways until it reaches what?

A

The endodermis - the layer of cells surrounding vascular tissue of the roots

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50
Q

Why is the endodermis particularly noticeable in the roots?

A

The effect of the Casparian strip

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51
Q

What is the Casparian strip?

A

A band of waxy material called Suberin that runs around each of the endoderm’s cells forming a waterproof layer

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52
Q

What pathway does the Casparian strip force water into and why?

A

Into the symplast pathway to regulate water entering xylem

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53
Q

The Casparian strip is important to force water into cytoplasm because it forces water to pass through what?

A

Selectively permeable plasma membrane - this excludes any potentially toxic solutes in soil water from reaching living tissues

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54
Q

What is the solute concentration in the cytoplasm of endodermal cells compared to xylem?

A

Relatively dilute = water potential is higher than xylem so increases rate of water moving into xylem

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55
Q

What does root pressure do?

A

Gives water a push up the xylem to produce movement

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56
Q

Evidence for the role of active transport in root pressure

What does cyanide do generally?

A

Affects the mitochondria and prevents the production of ATP

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57
Q

Evidence for the role of active transport in root pressure

What does cyanide do if applied to root cells?

A

The root pressure disappears as there is no energy supply

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58
Q

Evidence for the role of active transport in root pressure

What suggests chemical reactions are involved with root pressure?

A

Root pressure increases with a rise in temperature and falls with a fall in temperature

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59
Q

Evidence for the role of active transport in root pressure

What happens if oxygen/respiratory substances decrease?

A

Root pressure falls

60
Q

Evidence for the role of active transport in root pressure

What is guttation?

A

When xylem sap is forced out of special pores at the ends of leaves in some conditions from cut ends

61
Q

What is translocation?

A

When plants transport organic compounds in the phloem from sources to sinks

62
Q

Translocation

What are sinks?

A

Tissues that need the transported substance

63
Q

Translocation

Is it active or passive?

A

Active

64
Q

Translocation

What are the products of photosynthesis that are transported known as?

A

Assimilates

65
Q

Translocation

What is the main assimilate transported around plants?

A

Sucrose

66
Q

Translocation

What is the sucrose content of most cell sap?

A

0.5%

67
Q

Translocation

What is the sucrose content in phloem sap?

A

20-30%

68
Q

Translocation

What are the main sources of assimilates in plants?

A
  • green leaves and stems
  • storage organs such as tubers and tap roots that are unloading their stores at the beginning of a growth period
  • food stores in seeds when they germinate
69
Q

Translocation

What are the main sinks in a plant?

A
  • roots that are growing/actively absorbing mineral ions
  • meristems that are actively dividing
  • any part of the plant that’s laying down food stores (developing seeds/fruits/storage organs)
70
Q

Translocation

What is phloem loading?

A

When plants load assimilates into the phloem for transport

71
Q

Translocation

Phloem Loading

Is the symplast route active or passive?

A

Largely passive

72
Q

Translocation

Phloem loading

In some species of plants, how is the symplast route used?

A

The source moves through the cytoplasm of the mesophyll cells and on into the sieve tubes by diffusion

73
Q

Translocation

Phloem loading

How does sucrose move through the apoplast pathway?

A

Through cell walls to the companion cells and sieve elements

74
Q

Translocation

Phloem loading

In companion cells, how is sucrose moved into the cytoplasm?

A

Across the cell membrane in an active process

75
Q

Translocation

Phloem loading

What happens to H+ ions in companion cells during the apoplast route?

A

Actively pumped out into the surrounding tissue using ATP

They then return to the companion cell down a conc grad via a co-transport protein

76
Q

Translocation

Phloem loading

What molecule is co-transported?

A

Sucrose

77
Q

Translocation

Phloem loading

What does sucrose being co-transported do?

A

Increase sucrose concentration in the companion cells and in the sieve elements through the many plasmodesmata

78
Q

Translocation

Phloem Loading

What does the many infolding companion cells have do?

A

Increases SA for active transport of sucrose into cell cytoplasm

79
Q

Translocation

Phloem loading

What does the many mitochondria do in companion cells?

A

Supplies the ATP needed for the transport pumps

80
Q

Translocation

Phloem loading

What happens as a result of sucrose building up in the companion cells and sieve tube element?

A

Water moves in by osmosis = turgor pressure = water carrying assimilates moves into sieve tubes = reduces pressure in companion cells = moves up or down plant by mass flow to sinks

81
Q

Translocation

Phloem loading

What does solute accumulation do in source phloem?

A

Leads to an increase in turgor pressure that forces sap to regions of lower pressures in the sinks

82
Q

What is the pressure in phloem and how does this help?

A

2 MPa - helps move stuff rapidly

83
Q

Translocation

Phloem unloading

When is sucrose unloaded from the phloem?

A

At any point the cell needs it

84
Q

Translocation

Phloem unloading

What’s the main mechanism of phloem you loading?

A

Seems to be by diffusion of the sucrose from the phloem into the surrounding cells

85
Q

Translocation

Phloem unloading

Where does the sucrose go after it’s diffused out of the phloem?

A

Rapidly moves on into other cells / converted into another substance so that a conc grad of sucrose is mainatined

86
Q

Translocation

Phloem unloading

What does the loss of the solutes from the phloem lead to?

A

A rise in the water potential of the phloem as water moves out into the surrounding cells by osmosis

87
Q

Translocation

Evidence

What allows us to see the adaptations of the companion cells for active transport?

A

Advances in microscopy

88
Q

Translocation

Evidence

What happens if the mitochondria of companion cells are poisoned?

A

Translocation stops

89
Q

Translocation

Evidence

What suggests that it’s an active process driving the mass flow?

A

The fact that the flow of sugars in the phloem is 10,000 times faster than if it was diffusion alone

90
Q

Translocation

Evidence

How can aphids be used to demonstrate the translocation of organic solutes in the phloem?

A

Has been shown there is a positive pressure in the phloem that forces the sap out through the stylet

91
Q

What are xerophytes?

A

Plants in dry habitats that have evolved a wide range of adaptations that enable them to live and reproduce where water availability is low

92
Q

What’s an example of a xerophyte?

A

Conifers / cacti

93
Q

What is marram grass (xerophyte)?

A

A plant found widely on sand dunes and coastal areas in dry salty conditions

94
Q

Can plants in cold conditions be described as xerophytes?

A

Yes

95
Q

Xerophytes Conserving Water

How does a thick waxy cuticle help?

A

Minimise water loss by transpiration

96
Q

Xerophytes Conserving Water

How do sunken stomata located in pits help?

A

Reduces air movement = produces microclimate of still, humid air = reduces water vapour potential gradient = reduces transpiration

97
Q

Xerophytes Conserving Water

How does a reduced number of stoma help?

A

Reduces water loss by transpiration and reduces their gas exchange capabiltiies

98
Q

Xerophytes Conserving Water

How does reducing the amount of leaves help?

A

Reduces SA:V, minimising area of water loss by transpiration

99
Q

Xerophytes Conserving Water

How do hairy leaves help?

A

Reduces water vapour potential gradient = minimises loss of water by transpiration from surface of leaf

100
Q

Xerophytes Conserving Water

How do curled leaves help?

A

Confines stomata within microclimate = reduces diffusion of water vapour

101
Q

Xerophytes Conserving Water

How do succulents help?

A

Succulent plants store water in specialised parenchyma tissue in their stems and roots so it’s plentiful in times of need

102
Q

Xerophytes Conserving Water

How does leaf loss help?

A

Prevents any water loss through leaves by simply losing leaves when water isn’t available

103
Q

Xerophytes Conserving Water

How do deep roots help?

A

Can access water from deep in the ground

104
Q

Xerophytes Conserving Water

How do lots of shallow roots help?

A

Wide surface area which can absorb water straight after rainfall

105
Q

Xerophytes Conserving Water

How can daffodils survive without water?

A

Survive as storage organs such as bulbs

106
Q

What are hydrophytes?

A

Plants that live in water

107
Q

Examples of hydrophytes?

A

Water crews / water lilies

108
Q

Why is it important in surface water plants that the leaves float?

A

So they are near the surface over light needed for photosynthesis

109
Q

Why is water logging a major problem for hydrophytes?

A

The air spaces of the plant need to be full of air, not water, for the plant to survive

110
Q

Adaptations of hydrophytes

Why do they have very thin / no waxy cuticles?

A

They don’t need to conserve water

111
Q

Adaptations of hydrophytes

Why do they have many always-open stomata on the upper surfaces?

A

There is no risk to the plant of loss of turgor, so open stomata maximises gaseous exchange

112
Q

Adaptations of hydrophytes

Why do they have a reduced structure to the plant?

A

The water supports the leaves and flowers so there is no need for strong supporting structures

113
Q

Adaptations of hydrophytes

Why do they have wide, flat leaves?

A

Spread across the water to capture as much light as possible

114
Q

Adaptations of hydrophytes

Why do they have small roots?

A

As water can diffuse directly into stem and leaf tissue so less need for uptake by roots

115
Q

Adaptations of hydrophytes

Why do they have large SA of stems and roots under water?

A

Maximises area for photosynthesis

116
Q

Adaptations of hydrophytes

Why do they have air sacs?

A

to enable the leaves / flowers to float to the surface of the water

117
Q

Adaptations of hydrophytes

What do aerenchyma have?

A

Has many large air spaces which seem to be formed by apoptosis in normal parenchyma

118
Q

Adaptations of hydrophytes

What are the functions of aerenchyma?

A
  • making the leaves/stems more buoyant
  • forming a low resistance internal pathway for the movement of substances such as oxygen to tissues below the water
119
Q

Adaptations of hydrophytes

How does aerenchyma forming low resistance internal pathway help?

A

helps the plant to cope with anoxic (extreme low oxygen conditions) conditions in the mud, by transporting oxygen to tissues

120
Q

What is a major problem with aerenchyma?

A

They provide low resistance pathway by which methane produced by the rice plants can be vented into the atmosphere

121
Q

Transpiration

Why does the surface of the leaf have a waxy cuticle?

A

Makes them waterproof to prevent water loss from leaves by evaporation

122
Q

Transpiration

How do stomata open and close?

A

By guard cells

123
Q

Transpiration

How does CO2 / O2 move into / out of the leaf?

A

By diffusion down a conc grad through stomata

124
Q

Define transpiration

A

The loss of water vapour from the leaves and stems of plants by evaporation

125
Q

Transpiration

Why do (only) some stomata need to be open all the time?

A

In the day, plant needs to take in CO2 for photosynthesis. At night, plant needs to take in O2 for cellular respiration

126
Q

Transpiration

What is a transpiration steam?

A
  • pull of water up xylem
  • evaporates from cell walls of mesophyll cells
  • into the air spaces in leaves
  • water vapour moves out through stomata
127
Q

Transpiration Stream

What does the loss of water from a mesophyll cell do?

A

Lowers water potential of the cells, so water moves into the cell from adjacent cells

128
Q

Transpiration Stream

What is adhesion?

A

Water molecules form hydrogen bonds with the carbohydrates in the walls of the narrow xylem vessels

129
Q

Transpiration Stream

What is cohesion?

A

Water molecules form hydrogen bonds with each other and so tend to stick together

130
Q

Transpiration Stream

What is the transpiration pull?

A

Water is drawn up the xylem in a continuous stream to replace the water lost by evaporation

131
Q

Transpiration

What is the cohesion-tension theory?

A

The model of water moving from the soil in a continuous stream up the xylem and across the lead

132
Q

Transpiration

Evidence for the cohesion-tension theory

Why does the tree’s diameter change?

A

Day - tension in xylem vessels is high, so the tree shrinks in diameter

Night - tension in xylem vessels is low, so tree increases in diameter

133
Q

Transpiration

Evidence for the cohesion-tension theory

What happens when a xylem vessel is broken (eg when you cut stems)?

A

Air is drawn in the xylem rather than water leaking iut

134
Q

Transpiration

Evidence for the cohesion-tension theory

What happens when xylem vessel is broken and air is pulled in?

A

The plant can no longer move water up the stem as the continuous stream of water molecules held together by cohesive forces is broken

135
Q

Transpiration

What happens when turgor is low in the stomata?

A

The asymmetric configuration of the guard cell walls closes the pores

136
Q

Transpiration

How do guard cells increase their turgor?

A

When the environmental conditions are favourable, guard cells pump in solutes by active transport

137
Q

Transpiration

What prevents guard cells from swelling in width, only lengthways?

A

Cellulose hoops

138
Q

Transpiration

Why do guard cells become bean-shaped?

A

Because the inner wall is less flexible

139
Q

Transpiration

What happens to guard cells when water becomes scarce?

A

Hormonal signals from the roots can trigger turgor loss from the guard cells, which can close the stomatal pore and so conserve water

140
Q

Factors affecting Transpiration

How does light intensity affect it?

A

Increasing light intensity increases open of stomata, increasing rate of water vapour diffusing out, increasing evaportation

141
Q

Factors affecting Transpiration

What does a relatively high humidity do?

A

Lowers transpiration rate because of the reduced water vapour potential gradient between inside and outside of lead

142
Q

Factors affecting Transpiration

What does very very dry air do?

A

Increases rate of transpiration

143
Q

Factors affecting Transpiration

How does an increase in temperature affect KE?

A

Increases KE of water = increases rate of evaporation from spongy mesophyll cells into the air spaces of leaf

144
Q

Factors affecting Transpiration

How does an increase in temp affect concentration of water vapour?

A

Increases conc of water vapour that’s he external air can hold before it becomes saturated

= decreases relative humidity & water potential

145
Q

Factors affecting Transpiration

What does reducing air movement do?

A

Water vapour that diffuses out of lead accumulates in cells = so water vapour potential around stomata increases = reduces diffusion gradient l

146
Q

Factors affecting Transpiration

Does air movement or wind increase rate of transpiration?

A

Yes

147
Q

Factors affecting Transpiration

How does soil-water availability affect it?

A

If it is very dry the plant will be under water stress and the rate of transpiration will reduce

A-level Biology (23 decks)

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