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A level Biology > Unit 2.3b - Adaptations for transport in plants > Flashcards

Unit 2.3b - Adaptations for transport in plants Flashcards

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1
Q

What do plants need to transport?

A

Inorganic ions and water

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2
Q

Where do plants need to transport inorganic ions and water?

A

From the soil to where they’re synthesising new compounds, which is in the leaves (photosynthesis)

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3
Q

What’s the name of the transport system used to transport inorganic ions in plants?

A

The transpiration system

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4
Q

Transpiration

A

The loss of water vapour through the stomata of plants

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5
Q

What’s the first step of the transpiration system?

A

Inorganic ions are dissolved in water and carried up to the leaves to be used in the plants metabolism

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6
Q

Name some inorganic ions that are transported in a plant

A

Mg2+
NO3^2-
PO4^3-

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7
Q

Where is water “pulled up” in a plant?

A

The xylem vessels

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8
Q

How is water pulled up the xylem vessels?

A

Cohesion tension
Adhesion

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9
Q

Cohesion tension

A

Hydrogen bonding between H and O between different water molecules

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10
Q

Adhesion

A

The polar nature of water giving them an attraction to the cellulose in the walls of the xylem vessels - capillarity

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11
Q

What’s the name of the other transport system used in plants as opposed to the transpiration system?

A

Translocation

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12
Q

Translocation

A

The process of moving the products of photosynthesis from where they’re mad or stored to other parts of the plant

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13
Q

From where is large quantities of water lost from a plant and how?

A

Through the stomata
Via the transpiration stream

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14
Q

Why must water be replaced in the soil?

A

Large quantities of water are lost through the stomata via the transpiration stream

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15
Q

How is water replaced into a plant?

A

A specialised region of root - the root hair zone - absorbs water (and inorganic ions)

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16
Q

Which part of a plant is responsible for absorbing water from the soil?

A

The root hair zone - a specialised region of root

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17
Q

How does the root hair zone of root absorb water?

A

Via osmosis

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18
Q

How does the root hair zone of root absorb inorganic ions?

A

Via active transport or fascilitated diffusion

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19
Q

Root hair cell

A

Epidermal cells with the extension - the root hair zone

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20
Q

Root hair cells adaptations to their function

A

Large surface area for the absorption of water by osmosis
Thin cell walls for a short diffusion pathway

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21
Q

Draw and label the transverse section of the root of a plant

A

(See notes)

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22
Q

Where are root hairs on the root?

A

On the upper epidermis layer

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23
Q

What does xylem tissue do?

A

Transports water and minerals throughout the plant

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24
Q

Where is xylem tissue found?

A

At the centre of the root

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25
Q

What is xylem tissue surrounded by?

A

A single layer of cells - the endodermis

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26
Q

What does the endodermis surround?

A

Xylem tissue

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27
Q

What does the stele of a root contain?

A

Vascular tissue

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28
Q

Where is the stele of a root?

A

The central part of the stem
And
In the root

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29
Q

Draw and label a stem transection

A

(See notes)

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30
Q

Draw and label a high power view of the stele

A

(See notes)

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31
Q

Endodermis

A

A single layer of cells around the stele

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32
Q

What is the endodermis important for?

A

Absorbing water and inorganic ions into the plant

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33
Q

What does endodermis include and what does this do?

A

Water proof Casparian strip which stops transport via the apoplast route

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34
Q

What does Phloem do?

A

Transports the products of photosynthesis e.g - sucrose and amino acids

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35
Q

What does Xylem do?

A

Transports water and minerals

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36
Q

How are xylem tissues fit for their purpose?

A

They’re dead cells with thickened cell walls so the middle is empty for transporting water and inorganic ions

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37
Q

What makes up the vascular bundle?

A

Xylem
Cambium
Phloem

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38
Q

What do the xylem, cambium and phloem make up?

A

The vascular bundle

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39
Q

What chemical do two parts of the stem both have and what does this mean?

A

Xylem and schlerenchyma have lignin
Stain the same colour

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40
Q

Chemical of xylem and schlerenchyma

A

Lignin

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41
Q

What’s the schlerenchyma of the vascular bundle also known as?

A

Fibres

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42
Q

Fibres of the vascular bundle

A

Schlerenchyma

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43
Q

What do all 3 routes of transporting water and minerals in the root start with?

A

Water enters the root hairs on the epidermis via osmosis (water potential gradient from the soil into root hair cell)
Inorganic ions dissolved in water enter the root hair cells via facilitated diffusion or active transport

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44
Q

Where do the 3 routes for transport of water and minerals in the root go to and from?

A

From epidermis
To cortex
To the vascular tissue of the steel in the centre of the root

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45
Q

What are the 3 possible routes for the transport of water and minerals in the root?

A

Symplastic route
Apoplastic route
Vacuolar route

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46
Q

Symplastic route

A

Water and dissolved ions are absorbed into the cytoplasm of the root hair by osmosis active transport and fascilitated diffusion
Then move through the root tissues via the cytoplasm and plasmodesmata of adjacent cells

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47
Q

What are the symplastic, apoplastic and vacuolar routes all routs for?

A

The transport of water and minerals in the root

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48
Q

Apoplastic route

A

Water and dissolved ions move through the root tissues via the cell walls of adjacent cells (it doesn’t actually enter the cells)
There is no restriction to flow until the endodermis is reached

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49
Q

Why are water and dissolved ions able to move through the root tissues via the cell walls when taking the apoplasic route?

A

Cellulose cell walls and permeable to water and ions

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50
Q

At which point in the apoplastic route is there a restriction to the flow of water and why?

A

The endodermis
The endodermis contains a band of waterproof tissue known as the casparian strip which prevents water from going through the apoplast route

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51
Q

Where is the casparian strip?

A

The endodermis

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52
Q

What’s the purpose of the casparian strip in the endodermis?

A

To prevent water from going through the apoplast route

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53
Q

Vacuolar route

A

Water and dissolved ions move through the tissues of the root from the vacuole of one cell to the vacuole of the neck cell down a water potential gradient

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54
Q

Sketch the vacuolar route

A

(They look like coffee beans)

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55
Q

Sketch the symplastic route

A

(Nodiadau)

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56
Q

Sketch the apolastic route

A

(Nodiadau)

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57
Q

Draw a diagram to represent the transport of water and minerals in the route down both the apoplastic and symplastic route

A

Yes

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58
Q

How are inorganic ions taken from the soil solution?

A

Active transport

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59
Q

Ho do inorganic ions move through the plant once they’ve been absorbed?

A

Move along the apoplastic pathway (carried in solution by the water) in the transpiration system

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60
Q

How are inorganic ions carried in the transpiration stream?

A

In solution by the water

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61
Q

What happens when minerals reach the casparian strip?

A

It prevents further movement via the apoplast

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62
Q

What’s the casparian strip formed from?

A

Waterproof Suberin

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63
Q

What happens to minerals once they’ve been restricted by the casparian strip?

A

They must enter the cytoplasm and are transported from cell to cell via diffusion or active transport

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64
Q

How does nitrate enter a plant?

A

As nitrate or ammonium ions

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65
Q

Why do plants need nitrates?

A

To make amino acids

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66
Q

How do nitrate ions enter the apoplastic pathway?

A

Diffuse along a concentration gradient

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67
Q

How do inorganic ions travel from the apoplastic to the symplastic pathway when restricted by the casparian strip in the endodermis?

A

By active transport against the concentration gradient, through the selectively permeable cell membrane into the cytoplasm

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68
Q

What must ions do at the endodermis and why?

A

Enter the symplastic pathway by active transport to bypass the casparian strip

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69
Q

Is the apoplastic pathway living or non-living?

A

Non-living

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70
Q

Is the symplastic pathway living or non-living?

A

Living

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71
Q

How does the casparian strip actually help? How?

A

Allows the plant to selectively take up ions
When ions have to travel from the apoplastic to the symplastic pathway, they have to travel into the cytoplasm to get into it, through the selectively permeable membrane

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72
Q

How does the casparian strip in the endodermis allow a plant to selectively take up ions?

A

Inorganic ions have to travel from the apoplastic to the symplastic pathway, and to do this they need to travel into the cell’s cytoplasm, and to do THIS they need to travel through the selectively permeable membrane

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73
Q

What does root pressure do?

A

Helps move water up the plant
(Although not to the same extent as cohesion tension)

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74
Q

What IS the casparian strip?

A

A layer of Suberin within the cell walls of the endodermal cells

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75
Q

How is root pressure formed? [5]

A

The Suberin of the casparian strip is water proof and stops water and dissolved ions form following the apoplast root through the endodermis, forcing them to cross the cel membrane and enter the symplastic route
Transport proteins in the membrane of the endodermis cells actively transport dissolved ions/salts across the endodermis and into the xylem vessels
This lowers the water potential within the xylem vessels and water moves into the xylem by osmosis from the root cortex
The movement of water into the xylem creates a hydrostatic pressure which forces the xylem contents upwards - this is root pressure

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76
Q

What creates hydrostatic pressure in the roots and what does this cause?

A

The movement of water into the xylem, which forces the xylem contents upwards (root pressure)

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77
Q

Where does water move into the xylem by osmosis from to form root pressure?

A

The root cortex

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78
Q

What is the ultimate cause of root pressure?

A

The casparian strip forcing inorganic ions to cross the cell membranes and enter the symplastic route

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79
Q

What’s an experiment that we can do to test for root pressure?

A

Cut the plant close to the soil to leave a stump
Tightly seal to an s-shaped tube half filled with mercury, half filled with water
Over time, the mercury will be pushed to the top of the tube due to the hydrostatic pressure
Measure pressure of the liquid using a manometer

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80
Q

How can we measure the pressure of a liquid?

A

Manometer

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81
Q

Where are the vascular bundles in stems?

A

Around the periphery

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82
Q

Why are the vascular bundles around the periphery in stems?

A

Gives flexible support and resistance to bending strain due to the tough xylem cells - fibres

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83
Q

What gives flexible support and resistance to a stem?

A

Tough xylem cells - fibres

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84
Q

Draw and label the vascular bundle in a stem

A

(See notes)

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85
Q

What does the phloem contain?

A

Living material (e.g - nucleus, cytoplasm)

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86
Q

Which 2 tissues in vascular bundles contain lignin and what does this lead to?

A

Fibres
Xylem
Both stain red

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87
Q

Compare lignin to cellulose

A

Lignin is harder

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88
Q

What gives a plant the texture of wood?

A

Xylem vessels with lignin

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89
Q

What does lignin give plants?

A

Rigidity

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90
Q

What are the 4 types of xylem cells?

A

Vessels
Tracheids
Fibres
Parenchyma

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91
Q

What are vessels, tracheids, fibres and parenchyma all examples of?

A

Xylem cells

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92
Q

What happens when a xylem cell matures?

A

Gets thicker and fills with lignin

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93
Q

Is lignin permeable to water?

A

No

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94
Q

Why are xylem cells dead cells?

A

As they mature, the cell walls get thicker and fill with lignin
Lignin is impermeable to water and stronger than cellulose
Therefore, water can’t easily get in, so the cell contents die away

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95
Q

How does lignin lead to the dead of a xylem cell?

A

Impermeable to water and stronger than cellulose - water can’t get in easily, cell contents die away

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96
Q

What type of cells are xylem cells?

A

Dead

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97
Q

Why are xylem cells important?

A

Form tubes to carry water and dissolved ions
Provide mechanical strength to support the plant

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98
Q

Why is it useful that xylem cells are dead?

A

Form tubes to carry water and dissolved ions

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99
Q

Xylem function

A

Transports water and mineral salts from the root to the leaves

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100
Q

Phloem function

A

Transports soluble produce of photosynthesis (sucrose and amino acids) from the leaves to other parts of the plant

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101
Q

How are the functions of the xylem and phloem different?

A

Xylem - transports water and mineral salts from the root to the leaves
Phloem - transports soluble products of photosynthesis (sucrose and amino acids) from the leaves to other parts of the plant

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102
Q

Where does the phloem carry the products of photosynthesis to and from?

A

From the leaves to other parts of the plant

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103
Q

Where does xylem transport water and mineral salts/inorganic ions to and from?

A

From the root to the leaves

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104
Q

Describe tracheid xylem tissues

A

Longer, slender cell with an empty lumen to transport water and inorganic ions
Thick to support the plant

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105
Q

Describe the fibre xylem tissues

A

Specialised for support
Has almost no central cavity when the cell dies at maturity
Thickened cell walls
Lots of lignin

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106
Q

Describe the vessel xylem tissues

A

Specialised for water transport
Has a wide lumen to reduce the resistance to water flow through the tissue
Shorter and wider
No end walls between vessel elements (cells) that make up a vessel

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107
Q

Describe the parenchyma xylem tissue

A

Live cells that develop to form the other types of xylem cells
Contain cytoplasm, nuclei…
Cell walls thicken as they develop

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108
Q

Which xylem cells are the live cells that develop to form the other types?

A

Parenchyma

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109
Q

What are fibrous xylem tissues specialised for?

A

Support

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110
Q

What are tracheid xylem tissues specialised for?

A

Transporting water and inorganic ions

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111
Q

What are vessel xylem tissues specialised for?

A

Water transport

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112
Q

What would happen eventually when testing for root pressure and why?

A

There would be no more upward movement of mercury due to gravity resisting this movement

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113
Q

Describe the steps involved in transporting water FROM the xylem in the leaf

A
  1. Water arrives in the leaf through xylem vessels
  2. Water leaves the xylem vessels through the pits in the walls and travel through the living spongey mesophyll cells down a water potential gradient via osmosis
  3. Water evaporates from the surface of mesophyll cells into the sub stomatal air chamber
  4. When the stomata is open (sufficient light intensity), water vapour escapes - transpiration
    The water potential of the cells near the stomata has now lowered
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114
Q

Where does water evaporate from the surface of mesophyll cells into?

A

The sub stomatal air chamber

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115
Q

How does water leave the xylem vessels and where does it go to?

A

Through the pits in the walls
Travels through the living spongey mesophyll cells

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116
Q

How does water move from the xylem vessels through the living spongey mesophyll cells?

A

Down a water potential gradient via osmosis

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117
Q

What is the route taken when water is transported FROM the xylem in the leaf?

A

The same as for the transport of water and minerals in the root…
Symplastic
Apoplastic
Vacuolar

118
Q

How does water travel in the xylem to the leaves?

A

Via the apoplast, symplastic and vacuolar pathways

119
Q

What happens to most of the water as it travels from the xylem through the leaf?

A

Most is lost as it evaporates from the internal leaf surface and passes out as water vapour into the atmosphere

120
Q

Transpiration

A

Water loss from the surface of leaves by the evaporation through the stomata

121
Q

Why does transpiration happen at all?

A

Most of the water travelling in the apoplast, symplastic and Vacuolar pathways from the xylem throughout the leaf is lost as it evaporates from the internal leaf surface

122
Q

Transpiration pull

A

As water molecules leave xylem cells in the leaf, they pull up other water molecules - this pulling effect is known as the transpiration pull

123
Q

What is the name for the effect caused when other water molecules are pulled up when water molecules leave xylem cells in the leaf?

A

The transpiration pull

124
Q

What are the factors that effect transpiration rate?

A

Temperature
Humidity
Air movement
Light intensity

125
Q

Describe how temperature can effect transpiration rate

A

Rise in temperature = additional kinetic energy for the movement of water molecules = increased rate of evaporation from the walls of the mesophyll cells
Also, if the stomata are open, this speeds up the rate of diffusion of water vapour into the surrounding air
Also, the water potential of the air becomes lower as its temperature is raised as it can hold more moisture

126
Q

What happens to the water potential of the air as the temperature is raised and what does this mean?

A

It become lower
Can hold more moisture

127
Q

Humidity

A

The amount of water vapour in the air

128
Q

How much water vapour is there in the air inside the leaf?

A

Saturated with water vapour

129
Q

Which part of a leaf has a high humidity and why?

A

The sub-stomatal air chamber as it’s saturated with water vapour

130
Q

Relationship between humidity and rate of transpiration

A

Greater humidity = lower rate of transpiration

131
Q

Relationship between rate of transpiration and temperature

A

Increased temperature = increased transpiration rate

132
Q

Describe how humidity effects transpiration rate

A

Sub-stomatal air chamber has a very high humidity as it’s saturated with water vapour, giving it a high water potential
The humidity of the air surrounding a leaf varies (rarely exceeds 70% in Britain)
Therefore, a water potential gradient is always present between the leaf and the air
When the stomata open, water vapour rapidly diffuses out of the leaf from a high to low water potential
So, the greater the humidity, the lower the rate of transpiration

133
Q

Describe the rate of transpiration in still air

A

Water vapour accumulates around the leaf surface
This decreases the water potential gradient between the leaf and air
This decreases the rate of transpiration

134
Q

Describe the rate of transpiration in moving air (wind)

A

Removes the layer of saturated air
Increases the water potential gradient between the leaf and air
Increases the rate of transpiration

135
Q

Is it still or moving air that increases the rate of transpiration? Why?

A

Moving (windy conditions)
Removes the layer of saturated air, increasing the water potential gradient between the leaf and air

136
Q

What’s the relationship between the rate of transpiration and light intensity?

A

The higher the light intensity, the higher the rate of transpiration

137
Q

Describe how light intensity effects the rate of transpiration

A

Controls the degree of stomatal opening
Higher light intensity = greater number of open stomata
Increases the rate of transpiration

138
Q

What is the primary purpose of stomata?

A

To allow CO2 to enter for photosynthesis (but when it opens, water vapour DOES get released)

139
Q

Potometer

A

Apparatus used to measure the rate of uptake of water by a leafy shoot

140
Q

Apparatus used to measure the rate of uptake of water by a leafy shoot

A

Potometer

141
Q

How do we use a Potometer?

A

Cut stem from plant
Plug to Potometer
Plant continues to transpire
Air bubble moves to indicate the volume of water taken up by he shoot in a certain period of time

142
Q

How does a Potometer actually measure the rate of uptake of water by a leafy shoot?

A

Air bubble moves to indicate the volume of water taken up by the shoot in a certain period of time

143
Q

Draw the set up of a Potometer

A

(See notes)

144
Q

How must we cut the shoot of the plant to attach to a Potometer and why?

A

Cut it under water
To prevent air bubbles forming in the xylem. If air gets in, it’ll break the water column and break the cohesion tension

145
Q

What are 4 precautions to take when setting up a Potometer?

A

Cut the shoot under water
Keep the leaves dry
Set up apparatus under water
Ensure all joints are airtight

146
Q

Why is it important to keep the leaves dry when using a Potometer?

A

If there’s water vapour on the leaves, it’ll prevent water from leaving via transpiration

147
Q

How do we setup the apparatus of a Potometer and why?

A

Under water to prevent air bubbles

148
Q

How could we ensure that all joints are airtight on a Potometer and why is this important?

A

Use Vaseline to seal joints
Prevents air bubbles

149
Q

What does using a Potometer NOT measure and why?

A

The rate of transpiration
Not all the water taken up by the plant and drawn over the leaf goes through the stomata - the purpose of water being there is to photosynthesise, so some is used for this

150
Q

As well as measuring the rate of uptake of water by a leafy shoot, what else can we use a Potometer to measure? Give examples

A

Measure the factors that effect transpiration rate
e.g - lamp (light intensity)
Fan (air movement)

151
Q

What are the different types of plants depending on their different environments?

A

Mesophytes
Hydrophytes
Xerophytes

152
Q

What does the availability of for plants change depending on where they live?

A

The availability for water

153
Q

Mesophytes

A

Plants that live in habitats where there is sufficient water available for their survival

154
Q

Plants that live in habitats where there is sufficient water available for their survival

A

Mesophytes

155
Q

Which type of plants don’t really have any special adaptations to avoid water loss and why?

A

Mesophytes - they live in habitats where there is sufficient water available for their survival

156
Q

What are the general adaptations of mesophytes to avoid water loss?

A

Closing stomata (+ most on the base for slower water evaporation)
Waxy cuticle to prevent water from evaporating from the surface

157
Q

Why is it important that Mesophytes have a waxy cuticle?

A

They would otherwise lose a lot of water due to their large surface area

158
Q

What type of plants are most of those around us?

A

Mesophytes

159
Q

Hydrophytes

A

Plants that live in or on water and have a plentiful supply of water at all times

160
Q

Plants that live in or on water and have a plentiful supply of water at all times

A

Hydrophytes

161
Q

Which types of plants don’t have any specific adaptations to avoid water loss and why?

A

Hydrophytes - they have a plentiful supply of water at all times

162
Q

Xerophyte

A

Plants that live in areas of low water availability (e.g - deserts, sand dunes, tundra (frozen soil))

163
Q

Examples of areas of low water availability

A

Deserts, sad dunes, tundra (frozen soil)

164
Q

What type of plant is a lily pad an example of?

A

Hydrophyte

165
Q

Hydrophyte example

A

lily pad

166
Q

Why do sand dunes have low water availability?

A

Sand dries up quickly
Sea water is salty = drier air

167
Q

Draw and label a hydrophyte transection

A

(See notes)

168
Q

Which tissue do we observe when looking at a hydrophyte transection and where is this?

A

Specialised tissue - aerenchyma
Underneath the palisade layer

169
Q

What are the adaptations of a hydrophyte?

A

Large air spaces
Stomata on the upper epidermis
Thin or absent cuticle
Lack of supporting tissues
Less organised vascular tissue
Increased surface area
Roots usually reduced in size

170
Q

Why do hydrophytes have large air spaces?

A

Gives leaves buoyancy to float on the water surface
Reservoirs of O2 and CO2

171
Q

Why is the stomata on the upper epidermis of a hydrophyte?

A

Allows gas exchange with the air above from the floating leaf

172
Q

Why does the hydrophyte have a thin or absent cuticle?

A

Do not need to reduce water loss

173
Q

Why do hydrophytes have a lack of supporting tissues?

A

High density of water gives support to the submerged leaves and stems

174
Q

Name some supporting tissues that a hydrophyte lacks

A

Fibres
Collenchyma
Sclerenchyma

175
Q

What is the vascular tissue less organised in hydrophytes compared to?

A

Compared to the midrib in mesophytes

176
Q

Why is the vascular tissue of hydrophytes less organised than the midrib of mesophytes?

A

Don’t need a good supply of water

177
Q

Why do hydrophytes have a large surface area?

A

Increases the surface area for gas exchange and photosynthesis

178
Q

Why are the roots of hydrophytes usually reduced in size?

A

They act mainly to anchor the plant as water absorption can take place over the whole surface of the plant

179
Q

What type of specialised roots have some hydrophytes developed and why?

A

Roots that extend into the air and can absorb oxygen
(If anchored in mud at the bottom of water and they don’t receive sufficient oxygen)

180
Q

Pneumaphores

A

Specialised roots in hydrophytes that extend into the air to absorb oxygen as the roots would otherwise be anchored in mud at the bottom of water with insufficient oxygen

181
Q

Specialised roots in hydrophytes that extend into the air to absorb oxygen as the roots would otherwise be anchored in mud at the bottom of water with insufficient oxygen

A

Pneumaphores

182
Q

Draw and label a xerophute transection

A

(See notes)

183
Q

Name a xerophyte

A

Ammophila leaf

184
Q

What is an ammophila leaf an example of?

A

A xerophyte

185
Q

What are the adaptations of xerophytes?

A

Rolled leaves
Hairs
Thick waxy cuticle
Sunken stomata in pits
Hinge cells
Succulent (thick) leaves
White leaves/spines
Reduced number of stomata
CAM photosynthesis

186
Q

What causes the leaves of xerophytes to roll up?

A

Large, thin walled epidermal cells at the bases of the grooves shrink when they lose water from excessive transpiration, causing the leaf to roll inwards

187
Q

Why are xerophyte leaves rolled up?

A

It reduced the leaf area exposed to air, and so reduces transpiration

188
Q

Name for the hairs of xerophytes

A

Trichomes

189
Q

Trichomes

A

Hairs of xerophytes

190
Q

Why do xerophytes have Trichomes (hairs)?

A

Stiff, interlocking hairs trap water vapour and reduce the water potential gradient, thus reducing the rate of transpiration

191
Q

Why do xerophytes have a thick waxy cuticle?

A

Reduced water loss by evaporation from the epidermal tissue as they’re waterproof

192
Q

Why do xerophytes have sunken stomata in pits?

A

A more humid microenvironment is created, as they allow water vapour to accumulate above the stomatal pore
+ wind can’t blow the water vapour away (rolled leaf) - this decreases the water potential gradient between the inside of the leaf and the gas chamber, reducing transpiration rate

193
Q

What do hinge cells in xerophytes do and why is this important?

A

Absorb water from the surroundings to become turgid and open when it’s not too dry to increase the surface area for photosynthesis

194
Q

Why do xerophytes have succulent (thick) leaves?

A

To store water

195
Q

Why do xerophytes have white leaves/spines?

A

Light colours reflect light and heat, thereby cooling the plant

196
Q

Why do xerophytes have a reduced number of stomata?

A

Fewer gaps for water to evaporate out through

197
Q

What is CAM photosynthesis and why is it used by xerophytes?

A

Stomata open when it’s cooler at night
CO2 is fixed so that it can be used during the day for photosynthesis without having to open the stomata

198
Q

Draw and label the transection of a pine leaf

A

(See notes)

199
Q

Give an example of a xerophyte

A

Pine leaf

200
Q

What is a pine leaf an example of?

A

A xerophyte

201
Q

How do we improve the accuracy of the experiment with the Potometer?

A

Use a capillary tube with smaller graduations
Time over a greater distance

202
Q

What implies more reliable data with range bars?

A

If they do not overlap
If they’re smaller

203
Q

Translocation

A

The transport of the products of photosynthesis from source to sink in the plant

204
Q

Source for translocation

A

The site of photosynthesis in the leaves

205
Q

Sink in translocation

A

Areas that use the materials of photosynthesis for growth, respiration, storage and other metabolic processes

206
Q

Products of photosynthesis

A

Soluble organic materials, sucrose and amino acids

207
Q

Are the products of photosynthesis transported with inorganic ions and water?

A

No, they’re transported separately in the phloem

208
Q

Where are the products of photosynthesis carried to and from in the phloem?

A

From the source to the sink

209
Q

How is sucrose a product of photosynthesis?

A

Glucose (made during photosynthesis) + fructose —> sucrose

210
Q

What are the types of cell in phloem tissue?

A

Sieve tubes
Companion cells
Phloem fibres
Phloem parenchyma

211
Q

What is a sieve tube made up of?

A

Sieve cells/ sieve element

212
Q

Function of sieve tubes

A

Transport organic materials such as sucrose and amino acids (the products of photosynthesis)

213
Q

What are the cells of sieve tubes called?

A

Sieve elements

214
Q

Where are the sieve elements in sieve tubes?

A

End to end

215
Q

Sieve plates

A

The ends of the walls of each sieve cell do not break down, but are perforated by pores at either side, called sieve plates

216
Q

What’s the name for the pores at the ends of the walls of sieve cells?

A

Sieve plates

217
Q

Draw and label a sieve tube and it’s surroundings

A

(See notes)

218
Q

Describe sieve cells

A

Long, columnar
Not completely empty like xylem - contain living material such as a thin cytoplasm and a few organelles

219
Q

Adaptations of sieve cells/elements for their function

A

Sieve plates containing pores allow bidirectional flow form element to element throughout the plant
Thin cytoplasm with no large organelles, which allows the products of photosynthesis to flow without obstruction
Plasmodesmata are present in the walls, which allow the transport of ATP and other molecules from the companion cell to the sieve tube cell/element
No nucleus, and most of the other cell organelles disintegrate during sieve tube development
Cytoplasmic filaments contains phloem protein extend from one sieve cell to the next through the pores in the sieve plate

220
Q

Which part of sieve tubes contain pores and why?

A

Sieve plates
Allow bidirectional flow from element to element throughout the plant

221
Q

Describe and explain the cytoplasm of sieve cells/elements

A

Thin cytoplasm with no large organelles
Allow the products of photosynthesis to flow without obstruction

222
Q

Where are plasmodesmata present in sieve tubes and why?

A

In the walls of sieve tube cells/elements
Allow the transport of ATP and other molecules from the companion cell into the sieve tube cell/element

223
Q

Why do sieve cells/elements not have most of their organelles?

A

They disintegrate during sieve tube development

224
Q

What do cytoplasmic filaments contain in sieve tubes?

A

Phloem Protein

225
Q

What contain phloem protein in sieve tubes?

A

Cytoplasmic filaments

226
Q

How do cytoplasmic filaments extend from one sieve cell to the next?

A

Through the pores in the sieve plate

227
Q

Describe companion cells

A

Dense cytoplasm
Centrally placed large nuclei
Many mitochondria
Rough endoplasmic reticulum
Golgi body
Connected to the sieve tube elements by plasmodesmata
Make proteins and ATP for the sieve tube cells/elements

228
Q

What do companion cells make and for what?

A

Proteins and ATP for the sieve tube cells/elements

229
Q

How are companion cells connected to the sieve tube elements?

A

By plasmodesmata

230
Q

Where in sieve tubes is where metabolic activity takes place?

A

Companion cell

231
Q

What takes place in companion cells?

A

Metabolic activity

232
Q

How is a companion cell different to a sieve cell/element?

A

Contain a lot more material and a relatively small vacuole

233
Q

Wha are the 3 experiments for evidence for translocation?

A

Ringing experiments
Phloem sampling
Radioactive labelling

234
Q

What do ringing experiments support the idea of?

A

Translocation in the phloem

235
Q

How are ringing experiments done to provide evidence for translocation?

A

Cylinders of outer bark tissue are removed from all the way around a woody stem, in a ring
The phloem is removed when doing this (located towards the periphery), leaving the xylem (further in the stem)

236
Q

What are the results from the ringing experiment to provide evidence for translocation? Explain this

A

Sucrose (a product of photosynthesis) accumulated above the cut ring
Lowers the tissue’s water potential
Water moves into the cell via osmosis
Swells as water enters the cells

237
Q

What does the ringing experiment provide evidence for?

A

That sucrose was transported to this region of the stem by translocation in the phloem

238
Q

Why are too many aphids bad for a plant?

A

Take the nutrients from a plant

239
Q

What’s the name of the mouthpart of an aphid? Describe this

A

Stylet
Hollow and needle-like

240
Q

What does an aphid do with its stylet?

A

Inserts it directly into the sieve tube, allowing the aphid to feed on the sugary sap of the phloem

241
Q

Which part of a plant does an aphid insert its stylet and why?

A

The sieve tube of the phloem
To feed on the sugary sap

242
Q

What happens during phloem sampling?

A

The stylet of aphids is cut off using a laser, leaving it attached to the plant, forming a useful micro pipette
Sap exudes from the stylet after being cut - the contents of the phloem must be under pressure for it to be pushed up like this
Upon collection and analysis of this sap, it contains high levels of sucrose and amino acids - the products of photosynthesis

243
Q

How do we extract sap from the phloem of a plant?

A

Cut of the stylet of an aphid to use it as a micropipette

244
Q

How does phloem sampling give evidence for translation?

A

Upon collection and analysis of the sap from the stylet, it contains high levels of sucrose and amino acids - the products of photosynthesis

245
Q

What additional concept is proved by phloem sampling and why?

A

That the contents of the phloem are under pressure, a sap exudes from the stylet after being cut

246
Q

What happens during radioactive labelling to provide evidence for transpiration?

A

Carbon dioxide labelled with a radioactive carbon isotope (14C) is supplied to an illuminated plant leaf

247
Q

Which carbon isotope is supplies to a plant leaf dung radioactive labelling and why?

A

14C
Radioactive

248
Q

What’s the method of using radioactive labelling to provide evidence or translocation using aphids?

A

Aphids feed on the contents of phloem
Upon cutting the stylet, we can analyse the sap that exudes for radioactivity

249
Q

How is the radioactive carbon isotope transported to other parts of the plant to make radioactive labelling possible?

A

The radioactive carbon becomes fixed in the sucrose produced by photosynthesis and is translocated to other parts of the plant

250
Q

What’s the alternative method to using aphids to using radioactive labelling to provide evidence for translocation? Describe this

A

Trace the radioactive carbon in the sucrose using autoradiography
Source leaf and sink tissues are places firmly on photographic film in the dark for 24 hours
When the film is developed, the presence of radioactivity in parts of the plant tissue show up as fogging of the negatives

251
Q

What has radioactive labelling showed specifically about translocation in the phloem?

A

That sucrose is transported both upwards and downwards

252
Q

How did radioactive labelling prove that sucrose is transported both upwards and downwards during translocation ?

A

Radioactivity was observed both where products have been used for growth and in the roots, as most plants store carbohydrates in the form of starch in the roots

253
Q

What’s the most widely accepted theory for translocation?

A

The mass-flow hypothesis

254
Q

The mass-flow hypothesis

A

The most widely accepted theory for translocation

255
Q

When was the mass flow hypothesis proposed?

A

1937

256
Q

Summarise what the mass-flow hypothesis suggests

A

There’s a passive mass flow of sugars from the phloem of the source leaf, which has the highest concentration of sugar, to other areas of the plant, such as growing tissues, which have a lower sugar concentration

257
Q

Where does translocation occur to and from according to the mass-flow hypothesis?

A

From source to sink

258
Q

Source in the mass-flow hypothesis

A

Site of photosynthesis in the leaves

259
Q

Sink in the mass flow hypothesis

A

Roots and regions of growth

260
Q

Draw a diagram to represent the mass flow hypothesis

A

(See notes)

261
Q

Describe, in detail, the steps of the mass-flow hypothesis

A
  1. When sugar is made at the source, the water potential becomes more negative and water passes into the metabolically active source cells by osmosis
  2. As water enters the source cells, hydrostatic pressure increases, forcing sugars and other products of photosynthesis into the sieve tubes via active transport - phloem sieve tubes are loaded
  3. Mass flow occurs along the sieve tubes to the sink, the products if photosynthesis are forces along by the flow of water form a high to a low hydrostatic pressure
  4. Hydrostatic pressure will be lower at the sink because sugars are stored as starch or are used for respiration - this reduces the water potential
  5. Water passes form the sink cells to the xylem to be returned to the source
262
Q

Why is the hydrostatic pressure lower at the sink (mass flow hypothesis)?

A

Sugars are stored as starch or are used for respiration

263
Q

How are the products of photosynthesis forced along during mass flow-hypothesis along the sieve tubes to the sink?

A

The flow of water from a high to a low hydrostatic pressure

264
Q

Why does water move from the xylem to the phloem i the mass-flow hypothesis?

A

When the phloem sieve tubes are loaded with sugars and other products of photosynthesis, water moves via osmosis from a high to a low water potential

265
Q

What causes an increase in the phloem’s hydrostatic pressure?

A

Water moving from the xylem to the phloem via osmosis due to the sugars and products of photosynthesis in the phloem giving it a low water potential

266
Q

What explains the rising sap in the aphid experiment?

A

The increase in the phloem’s hydrostatic pressure when water moves form the xylem to the phloem via osmosis

267
Q

What creates a pressure gradient in the phloem?

A

The movement of water from the xylem to the phloem

268
Q

Why is the pressure gradient in the phloem important?

A

Contents of phloem move down a pressure gradient from source to sink

269
Q

Why does water move from the phloem to the xylem?

A

At the same time, sucrose is taken out of the phloem into sink cells, increasing the water potential in the phloem
Water moves from the phloem back into the xylem due to the water potential gradient

270
Q

What are the different arguments against the mass-flow theory?

A
  1. The rate of translocation is 10,000x faster than it would be if the substances were moving along by diffusion
  2. Sieve plates with tiny pores act as a barrier impeding flow
  3. Sucrose and amino acids move at different rates and in different directions in the same phloem tissue
  4. Phloem tissue has a high rate of oxygen consumption, and translocation is stopped when a respiratory position such as potassium cyanide enters the phloem
  5. Companion cells contain numerous mitochondria and produce ATP, but the mass flow hypothesis fails to suggest a role for the companion cells
271
Q

Describe the rate of translocation compared to substances moving by diffusion

A

10,000x faster

272
Q

How do we know the rate of translocation?

A

Can use radio labelling experiments to measure the rate of flow

273
Q

Why is the fact that sieve plates have tiny pores that act as a barrier impeding flow an argument against the mass-flow theory?

A

Would be expected that plants would evolve away from them - there may be an unexplained reason for them

274
Q

Why is glucose converted into sucrose in plants?

A

Too reactive for transport

275
Q

Bidirectional movement or organic molecules in a plant

A

Transported both upwards and downwards

276
Q

Name for the fact that organic molecules in a plant are tranported both upwards and downwards

A

Bidirectional

277
Q

What does xylem show a similar pattern of support material to?

A

That seen in an insects trachae

278
Q

What shows a similar pattern of support material to that seen in an insects trachae?

A

Xylem

279
Q

What do the Xylem vessels NOT transport?

A

Nutrients

280
Q

How many directions does mass-flow occur in?

A

1

281
Q

What other hypothesis could be used instead of the mass flow hypothesis if flow is bidirectional?

A

Active transport or diffusion

282
Q

If flow is bidirectional, what is it NOT and why?

A

Mass-flow, as this is unidirectional

283
Q

When could active transport or diffusion be used as a hypothesis for the movement of materials as opposed to mass-flow and why?

A

When it’s bidirectional, as mass flow is unidirectional

284
Q

What’s the importance of lignin in the xylem?

A

Mechanical support to the xylem and prevents it from collapsing

285
Q

What do all three of the apoplastic, symplastic and vacuolar routes rely on?

A

Osmosis

286
Q

Why is having the stomata sunken in pits beneficial to xerophytes?

A

Less air movement

287
Q

What’s closest to the stele in a root? The endodermis or pericycle?

A

Pericycle

288
Q

The transport of what are we talking about when discussing the apoplastic and symplastic routes with the casparian strip?

A

Mineral ions

289
Q

What do we always need to refine when discussing translocation?

A

Sources and sinks

290
Q

What is the main leaf tissue where 14C is incorporated into organic molecules? (Radioactive labelling as evidence for translocation)

A

Palisade mesophyll

A level Biology (26 decks)

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