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A Level OCR Biology > Unit 3 - Transport in plants > Flashcards

Unit 3 - Transport in plants Flashcards

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1
Q

Why do plants need a specialised transport system?

A
  • to move products of photosynthesis, water, and oxygen around from their place of origin
  • most plants are large and so have to transport substances huge distances from root to tip
  • SA: vol is small in plants (even though for leaves SA:vol high)
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2
Q

Define vascular system

A

a system of transport vessels in plants or animals

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3
Q

Define herbaceous

A

having a fleshy/soft stem

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4
Q

Define vascular bundle

A

The vascular system of herbaceous dicots, made up of xylem and phloem tissue

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5
Q

Define dicotyledonous

A

plants that produce two seed leaves

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6
Q

How do you tell if a plant is mono- or di- cotyledonous from its leaves?

A
  • Monocots have vessels parallel to the leave

- Dicots have vessels which branch out from a central vessel

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7
Q

What is the vascular bundle made up of?

A

Xylem and phloem tissue

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8
Q

What are the products of photosynthesis?

A

Carbohydrates, proteins, lipids, nucleic acids

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9
Q

What are the products of photosynthesis known as collectively?

A

Organic compounds

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10
Q

Why do plants need water? (5 reasons)

A
  • to maintain turgidity of cells
  • to transport nutrients around the plant
  • to create an aqueous environment for reactions to occur
  • to cool plants by evaporation
  • for photosynthesis
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11
Q

How is water transported in the plant?

A

Via the xylem

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12
Q

From the inside to the outside what tissues are present in a dicot root section?

A 
xylem
phloem
pericycle
endodermis
cortex
epidermis- root hair cells
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13
Q

In which part of the root is water taken up?

A

Root hairs

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14
Q

Which part of the root do the lateral roots grow from?

A

The pericycle

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15
Q

Why does the root have so many root hairs?

A

Increases the surface area able to take up water

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16
Q

How does water enter the root?

A

By osmosis

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17
Q

What must the water potential of the soil be relative to the root in order for water to be taken up?

A

The water potential of the soil must be less negative than the water potential of the root

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18
Q

How does the plant ensure the water potential of the root is more negative than the soil?

A

-ions from the soil are ACTIVELY pumped into the root

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19
Q

What does active pumping mean?

A

-Energy is required for the movement to occur

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20
Q

What pathway is taken by the water to go from the soil to the xylem?

A 
root hair cell
cortex
endodermis
pericycle
xylem
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21
Q

What are the 2 different routes the water can take?

A

Apoplast

Symplast

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22
Q

What is the function of the pericycle?

A

-it is meristematic and produces the lateral roots

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23
Q

What is the function of the endodermis?

A

-contains a ring of suberin which is impermeable to water

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24
Q

What is the function of the cortex?

A

-stores a large amount of starch

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25
Q

What shape is the xylem tissue?

A

-star-shaped

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26
Q

What is the apoplast pathway?

A

Water travels through the cellulose cell wall

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27
Q

What is the symplast pathway?

A

Water travels through the cytoplasm and from cell to cell via plasmodesmata

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28
Q

What is the advantage of travelling through the cellulose cell wall?

A

It offers the path of least resistance

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29
Q

What is the Casparian strip made of?

A

Suberin

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30
Q

What is the key property of the Casparian strip?

A

It is impermeable to water

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31
Q

What happens to water travelling via the apoplast pathway when it reaches the Casparian strip?

A

It cannot continue and so is diverted to the symplast pathway

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32
Q

What is the advantage of water being diverted into the symplast pathway?

A

It allows the plant to control the movement of water into the root via osmosis

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33
Q

How does water enter the xylem from the endoderm?

A
  • endodermal cells acitively pump salts into the xylem
  • this makes the water potential of the xylem more negative than the endodermal cells
  • this means water enters the xylem via osmosis
  • ensures a large water potential gradient is maintained
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34
Q

Where is the Casparian strip located?

A

In the endodermal cells

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35
Q

How do endodermal cells move ions into the xylem?

A

Active transport

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36
Q

Once water has entered the xylem how does it move?

A

As a continuous stream

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37
Q

What force is created by the bonds between water molecules?

A

Cohesion

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38
Q

What are force is created by the interaction between water molecules and the vessel holding the water?

A

Adhesion

39
Q

How is the continuous stream of water created?

A

Cohesion and adhesion

40
Q

What 3 processes are involved in the movement of water up the stem and through the leaf?

A
  • root pressure
  • capillarity
  • cohesion-tension theory
41
Q

What causes root pressure?

A
  • Endodermal cells actively pump ions into the xylem vessels
  • A water potential gradient is generated so water enters the xylem vessel by osmosis, as the water potential in the xylem is more negative than the water potential in endodermal cells
  • Pressure in the xylem increases, forcing water upwards
42
Q

What is the evidence for root pressure?

A
  • If cyanide is added to the root sap is no longer exuded
  • root pressure relies on the active pumping of ions which requires ATP
  • If there is no ATP no ions are pumped actively and no water potential gradient is created
  • therefore water cannot enter the xylem by osmosis
  • so there is no root pressure
43
Q

What causes capillarity?

A
  • The adhesive forces between xylem vessels and the water molecules
  • This pulls a water molecule up
  • due to the cohesive forces between water molecules other water molecules are pulled up with it
44
Q

Why is xylem a bundle of very narrow vessels rather than one wide vessel?

A

Greater heights of liquid are achieved in thinner tubes due to capillarity

  • with a smaller tube there is a greater contact with the vessel wall compared with the volume of water in the centre
  • so greater cohesive forces
45
Q

What is transpiration?

A

The loss of WATER VAPOUR from leaves and stems as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata

46
Q

Why is transpiration pull referred to as the Cohesion-tension theory?

A
  • The cohesive force between water molecules pulls other molecules upwards as it is a continuous stream
  • this puts pressure on the column of water
  • this inward pressure is called tension
47
Q

What effect does tension have on the column of water?

A

It produces a narrower column of water

48
Q

What happens if a xylem vessel is broken?

A

The continuous stream of water is broken so no water can be taken up

49
Q

If a xylem vessel becomes blocked can water still reach the leaves?

A

Yes

50
Q

Why can water still reach the leaves if a xylem vessel becomes blocked?

A

The pits in the xylem allows for the movement of water

51
Q

What makes up the vascular bundle, from inwards out?

A

Xylem
Cambium
Phloem
Sclerenchyma

52
Q

What is the function of the cambium?

A

It is meristematic and differentiates to form xylem and phloem as the plant grows

53
Q

What is the advantage of xylem vessels not being completely lignified?

A

It allows for the stem to flex and move slightly (e.g in the wind)

54
Q

What is the function of lignin in Xylem?

A

It strengthen the walls to resist the forces generated by water moving up the stem

55
Q

Give an example of what a plant uses glucose for

A

Aerobic respiration

56
Q

Give an example of what a plant uses lipids for

A

Cell membranes

57
Q

Give an example of what a plant uses proteins for

A

Enzymes for reactions

58
Q

Give an example of what a plant uses nucleic acids for

A

DNA replication

59
Q

What are assimilates?

A

The products of photosynthesis/respiration

60
Q

Describe how sucrose is transported from the mesophyll cells to the phloem

A
  • companion cells actively pump H+ ions out of the cell and into surrounding mesophyll cells
  • H+ diffuse back into the companion cell, down a diffusion gradient and co-transport sucrose into the companion cell
  • sucrose diffuses down a concentration gradient into sieve tube elements
61
Q

Describe how sucrose is moved along the phloem

A
  • sucrose enters the phloem which lowers the water potential of the phloem
  • water enters by osmosis
  • water also enter from the xylem
  • water entering the phloem forces the contents to flow
  • this is known as mass flow
62
Q

Describe how sucrose moves from the phloem to plant cells

A
  • sucrose and other assimilates leave the phloem by diffusion
  • the cells then use the sucrose
  • keeping the sucrose concentration of the cell lower than the xylem and maintaining a concentration gradient
63
Q

What do plant cells use sucrose for?

A
  • converting it to starch for storage

- use it for respiration

64
Q

How do guard cells differ from the lower epidermal cells?

A
  • they contain chloroplasts

- they have extra cellulose thickening on the inner side of the cell

65
Q

Outline how guard cells open

A
  • cells surrounding guard cells actively pump K+ ions into the guard cells, making their water potential more negative
  • water enters by osmosis as water potential of guard cells is more negative than surrounding cells
  • guard cells swell but because inner wall is thicker than outer wall as cell swells a pore opens up
66
Q

What is crucial about the cell walls of guard cells?

A

-the inner wall is thicker than the outer wall

67
Q

Outline how guard cells close

A
  • K+ ions diffuse out of the guard cells and back into epidermal cells
  • no longer more negative water potential in guard cells so water leaves by osmosis
  • guard cells become flaccid
68
Q

Give 4 ways plants generally conserve water

A
  • waxy cuticle
  • stomata on underside of leaf
  • closable stomata
  • roots that grow down to the water in the soil
69
Q

What is a xerophyte?

A

Plants with adaptions that enable them to survive in dry habitats or habitats where water is in short supply in the envrionment

70
Q

Give two examples of xerophytes

A

Confiers and marram grass

71
Q

In what kind of environment may water loss become a really problem for plants?

A

Hot, dry, breezy conditions

72
Q

How do sunken stomata help to adapt a plant to hot dry conditions?

A
  • reduce air movement
  • creating a microclimate of still, humid air
  • that reduces the water vapour potential gradient so reduces transpiration
73
Q

How does a reduction in the number of stomata adapt xerophytes?

A

-reduces water loss by transpiration

74
Q

What is a downside of reduced numbers of stomata?

A

-reduces gas exchange capillaries

75
Q

How does a reduction in the number of leaves adapt xerophytes?

A

-water loss is greatly reduced by minimising the amount of water loss by transpiration

76
Q

How do hairy leaves adapt xerophytes?

A
  • create a microclimate of still, humid air
  • this reduces the water vapour potential gradient
  • minimises the loss of water by transpiration from the surface of the leaf
77
Q

How do curled leaves adapt xerophytes?

A
  • confine all the stomata within a microenvironment of still, humid air
  • to reduce diffusion of water vapour from the stomata
78
Q

How are succulents adapted to their envrionment?

A
  • contain specialist parenchyma tissue in stems and roots

- water in stored in these and then used in times of drought

79
Q

How can losing leaves adapt a xerophyte?

A
  • leaves lost when water is not avaliable
  • reduces water loss by transpiration
  • trunk and branches turn green and photosynthesise
80
Q

How do xerophytes have roots adapted for their environment?

A
  • long tap roots grow deep into the ground below the surface
  • mass of widespread shallow roots with large surface area are able to absorb surface water before a rain shower evaporates
81
Q

How can some xerophytes ‘avoid the problem’ of their environments?

A
  • plants die but leave seeds to germinate and grow rapidly when it rains again
  • some survive as storage organs (e.g tubers, bulbs)
  • some plants can be completely dehydrated and recover when it rains again
82
Q

What is a hydrophyte?

A

-plants with adaptions that enable them to survive in very wet habitats or submerged at the surface of the water

83
Q

Give two examples of hydrophytes

A

Water lilies and water cress

84
Q

What are the problems faced by hydrophytes?

A
  • water logging, air spaces of plants need to be full of air not water
  • it is important that leaves float on water to enable photosynthesis
85
Q

How does having a thin/no waxy cuticle adapt hydrophytes?

A

-allows water to be lost through transpiration

86
Q

How does the waxy cuticle of hydrophytes and xerophytes differ?

A

Hydrophytes may have a very thin or no waxy cuticle whereas xerophytes have very thick waxy cuticles

87
Q

How does having many stomata that are permanently open adapt hydrophytes?

A

maximises gas exchange

88
Q

Why do hydrophytes have reduced structural support?

A
  • water supports the leaves and flowers

- so no need for strong supporting structures

89
Q

How do wide, flat leaves adapt hydrophytes?

A
  • spread across the surface of the water

- capture as much light as possible

90
Q

Why do hydrophytes have small roots?

A
  • water can diffuse directly into stem and leaf tissue

- so less need for uptake by roots

91
Q

How does have a large surface area of stems and roots under water adapt hydrophytes?

A

-maximises area for photosynthesis and for oxygen to diffuse into submerged plants

92
Q

How do air sacs adapt hydrophytes?

A

-enable leaves and/or flowers to float on the surface of the water

93
Q

What are aerenchyma?

A

Specialised parenchyma tissue which has many large air spaces

94
Q

How do aerenchyma adapt hydrophytes?

A
  • makes leaves and stems more buoyant
  • form a low resistance pathway for the movement of substances such as oxygen to tissues below water
  • this helps the plant to cope with extreme low oxygen conditions

A Level OCR Biology (42 decks)

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