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Biology > Module 3: Exchange And Transport 2 > Flashcards

Module 3: Exchange And Transport 2 Flashcards

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1
Q

Why do plants need a transport system??

A

Plants need to exchange CO2 in and O2 out

Water and minerals in

Waste products out

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2
Q

Why is there no need for specialised gas exchange surfaces in plants??

A

Leaves are adapted to allow gas exchange by diffusion

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3
Q

What are the 2 vascular tissues in a plant?

A

Xylem and phloem

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4
Q

Xylem

A

Upwards transport of water and mineral ions

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5
Q

Phloem

A

Bidirectional transport of organic food molecules

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6
Q

Vascular tissue structures of stems and roots

A

Share similar vascular tissue structures

But arrangement and position differs

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7
Q

Root structure: epidermis

A

Single layer of cells

Often have long extensions called root hairs

Increase surface area

A single plant may have 10^10 root hairs

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8
Q

Root structure: cortex

A

Thick layer of packaging cells often containing stored starch

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9
Q

Root structure: endodermis

A

Single layer of tightly packed cells containing a waterproof layer called the casparian strip

Prevents movement of water between cells

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10
Q

Root structure: pericycle

A

Layer of undifferentiated menstematic (growing) cells

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11
Q

Root structure: vascular tissue

A

Contains phloem and xylem cells

Continuous with stem vascular bundles

Arrangement is different

Xylem usually forms a star shape with 2-6 arms

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12
Q

Stem structure: epidermis

A

One cell thick

In young plants the epidermis cells may secrete a waterproof cuticle

In older plants, the epidermis may be absent replaced by bark

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13
Q

Stem structure: cortex

A

Composed of various ‘packaging’ cells

Give young plants strength and flexibility

Source of plant fibres such as sisol and hemp

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14
Q

Stem structure: vascular tissue

A

Contains phloem and xylem tissue

Grows out from the combium

In young plants the vascular tissue is arranged in vascular bundles

Phloem on the outside and xylem on the inside

In older plants the xylem bundles fuse together to form the bulk of the stem

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15
Q

Stem structure: parenohyma

A

The central region of a stem

Used for food storage in young plants

May be absent in older plants

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16
Q

Stem structure: cambium

A

Unspecialised meristem that can divide to form vascular tissues

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17
Q

Vascular tissue in the leaf: parenchyma

A

Relatively unspecialised cells

Make up the bulk of soft internal tissues of leaves, stem, roots and fruits

Thin flexible cell walls

Large water-filled vacuole

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18
Q

Vascular tissue in the leaf: Collenchyma

A

Living at maturity, never lignified

Support tissue in growing plant parts

Cell walls strengthened by cellulose and pectin but distortable when stretched

Found in strands beneath the epidermis

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19
Q

Vascular tissue in the leaf: schlerenchyma

A

Thick walled dead cells, heavily lignified

Fibres frequently grouped in bundles:

  • elongated cells, often with pointed ends
  • associated with vascular tissue
  • high load-bearing capacity and easily processed fibres
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20
Q

What is transported in xylem vessels

A

Water

Soluble mineral ions

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21
Q

What is a tissue

A

A group of cells working together to perform a particular function

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22
Q

What is the dual function of xylem tissue?

A

Has the dual functions of support and transport

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23
Q

Xylem as a tissue - what does it do?

A

Transport water and other minerals from the soil up to the roots and stem of a plant

Contain long elongated cells called Tracheids and shorter and wider cells called vessel elements

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24
Q

What are xylem vessels made up of?

A

Vessels are made up of elongated vessel elements arranged end to end

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25
Q

How does the xylem structure form?

A

Each element began as a normal plant cell

Substance called lignin is laid down

As lignin builds up around the cell, the cell dies which leaves an empty space inside

The end walls of neighbouring vessel elements would break down completely to form a continuous tube

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26
Q

What is lignin??

A

A hard strong substance which is impermeable to water

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27
Q

What are pits in the xylem??

A

In the area where plasmodesmata is present, no lignin would be laid down

These non-lignified areas can be seen as gaps in the walls of xylem vessels

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28
Q

Water movement in a plant

A

In the root, water crosses the cortex, endodermis and pericycle and moves into the xylem through the pits in their walls

Will then move towards the leaves and up the vessels

Water and dissolved minerals only move in one direction through the plants

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29
Q

Similarities between tracheids and xylem vessel elements

A

Both conduct water

Both are dead

Both develop lignin

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30
Q

What are tracheids

A

Spindle shapes cells with pits through which water flows from cell to cell

They have tapered ends and a function in support as well as water transport

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31
Q

What are pits

A

Thinner regions where water can pass through from cell to cell

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32
Q

What does TS mean

A

Transverse section

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33
Q

What does LS mean

A

Longitudinal section

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34
Q

Why is xylem a tissue?

A

Because it contains a variety of specialised, water conducting cells known as tracheory elements

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35
Q

What is the role of parenchyma cells

A

Fibres lend support

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36
Q

What is the role of fibres in the xylem??

A

Lend support to tissues

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37
Q

What is the difference between a tracheid and a xylem vessel??

A

Tracheids are thinner than xylem vessels

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38
Q

What is the purpose of lignin in xylem vessel cell walls?

A

Plays a crucial part in conducting water in plant stems

Gives support

Prevents collapse of xylem vessel

Prevents escape of water

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39
Q

What is the effect of the lignin on the xylem cells?

A

Prevents water loss from xylem cells as it is impermeable

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40
Q

What are the 4 basic ways that molecules can be transferred??

A

Diffusion

Osmosis

Active transport

Bulk transport

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41
Q

What is water potential??

A

Water potential is a measure of the ability of water molecules to move freely in solution

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42
Q

How does water move?

A

Water moves from a solution with high water potential to one of lower water potential

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43
Q

How is water potential decreased?

A

Decreased by the presence of solutes

44
Q

How is water transported from the root hair to the xylem?

A

Water is taken up by the root hair and crosses the cortex

Then it enters the xylem in the centre of the root

45
Q

Why does water move from the root hair to the xylem??

A

There is a lower water potential in the xylem vessels than there is in the root hairs

Water moves down the water potential gradient

46
Q

Does soil have a high or low water potential??

A

High

47
Q

Does the root hair cell have a high or low water potential??

A

Low

48
Q

The apoplast pathway

A

The cells of a cortex are surrounded by cell walls made of several layers of cellulose fibres criss crossing one another

Water can soak into these walls

Water can then deep across the root cortex from cell wall to cell wall until it reaches the xylem

49
Q

The symplast pathway

A

Water moves into the cytoplasm of a cortical cell and then into adjacent cells through their interconnecting plasmodesmata

The continuum of cytoplasm within a plant tissue requires only the crossing of a plasma membrane

50
Q

The vascular pathway

A

Similar to the symplast pathway except fluid can move into and out of the vacuoles

51
Q

What are the three pathways?

A

The apoplast pathway

The symplast pathway

The vascular pathway

52
Q

What is a casparian strip??

A

A bond which forms an impenetrable barrier to water in cell walls

53
Q

At the stele how does water cross the endodermis

A

Through the cytoplasm of cells

54
Q

What happens as the endodermis cells get older??

A

The Suberin deposits become more extensive

55
Q

What happens inside the stele

A

Once across the endodermis, water continues to move down the water potential gradient across the pericycle and towards the xylem vessels

56
Q

What is transpiration?

A

Loss of water by evaporation from the aerial parts of the plant

57
Q

In leaves where does water evaporate from?

A

Cell walls

58
Q

In leaves how does water evaporate?

A

The vapour accumulates in the air spaces and then diffuse out through open stomata

59
Q

What happens to the leaf cells as water evaporates??

A

The leaf cells are cooled

60
Q

Transpiration process

A

Water evaporates from the leaf cells

Water is drawn by osmosis from the xylem vessels of the leaf veins to replace the lost water

As a consequence water is drawn up through the plant

61
Q

What 3 processes does Transpiration involve??

A

1) osmosis from the xylem to the mesophyll cells
2) evaporation from the surface of the mesophyll cells into intercellular spaces
3) diffusion of water vapour from the intercellular spaces out through the stomata

62
Q

What is cohesion?

A

Attraction of molecules for other molecules of the same kind

63
Q

Why do water molecules have strong cohesive forces??

A

Because of the ability to form hydrogen bonds with one another

64
Q

What is Adhesion

A

Attraction of molecules of one kind, to molecules of a different kind

65
Q

Why is the attraction of molecules quite strong for water

A

Because other molecules bear positive or negative charges

66
Q

In what ways is the movement of water useful to the plant??

A

Water is required in the leaves for photosynthesis

Water is needed to enable cells to grow and elongate

Water keeps cells turgid so that stomata will open

The flow of the water passively carries minerals up the plant

Evaporation of water keeps the plants cool

67
Q

What is the transpiration pull

A

As water leaves the xylem in the leaf it must be replaced from below

Water moves up the xylem from the roots to replace the lost water

This is because it is under tension

68
Q

How is water moved up the xylem from the roots to the leaves?

A

Low pressure at the top, water is under tension

Adhesion of water molecules to the xylem

Water moves up through the xylem by mass flow

69
Q

Are the cells living or dead in a xylem??

A

Dead

70
Q

Are phloem sieve tube elements living or dead??

A

Living

71
Q

Do xylem vessels have bordered pits?

A

Yes

72
Q

Do phloem sieve tube elements have bordered pits??

A

No

73
Q

Is lignin present or absent in a xylem vessel

A

Present

74
Q

Is lignin present or absent in phloem sieve tube elements??

A

Absent

75
Q

What does the xylem vessel transport??

A

Water

Mineral ions

76
Q

What does the phloem sieve tube elements transport??

A

Organic solutes such as sugars and amino acids

77
Q

What direction is transport in a xylem vessel??

A

One way

78
Q

What direction of transport is the phloem sieve tube element??

A

Either direction

79
Q

What evidence the scientist might expect to see in companion cells, using an electron microscope??

A

Many mitochondria

Plasmodesmata between companion cell and sieve tube

Many ribosomes

80
Q

What are the 5 environmental factors that affect the rate of transpiration

A

Light

Temperature

Humidity

Wind

Soil water

81
Q

Affect of light on rate of transpiration

A

Plants transpire more rapidly in the light than in the dark

This is because light stimulates the opening of the stomata

82
Q

What is the affect of temperature on the rate of transpiration??

A

Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises

83
Q

What is the affect of humidity on the rate of transpiration??

A

The rate of diffusion of any substance increase as the difference in concentration of the substances in two regions increases

When the surrounding air is dry diffusion of the water out of the leaf goes on more rapidly

84
Q

What is the affect of wind on transpiration??

A

When there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration

85
Q

What occurs when a breeze is present

A

The humid air is carried away and replaced by drier air

86
Q

Effect of soil water on rate of transpiration

A

When absorption of water cannot equal the transpiration rate, the stomata close which reduces transpiration rate.

Therefore it is important that there is water present in the soil

87
Q

Describe two xeromorphic features

A

Hairs on the lower surface trap water vapour and reduce water potential gradient

Thick waxy cuticle reduces evaporation of water

88
Q

What is the cohesion tension theory??

A

As leaves transpire, the continual removal of water from the xylem vessels generates a pulling force that allows for water to be drawn through the root tissues and into the xylem

89
Q

Three possible routes for water to get into the xylem

A

The apoplast pathway

The symplast pathway

The vacuolar pathway

90
Q

What happens at the stele

A

As the endodermal cells get older, the Suberin deposits become more extensive, except in certain passage cells

91
Q

What is a xerophyte??

A

A plant that is adapted to very dry conditions

92
Q

Examples of xerophytes

A

Succulents
Bromeliads
Cacti

93
Q

How do cacti reduce water loss in their leaves

A

Their leaves are reduced to spines which reduces the surface area of the leaf in water loss

Thick, waxy cuticle covers the plants surfaces which reduces transpiration

94
Q

How do cacti reduce water loss in their stem

A

Tick and fleshy with numerous water storage cells to retain water absorbed by roots

95
Q

How do cacti reduce water loss in their root

A

Shallow, spreading root system to quickly absorb any water from rainfall

96
Q

What is the effect of a round and compact shape

A

Reduces surface area for water loss

97
Q

What is the effect of a shiney surface

A

Reflect heat and light

98
Q

What is the effect of stomata in reducing water loss

A

Closed during the day, reduces water loss

Open at night, absorb CO2, used for photosynthesis during the day

99
Q

What is the effect of rolling up leaves??

A

Protects the lower epidermis from the outside helps to trap air within the leaf

As this region becomes saturated with water, the water vapour potential is reduced

100
Q

What is the effect of hairy leaves??

A

Trap moist air next to leaf surface

Reduces water potential gradient between outside and inside the leaf

Less water loss by transpiration

101
Q

What is the effect of stomata in pits??

A

Traps water vapour in pits reducing water vapour potential gradients

102
Q

What are hydrophytes??

A

Plants which grow submerged or partially submerged in water

103
Q

Adaptations of a hydrophytes

A

Extensive system of air spaces in stems and leaves

Gases diffuse quickly

Provide buoyancy to keep the plants close to the light and are a resource of O2 and CO2

104
Q

Which vessels in the vascular bundle will water be moving in?

A

The xylem

105
Q

What is the purpose of the reservoir of water

A

Reset the apparatus so that multiple readings can be taken

106
Q

Other than transpiration, what may a very small percentage of water be used for in the plant?

A

Photosynthesis

Maintaining all turgour

107
Q

What precautions must be taken in setting up a potometer to ensure your results are valid?

A

Set up the apparatus under water to eliminate air bubbles

Avoid wetting leaves, ensure leaves are dry before taking readings

Consistent external environment conditions

Biology (7 decks)

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