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Transport In Plants Flashcards

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1
Q

Why do plants need a transport system?

A

To move water and minerals from the roots up to the leaves

To move sugars from the leaves to the rest of the plant

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2
Q

What does the transport system in plants consist of?

A

Specialised vascular tissue - xylem and phloem tissue

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3
Q

What is a dicotyledonous plant?

A

A plant that has two seed leaves and a branching pattern of veins in the leaf

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4
Q

Describe the distribution of vascular tissue in dicotyledonous plants?

A

The xylem and phloem are found together in vascular bundles which may also contain other types of tissue that give the bundle strength and the plant support

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5
Q

What is the typical arrangement of xylem and phloem in a young root?

A

Vascular bundle is found at the centre of a young root

A central core of xylem often in the shape of an X

The phloem is found between the arms of the X

Around the vascular bundle are cells called the endodermis

Inside the endodermis is a layer of meristem cells called the pericycle

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6
Q

What does the arrangement of the vascular bundle in the young root provide?

A

Strength to withstand the pulling forces to which roots are exposed

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7
Q

What is the typical arrangement of xylem and phloem in the stem?

A

Found near the outer edge of the stem

In non-woody plants the bundles are separate and in woody plants they become a continuous ring as it gets older

The xylem is found towards the inside of each bundle and the phloem towards the outside

In between each is a layer of cambium - a layer of meristem cells that divide to produce new xylem and phloem

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8
Q

What does the arrangement of vascular bundles in a stem provide?

A

Strength and flexibility to withstand bending forces to which stems and branches are exposed

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9
Q

How are xylem and phloem arranged in a leaf?

A

They form the midrib and veins of a leaf

The veins may get smaller as they spread away from the midrib (dicotyledonous plants)

Within each vein, the xylem is located on top of the phloem

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10
Q

How can you examine the distribution of vascular tissue?

A

By staining the tissue

The stem takes up water/stain by transpiration

It can then be cut longitudinally or transversely and examined with a hand lens or microscope

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11
Q

What is xylem?

A

A tissue used to transport water and mineral ions from the roots up to the leaves and other parts of the plants

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12
Q

What does xylem tissue consist of?

A

Vessels to carry water and dissolved mineral ions

Fibres to help support the plant

parenchyma cells which act as packing tissue to separate and support the vessels

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13
Q

How are xylem vessels formed?

A

Lignin impregnates the walls of the cells in developing xylem vessels, making the walls waterproof and killing the cells

The end walls and contents of the cells decay, leaving a long column of dead cells with no contents = xylem vessel

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14
Q

What does lignin do to xylem vessels?

A

Strengthens them and prevents them from collapsing, keeping them open at times when water may be in short supply

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15
Q

Why does lignin form patterns in the cell wall?

A

To prevent the vessel from being too rigid and allowing flexibility of the stem or branch

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16
Q

Why is lignification not complete in some places?

A

To form bordered pits allowing water to leave one vessel and pass into the next vessel (lateral movement) or leave the xylem and pass into living parts of the plant

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17
Q

How are xylem vessels adapted to its function?

A

They are made from dead cells aligned to form a continuous column

Narrow tubes so the water column doesn’t break easily allowing effective capillary action

Bordered pits

Lignin

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18
Q

What characteristics of xylem prevents flow of water being hindered?

A

No cross-walls

No cell contents, nucleus or cytoplasm

Lignin thickening prevents collapsion

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19
Q

What is the basic structure and function of phloem?

A

It is a tissue used to transport assimilates around the plant

Phloem tissue consists of sieve tubes made up of sieve tube elements and companion cells

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20
Q

What are sieve tube elements?

A

They make up the tubes in phloem tissue that carry sap up and down the plant

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21
Q

What is sap?

A

Sucrose dissolved in water in phloem

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22
Q

What is the structure of a sieve tube element?

A

Lined up to form sieve tubes

Contain no nucleus and little cytoplasm

Sieve plates at their ends allowing movement of sap from one element to the next

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23
Q

What are companion cells?

A

Small cells in between the sieve tubes that help to load sucrose into sieve tubes

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24
Q

What is the structure of a companion cell?

A

Large nucleus

Dense cytoplasm

Numerous mitochondria to produce ATP needed for active processes

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25
Q

What are plasmodesmata?

A

Cell junctions at which the cytoplasm of one cell is connected to that of another through a gap in their cell walls - cytoplasmic bridges

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26
Q

What are the three pathways taken by water?

A

Apoplast pathway

Symplast pathway

Vacuolar pathway

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27
Q

What happens in the apoplast pathway?

A

Water passes through the spaces in the cell walls and between the cells

It doesn’t pass through any plasma membranes into the cells meaning the water moves by mass flow rather than osmosis

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28
Q

What happens in the symplast pathway?

A

Water enters cytoplasm through the plasma membrane then passes through the plasmodesmata from one cell to the next

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29
Q

What happens in the vacuolar pathway?

A

Like the symplast pathway but water is not confined to the cytoplasm of the cells, it is able to enter and pass through vacuoles

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30
Q

What is water potential?

A

A measure of the tendency of water molecules to move from one place to another

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31
Q

Why do the mineral ions and sugars in a plant cell cytoplasm reduce the water potential?

A

Because there are fewer free water molecules available than in pure water

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32
Q

What is pressure potential?

A

The pressure exerted on the cell wall from water once the it is turgid

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33
Q

What is transpiration?

A

The loss of water vapour from the aerial parts of a plant mostly though the stomata of the leaves

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34
Q

What is water loss limited by?

A

The waxy cuticle

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35
Q

What is the typical pathway taken by most water leaving the leaf?

A

Water enters leaf through xylem and moves by osmosis into the spongy mesophyll cell

Water evaporates from the cell walls of the spongy mesophyll

Water vapour moves by diffusion out of the leaf through open stomata

36
Q

What does the diffusion of water vapour out of the leaf rely on?

A

The water vapour potential gradient - a difference in the concentration of water vapour molecules in the leaf compared with outside

37
Q

What is a transpiration stream?

A

The movement of water from the soil through the plant to the air surrounding the leaves

38
Q

What are the consequences of a transpiration stream?

A

Transports useful mineral ions up the plant

Maintains cell turgidity

Supplies water for growth, cell elongation and photosynthesis

Supplies water that keeps the plant cool as it evaporates

39
Q

What environmental factors affect transpiration rate?

A

Light intensity

Temperature

Humidity

Wind

Water availability

40
Q

How does light intensity affect transpiration rate?

A

In light the stomata open to allow gaseous exchange

light intensity = increased transpiration rate

41
Q

How does temperature affect transpiration rate?

A

Higher temperature = increased transpiration rate

Higher temperature increases evaporation from the cell surfaces so that the water vapour potential in the leaf rises

Higher temp increases diffusion through stomata because water molecules have more kinetic energy

Higher temp decreases water vapour potential in air allowing more rapid diffusion out of leaf

42
Q

How does humidity effect transpiration rate?

A

Higher humidity = decreased transpiration rate

Smaller water vapour potential gradient between air spaces in leaf and outside air

43
Q

How does wind affect transpiration rate?

A

Increased wind = increased transpiration rate

Air moving out the leaf will carry away water vapour that has just diffused out of leaf maintaining a high water vapour potential gradient

44
Q

How does water availability affect transpiration rate?

A

High water availability = increased transpiration rate

Little water in soil means plant can’t replace lost water, insufficient water in soil causes the stomata to close and the leaves will wilt

45
Q

What is a potometer?

A

A device that can measure the rate of water uptake as a leafy stem transpires

46
Q

What is the main driving force for transpiration streams?

A

The water potential gradient between the soil and the air in the leaf air spaces

47
Q

Where does water go when it enters the root hair cells?

A

Moves across the root cortex down a water potential gradient to the endodermis of the vascular bundle

48
Q

Why must water enter the symplast pathway once it gets to the endodermis when travelling through the apoplast pathway?

A

Because the apoplast pathway is blocked by the Casparian strip between the cortex and medulla

49
Q

What is the endodermis?

A

A layer of cells surrounding the medulla and xylem

Also known as the starch sheath as it contains granules of starch

50
Q

What is granules of starch a sign of?

A

That energy is being used

51
Q

What does the Casparian strip ensure?

A

That water and dissolved mineral ions have to pass into the cell cytoplasm and through plasma membranes

52
Q

What is the advantage of transporter proteins making the water potential of the medulla and xylem more negative?

A

Water will move from the cortex cells into the medulla and xylem by osmosis

53
Q

What is mass flow?

A

The movement of water and mineral ions up though the xylem in the same direction

54
Q

What processes help to move water up the stem?

A

Root pressure

Transpiration pull

Capillary action

55
Q

What role does root pressure have on movement of water up the stem?

A

Pressure in the root medulla builds up due to water being drawn up into the medulla by osmosis and forces water into the xylem

Root pressure can only push water a few metres up a stem

56
Q

What is transpiration pull?

A

As molecules of water are lost at the top of the column, the whole column is pulled up as one chain creating tension in the column of water which is why the xylem vessels must be lignified

57
Q

What is the cohesion-tension theory?

A

The mechanism involving cohesion between water molecules and tension in the column of water

58
Q

What does the cohesion-tension theory rely on?

A

The plant maintaining an unbroken column of water all the way up the xylem

59
Q

What is capillary action?

A

The same forces that hold together water molecules attracting them to the sides of the xylem vessel

60
Q

What is the advantage of the xylem vessels being narrow in regards to capillary action?

A

The forces of attraction can pull water up the sides of the vessel

61
Q

What’s the difference between adhesion and cohesion?

A

Adhesion is the attraction between water molecules and the walls of the xylem vessel

Cohesion is the attraction between water molecules caused by hydrogen bonds

62
Q

What is the sub-stomata air space?

A

The cells lining the cavity immediately above the guard cells where water evaporates from

63
Q

What effect does water leaving the leaf have on guard cells?

A

The water potential in the guard cells is lowered causing water to enter them by osmosis from neighbouring cells

In turn water is drawn from the xylem into the leaf by osmosis or from the apoplast pathway

64
Q

What must terrestrial plants be adapted to?

A

To reduce loss of water

To replace water that is lost

65
Q

How can terrestrial plants reduce water losses?

A

Structural and behavioural adaptations such as:

A waxy cuticle reducing water loss due to evaporation through epidermis

Stomata on the underside of leaves to reduce evaporation

Stomata are closed at night

Deciduous plants lose leaves in winter

66
Q

What is a xerophyte?

A

A plant adapted to living in dry conditions

67
Q

What is an example of a xerophyte?

A

Marram grass

68
Q

How is marram grass adapted to be a xerophyte?

A

Leaf is rolled longitudinally so air is trapped inside - air becomes humid reducing water loss

Think waxy cuticle on outer side of rolled leaf to reduce evaporation

Stomata on the inner side - protecting them - and in pits which is folded and covered by hairs reducing air movement

Dense spongey mesophyll, less surface area for evaporation

69
Q

How are cacti adapted to overcome dry conditions?

A

They are succulents - they store water in their stems which become swollen

Leaves reduced to spines reducing surface area - less water lost by transpiration

Stem is green for photosynthesis

Roots are widespread taking advantage of any rain

70
Q

What are examples of other xerophytic features?

A

Closing stomata when water availability is low reducing water loss and need to take up water

Some have low water potential in leaf cells achieve by a high salt concentration in them reducing the evaporation of water as the water potential gradient between cells and leaf air spaces is reduced

Long tap root that can reach water deep underground

71
Q

What are hydrophytes?

A

Plants that are adapted to living in water

72
Q

What issues are hydrophytes faced with?

A

Getting oxygen to their submerged tissues and keeping afloat to keep their leaves in the sunlight for photosynthesis

73
Q

What is an example of a hydrophyte?

A

Water lilies

74
Q

How are water lilies adapted to living in water?

A

Many large air spaces in leaf keeping them afloat so they are in air and can absorb sunlight

Stomata on upper epidermis exposing them to the air allowing gaseous exchange

Leaf stem has large air spaces helping with buoyancy and allowing oxygen to diffuse quickly to the roots for aerobic respiration

75
Q

How can plants transpire into water or air with a high humidity?

A

They contain hydathodes

76
Q

What is a hydathode?

A

Structures at the tips of leaves which can release water droplets which may evaporate from the leaf surface

77
Q

What is translocation?

A

The movement of assimilates throughout the plant that occurs in the phloem

78
Q

What are assimilates?

A

Substances made by the plant using substances absorbed from the environment

79
Q

What is a source and a sink?

A

A source is a part of the plant that loads assimilates into the phloem

A sink is a part of the plant that removes assimilates from the phloem sieve tubes

80
Q

How is sucrose loaded into the sieve tube?

A

By active loading involving the use of energy from ATP in the companion cells

81
Q

How does active loading work?

A

The energy from ATP is used to actively transport hydrogen ions out of the companion cells

This increases their concentration outside the cells and decreases it inside creating a concentration gradient

The ions diffuse back into the companion cells through cotransporter proteins (with sucrose molecules)

As the sucrose concentration in the companion cells increase it can diffuse through the plasmodesmata into the sieve tube

82
Q

Describe the movement of sap in the phloem

A

Sucrose actively loaded into the sieve tube element reducing the water potential

Water follows by osmosis increases the hydrostatic pressure in the sieve tube element

Sap moves from higher hydrostatic pressure at source to lower hydrostatic pressure as sink

Sucrose removed by surrounding cells increasing water potential in sieve tube

Water moves out of sieve tube reducing hydrostatic pressure

83
Q

What are some examples of a source in a plant?

A

Roots - starch can be converted to sucrose and moved

Leaves - sugars made during photosynthesis converted to sucrose and transported to other areas of the plants that may be growing or for storage

84
Q

What could the sucrose removed at the sink be used for?

A

Respiration

Growth in a meristem

Converted to starch for storage in a root

85
Q

Describe the possible directions of sap through the phloem

A

Sap can flow is either direction as long as its from higher pressure to lower pressure depending upon where sucrose is being produced and where it’s needed

Sap can flow in opposite directions in different sieve tubes at the same time

86
Q

What is mass flow?

A

Sap in one tube all moving in the same direction

Biology (7 decks)

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