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A level Biology - Unit 3 > Transport In Plants > Flashcards

Transport In Plants Flashcards

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1
Q

Why do plants require transport systems?

3 reasons

A

Metabolic demands
Size
Surface area : volume ratio

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2
Q

Why does a plant’s metabolic demand cause it to need a transport system?

A

Hormones made in one part of the plant are transported to the areas they effect.
Mineral ions absorbed by the roots are transported to all cells to make proteins and enzymes.
Parts of the plant that don’t photosynthesise need glucose and oxygen transported to them.

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3
Q

Why does a plant’s size cause it to need a transport system?

A

Substances need to be transported from the tip of the roots to the topmost leaf. Some plants grow to be enormous.

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4
Q

Why does a plant’s surface area : volume ratio cause it to need a transport system?

A

Plants have a relatively small SA:V ratio (apart (leaves alone have a large SA: V) so need a transport system as they cannot rely on diffusion alone.

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5
Q

What are dicotyledonous plants (dicots)?

A

Plants that made seeds that contain 2 cotyledons.

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6
Q

What are cotyledons?

A

Organs in a plant that act as food stores for the developing embryo plant.
They form the first leaves when the seeds germinate.

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7
Q

What characteristics do herbaceous dicots have?

A

soft tissues and relatively short life cycles.

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8
Q

What characteristics do woody dicots have?

A

hard, lignified tissues and a long life cycle.

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9
Q

What is another name for woody dicots?

A

arborescent dicots.

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10
Q

What is the vascular system of a plant?

A

A series of transport vessels running through the stem roots and leaves of a plant.

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11
Q

What is the vascular system, in herbaceous dicots, made up of?

A

Two main transport tissues;

xylem and phloem.

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12
Q

What are the xylem and phloem arranged into?

A

Vascular bundles

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13
Q

Where are the vascular bundles located in a stem?

A

around the edge. The phloem are the outermost part and xylem the innermost part.

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14
Q

Where are the vascular bundles located in a leaf?

A

In the midrib of the leaf. The xylem on top and phloem on bottom.

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15
Q

Where are the vascular bundles located in a root?

A

In the middle. Xylem is in the middle and phloem is surrounding it.

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16
Q

What is xylem?

A

Large non-living tissue in a plant.

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17
Q

What are the two main functions of the xylem?

A

To transport mineral ions and water up the plant.

To support the plant.

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18
Q

What is the direction of flow of mineral ions and water in a plant?

A

Up the plant from roots to leaves.

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19
Q

Describe the structure of xylem.

A

Long hollow xylem vessels made by joined cells end to end.
Thick-walled parenchyma around the xylem vessels.
Xylem fibres - long cells with lignified secondary walls

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20
Q

What are the 3 main ways lignin can be laid down in the walls of xylem?

A

Rings
Spirals
Solid tubes with lots of small unlignified areas.

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21
Q

What is lignin’s role in a plant?

A

Helps reinforce the xylem vessels so that they do not collapse under the transpiration pull.

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22
Q

What are the small unlignified areas called in xylem vessels?

A

Bordered pits.

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23
Q

What happens at the bordered pits?

A

Water leaves the xylem here and enters other parts of the plant.

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24
Q

What is the phloem?

A

A living tissue that transports food in the form of organic solutes from the source to the sink.

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25
Q

What is the direction of flow of the sugars in the phloem?

A

Both up and down the plant.

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26
Q

What are the main transporting vessels of the phloem?

A

The sieve tube elements.

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27
Q

Finish the sentence.

The sieve tubes are joined ……………………?

A

End to end.

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28
Q

How do sieve plates form?

A

The areas between the cells become perforated and large pores appear.

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29
Q

What is the tonoplast?

A

The vacuole membrane.

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30
Q

What is one similarity and one difference between xylem and phloem vessels?

A

Similarity
They both don’t have nuclei

Difference
Xylem is dead and Phloem is living.

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31
Q

What cells are linked to the sieve tubes by plasmodesmata?

A

Companion cells

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32
Q

What are plasmodesmata?

A

Microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells.

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33
Q

What are sclereids?

A

Cells with extremely thick walls that are supporting tissues of phloem.

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34
Q

Why is water important in the structure of plants?

3 reasons

A

1) Turgor pressure- formed from osmosis and creates a hydrostatic skeleton to support the stem and leaves.
2) Cell expansion- turgor pressure allows roots to force through the ground.
3) Evaporation- loss of water helps keep plant cool

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35
Q

Why is water important in the metabolism of plants?

2 reasons

A

1) Mineral ions and glucose are transported in aqueous solution.
2) Water is needed for photosynthesis.

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36
Q

What are the root hair cells?

A

The exchange surface in plants where water is taken into the body of the plant from the soil.

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37
Q

How are root hair cells adapted as exchange surfaces?

4 reasons

A

1) Microscopic size- penetrate easily between soil particles.
2) Large SA:V ratio- for maximum absorption
3) Thin surface layer- for quick diffusion and osmosis
4) Water potential gradient- maintained by solute concentration in root hair and soil.

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38
Q

How does water move into the roots?

A

Soil water has a low conc of dissolved minerals so a high water potential.
Cytoplasm of root has a higher conc of mineral ions and solutes so a lower water potential.
Water moves into the roots from a high to low water potential, down a water potential gradient by osmosis.

39
Q

How does water move across the root?

A

Either by the apoplast route or the symplast route.

40
Q

Explain how the water moves through the symplast pathway across the root.

A

Water moves continuously through the symplast (the continuous cytoplasm of the cells connected by the plasmodesmata) by osmosis.

41
Q

Explain how the water moves through the apoplast pathway across the root.

A

Water moves through the apoplast (the cell walls and the intercellular spaces).
As water moves into the xylem, more water is pulled into the apoplast behind them by cohesion.
A tension is created that allows a continuous flow of water through the cell walls.

42
Q

How does water move into the xylem?

A

Moves by the apoplast and symplast pathway until it reaches the endodermis.
Then water in the apoplast (cell walls) is forced into the cytoplasm of the cells into the symplast route due to the casparian strip.
Water potential of xylem is lower than cytoplasm of cells so water moves into xylem by osmosis.

43
Q

What is the Casparian strip?

A

A band of waxy material called suberin that runs around each of the endodermal cells forming a waterproof layer.

44
Q

What is the endodermis?

A

The layer of cells surrounding the vascular tissues of the roots.

45
Q

How is root pressure created?

A

The active pumping of mineral ions into the xylem to produce water movement by osmosis.

46
Q

How is cyanide evidence for the role of active transport in root pressure?

A

If cyanide is applied to root cells so there is no energy supply, root pressure disappears.
Cyanide prevents the production of ATP.

47
Q

How is temperature evidence for the role of active transport in root pressure?

A

Root pressure increases with rise in temperature and decreases with fall in temperature.
This shows chemical reactions are involved.

48
Q

How are oxygen/respiratory substrates evidence for the role of active transport in root pressure?

A

When oxygen levels fall then root pressure falls.

49
Q

How is guttation evidence for the role of active transport in root pressure?

A

Xylem sap is forced out of the ends of leaves in some conditions, like overnight when transpiration is low.

50
Q

What is the process called when water is lost by evaporation from the leaves of a plant?

A

Transpiration

51
Q

What is transpiration a result of?

A

An inevitable result of gaseous exchange in plants.

52
Q

Explain the tanspiration stream.

A

Water evaporates from mesophyll cells into air spaces and out of the leaf by stomata by diffusion.
Loss of water from mesophyll lowers water potential and water moves in from adjacent cell by osmosis.
Water moves out of the xylem into the leaf cells by osmosis.
Water rises up the xylem by adhesion and cohesion.
Tension builds and pulls water up from soil into roots.

53
Q

What is cohesion?

A

When the water molecules form hydrogen bonds with each other and stick together.

54
Q

What is adhesion?

A

When the water molecules form hydrogen bonds with the carbohydrates in the cell walls of narrow xylem vessels.

55
Q

What is the transpirational pull?

A

When water is pulled up the xylem in a continuous stream due to the effects of cohesion and adhesion.
AKA the cohesion-tension theory.

56
Q

What is evidence for the cohesion-tension theory?

2 points

A

1) Changes in diameter of trees- smaller when tension in xylem is higher
2) When xylem vessels are broken air pockets form in the stem

57
Q

What are the 5 main factors affecting transpiration?

A

1) Light
2) Humidity
3) Temperature
4) Air movement
5) Soil-water availability

58
Q

How does light affect transpiration?

A

More light means more photosynthesis.
So stomata open more for gas exchange.
So increased light intensity means increased transpiration.

59
Q

How does humidity affect transpiration?

A

High relative humidity will lower transpiration rate.

Dry air will increase transpiration rate.

60
Q

How does temperature affect transpiration?

A

Increased temp increases kinetic energy of water molecules so increased transpiration.
Increased temp increases conc of water vapour that external air can hold brfore it becomes saturated.

61
Q

How does air movement affect transpiration?

A

Air movement or wind will increase transpiration rate.

62
Q

How does soil water availability affect transpiration?

A

Very dry soil means decreased transpiration.

More wet soil means increased transpiration.

63
Q

What is translocation?

A

The process where plants transport organic compounds in the phloem from source to sink.

64
Q

What are the products of photosynthesis that get transported called?

A

Assimilates

65
Q

What are the main sources of assimilates in a plant?

A

Green leaves and stems
Tubers and tap roots- storage organs
food stores in seeds when they germinate

66
Q

What are the main sinks in a plant?

A

roots that are growing and actively absorbing mineral ions
meristems that are actively dividing
parts of the plant that are laying down food stores

67
Q

What is phloem loading?

A

The movement of the assimilates from the source into the phloem.

68
Q

What are the two main ways in which phloem loading occurs?

A

The symplast route and the apoplast route.

69
Q

Describe how sucrose is loaded into the phloem via the symplast route.

A

Moves through the cytoplasm of the mesophyll cells.

Moves into the sieve tubes through the plasmodesmata by diffusion.

70
Q

How is sucrose moved through the phloem?

A

By mass flow.

when water moves in by osmosis, a pressure builds that moves the sucrose.

71
Q

Describe how sucrose is loaded into the phloem via the apoplast route.

A

Sucrose travels through the cell walls and inter-cellular spaces.
Sucrose them diffuses into the sieve elements and companion cells.

72
Q

How is sucrose moved in the companion cells?

A

H+ ions actively pumped out of companion cells using ATP.
H+ ions diffuse back into companion cells via a co-transporter protein, carrying sucrose with them.
Sucrose flows into sieve elements by plasmodesmata links.

73
Q

What two adaptations of the companion cells help with phloem loading?

A

Infoldings in the cell membrane to give increased SA

Many mitochondria for ATP supply.

74
Q

How does pressure allow sucrose to go from source to sink?

A

Solute accumulation leads to turgor pressure that forces sap to regions of lower pressure (sinks).

75
Q

How is phloem unloaded into the cells that need it?

A

Sucrose diffuses from the phloem into the surrounding cells.

76
Q

How does water leave the phloem?

A

When sucrose leaves phloem, there is a rise in water potential in phloem. So water leaves phloem by osmosis down a conc gradient.

77
Q

What is the evidence for translocation?

4 points

A

1) Microscopy allows us to see adaptations of companion cells
2) If mitochondria of companion cells are poisoned, translocation stops
3) Flow of sugars is x10000 faster with active transport than diffusion alone
4) Pressure in phloem can be shown by using aphids.

78
Q

What are xerophytes?

A

Plants that have adapted to living in very dry conditions/very icy conditions by conserving water.

79
Q

Give examples of xerophytes.

A

Marram grass

Cacti

80
Q

Xerophytes use a range of ways of conserving water. What are they? (10 ways)

A 
Thick waxy cuticle
Sunken stomata
Reduced numbers of stomata
Reduced leaves
Hairy leaves 
Curled leaves
Succulents
Leaf loss
Root adaptations
Avoiding the problems
81
Q

How does a thick waxy cuticle help conserve water?

A

Minimise water loss through the cuticle

82
Q

How do sunken stomata help conserve water?

A

Reduces air movement near the stomata.

83
Q

How does a reduced number of stomata help conserve water?

A

Reduce water loss by transpiration.

84
Q

How does reduced leaves help conserve water?

A

Reduced loss by transpiration.

85
Q

How do hairy leaves help conserve water?

A

Create still humid air around the leaf so minimise water loss by transpiration.

86
Q

How do curled leaves help conserve water?

A

Confines all the stomata in still humid air to reduce water loss by transpiration.

87
Q

How do succulent plants conserve water?

A

Store water in specialised parenchyma tissue in stems and roots. Then is used in times of drought.

88
Q

How does the loss of leaves help conserve water?

A

Loss of leaves prevents water loss by transpiration.

89
Q

How do root adaptations help conserve water?

A

Helps get as much water from the soil as possible.

90
Q

How do plants avoid the problems altogether in order to conserve water/

A

Some die off and leave their seeds to germinate for the next season.
Some survive as tubers or bulbs (potatoes, onions)

91
Q

What are hydrophytes?

A

Plants that live in water/submerged in water or are on the surface of water.

92
Q

Give examples of hydrophytes.

A

Water lillies
Seaweed
Water cress

93
Q

What are the adaptations of hydrophytes? (8 points)

A 
Thin or no waxy cuticle
Always open stomata on upper surfaces
Reduced structure of the plant
Wide, flat leaves
Small roots
Large SA of stems and roots
Air sacs
Aerenchyma
94
Q

Why do hydrophytes have the adaptations they do?

A

There is always a supply of water so there is no need to conserve it. Loss of water by transpiration is not an issue.

A level Biology - Unit 3 (10 decks)

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