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A Level Biology OCR > 3.3 Plant Transport > Flashcards

3.3 Plant Transport Flashcards

1
Q

Why do plants need a transport system?

A

Because of their large size, high metabolic rate, and SA:V

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2
Q

What is the function of xylem tissues?

A

To transport water and mineral ions up the plant, and provide structural support to stems etc.

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3
Q

What is the function of phloem tissue?

A

To transport sugars/ solutes in solution up and down the plant from source to sink

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4
Q

Which plant vascular tissue is made from dead cells and which alive?

A

Xylem- Dead

Phloem- Living

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5
Q

Why do xylem cells have no end walls?

A

To make uninterrupted tube for water flow in a column

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6
Q

Xylem cells are supported by _____.

A

Lignin

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7
Q

How is lignin deposited on xylem vessel walls, and why?

A

In spirals or rings to allow flexibility and growth space

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8
Q

How does water move out of xylem vessels?

A

Through pits with no lignin

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9
Q

What are parenchyma?

A

Living cells which act as packing tissue between xylem vessels to support and separate them

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10
Q

What is sap made of?

A

Sucrose dissolved in water

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11
Q

What does phloem tissue consist of?

A

Sieve tube elements and companion cells

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12
Q

What are sieve plates?

A

End sieve tube element walls with many holes to allow assimilates through

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13
Q

Why do sieve tube elements have no nucleus, little cytoplasm and organelles?

A

To allow space for mass flow of sap to go through them

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14
Q

Why does a plant root need a lot of support?

A

To push through the soil and to anchor the plant

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15
Q

How are vascular tissues arranged in a root?

A

Xylem in an X in the middle with phloem around it

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16
Q

What is cambium?

A

Meristem cells that can produce vascular tissue

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17
Q

What is a vascular bundle?

A

Xylem, phloem and cambium

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18
Q

How is plant vascular tissue arranged in stems?

A

Vascular bundles found around outer edge of stem, with xylem inside and phloem outside with cambium in the middle

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19
Q

Why are vascular bundles found around the outer edge of the stem?

A

To provide strength, support and flexibility

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20
Q

How are xylem and phloem arranged in a plant leaf vein?

A

Xylem on top of phloem

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21
Q

What is the middle part of a leaf called?

A

Central midrib

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22
Q

Why do you cut a plant cross section (for examination) as thinly as possible?

A

To allow max light to pass through so structures are clear under light microscope

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23
Q

Why do you place a thin plant cross section in water before examining?

A

To prevent drying out

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24
Q

How do you stain a plant specimen cut thinly?

A

Place in dish containing stain for 1 min, then remove and rinse with water

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25
Q

What is a potometer used for?

A

To measure rate of water uptake of a plant and estimate the transpiration rate

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26
Q

Why do we set up a potometer underwater?

A

To ensure no air bubbles enter apparatus

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27
Q

How do you ensure that no air enters the xylem from a cut stem?

A

Cut it underwater

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28
Q

Why do we cut the stem at an angle?

A

To maximise SA in contact with water

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29
Q

What can you do to ensure a potometer experiment is fair?

A

Dry leaves before starting, allow time for plant to acclimatise before starting,ensure plant is healthy

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30
Q

How does water enter the roots of a plant?

A

Drawn in my osmosis, down water potential gradient

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31
Q

Cellulose cell walls are fully ________ permeable.

A

Water

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32
Q

Plant cells are joined together by _______________.

A

Plasmodesmata- cell channels

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33
Q

What is the symplast pathway?

A

Water travels through the living cell parts (cytoplasm, vacoule)

34
Q

How does water move through the symplast pathway?

A

Osmosis

35
Q

What is the apoplast pathway?

A

Water travels through the non living cell parts (cell walls)

36
Q

Water can carry dissolved mineral ions and salts through the ________ pathway.

A

Apoplast

37
Q

How does water move through the apoplast pathway?

A

Mass flow ( not osmosis as no membranes crossed, moves by pressure gradient )

38
Q

The _______ pathway is used more because it provides the least resistance.

A

Apoplast

39
Q

What is the Casparian strip and what does it do?

A

A waxy strip that forces water to take the symplast pathway

40
Q

Why is the Casparian strip useful?

A

Water must pass through the symplast pathway which has a partially permeable membrane which can control entry of substances.

41
Q

________ and ________ help water move up the transpiration stream against gravity.

A

Cohesion and tension

42
Q

How is tension made in the transpiration stream?

A

Water evaporates at the top creating suction and a pressure gradient, pulling water up towards the leaf

43
Q

Why is cohesion useful?

A

Water molecules stick together by hydrogen bonds and follow each other up the transpiration stream, making an uninterrupted column of water

44
Q

What is adhesion?

A

Water molecules stick to xylem vessel walls

45
Q

What is transpiration?

A

A side effect of gas exchange, the loss of water vapour from the top of the plant

46
Q

Why is transpiration a side effect of gas exchange?

A

Stomata must be open for gas exchange but in the process let out water vapour

47
Q

In what ways is transpiration vital to a plants survival?

A

Transports mineral ions up the plant, maintains cell turgidity, supplies water for photosynthesis, helps maintain temperature.

48
Q

Why does light intensity increase transpiration rate?

A

When light, stomata are open for photosynthesis gas exchange, when dark stomata are normally closed

49
Q

Why does temperature increase transpiration rate?

A
  • Higher temp increases evaporation of water rate

- Diffusion rate increases

50
Q

Why does humidity decrease transpiration rate?

A

More water in air decreases water vapour potential gradient

51
Q

Why does wind increase transpiration rate?

A

Water vapour blown away from stomata so water vapour potential gradient steeper

52
Q

How does water move through xylem?

A

Mass flow in transpiration stream

53
Q

What is root pressure?

A

When water is drawn into the root by osmosis pressure builds up forcing water into xylem and up the stem

54
Q

What is translocation?

A

The movement of dissolved substances to where they’re needed through phloem tissue

55
Q

Translocation requires _______ from ___.

A

Energy from ATP

56
Q

In what direction does translocation occur?

A

From source to sink,down a concentration and pressure gradient.

57
Q

Why are sugars transported as sucrose?

A

As its soluble and metabolically inactive so it doesn’t get used up during transport

58
Q

How do enzymes maintain the concentration gradient at the sink end?

A

By converting the assimilate to something else at the sink, e.g. sucrose to starch

59
Q

What is active loading?

A

Active transport used to move substances into companion cells and sieve tubes against a concentration gradient

60
Q

How does active loading work?

A

H+ are pumped out companion cell creating conc gradient, then H+ and solute bind to a cotransport protein and re-enter cell by facilitated diffusion.

61
Q

How does mass flow in phloem work?

A

High hydrostatic pressure at source end, low hydrostatic pressure at sink end creating pressure gradient for sap to travel down.

62
Q

What does a waxy cuticle do?

A

Reduces water lost from top of leaf by evaporation

63
Q

Why are stomata found on the underside of leaves?

A

To prevent evaporation of water from direct sun heating

64
Q

Why do deciduous plants lose their leaves in the winter?

A

Because water may be frozen (unavailable) or it may be too cold for photosynthesis

65
Q

What is a xerophyte?

A

A plant adapted to live in dry conditions

66
Q

What is the main concern for a xerophyte?

A

Losing water through transpiration and being unable to replace it

67
Q

What are the two examples of xerophytes?

A

Cacti and marram grass

68
Q

Why does marram grass have its stomata in sunken pits with hairs?

A

Shelter stomata from wind, traps humid air, reduces water loss

69
Q

Why does marram grass have a dense spongey mesophyll?

A

Little air gaps to reduce SA for evaporation

70
Q

Why do xerophytes have a long tap root?

A

To take advantage of any rain and to get the maximum amount of water possible

71
Q

Why do cacti have ribs and flutes?

A

Because they store water in their stems and they need to expand when full of water

72
Q

Why do xerophytes try to have a low water potential inside cells with a high salt content?

A

To reduce water vapour potential gradient between cells and outside air

73
Q

Why do cacti have spines?

A

Reduce SA for evaporation of water, and to prevent being eaten by predators

74
Q

Why do cacti have a green stem?

A

To carry out photosynthesis

75
Q

What are hydrophytes?

A

Plants adapted to living in water

76
Q

What is the main concern of a hydrophyte?

A

Oxygen availability for submerged tissues and keeping affloat

77
Q

Why do hydrophytes need to stay affloat?

A

So that the leaves can access sunlight for photosynthesis

78
Q

Why do hydrophytes have lots of large air spaces in the leaf?

A

To keep affloat and be a supply of oxygen

79
Q

Why do hydrophytes have stomata on upper leaf surface?

A

So they can be exposed to air for gas exchange

80
Q

Why do hydrophytes leaf stems have large air spaces?

A

To help with buoyancy and to allow oxygen to quickly diffuse to roots and submerged parts of the plant for respiration.

A Level Biology OCR (28 decks)

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