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Botany > Lecture: Xylem > Flashcards

Lecture: Xylem Flashcards

1
Q

what meristem produces primary xylem and phloem?

A

procambium

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2
Q

what is the function of primary xylem?

A

conduction of water and dissolved minerals

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3
Q

what is the function of secondary xylem?

A

strength

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4
Q

what makes up the structure of xylem?

A
  1. parenchyma
  2. sclerenchyma
  3. conducting (tracheary) elements
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5
Q

the parenchyma in xylem is arranged in

A

rows or strands

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6
Q

what is an important feature of parenchyma of xylem? How does that happen?

A

can resume cell division. Induced by pathogen

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7
Q

describe the structure of parenchyma transfer cells in xylem

A

cell wall protrudes into cell, which increases area of cell membrane.

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8
Q

transfer cells of parenchyma are important to ___ through ____

A

short-distance transport through lateral veins

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9
Q

what is the structure of sclerenchyma in xylem?

A

fibres/sclerides

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10
Q

what is the function of sclerenchyma in xylem?

A

strength, especially around vulnerable cells, like veins

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11
Q

what are the conducting elements of xylem?

A

tracheids and vessels

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12
Q

what are tracheids and vessels and what three things do they have in common?

A

elongated dead cells

  1. no protoplasts
  2. secondary cell walls
  3. have pits
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13
Q

what makes tracheary elements distinctive?

A
  1. wall thickenings

2. perforations

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14
Q

what are wall thickenings in tracheary elements, and their function?

A

secondary cell wall gradually laid in different patterns, that allow for elongation

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15
Q

what are perforation is tracheary elements and their function?

A

holes for passage of water

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16
Q

how are tracheary elements formed?

A

secondary cell wall laid down gradually, the cell dies (apoptosis), the nucleus and primary cell wall go deteriorate, making large channel for water

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17
Q

which tracheary element is most primitive and found in all vascular plants?

A

tracheids

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18
Q

describe the structural elements of tracheids

A

pits and pit fields with plasmodesmata, the pit membrane (primary cell wall) still intact

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19
Q

the primary walls of tracheids are

A

pit membranes across pits

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20
Q

vessels are made up of smaller

A

vessel elements stacked

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21
Q

what is different about the walls of vessels?

A

end walls degenerate (no 1/2 cell wall)

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22
Q

what replaces end walls in vessels?

A

perforation plates

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23
Q

what is a simple perforation plate?

A

fully open ends

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24
Q

what is a scalariform perforation plate?

A

bars across opening

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25
Q

perforations occur only in which tracheary element?

A

vessels

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26
Q

why do angiosperms keep their tracheids if they have vessels?

A

capillary action, and can contain air bubbles formed in vessels and relocate them

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27
Q

which angiosperms have vessels?

A

both monocots and dicots

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28
Q

what is the structure of vessels?

A

wide with no end walls

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29
Q

what is an advantage of vessels?

A

more water flows with less friction

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30
Q

what is a disadvantage of vessels?

A

no filter for air bubbles, which stop flow

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31
Q

what is the structure of tracheids?

A

narrow with end walls with only small openings

32
Q

what is an advantage of tracheids?

A

filters air bubbles, rerouting them and water

33
Q

what is a disadvantage of tracheids?

A

slow water flow

34
Q

what are the 4 cell types of xylem?

A
  1. parenchyma
  2. sclerenchyma
  3. tracheids
  4. vessels
35
Q

what is the source of water for plants

A

soil

36
Q

what is the sink of water for plants?

A

air

37
Q

what creates turgor pressure?

A

osmotic flow

38
Q

what prevents the cell from bursting when water flows in by osmosis?

A

cell wall is tough and pushes back. Equilibrium is reached by pushing out 1 water molecule each time a new one is brought in

39
Q

what does the cell look like when it is at maximum turgor pressure?

A

fully inflated

40
Q

how do root hairs increase water absorption?

A

increase surface area and do not have waxy cuticle

41
Q

best water uptake happens when the soil is

A

dilute (after rain)

42
Q

what happens to soil/plant after a dry spell or salt in snow?

A

soil concentration of minerals increases, osmotic flow decreases, water still lost to transpiration, so turgor pressure crashes and plant wilts

43
Q

how do plants in salt marshes not wilt?

A

they reverve the osmotic gradient and actively pump in salts, which are secreted by glands. This pulls water into the plant too

44
Q

what are the three ways water moves in from root hairs?

A
  1. apoplastic
  2. symplastic
  3. trans-cellular
45
Q

how does water move through the apoplastic pathway?

A

through cell walls

46
Q

how does water move through the symplastic pathway?

A

through protoplasms

47
Q

how does water move through the trans-cellular pathway?

A

through vacoules

48
Q

provide the process by which water is unloaded from a plant. What is it called?

A

Transpiration. Water in tracheary elements within Ps organ evaporates into stomatal chambers through stomates and out to the air

49
Q

what are the two long-distance transport theories?

A
  1. root pressure theory

2. transpiration cohesion theory

50
Q

what is the root pressure theory for long-distance transport?

A

water is pushed up by osmotic flow which creates turgor pressure and forces water to next cell

51
Q

what evidence supports the root pressure theory?

A

sap oozes out of cut; hydrathodes in some species

52
Q

what are some potential problems with the root pressure theory?

A
  1. only works in dilute soil

2. not powerful enough to push water to the top of the tree

53
Q

what is the transpiration -cohesion theory/ tension cohesion theory?

A

passive movement of water, which cohered by H bonds and adhered to cell wall and then pulled up by transpiration

54
Q

what three things are needed by the Ts-Cohesion theory?

A
  1. cohesion
  2. adhesion (capillary action)
  3. Ts to pull
55
Q

what is a problem with Ts sucking in Ts-cohesion? What is the solution?

A

soft tubes could collapse, solution: secondary cell walls of tracheids and vessels

56
Q

what action alone is enough to move water through plant?

A

cohesion/capillary action

57
Q

how much water absorbed is lost to Ts rather than used for growth and metabolism?

A

99%

58
Q

what are the benefits of Ts?

A
  1. evaporation cools leaf surface

2. creates faster upward flow, resulting in more absorption, therefore more water and nutrients

59
Q

what are the added benefits of the strength of xylem?

A

allows plant to grow taller to have more space and access to sunlight

60
Q

what is the direction of water in xylem? Can it reverse?

A

upwards. It cannot reverse because water must be lost through stomates, waxy cuticle of the endodermis in root prevents water leaving

61
Q

why are tracheids and vessels reinforced with secondary walls. Why are they inside?

A

strength so Ts sucking does not make them collapse. If only the outside was strong, the inside could still collapse

62
Q

In which tracheary element would water rise higher (even without Ts)?

A

tracheid because of capillary action (adhesion)

63
Q

what plants make syrup?

A

woody deciduous plants in temperate climates

64
Q

what do developing leaf buds need?

A
  1. PGS to break bud dormancy
  2. sugar to fuel mitosis
  3. water to enlarge new cells
65
Q

what makes sap sweet?

A

parenchyma in roots convert starch to sugar, along with PGS, move into tracheary elements, making a sweet sap

66
Q

what problem is faced when new leaves need to be formed?

A

need water to expand pre-formed leaves, and need Ts to do that, but Ts requires leaves, and there is noot enough root pressure alone

67
Q

how do woody diciduous plants cope with a lack of Ts when they have no leaves?

A

create pressure in stem by undergoing a freeze-thaw cycle (warm days, cold nights)

68
Q

how does the cold part of the freeze-thaw cycle increase stem pressure?

A

below 0C, gases in xylem dissolve, increasing pressure and bringing water in from adjacent cells. water willl freeze and the gas will compress

69
Q

how does the warm part of the freeze-thaw cycle increase stem pressure?

A

above 0C water melts, the compressed gases expand, increasing the turgor pressure, pushing the water containing sugar and PGS

70
Q

where would the sweetest syrup be in a tree?

A

closer to base of trunk, becasuse not yet made it to leaves

71
Q

is maple syrup sweet in the fall?

A

no, because its not freeze thaw, and the leaf buds have not formed, or do not yet need the sweet resources

72
Q

what is the function of parenchyma in xylem?

A

long-distance transport

73
Q

what induces division in parenchyma of xylem?

A

pathogen

74
Q

what is the function of wall-thickenings in tracheary elements?

A

allow for elongation

75
Q

are tracheids found in monocots or dicots of angiosperms?

A

both, baby!

76
Q

at maximum turgor pressure, the cell is fully __-

A

inflated

77
Q

why does the cell not burst at max turgor pressure?

A

equilibrium (as one water molecule is brought in, another is pushed out)

Botany (10 decks)

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