Lecture: Xylem

Question 1

what meristem produces primary xylem and phloem?

Answer 1

procambium

Question 2

what is the function of primary xylem?

Answer 2

conduction of water and dissolved minerals

Question 3

what is the function of secondary xylem?

Answer 3

strength

Question 4

what makes up the structure of xylem?

Answer 4

1. parenchyma
2. sclerenchyma
3. conducting (tracheary) elements

Question 5

the parenchyma in xylem is arranged in

Answer 5

rows or strands

Question 6

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

Answer 6

can resume cell division. Induced by pathogen

Question 7

describe the structure of parenchyma transfer cells in xylem

Answer 7

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

Question 8

transfer cells of parenchyma are important to ___ through ____

Answer 8

short-distance transport through lateral veins

Question 9

what is the structure of sclerenchyma in xylem?

Answer 9

fibres/sclerides

Question 10

what is the function of sclerenchyma in xylem?

Answer 10

strength, especially around vulnerable cells, like veins

Question 11

what are the conducting elements of xylem?

Answer 11

tracheids and vessels

Question 12

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

Answer 12

elongated dead cells

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

Question 13

what makes tracheary elements distinctive?

Answer 13

1. wall thickenings

2. perforations

Question 14

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

Answer 14

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

Question 15

what are perforation is tracheary elements and their function?

Answer 15

holes for passage of water

Question 16

how are tracheary elements formed?

Answer 16

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

Question 17

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

Answer 17

tracheids

Question 18

describe the structural elements of tracheids

Answer 18

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

Question 19

the primary walls of tracheids are

Answer 19

pit membranes across pits

Question 20

vessels are made up of smaller

Answer 20

vessel elements stacked

Question 21

what is different about the walls of vessels?

Answer 21

end walls degenerate (no 1/2 cell wall)

Question 22

what replaces end walls in vessels?

Answer 22

perforation plates

Question 23

what is a simple perforation plate?

Answer 23

fully open ends

Question 24

what is a scalariform perforation plate?

Answer 24

bars across opening

Question 25

perforations occur only in which tracheary element?

Answer 25

vessels

Question 26

why do angiosperms keep their tracheids if they have vessels?

Answer 26

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

Question 27

which angiosperms have vessels?

Answer 27

both monocots and dicots

Question 28

what is the structure of vessels?

Answer 28

wide with no end walls

Question 29

what is an advantage of vessels?

Answer 29

more water flows with less friction

Question 30

what is a disadvantage of vessels?

Answer 30

no filter for air bubbles, which stop flow

Question 31

what is the structure of tracheids?

Answer 31

narrow with end walls with only small openings

Question 32

what is an advantage of tracheids?

Answer 32

filters air bubbles, rerouting them and water

Question 33

what is a disadvantage of tracheids?

Answer 33

slow water flow

Question 34

what are the 4 cell types of xylem?

Answer 34

1. parenchyma 2. sclerenchyma 3. tracheids 4. vessels

Question 35

what is the source of water for plants

Answer 35

soil

Question 36

what is the sink of water for plants?

Answer 36

air

Question 37

what creates turgor pressure?

Answer 37

osmotic flow

Question 38

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

Answer 38

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

Question 39

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

Answer 39

fully inflated

Question 40

how do root hairs increase water absorption?

Answer 40

increase surface area and do not have waxy cuticle

Question 41

best water uptake happens when the soil is

Answer 41

dilute (after rain)

Question 42

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

Answer 42

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

Question 43

how do plants in salt marshes not wilt?

Answer 43

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

Question 44

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

Answer 44

1. apoplastic 2. symplastic 3. trans-cellular

Question 45

how does water move through the apoplastic pathway?

Answer 45

through cell walls

Question 46

how does water move through the symplastic pathway?

Answer 46

through protoplasms

Question 47

how does water move through the trans-cellular pathway?

Answer 47

through vacoules

Question 48

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

Answer 48

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

Question 49

what are the two long-distance transport theories?

Answer 49

1. root pressure theory | 2. transpiration cohesion theory

Question 50

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

Answer 50

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

Question 51

what evidence supports the root pressure theory?

Answer 51

sap oozes out of cut; hydrathodes in some species

Question 52

what are some potential problems with the root pressure theory?

Answer 52

1. only works in dilute soil | 2. not powerful enough to push water to the top of the tree

Question 53

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

Answer 53

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

Question 54

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

Answer 54

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

Question 55

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

Answer 55

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

Question 56

what action alone is enough to move water through plant?

Answer 56

cohesion/capillary action

Question 57

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

Answer 57

99%

Question 58

what are the benefits of Ts?

Answer 58

1. evaporation cools leaf surface | 2. creates faster upward flow, resulting in more absorption, therefore more water and nutrients

Question 59

what are the added benefits of the strength of xylem?

Answer 59

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

Question 60

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

Answer 60

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

Question 61

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

Answer 61

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

Question 62

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

Answer 62

tracheid because of capillary action (adhesion)

Question 63

what plants make syrup?

Answer 63

woody deciduous plants in temperate climates

Question 64

what do developing leaf buds need?

Answer 64

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

Question 65

what makes sap sweet?

Answer 65

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

Question 66

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

Answer 66

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

Question 67

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

Answer 67

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

Question 68

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

Answer 68

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

Question 69

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

Answer 69

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

Question 70

where would the sweetest syrup be in a tree?

Answer 70

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

Question 71

is maple syrup sweet in the fall?

Answer 71

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

Question 72

what is the function of parenchyma in xylem?

Answer 72

long-distance transport

Question 73

what induces division in parenchyma of xylem?

Answer 73

pathogen

Question 74

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

Answer 74

allow for elongation

Question 75

are tracheids found in monocots or dicots of angiosperms?

Answer 75

both, baby!

Question 76

at maximum turgor pressure, the cell is fully __-

Answer 76

inflated

Question 77

why does the cell not burst at max turgor pressure?

Answer 77

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