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Plant Physiology > CHAPTER 4: Water balance of plants > Flashcards

CHAPTER 4: Water balance of plants Flashcards

1
Q

The water content and the rate of water movement in soils depend to a large extent on (2)

A

soil type and soil structure

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2
Q

Particle Diameter (µm)
-Coarse sand
-Fine sand
-Silt Clay
-Clay

A

-Coarse sand 2000-200
-Fine sand 200-20
-Silt Clay 20-2
-Clay <3

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3
Q

Difference of Sandy Soils to Clay Soils

-diameter
-surface area
-channels

A

Sandy soils
diameter- 1 mm or more
surface area- low surface area
channels- low surface area

Clay Soils
diameter- 2 µm
surface area-greater surface areas
channels- smaller channels

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4
Q

(decomposing organic matter)

A

humus

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5
Q

help improve soil aeration and infiltration
of water

A

crumbs

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6
Q

clay crumbs help improve (2)

A

-soil aeration
-infiltration of water

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7
Q

the spaces in between particles are large that water drains from them;
water remains only on the soil particle surfaces and at interstices between soil
particles

A

sandy soil

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8
Q

Sandy soils, the spaces in between particles are __ that water ___ from them;
water remains only on the ____ and at ____

A

large
drains
soil particle surfaces
interstices between soil particles

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9
Q

Characteristics of Sandy Soil and Clay Soil in terms of
-water in soil
- surface of the soil particles

A

Sandy Soil- the spaces in between particles are large that water drains from them;
water remains only on the soil particle surfaces and at interstices between soil
particles

Clay Soil- water does not freely drain from them and is held more tightly

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10
Q

water does not freely drain from them and is held more tightly

A

clay soils

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11
Q

Clay soil, water ____ from them and is held ___

A

does not freely drain more tightly

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12
Q

he moisture-holding capacity of soils.

A

field capacity

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13
Q

water content of a soil after it has been saturated with water and
excess water has been allowed to drain away.

A

field capacity

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14
Q

clay soils or soils with__ have a large field capacity

A

humus

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15
Q

clay soils might retain ___water by volume ____ after being saturated

sandy soils, which retain __ water by volume after saturation

A

40%
a few days

3%

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16
Q

Soil has water potentials and can be dissected into two components:

A

o Osmotic Potential
o Hydrostatic Pressure

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17
Q

A Negative Hydrostatic Pressure in Soil Water Lowers__

A

Soil Water Potential

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18
Q

Lowers Soil Water Potential

A

Negative Hydrostatic Pressure

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19
Q

the osmotic potential of soil water is generally negligible because

A

solute concentrations are low

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20
Q

for soils with __ concentrations of salts, Ψs is significant

A

substantial

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21
Q

osmotic pressure
-soil water
-soil

A

Osmotic Potential (Ψs)
▪ the osmotic potential of soil water is generally negligible because solute concentrations are low
▪ but for soils with substantial concentrations of salts, Ψs is significant

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22
Q

Hydrostatic Pressure (Ψp)
▪ for wet soils, Ψp is very __
▪ as a soil dries out, Ψp ___ and can become __

A

close to zero
decreases, quite negative

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23
Q

reason why Ψp decreases and can become quite negative

A

soil dries out

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24
Q

Hydrostatic Pressure (Ψp)
-difference in wet soil and dry soil

A

▪ for wet soils, Ψp is very close to zero
▪ as a soil dries out, Ψp decreases and can become quite negative

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25
Q

Where does the negative pressure in soil water came from?

A

-water is removed from the soil

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26
Q

As the water content of the soil decreases, the water recedes into the interstices
between soil particles, and the air–water surface develops

A

curved air–water interfaces

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27
Q

The value of Ψp in soil water can become ___ because the __ of curvature of air–water surfaces may become___ in drying soils.

A

quite negative
radius
very small

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28
Q

Water moves through soils predominantly by bulk flow driven by a

A

pressure gradient

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29
Q

Water Moves through the Soil by

A

Bulk Flow

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30
Q

As plants absorb water from the soil, they deplete the soil of water near the

A

surface of the roots.

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31
Q

b. The rate of water flow in soils depends on two factors:

A

▪ Size of the pressure gradient through the soil
▪ Soil hydraulic conductivity

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32
Q

it is a measure of ease with which water moves through the soil and it varies with the: 1) type of soil; and
2) water content

A

Soil hydraulic conductivity

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33
Q

Soil hydraulic conductivity it is a measure of ease with which water moves through the soil and it varies with the:

A

1) type of soil
2) water content

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34
Q

Soil hydraulic conductivity
o Sandy soil
o Clay soil

A

o Sandy soil- large hydraulic conductivity
o Clay soil- low hydraulic conductivity

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35
Q

hydraulic conductivity as water content decreases

A

decreases drastically

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36
Q

the decreases in hydraulic conductivity is due primarily to the

A

replacement of water in the soil spaces by air

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37
Q

when air moves into a soil channel previously filled with water, water
movement through that channel is ____ of the channel.

A

restricted to the periphery

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38
Q

as more of the soil spaces become filled with air, water can flow through fewer and narrower channels ___

A

hydraulic conductivity falls

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39
Q

microscopic extensions of root epidermal cells

A

root hais

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40
Q

Rot hair helps in increasing the

A

surface area of the root

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41
Q

Increase in the surface area of the root provide

A

greater capacity for absorption of ions and
water from the soil.

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42
Q

Water enters the root most readily in the

A

apical part

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43
Q

More mature regions of the root have an outer protective tissue called

A

exodermis or hypodermis

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44
Q

characteristic exodermis or hypodermis

A

impermeable to water

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45
Q

Water Moves in the Root via(3)

A

the Apoplast, Transmembrane, and Symplast Pathways

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46
Q

In the symplast pathway, water flows between cells through the ____without crossing the plasma membrane.

A

plasmodesmata

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47
Q

In the symplast pathway, water flows between cells through the plasmodesmata _____

A

without crossing the plasma membrane

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48
Q

water flows between cells through the plasmodesmata without crossing the plasma membrane

A

symplast pathway,

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49
Q

, water moves across the plasma membranes, with
a short visit to the cell wall space.

A

In the transmembrane pathway

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50
Q

. In the transmembrane pathway, water moves across the plasma membranes, with
a short visit to the ___

A

cell wall space.

51
Q

In the transmembrane pathway, water moves _____, with a short visit to the cell wall space.

A

across the plasma membranes

52
Q

the apoplast pathway is blocked by the
Casparian strip at the

A

endodermis

53
Q

Difference between the water movement in
-Apoplast Pathway
-Transmembrane Pathway

A

-Apoplast Pathway, water moves without crossing any membranes
-Transmembrane Pathway, water crosses at least two membrane

54
Q

water moves exclusively through the cell wall without crossing any membranes

A

Apoplast Pathway

55
Q

continuous system of cell walls and intercellular air spaces in plant
tissues

A

Apoplast Pathway

56
Q

the route followed by water that sequentially enters a cell on one side, exits the cell on the other side, enters the next in the series, and so on

A

Transmembrane Pathway

57
Q

water crosses at least two membranes for each cell in its path (the
plasma membrane on entering and on exiting)

A

Transmembrane Pathway

58
Q

transport across the tonoplast may also be involved

A

Transmembrane Pathway

59
Q

Transmembrane Pathway transport across the ______ may also be involved

A

tonoplast

60
Q

water travels from one cell to the next via the plasmodesmata

A

Symplast Pathway

61
Q

entire network of cell cytoplasm interconnected by plasmodesmata

A

Symplast Pathway

62
Q

Symplast Pathway water travels from one cell to the next via the

A

plasmodesmata

63
Q
A
64
Q

symplast consists of the _____ interconnected by plasmodesmata

A

entire network of cell cytoplasm

65
Q

At the endodermis, water movement through the apoplast pathway is obstructed by the

A

Casparian strip

66
Q

is a band of radial cell walls in the endodermis that is impregnated with the wax-like,
hydrophobic substance suberin

A

Casparian strip.

67
Q

Casparian strip is a band of radial cell walls in the endodermis that is impregnated with the wax-like, hydrophobic substance

A

suberin

68
Q

acts as a barrier to water and solute movement

A

suberin

69
Q

breaks the continuity of the apoplast pathway, and forces water
and solutes to cross the endodermis by passing through the plasma membrane.

A

casparian strip

70
Q

The casparian strip breaks the continuity of the apoplast pathway, and forces water
and solutes to cross the ___ by passing through the ___.

A

endodermis

plasma membrane

71
Q

water movement across the endodermis occurs through the

A

symplast

72
Q

Solute Accumulation in the Xylem Can Generate

A

“Root Pressure”

73
Q

What can Generate “Root Pressure”

A

Solute Accumulation in the Xylem

74
Q

Roots generate____ by absorbing ions from the dilute soil solution and transporting them into the xylem.

A

positive hydrostatic pressure

75
Q

Roots generate positive hydrostatic pressure by absorbing ions from the dilute soil solution and transporting them into the

A

xylem.

76
Q

The buildup of solutes in the xylem sap leads
-osmotic potential
-water potention

A

-decrease in the xylem osmotic
potential (Ψs)
-decrease in the xylem water potential (Ψw).

77
Q

This lowering of the xylem Ψw provides a driving force for water absorption, which
in turn leads to a____ in the xylem.

A

positive hydrostatic pressure

78
Q

In effect, the whole root acts like an osmotic cell; the multicellular root tissue behaves as an osmotic membrane does, building up a____ in the xylem in response to the ___

A

positive hydrostatic pressure
accumulation of solutes

79
Q

is most likely to occur when soil water potentials are high and
transpiration rates are low

A

root pressure

80
Q

Plants that develop root pressure frequently produce liquid droplets on the edges of their leaves, a phenomenon known as

A

guttation

81
Q

constitutes the longest part of the pathway of water transport.

A

xylem

82
Q

xylem is a ___ with __ to flow of water unlike
the ____across the root tissue.

A

simple pathway
low resistance
complex pathway

83
Q

WATER TRANSPORT THROUGH THE

A

XYLEM

84
Q

Xylem Consists of Two Tracheary Elements

A

Tracheids
Vessel Elements

85
Q

only found in angiosperms, Gnetales (a group of gymnosperms) and
some ferns

A

Vessel Elements

86
Q

both found in gymnosperms and angiosperms

A

Tracheids

87
Q

Difference between
-tracheids
-vessel elements

A

Tracheids – both found in gymnosperms and angiosperms
Vessel Elements – only found in angiosperms

88
Q

The maturation of both tracheids and vessel elements involves the “___” of the cell.

A

death

89
Q

are elongated, spindle-shaped cells that are arranged in overlap- ping vertical files

A

tracheids

90
Q

Tracheids-water flows between tracheids by means of numerous pits on their

A

lateral walls

91
Q

are microscopic regions where secondary wall is absent and the primary
wall is thin and porous.

A

Pits

92
Q

Pits of one tracheid are typically located opposite pits of an Adjoining
tracheid, forming

A

pit pairs

93
Q

constitute a low-resistance path for water movement between
tracheids.

A

Pit pairs

94
Q

a porous layer between pit pairs, consisting of two primary
walls and a middle lamella.

A

Pit membrane

95
Q

In some species of conifers, pit membranes have a central thickening known as

A

torus

96
Q

acts like a valve to close the pit by lodging themselves on the circular
wall thickenings bordering the pits

A

Torus -

97
Q

dangerous gas bubbles formation

A

cavitation

98
Q

this act thereby prevents dangerous gas bubbles from forming and invading neighboring tracheids

A

torus

99
Q

this tends to be shorter and wider and have perforiated end walls that form a perforiation plate at each end of the cell

A

vessele elements

100
Q

perforiated end walls that form

A

perforiation plate

101
Q

Similarity between
-tracheids
-vessel elements

A

like- pit on their lateral walls
unlike- perforiated walls
tracheids- allow movement
vessel elements- allow stack

102
Q

Tension Theory Explains Water Transport in the Xylem

A

cohesion

103
Q

the pressure gradients needed to move water through the xylem could result
from the generation of (2)

A

o positive pressures at the base of the plant; or
o negative pressures at the top of the plant.

104
Q

the pressure gradients needed to move water through the

A

xylem

105
Q

root pressure is typically less than 0.1 MPa and disappears when the transpiration rate is

A

high

106
Q

Instead, the water at the top of a tree develops a _____, and this tension pulls water through the xylem.

A

large tension (a negative hydrostatic pressure)

107
Q

This mechanism, first proposed toward the end of the 19th century, is called

A

cohesion–tension theory of sap ascent

108
Q

Xylem Transport of Water in Trees faces

A

physical challenges

109
Q

Water under tension transmits an ___ force to the walls of the xylem and if cell
walls are weak, they would __ under the influence of this tension.

A

inward
collapse

110
Q

adaptations to offset this tendency for tracheids and vessels to collapse.

A

-secondary wall thickening
-lignification

111
Q
  • this is the increased tendency for air to be pulled through microscopic
    pores in the xylem cell walls due to increasing water tension.
A

Air seeding

112
Q
  • the phenomenon of air formation and expansion
A

Cavitation

113
Q

Cavitation is also known as

A

embolism

114
Q

once a gas bubble has formed within the water column under tension, it will
expand because gases cannot resist tensile forces

A

cavitation

115
Q

breaks the continuity of the water column and prevents water transport in
the xylem.

A

cavitation

116
Q

by blocking the main transport pathway of water, cause the dehydration and death of the leaves

A

cavitation

117
Q

Since the capillaries in the xylem are interconnected, one gas bubble___
completely stop water flow.

A

does not

118
Q

Thus, the finite length of the tracheid and vessel conduits of the xylem, while
resulting in an increased resistance to water flow, also provides a way to

A

restrict cavitation

119
Q

Finally, many plants have _____ in which new xylem forms each
year.

A

secondary growth

120
Q

Water Evaporation in the Leaf Generates a ____ in the Xylem

A

Negative Pressure

121
Q

The tensions needed to pull water through the xylem are the result of

A

evaporation

122
Q

The negative pressure that causes water to move up through the xylem develops at the

A

surface of the cell walls in the leaf

123
Q

as more water is removed from the wall, the radius of curvature of the air
water interfaces ___ and the pressure of the water becomes more ___

A

decreases
negative

124
Q

the motive force for xylem transport is generated at the ____ within the leaf

A

air-water interfaces

Plant Physiology (4 decks)

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