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Plant Physio > Chapter 4 > Flashcards

Chapter 4 Flashcards

1
Q

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

A

soil type and soil structure.

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2
Q

have a relatively low surface particles may be 1 mm or more in diameter

A

Sandy Soils

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3
Q

have a relatively low surface area per gram of soil and have large spaces or channels between particles

A

Sandy Soils

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4
Q

have particles that are smaller than 2 µm in diameter

A

clay Soils

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5
Q

have much greater surface areas and smaller channels between particles

A

clay soils

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6
Q

with the aid of organic substances such as ___(decomposing organic matter), clay particles may aggregate into “___” that help improve soil ___ and ____
of water

A

humus;
crumbs;
aeration and infiltration

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7
Q

Water in the soil may exist as a __adhering to the surface of the soil particles, or it may
fill the entire channel between particles

A

film

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8
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 soils

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9
Q
  • water does not freely drain from them and is held more tightly
A

clay soils

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10
Q
  • the moisture-holding capacity of soils.
A

Field capacity

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11
Q

___is the 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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12
Q

these soils have a large field capacity

A

clay soils or soils with humus

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13
Q

clay soils might retain ___ by volume a few days after being saturated unlike
sandy soils, which retain ___ by volume after saturation

A

40% water; 3% water

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14
Q

A ____ in Soil Water Lowers Soil Water Potential

A

Negative Hydrostatic Pressure

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15
Q

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

A

o Osmotic Potential
o Hydrostatic Pressure

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16
Q

the osmotic potential of soil water is generally ___ because solute
concentrations are ___

A

negligible; low

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17
Q

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

A

zero;
decreases; negative

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18
Q

The soil is a mixture of (4)

A

particles
(sand, clay, silt, and organic material), water, dissolved solutes, and air.

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19
Q

At the air–water
interfaces, this recession causes the surface of the soil solution to develop ______
(curved interfaces between air and water marked in the figure by arrows), and brings the
solution into___ by surface tension.

A

concave menisci;
tension (negative pressure)

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20
Q

Because of ___, water tends to cling to the surfaces of
soil particles, so a large ___between soil water and soil air develops.

A

adhesive forces; surface area

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21
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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22
Q

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

A

negative; radius; very small

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23
Q

Water moves through soils predominantly by ___driven by a ___

A

bulk flow;
pressure gradient.

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24
Q

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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25
Q

it is a measure of ease with which water moves through the soil

A

Soil hydraulic conductivity

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26
Q

Soil hydraulic conductivity varies with the:

A

type of soil;
water content

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27
Q

Sandy soil - __ hydraulic conductivity
Clay soil - ___ hydraulic conductivity

A

large;
low

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28
Q

as water content ___ = hydraulic conductivity ____ drastically

A

decreases (both)

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29
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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30
Q

as more of the soil spaces become filled with air, water can flow
through__ and ___channels, and the hydraulic conductivity __

A

fewer and narrower; falls

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31
Q
  • microscopic extensions of root epidermal cells that greatly increase the surface area of the root,
A

Root hairs

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32
Q

Water enters the root most readily in the __ part of the root

A

apical part

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33
Q

More mature regions of the root have an outer protective tissue called
____which are ___ to water

A

exodermis or hypodermis;
impermeable

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34
Q

Water Moves in the Root via the (3)

A

Apoplast, Transmembrane, and Symplast Pathways

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35
Q

In the ____, water flows between cells through the plasmodesmata without crossing the plasma
membrane.

A

symplast pathway;

36
Q

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

A

transmembrane pathway

37
Q

At the ___, the ___ pathway is blocked by the Casparian strip

A

endodermis; apoplast

38
Q

water moves exclusively through the cell wall without crossing any membranes

A

Apoplast Pathway

39
Q

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

A

apoplast

40
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

41
Q

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

A

Transmembrane Pathway

42
Q

transport across the tonoplast may also be involved

A

Transmembrane Pathway

43
Q

water travels from one cell to the next via the plasmodesmata

A

Symplast Pathway

44
Q

the ___consists of the entire network of cell cytoplasm interconnected by
plasmodesmata

A

symplast

45
Q

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

A

Casparian strip

46
Q

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

A

Casparian strip

47
Q

wax-like, hydrophobic substance; acts as a barrier to water and solute movement

A

Suberin

48
Q

The ___ 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

49
Q

water movement across the endodermis occurs through the ___

A

symplast

50
Q

Solute Accumulation in the Xylem Can Generate “____

A

Root Pressure

51
Q

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

A

positive hydrostatic pressure

52
Q

The buildup of solutes in the xylem sap leads to a decrease in the ___ and thus an decrease in the xylem ____

A

xylem osmotic potential (Ψs);
water potential (Ψw).

53
Q

This ____provides a driving force for water absorption, which
in turn leads to a ___ in the xylem.

A

lowering of the xylem Ψw;
positive hydrostatic pressure

54
Q

In effect, the whole root acts like an ___; the multicellular root tissue behaves
as an osmotic membrane does, building up a positive hydrostatic pressure in the
xylem in response to the accumulation of solutes

A

osmotic cell

55
Q

___ is most likely to occur when soil water potentials are ___and
transpiration rates are ___

A

Root pressure;
high; low

56
Q

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

A

guttation

57
Q

___constitutes the longest part of the pathway of water transport

A

Xylem

58
Q

xylem is a simple pathway with ___ to flow of water unlike
the complex pathway across the root tissue.

A

low resistance

59
Q

Two Types of Tracheary Elements of xylem

A

Tracheids;
vessel element

60
Q

______ – both found in gymnosperms and angiosperms

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

A

Tracheids;
Vessel Elements

61
Q

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

A

death

62
Q

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

A

Tracheids

63
Q

water flows between tracheids by means of numerous ___on their lateral walls.

A

pits

64
Q

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

A

Pits

65
Q

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

A

pit pairs.

66
Q

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

A

Pit pairs

67
Q

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

A

Pit membrane

68
Q

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

A

torus
(pl. tori)

69
Q
  • acts like a valve to close the pit by lodging themselves on the circular
    wall thickenings bordering the pits
A

Torus

70
Q

torus thereby prevents dangerous gas bubbles from forming (process called
____) and invading neighboring tracheids

A

cavitation

71
Q

____-this tends to be shorter and wider than tracheids and have perforiated end walls that
form a ___ at each end of the cell

A

vessel elements;
perforiation plate

72
Q

unlike tracheids, the perforiated end walls allows vessel elements to be stacked end to end to form conduit called ___

A

vessel

73
Q

The ___ Explains Water Transport in the Xylem

A

Cohesion – Tension Theory

74
Q

In theory, the pressure gradients needed to move water through the xylem could result
from the generation of
o ____ at the base of the plant; or
o ____ at the top of the plant.

A

positive pressures;
negative pressures

75
Q

a mechanism, first proposed toward the end of the 19th century, called
the ______ requires the cohesive
properties of water to sustain large tensions in the xylem water columns

A

cohesion–tension theory of sap ascent

76
Q

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

A

inward force; weak;

77
Q

The _____
are adaptations of cell walls to offset this tendency to collapse.

A

secondary wall thickenings and lignifications of tracheids and vessels

78
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

79
Q
  • the phenomenon of air formation and expansion; also known as __
A

Cavitation; embolism

80
Q

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

A

Cavitation

81
Q

____ in the Leaf Generates a ____Pressure in the Xylem

A

Water Evaporation;
Negative

82
Q

The tensions needed to pull water through the xylem are the result of ___ from leaves.

A

evaporation of water

83
Q

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

A

surface of the cell walls

84
Q

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

A

air-water interfaces

85
Q

Tensions or negative pressures originate in __

A

leaves

Plant Physio (4 decks)

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