Chapter 4

Question 1

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

Answer 1

soil type and soil structure.

Question 2

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

Answer 2

Sandy Soils

Question 3

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

Answer 3

Sandy Soils

Question 4

have particles that are smaller than 2 µm in diameter

Answer 4

clay Soils

Question 5

have much greater surface areas and smaller channels between particles

Answer 5

clay soils

Question 6

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

Answer 6

humus;
crumbs;
aeration and infiltration

Question 7

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

Answer 7

film

Question 8

• 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

Answer 8

sandy soils

Question 9

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

Answer 9

clay soils

Question 10

• the moisture-holding capacity of soils.

Answer 10

Field capacity

Question 11

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

Answer 11

Field capacity

Question 12

these soils have a large field capacity

Answer 12

clay soils or soils with humus

Question 13

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

Answer 13

40% water; 3% water

Question 14

A ____ in Soil Water Lowers Soil Water Potential

Answer 14

Negative Hydrostatic Pressure

Question 15

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

Answer 15

o Osmotic Potential
o Hydrostatic Pressure

Question 16

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

Answer 16

negligible; low

Question 17

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

Answer 17

zero;
decreases; negative

Question 18

The soil is a mixture of (4)

Answer 18

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

Question 19

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.

Answer 19

concave menisci;
tension (negative pressure)

Question 20

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

Answer 20

adhesive forces; surface area

Question 21

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

Answer 21

curved air–water interfaces.

Question 22

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

Answer 22

negative; radius; very small

Question 23

Water moves through soils predominantly by ___driven by a ___

Answer 23

bulk flow;
pressure gradient.

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Soil hydraulic conductivity

Question 26

Soil hydraulic conductivity varies with the:

Answer 26

type of soil; water content

Question 27

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

Answer 27

large; low

Question 28

as water content ___ = hydraulic conductivity ____ drastically

Answer 28

decreases (both)

Question 29

the decreases in hydraulic conductivity is due primarily to the ___

Answer 29

replacement of water in the soil spaces by air

Question 30

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

Answer 30

fewer and narrower; falls

Question 31

- microscopic extensions of root epidermal cells that greatly increase the surface area of the root,

Answer 31

Root hairs

Question 32

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

Answer 32

apical part

Question 33

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

Answer 33

exodermis or hypodermis; impermeable

Question 34

Water Moves in the Root via the (3)

Answer 34

Apoplast, Transmembrane, and Symplast Pathways

Question 35

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

Answer 35

symplast pathway;

Question 36

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

Answer 36

transmembrane pathway

Question 37

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

Answer 37

endodermis; apoplast

Question 38

water moves exclusively through the cell wall without crossing any membranes

Answer 38

Apoplast Pathway

Question 39

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

Answer 39

apoplast

Question 40

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

Answer 40

Transmembrane Pathway

Question 41

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

Answer 41

Transmembrane Pathway

Question 42

transport across the tonoplast may also be involved

Answer 42

Transmembrane Pathway

Question 43

water travels from one cell to the next via the plasmodesmata

Answer 43

Symplast Pathway

Question 44

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

Answer 44

symplast

Question 45

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

Answer 45

Casparian strip

Question 46

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

Answer 46

Casparian strip

Question 47

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

Answer 47

Suberin

Question 48

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

Answer 48

casparian strip

Question 49

water movement across the endodermis occurs through the ___

Answer 49

symplast

Question 50

Solute Accumulation in the Xylem Can Generate “____

Answer 50

Root Pressure

Question 51

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

Answer 51

positive hydrostatic pressure

Question 52

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

Answer 52

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

Question 53

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

Answer 53

lowering of the xylem Ψw; positive hydrostatic pressure

Question 54

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

Answer 54

osmotic cell

Question 55

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

Answer 55

Root pressure; high; low

Question 56

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

Answer 56

guttation

Question 57

___constitutes the longest part of the pathway of water transport

Answer 57

Xylem

Question 58

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

Answer 58

low resistance

Question 59

Two Types of Tracheary Elements of xylem

Answer 59

Tracheids; vessel element

Question 60

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

Answer 60

Tracheids; Vessel Elements

Question 61

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

Answer 61

death

Question 62

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

Answer 62

Tracheids

Question 63

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

Answer 63

pits

Question 64

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

Answer 64

Pits

Question 65

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

Answer 65

pit pairs.

Question 66

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

Answer 66

Pit pairs

Question 67

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

Answer 67

Pit membrane

Question 68

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

Answer 68

torus (pl. tori)

Question 69

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

Answer 69

Torus

Question 70

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

Answer 70

cavitation

Question 71

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

Answer 71

vessel elements; perforiation plate

Question 72

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

Answer 72

vessel

Question 73

The ___ Explains Water Transport in the Xylem

Answer 73

Cohesion – Tension Theory

Question 74

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.

Answer 74

positive pressures; negative pressures

Question 75

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

Answer 75

cohesion–tension theory of sap ascent

Question 76

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

Answer 76

inward force; weak;

Question 77

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

Answer 77

secondary wall thickenings and lignifications of tracheids and vessels

Question 78

- this is the increased tendency for air to be pulled through microscopic pores in the xylem cell walls due to increasing water tension

Answer 78

Air seeding

Question 79

- the phenomenon of air formation and expansion; also known as __

Answer 79

Cavitation; embolism

Question 80

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

Answer 80

Cavitation

Question 81

____ in the Leaf Generates a ____Pressure in the Xylem

Answer 81

Water Evaporation; Negative

Question 82

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

Answer 82

evaporation of water

Question 83

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

Answer 83

surface of the cell walls

Question 84

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

Answer 84

air-water interfaces

Question 85

Tensions or negative pressures originate in __

Answer 85

leaves