3 Plant-Water Relations Flashcards
1
Q
Water plays a crucial role in the life of the plant. For every gram of organic matter made by the plant, approximately _ g of water is absorbed by the roots, transported through the plant body and lost to the atmosphere.
A
500
2
Q
Cell walls allow plant cells to build up large internal hydrostatic pressures, called _ pressure, which are a result of their normal water balance
A
turgor
3
Q
Turgor pressure is essential for many physiological processes,
including (5)
A
- cell enlargement,
- gas exchange in the leaves,
- transport in the phloem, and
- various transport processes across membranes
- contributes to the rigidity and mechanical stability of nonlignified plant tissues
4
Q
- Water makes up most of the mass of plant cells
- Water typically constitutes _ % of the mass of growing plant tissues
- each cell contains a large-water filled vacuole
- cells the cytoplasm makes up only _ % of the cell volume; the remainder is vacuole
A
80 to 95
5 to 10
5
Q
Water is the most abundant and arguably the best solvent known
- As a solvent, it makes up the _ for the movement of molecules within and between cells and greatly influences the structure of _ , and other cell constituents
- Water forms the environment in which most of the biochemical reactions of the cell occur, and it directly participates in many essential chemical reactions
A
- medium
- proteins, nucleic acids, polysaccharides
6
Q
Plants continuously absorb and lose water
- Most of the water lost by the plant evaporates from the leaf as the CO2 needed for photosynthesis is absorbed from the atmosphere
- On a warm, dry, sunny day a leaf will exchange up to _ % of its water in a single hour
- During the plant’s lifetime, water equivalent to _ times the fresh weight of the plant may be lost through the leaf surfaces.
- water loss is called _
A
- 100
- 100
- transpiration
7
Q
Transpiration is an important means of _ input from sunlight
- Heat dissipates because the water molecules that escape into the atmosphere have _ than-average energy, which breaks the bonds holding them in the liquid
- When these molecules escape, they leave behind a mass of molecules with lower-than-average energy and thus a cooler body of water.
- For a typical leaf, nearly _ of the net heat input from sunlight is dissipatedby transpiration.
- the stream of water taken up by the roots is an important means of
bringing _ to the root surface for absorption.
A
- dissipating the heat
- higher
- half
- dissolved soil minerals
8
Q
property of water that made it act as a best solvent and can transport through the body of the plant
A
polarity
polar structure of water molecule
9
Q
Diagram of the Water Molecule
A
- two intramolecular hydrogen–oxygen bonds form an angle of 105°
- opposite partial charges (δ– and δ+) on the water molecule lead to the formation of intermolecular hydrogen bonds with other water molecules
10
Q
- Because the oxygen atom is more electronegative than hydrogen, it tends to attract the electrons of the covalent bond.
- This attraction results in a partial negative charge at the _ end of the molecule and a partial positive charge at _
A
- oxygen
- each hydrogen
11
Q
- weak electrostatic attraction between molecules;
- responsible for many of the unusual properties of water
A
Hydrogen Bond
12
Q
The Polarity of Water Molecules Gives Rise to _ and makes water an _
A
- Hydrogen Bonds
- excellent solvent
13
Q
versatility of water as solvent is due to
A
- small size of water molecule
- its polar nature
14
Q
Polarity makes water a particularly good solvent for ionic substances and for molecules such as sugars and proteins that contain polar _
A
—OH or —NH2 groups
15
Q
what 3 properties of Water Result from Hydrogen Bonding
A
- thermal property
- Cohesive property
- Adhesive Properties
16
Q
The extensive hydrogen bonding between water molecules results in unusual thermal properties, such as _
A
- high specific heat
- high latent heat of vaporization
17
Q
- the heat energy required to raise the temperature of a substance by a specific amount.
A
Specific heat
18
Q
– the energy needed to separate molecules from the liquid phase and move them into the gas phase at constant temperature
A
Latent heat of vaporization
19
Q
– a process that occurs during transpiration [important component of temperature regulation in palnts
A
Latent heat of vaporization
20
Q
The _ of water enables plants to cool themselves by evaporating water from leaf surfaces, which are prone to heat up because of the radiant input from the sun.
A
high latent heat of vaporization
21
Q
- Water molecules at an air–water interface are more strongly attracted to neighboring water molecules than to the gas phase-water surface.
- As a consequence of this unequal attraction, an air–water interface _ its surface area.
- To increase the area of an air–water interface, hydrogen bonds must be _ , which requires an input ofenergy.
A
minimizes
broken
22
Q
the energy required to increase the surface area.
A
Surface tension
23
Q
Surface tension not only influences the _ but also may
create a _ in the rest of the liquid
A
shape of the surface
pressure
24
Q
Surface tension at the evaporative surfaces of leaves generates the physical forces that _ through the plant’s _ system
A
pull water
vascular
25
the mutual attraction between molecules
Cohesion
26
attraction of water to a solid phase such as cell wall or glass surface
Adhesion
27
movement of water along a capillary tube; result of cohesion, adhesion and surface tension
Capillarity
28
Cohesion gives water a _
High Tensile strength
29
the maximum force per unit
area that a continuous column of water can withstand before breaking
tensile strength
30
unit of measurement of pressure
pascals (Pa)
[more convenient is megapascals
(MPa = approximately 9.9 atmospheres)]
31
# Function of Water in Plant Life
Water is a constituent of _
protoplasm
32
# Function of Water in Plant Life
Water acts as a solvent.
Plants can absorb nutrients when these nutrients are _ in water
dissolved
33
# Function of Water in Plant Life
Water is used for _ from the soil to green plant tissues.
transpiration carrier of nutrients
34
# Function of Water in Plant Life
They are used for _ and the end product is also conveyed through water to various plant parts
photosynthesis
35
# Function of Water in Plant Life
Water forms over _ % of the plant body by green or fresh weight basis.
90
36
# Function of Water in Plant Life
Plants can _ through photosynthesis only in the presence of water in their
system
synthesis food
37
# Function of Water in Plant Life
Water helps to maintain the _ . Water helps in _ due to turgor pressure and cell division which ultimately **increase the growth of plant**.
turgidity of cell walls
cell enlargement
38
# Function of Water in Plant Life
Water is essential for the _ , **growth of plant roots**, and _ of soil organism
germination of seeds
nutrition and multiplication
39
# Function of Water in Plant Life
Water is essential in _ in the plant. It helps in the **conversion of starch to sugar**
hydraulic process
40
# Function of Water in Plant Life
Water helps in the transpiration, which is very essential for maintaining the _ from the soil.
absorption
of nutrient
41
# Function of Water in Plant Life
Water regulates the _ and cools the plant.
temperature
42
# Function of Water in Plant Life
Water helps in the _ reaction in soil.
chemical, physical and biological
43
– integral membrane proteins that form water-selective channels across the membrane
Aquaporins
44
Because water diffuses faster through such channels than through a lipid bilayer, _ facilitate water movement into plant cells
Aquaporins
## Footnote
aquaporins may alter rate of water movement across movement but not the direction off transport or driving force for water movement
45
Water molecules in a solution are not static; they are in **continuous motion, colliding with one another** and exchanging _
kinetic energy
46
molecules intermingle as a result of their random _
thermal agitation
47
This random motion is called _ . As long as other forces are not acting on the molecules,
diffusion
48
diffusion causes the net movement of molecules from
regions of high concentration to regions of low concentration—that is, down a _
concentration gradient
49
– German scientist discovered that the rate of **diffusion** is
**directly proportional** to the **concentration gradient**
Adolf Fick (1880s)
50
**rate of transport**; amount of substance crossing a unit area per unit time.
Flux density (Js)
51
* proportionality constant that measures how easily substance moves through a particular medium;
* characteristic of the substance and depends on the medium
* the negative sign in the equation
indicates that the flux moves down a concentration gradient.
Diffusion coefficient
## Footnote
movement is in response to a concentration gradient not for movement
in response to other forces such as pressure, electric fields, etc
52
Diffusion is Rapid over _ Distances but Extremely Slow over _ Distances
short
Long
53
**diffusion** in solutions can be effective within _ dimensions but is far too slow for mass transport over long distances.
cellular
54
**Pressure-Driven Bulk Flow** Drives _ -Distance Water Transport
Long
55
* second process by which water moves;
* a concerted movement of groups of molecules en masse, most often in response to a **pressure gradient**.
Bulk Flow or Mass Flow
56
In a bulk flow through a tube, the rate of volume flow depends on the _ of the tube, the _ of the liquid and the _ that drives the flow
* radius
* viscosity
* pressure gradient
57
If the radius is doubled, the volume flow rate increases by a factor of _
16 (2^4)
58
_ of water is the predominant mechanism responsible for long-distance transport of water in the xylem
Pressure-driven bulk flow
## Footnote
It also accounts for much of the water flow through the soil and through the cell walls of plant tissues.
59
Osmosis is Driven by a _
Water Potential Gradient
60
* In **simple diffusion**, substances move **down a concentration gradient**;
* in **pressure-driven bulk flow**, substances move **down a pressure gradien**t;
* in osmosis, _ influence transport.
both types of gradients
61
The Chemical Potential of Water Represents the _ of Water
Free-Energy Status
62
All living things, including plants, require a continuous input of_ to maintain and repair their highly organized structures, as well as to grow and reproduce
free energy
63
Processes such as _ are all driven by an input of free energy into the plant.
* biochemical reactions,
* solute accumulation,
* long-distance transport
64
a quantitative expression of the free energy
associated with water.
Chemical potential (of water)
65
- a measure of the free energy of water per unit volume
Water Potential
66
Three Major Factors Contribute to Cell Water Potential
1. solutes
2. pressure
3. gravity
67
represents the effect of dissolved solutes on
water potential.
Solute potential or osmotic potential
68
Solutes reduce the free energy of water by _
diluting the water.
69
This is primarily an **entropy effect;** that is, the mixing of solutes and water increases the disorder of the system and thereby _
lowers free energy
## Footnote
This means that the osmotic potential is independent of the specific nature of the
solute.
70
Hydrostatic pressure of the solution
Pressure
71
Sometimes called pressure potential
Pressure
72
Positive pressures _ the water potential; negative pressures _ it
raise
reduce
73
The **positive hydrostatic pressure** within cells is the pressure referred to as _
turgor
pressure
74
The value of pressure potential can also be negative, as is the case in the xylem and in the walls between cells, where a _ or **negative hydrostatic pressure**, can
develop.
tension
75
causes water to move downward unless its force is opposed by an
equal and opposite force
gravity
76
* _ are all strongly influenced by water potential and its components.
* Like the body temperature of humans, _ is a good overall indicator of plant health.
* Cell growth,
* photosynthesis,
* crop productivity
* water potential
77
Water Enters the Cell along a _
Water Potential Gradient
78
Water Can Also Leave the Cell in Response to a _
Water Potential Gradient
79
Small Changes in **Plant Cell Volume** Cause Large Changes in _
Turgor Pressure
80
Water Transport Rates Depend on _
Driving Force and Hydraulic Conductivity
81
The _ Concept Helps Us Evaluate the Water Status of a Plant
Water Potential
82
The Components of Water Potential Vary with _ within the Plant
Growth Conditions and Location
83
Water is important in the life of plants because it makes up the _ and _ in which most biochemical processes essential for life take place.
matrix
medium
84
The _ and _ of water strongly influence the structure and properties of
proteins, membranes, nucleic acids, and other cell constituents
structure
properties
85
In most land plants, water is continually lost to the _ and taken up from the _.
atmosphere
soil
86
The movement of water is driven by a _ , and water may move
by diffusion, by bulk flow, or by a combination of these fundamental transport mechanisms
reduction in free energy
87
Water diffuses because molecules are in constant _, which **tends to even out concentration differences.**
thermal agitation
88
Water moves by bulk flow in response to a _, whenever there is a suitable pathway for bulk movement of water.
pressure difference
89
Osmosis, the movement of water across membranes, depends on a gradient in free energy of water across the membrane—a gradient commonly measured as a
_.
difference in water potential
90
_ are the two major factors that affect water potential, although when **large vertical distances** are involved, **gravity** is also important
Solute concentration and hydrostatic pressure
91
Plant cells come into water potential equilibrium with their local environment by _
absorbing or losing water
92
Usually this change in cell volume results in a change in _ , accompanied by minor changes in _.
cell water potential
cell solute potential
93
The rate of water transport across a membrane depends on the _ across the membrane and the _ of the membrane.
water potential difference
hydraulic conductivity
94
In addition to its importance in transport, water potential is a useful measure of the _ of plants.
water status
