Bio 206 Ch 35: Water and Sugar Transport in Plants
positive
pressure potential from turgor pressure is _____ inside living cells
living
pressure potential from turgor pressure is positive inside ______ cells
vessel elements
pressure potential in dead cells such as ____ ___ can sometimes be negative
lowers
light/xylem probe experiments lead biologists to believe that increased transpiration leads to increased tension on xylem sap. Rising tension, in turn, _____ the water potential of leaves and exerts a pull on water in the roots, where the water potential is high
pressure potential
like the cohesion-tension theory for water transport in xylem, the pressure-flow hypothesis is based on movement along a water-potential gradient created by changes in ____ ____
adhesion, cohesion
menisci form because _____ and _____ pull water molecules up along the sides of the tube, while gravity pulls the water surface down in the middle
high
moist soil's water potential is ____ compared to the water potential found in plant's roots
capillary action
movement of water up a narrow tube
lower
normally, the water potential of the atmosphere is ______ than the water potential inside a leaf, so water in the leaf evaporates quickly
energy
one of the most important features of the cohesion-tension theory is that it doesn't require plants to expend _____
potential
osmosis occurs as a direct result of differences in water ____ from one region to another
sucrose
phloem sap flowing through vascular tissue is often dominated by the disaccharide _____.
turgor
the differences between _____ pressure in the phloem near the source tissues and near sink tissues generates the force for the pressure-flow hypothesis
gravity
the effects of adhesion, cohesion, and _____ are responsible for the formation of a concave surface boundary called a meniscus
meniscus
the effects of adhesion, cohesion, and gravity are responsible for the formation of a concave surface boundary called a _____
wall pressure
the force exerted by the cell wall is called ____ ____
cohesion-tension
the leading hypothesis to explain long distance water movement in vascular plants is the _____-_____ theory, which states that water is pulled from roots to the tops of trees along a water potential gradient, via forces generated by transpiration at leaf surfaces
tension, xylem
the negative force or pull (______) generated at the air-water interface is transmitted through the water outside of leaf cells, to the water in _____, to the water in vascular tissue of roots, and finally to the water in the soil
megapascals
water potential is measured in units called _____, which is force per unit area.
adhesion, cohesion, surface tension
what are the three forces that cause capillary action?
sieve tube elements, companion cells
what two cell types does phloem consist of ?
water-potential, steeper
when a stoma opens, humid air is exposed to the atmosphere, which is in most cases much drier. This creates a steep ______-_____ gradient between the leaf interior and its surroundings. The _____ the gradient, the faster water vapor diffuses out through the stomata
increased
when experimenters raised light levels and measured xylem pressure, they found that as light intensity ______, the xylem pressure probe documented increased tension, or negative pressure
isotonic
when solute concentrations inside and out of the cell are the same, the solution is said to be ______
drops
when the water potential in soil ___, water is less likely to move from soil into roots
less
when water potential in soil drops, water is ___ likely to move from soil into roots
high, low
xylem acts as a passive conduit- a set of narrow pipes that allows water to move from a region of ____ water potential (the roots) to a region of ___ water potential (the leaves)
decreases
xylem pressure _____ when light intensity increases. This supports the cohesion tension theory
sink
Munch proposed that cells in the ____ remove sucrose from the phloem sap by passive or active transport
source
in vascular plants, a ____ is a tissue where sugar enters the phloem
phloem, xylem
______ sap moves via pressure flow and _____ sap moves via transpirational pull
sinks
During the growing season, apical meristems, lateral meristems, developing leaves, flowers, developing seeds and fruits, and storage cells in roots all act as ____
surface tension
_____ ____ is a force that exists among water molecules at an air-water interface
salt
_____ adapted species often respond to low water potentials in soil by accumulating solutes in their root cells, which lowers their solute potential
companion cells
______ ____ are located adjacent to sieve tube elements and function as their support staff
pressure potential
______ ____ refers to any kind of physical pressure on water
transipration
______ is evaporation of water from the stomata of leaves. It occurs virtually no energy.
cohesion
______ is the molecular attraction among like molecules, such as the hydrogen bonding that occurs among water molecules
adhesion, hydrogen
_______ is a molecular attraction among unlike molecules. In this case, water interacts with a solid substrate-like the glass walls of a tube or cell walls of tracheids/vessel elements- through _____ bonding
passive
_______ transport occurs when ions or molecules move across a plasma membrane by diffusion- that is, along their electrochemical gradient
flaccid
a cell that is _____ has no turgor pressure and therefore has a pressure potential of 0 MPa
hypotonic
a solution is ______ relative to the cell when the surrounding solution has a lower solute concentration than the cell
lower
a solution is hypotonic relative to the cell when the surrounding solution has a _____ solute concentration than the cell
pressure
although solute potential is always negative, the _____ potential from turgor pressure is positive inside living cells
menisci
as more water evaporates from leaf cells, the ____ become steeper and the total area of the air-water interface increases. The formation of this produces a force capable of pulling water up from the roots
decreases
as soils dry, their water potential _____
drops
as soils dry, their water potential decreases. But if a plant's solute potential ____, it can maintain a water potential gradient that continues to bring water into the plant.
below
as the summer progresses and water potential in soil drops, ninebark shrubs are able to keep acquiring water and grow because the solute potential of their tissues stays ______ the soil water potential
turgor pressure
as water moves into the cell, the pressure inside the cell, known as ____ ____, increases until water pressure is induced.
stronger
because they have fewer neighbors nearby, surface water molecules share _____ attractive forces and bind together more tightly. This is what causes surface tension
dead
because tracheids and vessels are ____ at maturity, the water in xylem does not cross plasma membranes
water potential
biologists use the term ____ ___ to indicate the potential energy that water has in a particular environment compared with the potential energy of pure water at room temperature and atmospheric pressure
exits
in vascular plants, a sink is a tissue where sugar ___ the phloem
enters
in vascular plants, a source is a tissue where sugar _____ the phleom
turgid
cells that are firm and that experience wall pressure are said to be _____
hydrogen
cohesion is the molecular attraction among like molecules, like _____ bonding that occurs among water molecules
capillary action
cohesion-tension theory relies on two of the forces involved in _____ _____, namely, cohesion and tension
low
compared to the water in the adjacent xylem cells in a vascular bundle, the phloem sap has a very _____ solute potential
yes
does the pressure-flow hypothesis process require energy?
sources
during the growing season, mature leaves and stems that are actively photosynthesizing produce sugar in excess of their own needs. These tissues act as _____
sinks
early in the growing season, developing leaves act as ____
sources
early in the growing season, storage cells in roots and stems act as _____
apical meristems, roots
experiments with tall plants show that leaves on the upper part of the stem send sugar to ____ ____, but leaves on the lower part of the plant send sugar to the ____
transpiration
higher light levels reduced the weight of plants in an experiment, suggesting that higher ______ rates caused water loss
close
if water is not replaced fast enough, leaves and branches begin to wilt. In response, stomata may ____ down partially or completely to reduce transpiration rates. However, this affects the ability of plants to do photosynthesis
lowers
in dry soil, water no longer flows freely in spaces and all the remaining water adheres tightly to soil particles, creating a tension that _____ the water potential of soil water
cohesion-tension
in effect, the _____-_____ theory of water movement states that, because of hydrogen bonds between water molecules, water is pulled up through xylem in continuous columns
high
in moist soil, water that fills crevices between soil particles usually contains relatively few solutes and normally is under little pressure. As a result, its water potential tends to be ____ relative to the water potential found in a plant's roots, which is higher in solutes
highest, lower, lower, lowest, gradient
in most cases, water potential is ______ in soil, _____ in roots, ______ yet in leaves, and _____ in the atmosphere. This is the water potential ______
lower
in salty soils, the water potential is ____ than the water potential found in plant's roots
diffuses, evaporates, xylem, up, root, soil
in the cohesion tension theory, there are 6 main steps: 1. water vapor _____ out of the leaf 2. water _____ inside the leaf 3. water is pulled out of _____ 4. water is pulled ___ xylem 5. water is pulled out of _____ cortex 6.water is pulled from _____ into root
high
in the pressure-flow hypothesis, ____ turgor pressure near sources causes phloem sap to flow to sinks
sink
in vascular plants, a ____ is a tissue where sugar exits the phloem
lower
salt adapted plants have enzymes that increase the concentration of certain organic molecules in the cytoplasm. As a result, they can keep the water potential of their tissues ____ than that of salty soils and are able to absorb what little water is available.
lowers
salt adapted species often respond to low water potentials in soil by accumulating solutes in their root cells, which _____ their solute potential
alive
sieve tube elements are ____ at maturity
sieve plates
sieve tube elements lack nuclei and most other organelles. They are connected to one another, end to end, by perforated ____ ____
negative
solute potentials are always ______ because they are measured relative to the solute potential of pure water
negative
solutions that consist of water and solutes have water potentials that are _____.
low
solutions with high concentrations of solutes have ____ solute potentials
companion cells, sieve tube elements
sucrose moves from source cells into _____ ____ and from there into ____ ______ ____
pressure-flow, bulk flow
the ______-____ hypothesis states that events at source tissues and sink tissues create a pressure gradient in phloem. The water in phloem sap moves down this pressure gradient, and sugar molecules are carried along by _____ _____.
lignin
the cells in vascular tissue have walls that are reinforced with tough ____ molecules. As a result, xylem consists of rigid pipes that can withstand internal tension without collapsing
water potential, transpiration
the cohesion-tension theory states that water is pulled from roots to the tops of trees along a ______ _____ gradient, via forces generated by ______ at leaf surfaces
bulk flow
the difference in pressure drives phloem sap from source to sink via ____ ____
sun
the plant does not expend energy to create the pulling force in water transport. The _____ provides energy for the force.
pressure, solute
the potential energy of water in a particular location is the sum of the ____ potential and the ____ potential that it experiences
pressure
the pressure-flow hypothesis predicts that water cycles between xylem and phloem, and that water movement in phloem is a response to a gradient in _____ potential
trichomes
the stomata of oleanders are located on the undersides of their leaves, inside deep pits in the epidermis. Hairlike extensions of epidermal cells called ______ shield these pits from the atmosphere
solute potential
the tendency for water to move in response to differences in solute concentrations is called the _______ ____.
xylem, hydrogen
the transmission of pulling force from the leaf surface to the root is possible because 1) ____ forms a continuous network from roots to leaves, so there are continuous columns of water throughout the plant, and 2) all of the water molecules are bonded to each other through _____ bonds (cohesion)
bulk flow
the water in a column of xylem cells moves by ____ ____- a mass movement of molecules along a pressure gradient
high, low
there is ____ turgor pressure in phloem at a source tissue and ____ turgor pressure at the sink, created by the loading and unloading of sugars, respectively.
low
there is _____ turgor pressure in phloem at a sink tissue
high
there is _____ turgor pressure in phloem at a source tissue
source, sink
there is high turgor pressure in phloem at a ____ tissue and low turgor pressure at the ____, created by the loading and unloading of sugars
solute
to establish a high pressure potential in sieve tube elements near source cells, large amounts of sugar have to be transported into the phloem sap- enough to raise the _____ concentration of sieve tube elements. This can take energy or be passive.
down
to move up a plant, water moves _____ the water-potential gradient that exists between the soil, its tissues, and the atmosphere.
open, drier
transpiration occurs when two conditions are met: stomata are ____ and the air surrounding leaves is ____ than the air inside leaves
channels, carriers
two types of membrane proteins- _____ and ______- form pores that selectively admit certain ions
