Deck 37: Water and Sugar Transport in Plants

Question 1

Water potential in plants consists mainly of

A)solute potential and osmotic potential.
B)solute potential and membrane potential.
C)pressure potential and solute potential.
D)pressure potential and membrane potential.
E)solute potential only.

Answer 1

C

Question 2

Which of the following features of plant cells allows for symplastic movement of water?

A)porous cell walls
B)cytoskeleton
C)plasmodesmata
D)large central vacuole
E)semipermeable membranes of mitochondria

Answer 2

C

Question 3

Which of the following observations provides the strongest evidence against root pressure being the principal mechanism of water transport in the xylem?

A)Not all plants have roots.
B)Not all soils have high concentrations of ions.
C)It requires movement of water into the xylem from surrounding cells in the roots.
D)Over long distances,the force of root pressure is not enough to overcome the force of gravity.
E)It requires development of a water potential gradient between roots and shoots.

Answer 3

D

Question 4

Root pressure can result in the early morning appearance of water droplets on leaves and flowers of low-growing plants.Which of the following does not contribute to the development of root pressure?

A)creation of tension in the xylem water column that leads to short-distance water movement
B)closed stomata
C)accumulation of ions from the soil by root epidermal cells
D)movement of ions from epidermis to xylem
E)creation of a water potential gradient between the xylem (lower ψ)and surrounding cells (higher ψ)in the root

Question 5

When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis,the volume of the cell increases until it bursts.This does not happen to plant cells,because

A)they have large central vacuoles,which provide abundant space for storage of incoming water.
B)the composition of their plasma membranes differs from that of animal-cell plasma membranes in a way that provides much greater strength.
C)they have cell walls,which prevent the entry of water by osmosis.
D)they have cell walls,which provide pressure to counteract the pressure of the incoming water.
E)certain proteins embedded in their plasma membranes act as "check valves," releasing excess water before it can cause the cell to burst.

Question 6

As an undergraduate research assistant in the lab of the famous Dr.S.Nameerf,your duties involve measuring water potential in experimental soil-plant-atmosphere systems.Assume you make a series of measurements in a system under normal daylight conditions,with stomata open and photosynthesis occurring.Which of the following correctly depicts the trend your measurement data should follow if the cohesion-tension mechanism is operating?

A)ψsoil < ψroots = ψleaves < ψatmosphere
B)ψatmosphere < ψleaves = ψroots < ψsoil
C)ψsoil < ψroots < ψleaves < ψatmosphere
D)ψatmosphere < ψleaves < ψroots < ψsoil

Question 7

Which theory of water transport in xylem can also be used to explain the movement of water in nonvascular plants such as mosses?

A)cohesion-tension
B)capillarity
C)proton pump
D)pressure flow
E)root pressure

Question 8

Researchers using a dendrograph found that the trunk diameter of a beech tree increased and decreased slightly on a daily basis and that this variation correlated negatively with transpiration rate.Under which of the following sets of conditions should the daily changes in trunk diameter be the smallest?

A)cool spring day,no wind,high soil moisture
B)cool spring day,no wind,soil partially frozen
C)hot summer day,windy,low soil moisture
D)hot summer day,no wind,low soil moisture
E)hot summer day,windy,high soil moisture

Question 9

Which of the following does not support the cohesion-tension theory of xylem transport?

A)Dendrograph measurements detect small daily changes in the diameter of tree trunks.
B)Following cutting of a petiole,the xylem sap withdraws from the cut edge toward the blade of the leaf.
C)Following application of a respiration inhibitor to a plant,xylem transport decreases substantially.
D)Measurements using a root bomb and xylem pressure probe detect negative pressures in xylem tissue.
E)Pressure bomb measurements detect daily changes in the water potential of leaf tissue.

Question 10

Which mechanism of water transport in xylem can contribute to recovery from cavitation?

A)cohesion-tension
B)capillarity
C)proton pump
D)pressure flow
E)root pressure

Question 11

Water potential of plants during night is ________ compared to day water potential due to ________.

A)increased;open stomata
B)increased;closed stomata
C)decreased;open stomata
D)decreased;closed stomata

Question 12

Formation of menisci,such as occurs in a tube filled with water,is an important factor in plant water movement.A meniscus is created by

A)the downward pull of gravity on the water column in the tube.
B)downward pressure from the atmosphere on the topmost layer of water molecules.
C)the water molecules along the walls of the tube being pulled upward by adhesion.
D)the topmost layer of water molecules being pulled downward by the water molecules below.

Question 13

Compared to plants from other environments,the cells of many desert plants contain high concentrations of solutes.This helps them survive in their arid surroundings because the high solute concentrations create relatively ________,which help reduce water loss.

A)low solute potentials
B)high pressure potentials
C)low pressure potentials
D)high solute potentials

Question 14

If you cut a stalk (petiole)of celery and place it in a beaker of water that has food coloring dissolved in it,colored water will move up the stalk and into the leaf blades.This provides evidence against which of the following theories of xylem transport?

A)pressure flow
B)root pressure
C)capillarity
D)proton pump
E)cohesion-tension

Question 15

Water potential (ψ)can be thought of as the tendency for water to move from one place to another.In plants,it is made up mainly of solute potential and pressure potential.Hypothetical plant cells A and B are adjacent to each other.The solute potential (ψS)of cell A is -0.35 MPa,and its pressure potential (ψP)is +0.15 MPa.The solute potential (ψS)of cell B is -0.30 MPa,and its pressure potential (ψP)is +0.05 MPa.In which direction will net water movement occur?

A)Neither;cells A and B are in equilibrium with each other.
B)from cell A to cell B
C)from cell B to cell A

Question 16

Cell-to-cell water movement always occurs from

A)higher to lower pressure potential.
B)higher to lower solute potential.
C)lower to higher solute potential.
D)higher to lower water potential.
E)lower to higher water potential.

Question 17

Researchers using a dendrograph found that the trunk diameter of a beech tree increased and decreased slightly on a daily basis and that this variation correlated negatively with transpiration rate.Under which of the following sets of conditions should the daily changes in trunk diameter be the highest?

A)cool spring day,no wind,soil partially frozen
B)cool spring day,no wind,high soil moisture
C)hot summer day,windy,low soil moisture
D)hot summer day,no wind,low soil moisture
E)hot summer day,windy,high soil moisture

Question 18

Loss of water from the aerial parts of plants is called

A)pressure flow.
B)cohesion-tension.
C)respiration.
D)evaporation.
E)transpiration.

Question 19

How does a flaccid cell differ from a turgid cell?

A)Flaccid cell has higher pressure potential.
B)Flaccid cell has lower pressure potential.
C)Flaccid cell has higher solute potential.
D)Flaccid cell has lower solute potential.

Question 20

Which of the following features of plant cells allows for apoplastic movement of water?

A)porous cell walls
B)cytoskeleton
C)plasmodesmata
D)large central vacuole
E)semipermeable plasma membrane

Question 21

The research by Natalie De Witt and Michael Sussman showed that proton pump AHA3 is localized in the membrane of companion cells of the source tissue.What is the function of this pump?

A)to move protons from inside of a companion cell to outside
B)to move protons from outside of a companion cell to inside
C)to move protons from inside of a companion cell to a source cell
D)to move protons and sucrose from inside of a companion cell to outside
E)to move protons and sucrose from outside of a companion cell to inside

Question 22

CAM and C₄ plants conduct photosynthesis in ways that allow them to live in drier areas than most C₃ plants can tolerate.The effectiveness of different plants in restricting water loss while still allowing for influx of adequate CO₂ can be compared using the transpiration ratio,which is calculated by dividing the amount of water transpired by the amount of CO₂ fixed by photosynthesis.If a typical transpiration ratio for a C₃ plant is 500,then possible values for CAM and C₄ plants could be

A)750-1000.
B)500.
C)50-250.

Question 23

Which of the following cross-membrane transport mechanisms occur without expenditure of energy?

A)facilitated diffusion
B)antiporter
C)symporter
D)cotransporter
E)pump

Question 24

Most biologists consider loss of water from plant tissues to be a negative thing,and,in fact,many plants have features that reduce water loss.Yet,plants still transpire.Which of the following is the least likely explanation for the fact that plants continue to transpire?

A)Transpiration drives water flow through the plant,which is necessary for uptake and distribution of essential nutrients.
B)Transpiration must be occurring for photosynthesis to take place.
C)It is difficult to produce a means of gas exchange that doesn't also allow water loss.
D)Evaporative cooling during transpiration may help prevent leaves from overheating.

Question 25

The processes of water flow in xylem and sugar translocation in phloem differ in many respects.Which of the following is not a difference between xylem and phloem transport?

A)Water potential gradients are required for xylem transport to occur,but not for phloem transport.
B)Xylem transport is a wholly passive process;phloem transport includes active (energy-requiring)processes.
C)Cells through which xylem transport occurs are "dead" at maturity;those in phloem transport are "alive."
D)Xylem transport always occurs in the same direction;phloem transport does not.

Question 26

Which of the following cross-membrane transport mechanisms requires the expenditure of energy?

A)direct diffusion
B)channel
C)antiporter
D)facilitated diffusion
E)carrier

Question 27

The pressure-flow mechanism for sugar translocation you have learned about in this class is based on research on angiosperms,and thus might not occur in other vascular plants.Which of the following real or hypothetical observations on gymnosperms would suggest they possess a different mechanism?

A)Pores in the sieve areas of their sieve-tube members are filled with numerous membranes.
B)Gymnosperms do not possess vessels.
C)Bidirectional phloem transport occurs in gymnosperms.
D)Asymmetric annual growth rings occur in gymnosperms.
E)Formation of buds is supported by products of photosynthesis primarily from leaves on the same branch.

Question 28

The mechanisms that regulate the loading of sucrose from the apoplast to the sieve-tube members by sucrose-H⁺ symporters are not well understood.Of the following possible regulatory factors,which is least likely to be of direct importance?

A)turgor pressure of sieve-tube members
B)sucrose concentration in the apoplast
C)density of direct cytoplasmic connections between companion cells and sieve-tube members
D)number of available symporter protein molecules in the plasma membranes of sieve-tube members

Question 29

Researchers have investigated bidirectional transport in phloem by applying different radioisotope tracers to two source leaves and monitoring a point between the two sources for the presence of the tracers.Which of the following observations would not support the pressure-flow hypothesis? Appearance of the two tracers in

A)sieve-tube members of different vascular bundles.
B)a single sieve-tube member.
C)adjacent sieve-tube members of the same vascular bundle.

Question 30

Which of the following supports the finding that sugar translocation in phloem is an active (energy-requiring)process?

A)Sucrose occurs in higher concentrations in companion cells than in the mesophyll cells where it is produced.
B)Movement of water occurs from xylem to phloem and back again.
C)Strong pH differences exist between the cytoplasm of the companion cell and the mesophyll cell.
D)H⁺-ATPases are abundant in the plasma membranes of the mesophyll cells.
E)All of the above apply.

Question 31

James Richards and Martyn Caldwell conducted an experiment to test the hypothesis that hydraulic lift occurs in Artemisia tridentata,a species of sagebrush common in the western United States.Each plant in the experimental group was covered with an opaque plastic bag for more than two days to prevent photosynthesis and greatly reduce transpiration,and control plants were left uncovered.Fluctuations in soil water potential were measured,and other aspects of the experimental systems were observed.Which of the following observations from such an experiment provides the strongest support for the occurrence of hydraulic lift in A.tridentata?

A)finding,in the experimental plants,that the water potential of upper roots is greater than that of the leaves
B)finding,in the experimental plants,that the water potential of the lower roots is greater than that of the upper roots
C)finding,in the experimental plants,that the water potential of the lower roots is less than that of the upper roots
D)finding that the shallow soil beneath the experimental plants is drier than beneath the control plants
E)finding that the shallow soil beneath the experimental plants is moister than beneath the control plants

Question 32

In the pressure-flow mechanism,loading of sucrose from companion cells to sieve-tube elements takes place through

A)plasmodesmata.
B)facilitated diffusion.
C)sucrose-H⁺ symporters.
D)sucrose-H⁺ antiporters.
E)carriers.

Question 33

Which of the following is not a net sink for products of photosynthesis in a deciduous angiosperm tree?

A)leaves in early spring
B)flowers in summer
C)fruits in summer
D)roots in early spring
E)roots in early autumn

Question 34

Which of the following would not be expected to contribute to high rates of transpiration?

A)high atmospheric CO₂ concentration
B)bright sunlight
C)warm air temperature
D)brisk wind
E)high soil moisture

Question 35

Which of the following is a similarity between xylem and phloem transport?

A)Many cells in both tissues have sieve plates.
B)Expenditure of energy from ATP is required.
C)Transpiration is required for both processes.
D)Bulk flow of water is involved.

Question 36

As an undergraduate research assistant in the lab of the famous Dr.S.Nameerf,you are assisting with a radioisotope tracer experiment.You expose a mature leaf on one side of the lower shoot of a sugar beet plant to ¹⁴CO₂ and then track the movement of the ¹⁴C atoms by radiography.Where are you least likely to detect ¹⁴C?

A)the treated leaf
B)the shoot apical meristem
C)the roots
D)a mature upper leaf on the opposite side of the plant from the treated leaf
E)a young leaf directly above the treated leaf

Question 37

Which of the following structural features of plants would not be expected to reduce transpiration?

A)thick cuticle on leaves and stems
B)abundant epidermal hairs on leaves and stems
C)sunken stomata
D)stomata on upper and lower surfaces of the leaves
E)reduced leaf size

Question 38

Which of the following statements about phloem unloading at sinks is not consistent with our current understanding?

A)Passive transport plays a role.
B)Regardless of the type of sink,the conversion of sucrose to storage compounds,such as starch,is a major part of the process.
C)The mechanisms of sucrose movement and the membrane proteins involved vary among different plant species.
D)The mechanisms of sucrose movement and the membrane proteins involved vary among different sinks within a plant.
E)Active transport plays a role.

Question 39

Which of the following would be expected to contribute to relatively high rates of transpiration?

A)heavy cloud cover
B)cool air temperature
C)calm air
D)low atmospheric CO₂ concentration
E)low soil moisture

Question 40

J.A.Milburn and R.P.C.Johnson developed an acoustic method for detecting cavitation in plants.This involves "listening" for characteristic clicks produced during air-bubble formation,using sensitive microphones and amplifiers.In one experiment with the castor bean plant (Ricinus communis),they detached leaves by cutting the petioles and subjected them to various treatments.Which of the following would be least likely to be observed in such an experiment?

A)as the leaf is allowed to wilt,recording many clicks that approximately equal the estimated number of vessels in the cut petiole
B)after increasing transpiration by blowing warm air across the leaf,recording an increased rate of clicking
C)after adding water to the cut end of the petiole,recording an increased rate of clicking

Question 41

Irrigation reduces soil quality and rains usually don't.Why?

A)Rains deliver less water to soil than irrigation does.
B)Water used for irrigation contains fertilizer and pesticides that affect soil quality.
C)Rainwater contains less inorganic material.
D)The fast water flow during irrigation removes organic material from soil.
E)The fast water flow during rains is able to remove toxic materials from topsoil.

Question 42

The researchers discovered a new proton pump that is involved in phloem unloading in the sugar storage tissue.Predict the movement of ions carried out by this pump.

A)active transport of protons from cytoplasm to vacuole
B)active transport of protons from vacuole to tonoplast
C)active transport of protons from vacuole to cytoplasm
D)active transport of sugar from cytoplasm to vacuole
E)passive transport of sugar from cytoplasm to vacuole