Deck 35: Water and Sugar Transport in Plants

Question 1

What drives the flow of water through the xylem?

A) passive transport by the endodermis
B) the evaporation of water from the leaves
C) active transport by parenchyma cells within xylem tissue
D) the number of companion cells in the phloem
E) active transport by tracheid and vessel elements

Answer 1

B

Question 2

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

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

Answer 2

B

Question 3

Water potential in plants consists mainly of

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

Answer 3

B

Question 4

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

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

Question 5

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

A) cytoskeleton
B) aquaporins
C) porous cell walls
D) plasmodesmata
E) large central vacuole

Question 6

Cavitation is defined as the formation of bubbles within a liquid. Based on this definition, which mechanism of water transport in xylem can contribute to recovery from cavitation?

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

Question 7

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

A) A water potential gradient between roots and shoots.
B) The movement of water into the xylem from surrounding cells in the roots.
C) Not all plants have roots.
D) Not all soils have high concentrations of ions.
E) Shoots with roots removed can transport water when placed in a container of water.

Question 8

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) ƒsoil < ƒroots < ƒleaves < ƒatmosphere
B) ƒatmosphere < ƒleaves = ƒroots < ƒsoil
C) ƒsoil < ƒroots = ƒleaves < ƒatmosphere
D) ƒatmosphere < ƒleaves < ƒroots < ƒsoil

Question 9

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

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

Question 10

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

Question 11

In which plant cell or tissue would the pressure component of water potential most often be negative?

A) stem xylem
B) stem phloem
C) root epidermis
D) root cortex cell
E) leaf mesophyll cell

Question 12

How does a flaccid cell differ from a turgid cell?

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

Question 13

Hypothetical plant cells A and B are adjacent to each other. The solute potential ƒS) of cell A is - 0.35 MPa, and its pressure potential ƒP) is +0.15 MPa. The solute potential ƒS) of cell B is - 0.30 MPa, and its pressure potential ƒP) 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 B to cell A
C) from cell A to cell B

Question 14

Loss of water from the aerial parts of plants is called

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

Question 15

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

Question 16

Cell- to- cell water movement always occurs from

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

Question 17

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

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

Question 18

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

Question 19

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

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

Question 20

Which cells in a root form a protective barrier to the vascular system where all materials must move through the symplast?

A) endodermis
B) cortex
C) pericycle
D) exodermis
E) epidermis

Question 21

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

A) antiporter
B) channel
C) cotransporter
D) pump
E) symporter

Question 22

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

Question 23

Which of the following adaptations are least likely to be found in plants that regularly experience dry, hot conditions?

A) a thick cuticle on fleshy leaves
B) plants that do not produce abscisic acid and have a short, thick taproot
C) CAM plants that grow rapidly
D) large, fleshy stems with the ability to carry out photosynthesis
E) small, thick leaves with stomata on the lower surface

Question 24

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

A) Active and passive transport play a role.
B) The mechanisms of sucrose movement and the membrane proteins involved vary among different plant species.
C) Regardless of the type of sink, the conversion of sucrose to storage compounds, such as starch, is a major part of the process.
D) Water moves by osmosis from phloem to xylem.
E) The mechanisms of sucrose movement and the membrane proteins involved vary among different sinks within a plant.

Question 25

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

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

Question 26

As an undergraduate research assistant, 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 shoot apical meristem
B) a young leaf directly above the treated leaf
C) a mature upper leaf on the opposite side of the plant from the treated leaf
D) the treated leaf
E) the roots

Question 27

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) 50- 250.
C) 500.

Question 28

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

Question 29

CAM plants perform photosynthesis during the day even though their stomata are closed. How do these plants obtain carbon dioxide in order to carry out photosynthesis?

A) CAM plants use glucose as their main source of carbon dioxide during periods of drought.
B) CAM plants transport carbon dioxide from the soil through the phloem to offset the loss of carbon dioxide uptake in the leaves.
C) Carbon dioxide is stored within specialized bundle sheath cells during mild temperatures for use during drought.
D) CAM plants open their stomata at night to obtain carbon dioxide.

Question 30

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

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

Question 31

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) Sugar is translocated in a bi- directional manner.
C) Strong pH differences exist between the cytoplasm of the companion cell and the mesophyll cell.
D) Movement of water occurs from xylem to phloem and back again.
E) H⁺- ATPases are abundant in the plasma membranes of the mesophyll cells.

Question 32

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

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

Question 33

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

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

Question 34

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

Question 35

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

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

Question 36

J. A. Milburn and R. P. C. Johnson developed an acoustic method for detecting cavitation formation of air bubbles) 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 adding water to the cut end of the petiole, recording an increased rate of clicking
C) after increasing transpiration by blowing warm air across the leaf, recording an increased rate of clicking

Question 37

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

Question 38

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

Question 39

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

Question 40

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

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

Question 41

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

Question 42

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

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