Deck 35: Water and Sugar Transport in Plants

Question 1

Which of the following would be LEAST likely to affect osmosis in plants?

A) temperature
B) a difference in solute concentrations
C) receptor proteins in the membrane
D) aquaporins
E) a difference in water potential

Answer 1

C

Question 2

What would enhance water uptake by a plant cell?

A) decreasing the Ψ of the surrounding solution
B) increasing the pressure exerted by the cell wall
C) the loss of solutes from the cell
D) increasing the Ψ of the cytoplasm
E) positive pressure on the surrounding solution

Answer 2

E

Question 3

As an undergraduate research assistant, 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

Answer 3

D

Question 4

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

Question 5

Which of the following has the lowest (most negative) water potential?

A) root cortical cells
B) root xylem vessels
C) leaf air spaces
D) leaf mesophyll cells

Question 6

What drives the flow of water through the xylem?

A) passive transport by the endodermis
B) the number of companion cells in the phloem
C) the evaporation of water from the leaves
D) active transport by sieve-tube elements
E) active transport by tracheid and vessel elements

Question 7

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

A) porous cell walls
B) plasmodesmata
C) large central vacuole
D) endodermal cells

Question 8

Which of the following statements about bulk flow are correct?
I) Bulk flow is driven primarily by pressure potential.
II) Bulk flow depends on a difference in pressure potential at the source and sink.
III) Bulk flow depends on the force of gravity on a column of water.
IV) Bulk flow may be the result of either positive or negative pressure potential.

A) I and III
B) II and III
C) I, II, and IV
D) I, II, III, and IV

Question 9

Root hairs are most important to a plant because they ________.

A) anchor a plant in the soil
B) store starches
C) increase the surface area for absorption
D) provide a habitat for nitrogen-fixing bacteria
E) contain xylem tissue

Question 10

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 gated channel proteins embedded in their plasma membranes open as osmotic pressure decreases, allowing excess water to leave the cell

Question 11

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 12

If isolated plant cells with a water potential averaging −0.5 MPa are placed into a solution with a water potential of −0.3 MPa, which of the following would be the most likely outcome?

A) The pressure potential of the cells would increase.
B) Water would move out of the cells.
C) The cell walls would rupture, killing the cells.
D) Solutes would move out of the cells.
E) The osmotic pressure of the cells would decrease.

Question 13

How does a flaccid cell differ from a turgid cell?

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

Question 14

Irrigation reduces soil quality, but rains usually do not. 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 lower amounts of salt.
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 15

Most of the water taken up by a plant is ________.

A) used as a solvent
B) used as a hydrogen source in photosynthesis
C) lost during transpiration
D) converted to carbon dioxide
E) used to keep cells turgid

Question 16

If ΨP = 0.3 MPa and ΨS = −0.45 MPa, the resulting Ψ is ________.

A) +0.75 MPa
B) −0.75 MPa
C) −0.15 MPa
D) +0.15 MPa
E) −0.42 MPa

Question 17

Water potential is generally most negative in which of the following parts of a plant?

A) mesophyll cells of the leaf
B) xylem vessels in leaves
C) xylem vessels in roots
D) cells of the root cortex
E) root hairs

Question 18

The value for Ψ in root tissue was found to be −0.15 MPa. If you take the root tissue and place it in a 0.1 M solution of sucrose (Ψ = −0.23 MPa), the net water flow would ________.

A) be from the tissue into the sucrose solution
B) be from the sucrose solution into the tissue
C) be in both directions and the concentration of water would remain equal
D) occur only as ATP was hydrolyzed in the tissue
E) be impossible to determine from the values given here

Question 19

The water lost during transpiration is a side effect of the plant's exchange of gases. However, the plant derives some benefit from this water loss in the form of ________.

A) increased turgor and increased growth
B) sucrose transport and increased growth
C) evaporative cooling and increased turgor
D) evaporative cooling and mineral transport

Question 20

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 21

Phloem transport of sucrose is often described as going from source to sink. Which of the following is most likely to function as a source?

A) a growing leaf in early spring
B) a growing root in late summer
C) a bulb in early spring
D) a shoot tip in late fall

Question 22

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

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

Question 23

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

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

Question 24

Photosynthesis ceases when leaves wilt, mainly because ________.

A) the chlorophyll in wilting leaves is degraded
B) flaccid mesophyll cells are incapable of photosynthesis
C) stomata close, preventing carbon dioxide from entering the leaf
D) photolysis, the water-splitting step of photosynthesis, cannot occur when there is a water deficiency
E) accumulation of carbon dioxide in the leaf inhibits enzymes

Question 25

Movement of phloem sap from a source to a sink ________.

A) occurs through the apoplast of sieve-tube elements
B) depends upon active transport of sugars into the sieve-tube elements
C) depends on tension, or negative pressure potential
D) depends on active transport of water into sieve-tube elements at the source
E) results mainly from diffusion of sugars into companion cells

Question 26

The following factors may sometimes play a role in the movement of sap through xylem. Which one depends on the direct expenditure of ATP by the plant?

A) capillarity movement of water within the xylem
B) evaporation of water from leaves
C) cohesion among water molecules
D) concentration of ions in the symplast
E) bulk flow of water in the root apoplast

Question 27

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 28

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

A) cohesion-tension
B) capillarity
C) proton pump
D) air pressure

Question 29

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

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

Question 30

Which of the following supports the finding that sugar translocation from mesophyll cells into companion cells 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) ATPase proteins are not associated with sucrose transport.
D) Channel and carrier proteins are abundant in the plasma membranes of the mesophyll cells.

Question 31

Compared to a cell with few aquaporins in its membrane, a cell containing many aquaporins will ________.

A) have a faster rate of osmosis
B) have a lower water potential
C) have a higher water potential
D) have a faster rate of active transport
E) be flaccid

Question 32

Active transport would be LEAST important in the normal functioning of which of the following plant tissue types?

A) leaf transfer cells
B) stem tracheids
C) root endodermal cells
D) leaf mesophyll cells
E) root sieve-tube elements

Question 33

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 carbon dioxide can be compared using the transpiration ratio, which is calculated by dividing the amount of water transpired by the amount of carbon dioxide 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 34

Why does overwatering a plant kill it?

A) Water does not have all the necessary minerals a plant needs to grow.
B) Water neutralizes the pH of the soil.
C) The roots are deprived of oxygen.
D) Water supports the growth of root parasites.
E) Water lowers the water potential of the roots.

Question 35

Which structure or compartment is part of the symplast?

A) the interior of a vessel element
B) the interior of a sieve tube
C) the cell wall of a mesophyll cell
D) an extracellular air space
E) the cell wall of a root hair

Question 36

Arrange the following five events in an order that explains the mass flow of materials in the phloem.
1) Water diffuses into the sieve tubes.
2) Leaf cells produce sugar by photosynthesis.
3) Solutes are actively transported into sieve tubes.
4) Sugar is transported from cell to cell in the leaf.
5) Sugar moves down the stem.

A) 2, 1, 4, 3, 5
B) 1, 2, 3, 4, 5
C) 2, 4, 3, 1, 5
D) 4, 2, 1, 3, 5
E) 2, 4, 1, 3, 5

Question 37

Which of the following would tend to increase transpiration?

A) a rainstorm
B) sunken stomata
C) dry soils
D) higher stomatal density
E) spiny leaves

Question 38

What drives the flow of water through the xylem?

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

Question 39

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 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 40

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 41

Active transport involves ________.

A) diffusion of solute through the lipid bilayer of a membrane
B) pumping of solutes across the membrane
C) production of adenosine triphosphate (ATP)
D) transport of solute down a concentration gradient

Question 42

The research by Michael Sussman showed that a gene called SUC2 is expressed in vascular tissue, encoding a proton-sucrose symporter. Mutant plants lacking a functional SUC2 gene were unable to ________.

A) export sugar from mesophyll cells to the rest of the plant
B) accumulate starch in plant chloroplasts
C) load sucrose into mesophyll cells
D) carry out facilitated diffusion

Question 43

Which of the following transmembrane transport mechanisms requires the expenditure of energy?

A) channel
B) antiporter
C) facilitated diffusion
D) aquaporin

Question 44

Which one of the following statements about transport of nutrients in phloem is correct?

A) Solute particles are actively transported from phloem to xylem.
B) Companion cells control the rate and direction of movement of phloem sap.
C) Differences in osmotic concentration at the source and sink cause a hydrostatic pressure gradient to be formed.
D) A sink is the part of a plant where a particular solute is produced.

Question 45

Water flows into the source end of a sieve tube because ________.

A) sucrose has diffused into the sieve tube, making it hypotonic
B) sucrose has been actively transported into the sieve tube, making it hypertonic
C) water pressure outside the sieve tube forces in water
D) the companion cell of a sieve tube actively pumps in water
E) sucrose has been transported out of the sieve tube by active transport

Question 46

Active transport of sucrose in plants at the cellular level requires ________.

A) NADP and channel proteins
B) xylem membranes and channel proteins
C) sodium/potassium pumps and xylem membranes
D) ATP, transport proteins, and a proton gradient

Question 47

According to the pressure-flow hypothesis of phloem transport, ________.

A) solute moves from a high concentration in the source to a lower concentration in the sink
B) water is actively transported into the source region of the phloem to create the turgor pressure needed
C) the combination of a high turgor pressure in the source and transpiration water loss from the sink moves solutes through phloem conduits
D) the formation of starch from sugar in the sink increases the osmotic concentration
E) the pressure in the phloem of a root is normally greater than the pressure in the phloem of a leaf