Deck 30: The Movement of Water and Solutes in Plants

Question 1

The rate of transpiration is affected by stomatal movements and:

A) air currents only.
B) humidity only.
C) temperature only.
D) temperature and air currents only.
E) temperature, humidity, and air currents.

Answer 1

E

Question 2

Which of the following statements is NOT consistent with the cohesion-tension theory?

A) A gradient of water potential exists between the stem and the root.
B) Transpiration brings about a lowered water potential in the leaves.
C) Water in the xylem is under tension.
D) A gradient of water potential provides the driving force for the movement of water from the soil through the plant to the atmosphere.
E) Root pressure is essential to the movement of water from roots to leaves.

Answer 2

E

Question 3

Which of the following statements concerning nocturnal transpiration is FALSE?

A) For some species it constitutes a significant fraction of the daily water use.
B) It may enhance nutrient uptake.
C) It occurs when evaporation rates are higher than in the day.
D) It is due to stomata not closing completely in the dark.
E) It is found in many trees and shrubs.

Answer 3

C

Question 4

In vascular plants, cavitation is the:

A) rupture of water columns.
B) expulsion of air from water columns.
C) formation of air bubbles due to particulate matter.
D) reduction of surface tension at the meniscus spanning pores in the pit membrane.
E) filling of vessels with water vapor.

Question 5

Which of the following statements about stomatal movements is FALSE?

A) An increase in CO₂ levels usually causes stomata to close.
B) Sensors for carbon dioxide are located in guard cells.
C) Stomatal opening and closing exhibit circadian rhythms.
D) Cacti and pineapple open their stomata at night.
E) Temperatures above 30°-35°F usually stimulate stomatal opening. [OK to add F?]

Question 6

The rate of water evaporation doubles for every _____ degree C rise in temperature.

A) 2
B) 5
C) 10
D) 15
E) 20

Question 7

Which of the following statements about xylem and phloem is FALSE?

A) They are closely associated spatially.
B) They are closely associated functionally.
C) They form a continuous vascular system.
D) They are involved in long-distance transport.
E) Xylem transports only water, and phloem transports only nutrients.

Question 8

A dry breeze increases the rate of transpiration mainly because it:

A) cools the leaf.
B) warms the leaf.
C) increases the CO₂ gradient across the leaf surface.
D) decreases the CO₂ gradient across the leaf surface.
E) increases the vapor pressure difference across the leaf surface.

Question 9

Which of the following statements concerning the uptake of K⁺ by guard cells is FALSE?

A) Uptake of K⁺ is driven by a proton gradient.
B) Uptake of K⁺ is mediated by a red-light activated ATPase.
C) Uptake of K⁺ is accompanied by the uptake of Cl^-.
D) Uptake of K⁺ is accompanied by the accumulation of malate.
E) Uptake of K⁺ creates the necessary water potential gradient.

Question 10

A plant loses the greatest amount of water through the:

A) leaf cuticle.
B) stem cuticle.
C) root cuticle.
D) stomata.
E) lenticels.

Question 11

The principle solute involved in creating a water potential gradient in guard cells is:

A) H⁺.
B) K⁺.
C) glucose.
D) malate.
E) Cl^-.

Question 12

Phototropins are:

A) osmoticums.
B) photoreceptors.
C) microfibrils.
D) enzymes.
E) active-transport proteins.

Question 13

In the process of stomatal opening, the ________ walls of the guard cells ________ relative to their common walls.

A) inner; move inward
B) inner; move outward
C) outer; move inward
D) outer; move outward
E) outer; remain unchanged

Question 14

Plants in hot climates regularly close their stomata at midday because ______ accumulates in the leaf, and the leaves become _______.

A) carbon dioxide; dehydrated
B) carbon dioxide; turgid
C) oxygen; dehydrated
D) oxygen; turgid
E) oxygen; depleted of carbon dioxide

Question 15

In guard cells, _____ is the dominant osmoticum in the morning, and ______ is the dominant osmoticum in the afternoon.

A) Cl^-; sucrose
B) malate; K⁺
C) K⁺, malate
D) sucrose; K⁺
E) K⁺; sucrose

Question 16

Transpiration is the:

A) flow of water through the xylem.
B) loss of water vapor from plants.
C) absorption of water by roots.
D) loss of carbon dioxide from leaves.
E) entry of carbon dioxide into leaves.

Question 17

Radial micellation refers to the ______ of guard cells.

A) shape
B) opening and closing
C) orientation of proteins in the plasma membrane
D) orientation of cellulose microfibrils in the cell walls
E) mode of attachment between the ends

Question 18

Stomatal transpiration involves two steps:

A) evaporation and diffusion.
B) evaporation and active transport.
C) osmosis and evaporation.
D) osmosis and active transport.
E) photosynthesis and respiration.

Question 19

Plants with crassulacean acid metabolism:

A) open their stomata when conditions are favorable to transpiration.
B) convert CO₂ to organic acids during the day.
C) convert organic acids to CO₂ during the night.
D) are exemplified by members of the stonecrop family.
E) have a pathway for carbon flow much different from that of C₄ plants.

Question 20

In the process of stomatal closing, which of the following events occurs first?

A) Water moves out of guard cells.
B) Water moves into guard cells.
C) Guard cell turgor pressure decreases.
D) Guard cell solute concentration declines.
E) Guard cell water potential increases.

Question 21

When water moving through the cortex via the apoplastic pathway reaches the endodermis:

A) it continues through the apoplast.
B) it enters the cell walls.
C) apoplastic movement is stopped by the Casparian strips.
D) the symplastic pathway is blocked.
E) the transcellular pathway is blocked.

Question 22

An ion moving across the root via the symplastic pathway would NOT pass across the:

A) plasma membrane of the epidermis.
B) epidermal cell protoplast.
C) cell walls of the exodermis.
D) plasmodesmata in the epidermal-cortical cell walls.
E) endodermis.

Question 23

Which of the following statements about sources and sinks in assimilate movement is FALSE?

A) A plant part unable to meet its nutritional needs functions as a sink.
B) In seedlings, the cotyledons commonly act as the major sinks.
C) In mature plants, the upper leaves commonly act as sources for the shoot apex.
D) In mature plants, the lower leaves commonly act as sources for the roots.
E) Developing fruits are highly competitive sinks.

Question 24

A pressure chamber can be used to test the cohesion-tension theory by:

A) measuring the tensile strength of water.
B) following the movement of colored water in the xylem.
C) measuring the shrinkage of a trunk caused by negative xylem pressure.
D) detecting the rate at which heated water moves through a plant.
E) determining the magnitude of the tension in a twig.

Question 25

In vascular plants, hydraulic redistribution is the:

A) movement of water from roots to leaves.
B) flow of water against a water potential gradient.
C) movement of water across the endodermis.
D) transfer of water across Casparian strips.
E) transfer of water by roots from moist to dry regions of the soil.

Question 26

Which of the following indicates the correct sequence of tissues through which water moves from the soil into the root?

A) Root hairs, endodermis, exodermis, cortical cells, vascular cylinder
B) Root hairs, endodermis, cortical cells, vascular cylinder, exodermis
C) Exodermis, endodermis, epidermis, vascular cylinder, cortical cells
D) Epidermis, exodermis, cortical cells, endodermis, vascular cylinder
E) Epidermis, endodermis, exodermis, cortical cells, vascular cylinder

Question 27

Which of the following is/are present in the highest concentration in sieve-tube sap?

A) glucose
B) amino acids
C) magnesium
D) sorbitol
E) sucrose

Question 28

Water moving from the cytosol of a cortical cell directly into the cytosol of an adjacent cortical cell via plasmodesmata follows the:

A) symplastic pathway only.
B) apoplastic pathway only.
C) transcellular pathway only.
D) symplastic and apoplastic pathways.
E) apoplastic and transcellular pathways.

Question 29

Transport of inorganic ions within the leaf occurs via the:

A) apoplastic pathway only.
B) symplastic pathway only.
C) transpiration stream only.
D) apoplastic and symplastic pathways only.
E) transpiration stream and the apoplastic and symplastic pathways.

Question 30

Which of the following is NOT evidence supporting the role of phloem in sugar transport?

A) Honeydew contains amino acids but not sucrose.
B) ¹⁴C-labeled sucrose is transported in sieve tubes.
C) The exudate from the stylets of feeding aphids is mainly sucrose.
D) Radioactive assimilates are transported in the phloem.
E) When a tree is girdled, the bark above the ring becomes swollen.

Question 31

An air bubble in a vessel can be prevented from spreading to an adjacent vessel by:

A) air seeding.
B) transport upward in the transpiration stream.
C) movement of a torus away from an aperture of a bordered pit-pair.
D) the surface tension of the meniscus spanning the pores of the bordered pit-pair membrane.
E) the filtering effect of the roots.

Question 32

The major difference between the symplastic and the transcellular pathways of the root is that the transcellular pathway involves:

A) plasmodesmata.
B) protoplasts.
C) plasma membranes.
D) cell walls.
E) vacuoles.

Question 33

In roots, active transport of minerals is required for:

A) uptake by epidermal cells only.
B) secretion into the vessels only.
C) transport through the apoplast and the symplast only.
D) uptake by epidermal cells and secretion into the vessels only.
E) uptake by epidermal cells, transport through the symplast, and secretion into the vessels.

Question 34

As a consequence of girdling a tree:

A) its leaves stop exporting solutes.
B) its leaves stop importing solutes.
C) the bark above the girdle swells.
D) the bark above the girdle dies.
E) the bark begins to act as a source.

Question 35

When transpiration is proceeding at a high rate:

A) stomata usually close.
B) guttation is at its greatest.
C) root pressure can push water to the top of a tall tree.
D) water is pulled into the roots by bulk flow.
E) hydraulic lift forces water into roots.

Question 36

In the process of guttation, all of the following events occur EXCEPT:

A) dew-like drops of water form at the tips of grass.
B) dew-like drops of water form at the tips of leaves.
C) water exudes through stomata that lack the ability to open and close.
D) water exudes through openings in structures called hydathodes.
E) water forms from the condensation of water from the air.

Question 37

Mycorrhizae are especially important in the plant's absorption of:

A) zinc.
B) phosphorus.
C) manganese.
D) copper.
E) iron.

Question 38

Which of the following does NOT provide evidence supporting the cohesion-tension theory?

A) Water has sufficient tensile strength.
B) The water potential in a stem is sufficient.
C) In the morning, heated water begins to flow close to the leaves.
D) In the morning, the diameter of a tree decreases first in the upper trunk.
E) In the evening, the diameter of a tree increases first in the lower trunk.

Question 39

Which of the following is NOT a benefit of hydraulic redistribution?

A) It prevents the dry-season transpiration of Amazonian trees.
B) It reduces the possibility of water logging in surface soils.
C) It allows mycorrhizae to persist in dry soils.
D) It transfers water from the wet soil surface to deep soil layers that are dry.
E) It makes water available to neighboring plants that are less deeply rooted.

Question 40

All of the following can induce embolisms in a vessel or tracheid EXCEPT:

A) an air bubble coming in contact with a torus blocking an aperture of a bordered pit-pair.
B) air being sucked in through a pit-membrane pore.
C) an insect bite that damages xylem tissue.
D) freezing of the xylem sap.
E) drought.

Question 41

Which of the following statements about apoplastic phloem loading is FALSE?

A) It is driven by a proton gradient.
B) It occurs via sucrose-proton symport.
C) Apoplastic loaders have numerous plasmodesmatal connections.
D) In some cases, active transport occurs across the plasma membrane of the sieve tube.
E) In some cases, active transport occurs across the plasma membrane of the companion cell.

Question 42

The transport of the assimilate stream in the phloem is called translocation.

Question 43

Calcium is a phloem-immobile element.

Question 44

Which of the following statements about phloem unloading and transport is FALSE?

A) Unloading can be apoplastic.
B) Unloading can be symplastic.
C) In young leaves and roots, unloading is probably passive.
D) In storage organs, energy is needed to accumulate sugars in sink cells.
E) In young leaves and roots, post-sieve-tube transport is passive.

Question 45

Even when stomata are closed, photosynthesis can occur as long as light is available.

Question 46

Nocturnal transpiration occurs in CAM plants but not C₃ plants.

Question 47

According to the pressure-flow mechanism, sugars are transported in the phloem by flowing down a gradient of turgor pressure.

Question 48

Sucrose is translocated through sieve tubes:

A) via active transport.
B) passively.
C) via facilitated diffusion.
D) via a proton-pumping mechanism.
E) via a combination of exocytosis and endocytosis.

Question 49

In the process of stomatal movement, blue light activates a proton pump in the plasma membrane of the guard cell.

Question 50

The stomata of many species open in the morning and close at night regardless of the amount of water available to the plant.

Question 51

The driving force for assimilate transport is:

A) diffusion.
B) active transport.
C) transpiration.
D) osmosis.
E) pressure-flow.

Question 52

Once it has crossed the exodermis, water can pass into the root's vascular cylinder by the apoplastic pathway.

Question 53

In the process of hydraulic redistribution, leaves move water from air spaces into mesophyll cells.

Question 54

The greater the vapor pressure difference between the intercellular spaces and the leaf surface, the faster is the rate of transpiration.

Question 55

Approximately 99 percent of the water taken in by the roots is released via transpiration.

Question 56

Which of the following statements concerning the polymer trapping mechanism is FALSE?

A) It is a type of symplastic loading.
B) The companion cells are intermediary cells.
C) Sucrose is used to synthesize polymers.
D) Raffinose and stachyose are actively transported into the sieve tubes.
E) Energy is used to create a concentration difference between the mesophyll and the phloem.

Question 57

It is the smallest pores in the walls or pit membranes of vessels or tracheids that are the most susceptible to air seeding.

Question 58

In the process of guttation, water is exuded from leaves through hydathodes.

Question 59

The cuticle is largely impermeable to both water and carbon dioxide.

Question 60

Stomata open when the turgor pressure of the guard cells decreases.

Question 61

Both symplastic and apoplastic loading can occur in the same species.

Question 62

In sucrose-proton symport, ATP is utilized more directly for the transport of protons than for the transport of sucrose.

Question 63

In the pressure-flow mechanism, sugars are transported passively through sieve tubes.

Question 64

The polymer trapping mechanism is a symplastic loading mechanism.