Question 1

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

Accepted Answer

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 
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

Question 2

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

Accepted Answer

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 
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 3

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

Accepted Answer

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

Question 4

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

Accepted Answer

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 
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 5

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 ________.

Accepted Answer

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 
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 6

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?

Accepted Answer

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

Question 7

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

Accepted Answer

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

Question 8

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

Accepted Answer

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 
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 9

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

Accepted Answer

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

Question 10

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

Accepted Answer

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. 
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 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.

Accepted Answer

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

Question 12

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.

Accepted Answer

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 
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 13

How does a flaccid cell differ from a turgid cell?

Accepted Answer

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. 
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

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 ________.

Accepted Answer

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

Question 15

Which structure or compartment is part of the symplast?

Accepted Answer

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 
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 16

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

Accepted Answer

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 
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 17

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

Accepted Answer

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 
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 18

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

Accepted Answer

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

Question 19

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?

Accepted Answer

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 
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 20

Photosynthesis ceases when leaves wilt, mainly because ________.

Accepted Answer

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 
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

Exam 35: Water and Sugar Transport in Plants

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

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

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

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

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 ________.

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

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

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

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

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.

How does a flaccid cell differ from a turgid cell?

Which structure or compartment is part of the symplast?

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

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

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

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?

Photosynthesis ceases when leaves wilt, mainly because ________.

Biology and the Tree of Life

Water and Carbon: the Chemical Basis of Life

Protein Structure and Function

Nucleic Acids and the Rna World

An Introduction to Carbohydrates

Ecosystems and Global Ecology

Lipids, Membranes, and the First Cells

Inside the Cell

Energy and Enzymes: an Introduction to Metabolism

Cellular Respiration and Fermentation

Photosynthesis

Cellcell Interactions

The Cell Cycle

Meiosis

Mendel and the Gene

Dna and the Gene: Synthesis and Repair

How Genes Work

Transcription, Rna Processing, and Translation

Control of Gene Expression in Bacteria

Control of Gene Expression in Eukaryotes

The Molecular Revolution: Biotechnology and Beyond

Genes, Development, and Evolution

Evolution by Natural Selection

Evolutionary Processes

Speciation

Phylogenies and the History of Life

Bacteria and Archaea

Protists

Green Algae and Land Plants

Fungi

An Introduction to Animals

Protostome Animals

Deuterostome Animals

Viruses

Plant Form and Function

Plant Nutrition

Plant Sensory Systems, Signals, and Responses

Plant Reproduction and Development

Animal Form and Function

Water and Electrolyte Balance in Animals

Animal Nutrition

Gas Exchange and Circulation

Animal Nervous Systems

Animal Sensory Systems

Animal Movement

Chemical Signals in Animals

Animal Reproduction and Development

The Immune System in Animals

An Introduction to Ecology

Behavioral Ecology

Population Ecology

Community Ecology

Biodiversity and Conservation Biology

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