) Which of the following would be least likely to affect osmosis in plants?
A) proton pumps in the membrane
B) a difference in solute concentrations
C) receptor proteins in the membrane
E) a difference in water potential
Active transport involves all of the following except the
A) slow movement through the lipid bilayer of a membrane.
B) pumping of solutes across the membrane.
C) hydrolysis of ATP.
D) transport of solute against a concentration gradient.
E) a specific transport protein in the membrane
Like many plant processes, transport of various materials in plants at the cellular level requires all of the following except
A) a proton gradient.
C) specific membrane proteins.
D) active transport.
E) xylem membranes.
Which of the following is not a function of the plasma membrane proton pump?
A) hydrolyzes ATP
B) produces a proton gradient
C) generates a membrane potential
D) equalizes the charge on each side of a membrane
E) stores potential energy on one side of a membrane
A unifying principle of cellular energetics that links energy-releasing processes to energy-consuming processes is
A) active transport.
C) ATP hydrolysis.
D) water potential.
E) source-sink relationships.
Which of the following is an example of osmosis?
A) flow of water out of a cell
B) pumping of water into a cell
C) flow of water between cells
D) both A and B
E) both A and C
The amount and direction of movement of water in plants can always be predicted by measuring which of the following?
A) air pressure
C) proton gradients
D) dissolved solutes
E) water potential (Ψ)
Which of the following is true concerning the water potential of a plant cell?
A) It is higher than that of air.
B) It is equal to zero when the cell is in pure water and is turgid.
C) It is equal to 0.23 MPa.
D) It becomes higher when K+ is actively moved into the cell.
E) It becomes lower after the uptake of water by osmosis.
Your laboratory partner has an open beaker of pure water. By definition, the water potential (Ψ) of this water is
A) not meaningful, because it is an open beaker and not plant tissue.
B) a negative number set by the volume of the beaker.
C) a positive number set by the volume of the beaker.
D) equal to the atmospheric pressure.
Which of the following has an effect on water potential (Ψ) in plants?
A) air pressure
B) water-attracting matrices
C) dissolved solutes
D) A and C only
E) A, B, and C
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) impossible to calculate with this information
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), 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 concentrations would remain equal.
D) occur only as ATP was hydrolyzed in the tissue.
E) be impossible to determine from the values given here
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.
Some botanists argue that the entire plant should be considered as a single unit rather than a composite of many individual cells. Which of the following cellular structures cannot be used to support this view?
A) cell wall
B) cell membrane
Which of the following statements is false about bulk flow?
A) It is driven primarily by pressure potential.
B) It is more effective than diffusion over distances greater than 100 μm.
C) It depends on a difference in pressure potential at the source and sink.
D) It depends on the force of gravity on a column of water.
E) It may be the result of either positive or negative pressure potential
) Which of the following statements about xylem is incorrect?
A) It conducts material upward.
B) It conducts materials within dead cells.
C) It transports mainly sugars and amino acids.
D) It has a lower water potential than soil does.
E) No energy input from the plant is required for xylem transport.
Which of the following would likely not contribute to the surface area available for water absorption from the soil by a plant root system?
A) root hairs
D) fungi associated with the roots
E) fibrous arrangement of the roots
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.
What is the role of proton pumps in root hair cells?
A) establish ATP gradients
B) acquire minerals from the soil
C) pressurize xylem transport
D) eliminate excess electrons
E) A and D only
In plant roots, the Casparian strip is correctly described by which of the following?
A) It is located in the walls between endodermal cells and cortex cells.
B) It provides energy for the active transport of minerals into the stele from the cortex.
C) It ensures that all minerals are absorbed from the soil in equal amounts.
D) It ensures that all water and dissolved substances must pass through a cell before entering the stele.
E) It provides increased surface area for the absorption of mineral nutrients
) All of the following describe an important component of the long-distance transport process in plants except
C) endodermis Casparian strip.
D) active transport.
E) bulk flow from source to sink.
Pine seedlings grown in sterile potting soil grow much slower than seedlings grown in soil from the area where the seeds were collected. This is most likely because
A) the sterilization process kills the root hairs as they emerge from the seedling.
B) the normal symbiotic fungi are not present in the sterilized soil.
C) sterilization removes essential nutrients from the soil.
D) water and mineral uptake is faster when mycorrhizae are present.
E) both B and D
A water molecule could move all the way through a plant from soil to root to leaf to air and pass through a living cell only once. This living cell would be a part of which structure?
A) the Casparian strip
B) a guard cell
C) the root epidermis
D) the endodermis
E) the root cortex
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 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
) The soil solution is usually very dilute. After fertilizing a lawn, the concentration of salts in the soil builds up. What would be a response of grass roots to this increase?
A) Water absorption would increase because of the higher solute potential in the soil.
B) K+ will be actively transported into the root cells.
C) Root cells will immediately dehydrate and die.
D) Nutrient salts will diffuse into the root faster.
E) There will be no noticeable effect.
What is the main cause of guttation in plants?
A) root pressure
C) pressure flow in phloem
D) plant injury
E) condensation of atmospheric water
One is most likely to see guttation in small plants when the
A) transpiration rates are high.
B) root pressure exceeds transpiration pull.
C) preceding evening was hot, windy, and dry.
D) water potential in the stele of the root is high.
E) roots are not absorbing minerals from the soil.
What is the main force by which most of the water within xylem vessels moves toward the top of a tree?
A) active transport of ions into the stele
B) atmospheric pressure on roots
C) evaporation of water through stoma
D) the force of root pressure
E) osmosis in the root
) 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
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
) Which of the following has the lowest (most negative) water potential?
B) root xylem
C) trunk xylem
D) leaf cell walls
E) leaf air spaces
Which of the following is responsible for the cohesion of water molecules?
A) hydrogen bonds between the oxygen atoms of a water molecule and cellulose in a vessel cell
B) covalent bonds between the hydrogen atoms of two adjacent water molecules
C) hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule
D) covalent bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule
E) Cohesion has nothing to do with the bonding but is the result of the tight packing of the water molecules in the xylem column.
Transpiration in plants requires all of the following except
A) adhesion of water molecules to cellulose.
B) cohesion between water molecules.
C) evaporation of water molecules.
D) active transport through xylem cells.
E) transport through tracheids.
Which of the following statements about transport in plants is false?
A) Weak bonding between water molecules and the walls of xylem vessels or tracheids helps support the columns of water in the xylem.
B) Hydrogen bonding between water molecules, which results in the high cohesion of the water, is essential for the rise of water in tall trees.
C) Although some angiosperm plants develop considerable root pressure, this is not sufficient to raise water to the tops of tall trees.
D) Most plant physiologists now agree that the pull from the top of the plant resulting from transpiration is sufficient, when combined with the cohesion of water, to explain the rise of water in the xylem in even the tallest trees.
E) Gymnosperms can sometimes develop especially high root pressure, which may account for the rise of water in tall pine trees without transpiration pull.
Active transport would be least important in the normal functioning of which of the following plant tissue types?
A) leaf transfer cells
B) stem xylem
C) root endodermis
D) leaf mesophyll
E) root phloem
Which of the following statements is false concerning the xylem?
A) Xylem tracheids and vessels fulfill their vital function only after their death.
B) The cell walls of the tracheids are greatly strengthened with cellulose fibrils forming thickened rings or spirals.
C) Water molecules are transpired from the cells of the leaves, and replaced by water molecules in the xylem pulled up from the roots due to the cohesion of water molecules.
D) Movement of materials is by mass flow materials move owing to a turgor pressure gradient from "source" to "sink."
E) In the morning, sap in the xylem begins to move first in the twigs of the upper portion of the tree, and later in the lower trunk.
) Xylem vessels, found in angiosperms, have a much greater internal diameter than tracheids, the only xylem conducting cells found in gymnosperms. The tallest living trees, redwoods, are gymnosperms. Which of the following is an advantage of tracheids over vessels for long-distance transport to great heights?
A) Adhesive forces are proportionally greater in narrower cylinders than in wider cylinders.
B) The smaller the diameter of the xylem, the more likely cavitation will occur.
C) Cohesive forces are greater in narrow tubes than in wide tubes of the same height.
D) Only A and C are correct.
E) A, B, and C are correct.
Water rises in plants primarily by the cohesion-tension model. Which of the following is not true about this model?
A) Water loss (transpiration) is the driving force for water movement.
B) The "tension" of this model represents the excitability of the xylem cells.
C) Cohesion represents the tendency for water molecules to stick together by hydrogen bonds.
D) The physical forces in the capillary-sized xylem cells make it easier to overcome gravity.
E) The water potential of the air is more negative than the xylem.
Assume that a particular chemical interferes with the establishment and maintenance of proton gradients across the membranes of plant cells. All of the following processes would be directly affected by this chemical except
B) phloem loading.
C) xylem transport.
D) cellular respiration.
E) stomatal opening.
Guard cells do which of the following?
A) protect the endodermis
B) accumulate K+ and close the stomata
C) contain chloroplasts that import K+ directly into the cells
D) guard against mineral loss through the stomata
E) help balance the photosynthesis-transpiration compromise
) All of the following normally enter the plant through the roots except
A) carbon dioxide.
) Photosynthesis begins to decline when leaves wilt because
A) flaccid cells are incapable of photosynthesis.
B) CO2 accumulates in the leaves and inhibits photosynthesis
C) there is insufficient water for photolysis during light reactions.
D) stomata close, preventing CO2 entry into the leaf.
E) the chlorophyll of flaccid cells cannot absorb light.
) The water lost during transpiration is an unfortunate side effect of the plant's exchange of gases. However, the plant derives some benefit from this water loss in the form of
A) evaporative cooling.
B) mineral transport.
C) increased turgor.
D) A and B only
E) A, B, and C
) Ignoring all other factors, what kind of day would result in the fastest delivery of water and minerals to the leaves of a tree?
A) cool, dry day
B) warm, dry day
C) warm, humid day
D) cool, humid day
E) very hot, dry, windy day
If the guard cells and surrounding epidermal cells in a plant are deficient in potassium ions, all of the following would occur except
A) photosynthesis would decrease.
B) roots would take up less water.
C) phloem transport rates would decrease.
D) leaf temperatures would decrease.
E) stomata would be closed.
The opening of stomata is thought to involve
A) an increase in the osmotic concentration of the guard cells.
B) a decrease in the osmotic concentration of the stoma.
C) active transport of water out of the guard cells.
D) decreased turgor pressure in guard cells.
E) movement of K+ from the guard cells.
Which of the following experimental procedures would most likely reduce transpiration while allowing the normal growth of a plant?
A) subjecting the leaves of the plant to a partial vacuum
B) increasing the level of carbon dioxide around the plant
C) putting the plant in drier soil
D) decreasing the relative humidity around the plant
E) injecting potassium ions into the guard cells of the plant
Guard cells are the only cells in the epidermis that contain chloroplasts and can undergo photosynthesis. This is important because
A) chloroplasts sense when light is available so that guard cells will open.
B) photosynthesis provides the energy necessary for contractile proteins to flex and open the guard cells.
C) guard cells will produce the O2 necessary to power active transport.
D) ATP is required to power proton pumps in the guard cell membranes.
E) both A and C
All of the following are adaptations that help reduce water loss from a plant except
B) sunken stomata.
C) C4 photosynthesis.
D) small, thick leaves.
E) crassulacean acid metabolism
Which of the following best explains why CAM plants are not tall?
A) They would be unable to move water and minerals to the top of the plant during the day.
B) They would be unable to supply sufficient sucrose for active transport of minerals into the roots during the day or night.
C) Transpiration occurs only at night, and this would cause a highly negative Ψ in the roots of a tall plant during the day.
D) Since the stomata are closed in the leaves, the Casparian strip is closed in the endodermis of the root.
E) With the stomata open at night, the transpiration rate would limit plant height.
As a biologist, it is your job to look for plants that have evolved structures with a selective advantage in dry, hot conditions. Which of the following adaptations would be least likely to meet your objective?
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 tap root
Phloem transport of sucrose can be described as going from "source to sink." Which of the following would not normally function as a sink?
A) growing leaf
B) growing root
C) storage organ in summer
D) mature leaf
E) shoot tip
Which of the following is a correct statement about sugar movement in phloem?
A) Diffusion can account for the observed rates of transport.
B) Movement can occur both upward and downward in the plant.
C) Sugar is translocated from sinks to sources.
D) Only phloem cells with nuclei can perform sugar movement.
E) Sugar transport does not require energy.
Water flows into the source end of a sieve tube because
A) sucrose has diffused into the sieve tube, making it hypertonic.
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 dumped from the sieve tube by active transport
Which one of the following statements about transport of nutrients in phloem is false?
A) Solute particles can be actively transported into phloem at the source.
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 that part of the plant where a particular solute is consumed or stored.
E) A sink may be located anywhere in the plant.
) 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.
As predicted by the pressure flow hypothesis of translocation in plants, phloem exudates from the severed stylets of aphids near photosynthetic cells are sites of
A) relatively high hydrostatic pressure.
B) relatively low hydrostatic pressure.
C) relatively high concentrations of organic nutrients.
D) active pumping of sucrose out of the sieve tube.
E) A and C only
Plants do not have a circulatory system like that of some animals. If a given water molecule did "circulate" (that is, go from one point in a plant to another and back), it would require the activity of
A) only the xylem.
B) only the phloem.
C) only the endodermis.
D) both the xylem and the endodermis.
E) both the xylem and the phloem.
Phloem transport is described as being from source to sink. Which of the following would most accurately complete this statement about phloem transport as applied to most plants in the late spring? Phloem transports ________ from the ________ source to the ________ sink.
A) amino acids; root; mycorrhizae
B) sugars; leaf; apical meristem
C) nucleic acids; flower; root
D) proteins; root; leaf
E) sugars; stem; root
) 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