34. Vascular Plant Transport

The purpose of the xylem is to __________.

The proton pump in plant cells __________.

A plant cell placed in a solution with a higher water potential will __________.

The water potential of a cell is defined by the equation Ψ = Ψ_S + Ψ_P. Which of the following statements is true?

A cell has a pressure potential of 0 and a solute potential of -0.7 MPa. What is its water potential?

In a turgid cell, __________.

Why does rapid movement of water molecules across the plasma membrane of a plant cell occur?

In order to be transported throughout a plant, viruses exploit __________.

The cytoplasmic continuum connecting neighboring cells is called the __________.

The continuum of cell walls connecting neighboring cells is defined as the __________.

Which of the cells below are involved with bulk flow?

When referring to phloem transport, what creates the sink in roots?

Cells that are specialized for the transport of sugar between apoplast and symplast are __________ cells.

In an apple tree that is producing sugars, sugar might flow from __________ to __________.

Which of the following describes how some plants are adapted to arid environments?

Stomata open during the day in response to __________.

What process contributes directly to the turgor pressure that opens and closes stomata?

The rate of transpiration is expected to be greatest on a __________ day.

What is the ultimate source of energy that moves water upward in the trunk of a tree?

During winter, tree sap can sometimes freeze, and cavitation (the formation of an air pocket) may occur. Which of the following mechanisms of sap transport would you expect to be most immediately affected by cavitation?

The last thing all water and solute molecules pass through before they enter the vascular system of roots and move upward to the leaves is __________.

A botanist discovered a mutant plant that is unable to produce the material that forms the Casparian strip. This plant is __________.

In a plant root, the one structure that water cannot move past via the apoplast is the __________.

Normally, when an aphid feeds by puncturing plant tissues, it does not have to suck the sap out. If an aphid, however, inserted its feeding tube in the wrong place, the fluid in the aphid's guts could be sucked out through the feeding tube. What could explain this phenomenon?

One of your friends has a terrarium on her windowsill containing various houseplants. She wonders why the glass is often fogged with water droplets. What would you tell her is the cause of the droplets?

Root pressure is attributable to __________.

Which of the following conditions will result in the fastest transport through the xylem in a tree, assuming adequate water supply in the roots?

What keeps the force of gravity from overcoming transpirational pull?

Which of the following is an adaptation that enhances the uptake of water and minerals by roots? a. mycorrhizae b. pumping through plasmodesmata c. active uptake by vessel elements d. rhythmic contractions by cells in the root cortex

Fill in the blanks in this concept map to help you tie together key concepts concerning transport in plants.

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

What important role does the Casparian strip play in the movement of water through plants? a. forces water to move through the cytoplasm of living endodermal cells as it makes its way from the soil to the xylem b. causes cells to shrink, thereby increasing pressure within cells c. loads sugars into xylem, thereby causing water to enter the xylem by osmosis d. acts as a filter that prevents salts, heavy metals, and other pollutants from entering root hairs

Movement of phloem sap from a source to a sink a. occurs through the apoplast of sieve-tube elements. b. depends ultimately on the activity of proton pumps. c. depends on tension, or negative pressure potential. d. results mainly from diffusion.

Photosynthesis ceases when leaves wilt, mainly because a. the chlorophyll in wilting leaves is degraded. b. accumulation of CO2 in the leaf inhibits enzymes. c. stomata close, preventing CO2 from entering the leaf. d. photolysis, the water-splitting step of photosynthesis, cannot occur when there is a water deficiency.

Consider the following statements regarding the transport of phloem sap. Select True or False for each statement. T/F This is a passive process that is driven by the evaporation of water from leaves. T/F Sugars tend to move from sources to sinks. T/F Phloem sap moves through sieve-tube elements under positive pressure. T/F Sieve-tube elements and vessel elements are commonly involved in the transport of phloem sap.

What would enhance water uptake by a plant cell? a. decreasing the Ψ of the surrounding solution b. positive pressure on the surrounding solution c. the loss of solutes from the cell d. increasing the Ψ of the cytoplasm

The cells of a certain plant species can accumulate solutes to create very low solute potentials. Which of these statements is correct? a. The plant's transpiration rates will tend to be extremely low. b. The plant can compete for water effectively and live in c. relatively dry soils. d. The plant will grow most effectively in soils that are saturated with water year-round. e. The plant's leaves will wilt easily.

A plant cell with a ΨS of −0.65 MPa maintains a constant volume when bathed in a solution that has a ΨS of −0.30 MPa and is in an open container. The cell has a a. ΨP of +0.65 MPa. b. Ψ of −0.65 MPa. c. ΨP of +0.35 MPa. d. ΨP of 0 MPa.

Explain how guard cells limit water loss from a plant on a hot, dry day. How can this be harmful to the plant?

Draw a plant cell in pure water. Add dots to indicate solutes inside the cell. Now add more dots to indicate an increase in solute potential inside the cell. Add an arrow showing the net direction of water movement in response. Add arrows showing the direction of wall pressure and turgor pressure in response to water movement. Repeat the same exercise, but this time, add solutes to the solution outside the cell at a concentration that is greater than inside the cell.

Compared with a cell with few aquaporin proteins in its membrane, a cell containing many aquaporin proteins will a. have a faster rate of osmosis. b. have a lower water potential. c. have a higher water potential. d. accumulate water by active transport.

Transpiration is fastest when humidity is low and temperature is high, but in some plants it seems to increase in response to light as well. During one 12-hour period when cloud cover and light intensity varied frequently, a scientist studying a certain crop plant recorded the data in the table (top right). (The transpiration rates are grams of water per square meter of leaf area per hour.) Do these data support the hypothesis that the plants transpire more when the light is more intense? If so, is the effect independent of temperature and humidity? Explain your answer. (Hint: Look for overall trends in each column, and then compare pairs of data within each column and between columns.)

A mutant plant lacking the ability to pump protons out of leaf companion cells will be unable to do which of the following? a. initiate transpiration b. load sucrose into sieve-tube elements c. carry out photosynthesis d. transport water through the xylem

Which of the following would tend to increase transpiration? a. spiny leaves b. sunken stomata c. a thicker cuticle d. higher stomatal density

Your friend claims that phloem always carries sugars down a plant. What, if anything, is wrong with that statement?

Consider a tree that is 50 m tall and is transpiring roughly 90 liters of water each day. Approximately how many calories will the tree use to transpire this quantity of water?

Salt is used to melt snow and keep roads clear during the winter in many cities. Land adjacent to de-iced roads often ends up with a high concentration of salt in the soil. Explain why plants growing near salted roads may appear wilted in the spring.

Agriculture is by far the biggest user of water in arid western states, including Colorado, Arizona, and California. The populations of these states are growing, and there is an ongoing conflict between cities and farm regions over water. To ensure water supplies for urban growth, cities are purchasing water rights from farmers. This is often the least expensive way for a city to obtain more water, and some farmers can make more money selling water than growing crops. Discuss the possible consequences of this trend. Is this the best way to allocate water for all concerned? Why or why not?

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? Which of these structural features can help to limit water loss in plants that occupy dry habitats? a. abundant companion cells and sieve-tube elements b. stomata that are located in pits on the undersides of their leaves, or narrow, needlelike leaves c. extensive networks of xylem and phloem d. stomata that are located on the top surface of leaves, or broad leaves

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? What impact, if any, do you predict elevated CO2 levels will have on the number of stomata in leaves, and on the transpiration rate?

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? The amount of water that evaporates from stomata over a period of time is referred to as stomatal conductance, which is determined largely by the number of stomata in a given area of leaf surface. Researchers obtained specimens from preserved collections and measured stomatal conductance in leaves from oak trees and pine trees that grew at various times under different CO2 levels. The data are shown in the following graph. In general, is the maximum stomatal conductance rate in plants more or less than it was a century ago?

Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? One prediction of global climate change is that there will be an increase in periods of drought in some regions. Given the data just presented, will plants be more or less likely to survive periods of drought as they are exposed to rising CO2 levels?

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? In the year 1915, the stomatal conductance of oak was approximately how many times higher than that of pine? How about in the year 2010?

Atmospheric CO2 has been increasing rapidly since the late 1800s, largely due to human activities. Recall that CO2 enters leaves through stomata and can then be used for photosynthesis. However, transpiration occurs as a result of water evaporating through stomata. How have plants responded to elevated CO2 levels? Assuming that the CO2 level continues to increase with time, how likely are plants to be able to continue to adapt by adjusting stomatal conductance?