34. Vascular Plant Transport

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

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.

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.

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.

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?