BackWhich 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 relatively dry soils.
c. The plant will grow most effectively in soils that are saturated with water year-round.
d. The plant's leaves will wilt easily.
A plant cell with a ΨS of −0.65MPa maintains a constant volume when bathed in a solution that has a ΨS of −0.30MPa and is in an open container. The cell has a
a. ΨP of +0.65MPa
b. Ψ of −0.65MPa
c. ΨP of +0.35MPa
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
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