34. Vascular Plant Transport

Which structure or compartment is part of the symplast?a. the interior of a vessel elementb. the interior of a sieve tubec. the cell wall of a mesophyll celld. 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 xylemb. causes cells to shrink, thereby increasing pressure within cellsc. loads sugars into xylem, thereby causing water to enter the xylem by osmosisd. 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 sinka. 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 becausea. 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 solutionb. positive pressure on the surrounding solutionc. the loss of solutes from the celld. 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 inc. 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 −0.65MPa 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 aa. ΨP of +0.65MPa.b. Ψ of −0.65MPa.c. ΨP of +0.35MPa.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 willa. 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 transpirationb. load sucrose into sieve-tube elementsc. carry out photosynthesisd. transport water through the xylem

Which of the following would tend to increase transpiration?a. spiny leavesb. sunken stomatac. a thicker cuticled. higher stomatal density

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