Exam 37: Water and Sugar Transport in Plants

Most biologists consider loss of water from plant tissues to be a negative thing,and,in fact,many plants have features that reduce water loss.Yet,plants still transpire.Which of the following is the least likely explanation for the fact that plants continue to transpire?

Which of the following structural features of plants would not be expected to reduce transpiration?

Which of the following does not support the cohesion-tension theory of xylem transport?

Which mechanism of water transport in xylem can contribute to recovery from cavitation?

Which of the following cross-membrane transport mechanisms requires the expenditure of energy?

The pressure-flow mechanism for sugar translocation you have learned about in this class is based on research on angiosperms,and thus might not occur in other vascular plants.Which of the following real or hypothetical observations on gymnosperms would suggest they possess a different mechanism?

Which of the following features of plant cells allows for symplastic movement of water?

How does a flaccid cell differ from a turgid cell?

The researchers discovered a new proton pump that is involved in phloem unloading in the sugar storage tissue.Predict the movement of ions carried out by this pump.

If you cut a stalk (petiole)of celery and place it in a beaker of water that has food coloring dissolved in it,colored water will move up the stalk and into the leaf blades.This provides evidence against which of the following theories of xylem transport?

In the pressure-flow mechanism,loading of sucrose from companion cells to sieve-tube elements takes place through

Researchers have investigated bidirectional transport in phloem by applying different radioisotope tracers to two source leaves and monitoring a point between the two sources for the presence of the tracers.Which of the following observations would not support the pressure-flow hypothesis? Appearance of the two tracers in

Which of the following is a similarity between xylem and phloem transport?

As an undergraduate research assistant in the lab of the famous Dr.S.Nameerf,you are assisting with a radioisotope tracer experiment.You expose a mature leaf on one side of the lower shoot of a sugar beet plant to ¹⁴CO₂ and then track the movement of the ¹⁴C atoms by radiography.Where are you least likely to detect ¹⁴C?

Water potential (ψ)can be thought of as the tendency for water to move from one place to another.In plants,it is made up mainly of solute potential and pressure potential.Hypothetical plant cells A and B are adjacent to each other.The solute potential (ψS)of cell A is -0.35 MPa,and its pressure potential (ψP)is +0.15 MPa.The solute potential (ψS)of cell B is -0.30 MPa,and its pressure potential (ψP)is +0.05 MPa.In which direction will net water movement occur?

James Richards and Martyn Caldwell conducted an experiment to test the hypothesis that hydraulic lift occurs in Artemisia tridentata,a species of sagebrush common in the western United States.Each plant in the experimental group was covered with an opaque plastic bag for more than two days to prevent photosynthesis and greatly reduce transpiration,and control plants were left uncovered.Fluctuations in soil water potential were measured,and other aspects of the experimental systems were observed.Which of the following observations from such an experiment provides the strongest support for the occurrence of hydraulic lift in A.tridentata?

Which of the following features of plant cells allows for apoplastic movement of water?

The research by Natalie De Witt and Michael Sussman showed that proton pump AHA3 is localized in the membrane of companion cells of the source tissue.What is the function of this pump?

The mechanisms that regulate the loading of sucrose from the apoplast to the sieve-tube members by sucrose-H⁺ symporters are not well understood.Of the following possible regulatory factors,which is least likely to be of direct importance?

Which of the following statements about phloem unloading at sinks is not consistent with our current understanding?