Exam 37: Water and Sugar Transport in Plants

When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis,the volume of the cell increases until it bursts.This does not happen to plant cells,because _____.

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?

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

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

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

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

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?

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?

How does a flaccid cell differ from a turgid cell?

As an undergraduate research assistant in the lab of the famous Dr.S.Nameerf,your duties involve measuring water potential in experimental soil-plant-atmosphere systems.Assume you make a series of measurements in a system under normal daylight conditions,with stomata open and photosynthesis occurring.Which of the following correctly depicts the trend your measurement data should follow if the cohesion-tension mechanism is operating?

Root pressure can result in the early morning appearance of water droplets on leaves and flowers of low-growing plants.Which of the following does not contribute to the development of root pressure?

Water potential of plants during night is _____ compared to day water potential due to _____.

Which theory of water transport in xylem can also be used to explain the movement of water in non-vascular plants such as mosses?

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.

Which of the following cross-membrane transport mechanisms occur without expenditure of energy?

J.A.Milburn and R.P.C.Johnson developed an acoustic method for detecting cavitation in plants.This involves "listening" for characteristic clicks produced during air-bubble formation,using sensitive microphones and amplifiers.In one experiment with the castor bean plant (Ricinus communis),they detached leaves by cutting the petioles and subjected them to various treatments.Which of the following would be least likely to be observed in such an experiment?

Which of the following observations provides the strongest evidence against root pressure being the principal mechanism of water transport in the xylem?

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