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Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

As you already know, photosynthesizing plant cells require water delivered in the xylem. Recent experiments have revealed that the concentration of ions, especially potassium (K+), in xylem water influences the velocity of water flow through the xylem, possibly by affecting the pit membranes between xylem vessels. Roots take up K+ in soil water, but phloem sap also contains K+ that “recycles” back to the xylem. M. A. Zwieniecki and his colleagues hypothesized that changes in the flow of ions from phloem to xylem can alter the velocity (flow rate) at which water moves through the xylem. Working with red maples (Acer rubrum) and sugar maples (Acer saccharum), they devised a girdling experiment that would prevent the recycling of phloem K+ to xylem without disrupting the movement of xylem water. (Recall that girdling a tree or branch stops the movement of phloem sap beyond the cut.) The experimental design included an apparatus for maintaining normal pressure in the xylem and for adding either deionized water or water containing potassium chloride (KCl), a source of ions, to it. After experimental testing on 43 tree branches, they obtained results for xylem sap flow through the branches as shown in the graphs below.

Chapter 34, Problem 3ITD, As you already know, photosynthesizing plant cells require water delivered in the xylem. Recent

Were results substantially similar or substantially different for the two species used in the experiment?

Source: M. A. Zwieniecki et al. 2004. A potential role for xylem-phloem interactions in the hydraulic architecture of trees. Tree Physiology 24:911–917.

Summary Introduction

To review:

Whether the results were substantially similar or different for the two species used in the given experiment.

Introduction:

The transpiration process from leaves create negative pressure that helps to pull xylem sap upward. This is called cohesion–tension theory of water transport. It also takes place in the root system of the plant. The concentration of ions also influences the flow rate of water through xylem sap.

Explanation

The study shows that the hypothesis of M.A. Zwieniecki and his colleagues on changing the flow of ions from phloem to xylem, the flow of water through the xylem can be altered. The experimental design includes an apparatus for maintaining normal pressure in xylem by adding water containing KCl and deionized water (Potassium chloride) as the source of ions. They tested this experiment on 43 tree branches and the results obtained can be read from the graphs.

The results were substantially similar for the red maple and sugar maple species used in the experiment. The experiment in the red maple shows an initial increase in the flow rate on perfusion from deionized water to ionized water containing 100 mM KCl solution...

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