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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 1ITD, As you already know, photosynthesizing plant cells require water delivered in the xylem. Recent

What do the different-colored blocks represent?

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:

What the different colored blocks in the diagram represent.

Introduction:

Plants contain xylem for transportation of water and minerals from the roots to the various body parts. The phloem vessels conduct food from leaves to different parts of the plant. The ions in water influence the flow of water through the xylem.

Explanation

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

The experimental graph shows the effect of solution composition on the flow of water through the xylem...

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