Concept explainers
To write:
The reason behind a column of water in a xylem tube that remains intact despite tremendous tension.
Introduction:
Water and minerals are taken from the soil, together called xylem sap, travel up the xylem, and the cells that help absorb water inside a plant. The tendency for similar molecules to bond such as molecules of water linked by hydrogen bonding, is said as cohesion. The tendency for unlike molecules to stick together, such as water is hydrogen-bonded to other polar molecules, is called adhesion.
Explanation of Solution
The pulling force on a column of xylem sap is generated by the water evaporated from leaves. Stomata, the pores on leaf surfaces, control the exchange of gas and water loss in plants. From stomata, when water evaporates, the forces of adhesion and cohesion on the water molecules that remain inside the leaves create tension or negative water pressure. Tension is the force that allows the plunger to pull a column of water into a syringe.
Water adhesion to xylem cell walls and cohesion to other molecules of water even under extreme tension maintain continuity of xylem sap. Tension in plants causes water molecules to be drawn out into the leaf from the xylem to take the place of water that has evaporated. This in turn, increases tension on the water molecules immediately below them in the xylem, causing water molecules to move toward the leaves, roots and the soil.
Tension in leaf cell walls is important because it helps to maintain the transpiration stream. When water is sucked through the xylem, it creates low pressure in the xylem. The continuity is maintained together by cohesion and adhesion during transpiration.
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Chapter 26 Solutions
Biology: Science for Life with Physiology (6th Edition) (Belk, Border & Maier, The Biology: Science for Life Series, 5th Edition)
- Ground tissue in monocot stems performs the same functions as _______________ and _______________ in herbaceous eudicot stems. (a) phloem; xylem (b) cork cambium; vascular cambium (c) epidermis; periderm (d) primary xylem; secondary xylem (e) cortex; pitharrow_forwardDescribe how roots absorb positively charged mineral ions by the process of cation exchange.arrow_forwardWhy is the ability of water molecules to form hydrogen bondsimportant for the movement of xylem sap?arrow_forward
- Why is the secondary xylem and phloem always to either side of the vascular cambium?arrow_forwardAside from conducting water and minerals, what is another important function of secondary xylem?arrow_forwardEvery winter, the cohesion of water molecules in xylem is interrupted by ice formation. What do trees do in the spring that compensates for this problem?*arrow_forward
- In a cross-section of a tree, where are the oldest growth rings—in the outer region or nearer the pith? Where is the oldest secondary phloem—near the outside of the tree or near the cambium?arrow_forwardIf the excised cotyledon were incubated for a longer period, would you expect more roots to form? Why?arrow_forwardWhat are differences between the transport of materials in xylem and phloem?arrow_forward
- Why root pressure is seen only under favorable conditions,like spring and rainy season?arrow_forwardSome liquid is collected from the xylem in the stem of the plant. What is present in the liquid?arrow_forwardWhich of the following forces make the movement of water through the xylem possible? * A. Cohesion and adhesion B. Transpiration C. Root pressure D. A and B E. A, B, and Carrow_forward
- Biology (MindTap Course List)BiologyISBN:9781337392938Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. BergPublisher:Cengage Learning