Inquiry Summary

Most dicots have a taproot system consisting of a large taproot and smaller branch roots that maximize storage. Monocots have fibrous root systems consisting of similarly sized roots that maximize absorption. Adventitious roots form on organs other than roots. Roots, as well as other plant structures, conform to the principle of form and function. Ends of roots are covered by a root cap, which produces mucigel, a substance that protects a root, lubricates it, and helps it absorb materials from the soil. The subapical region of the root includes the zones of cell division, cell elongation, and cell maturation. The epidermis surrounds the cortex, which has three layers: hypodermis, storage parenchyma, and endodermis. The hypodermis protects roots, and storage parenchyma tissue stores reserves for subsequent use. The endodermis is lined with the Casparian strip, which diverts water and dissolved minerals into the cytoplasm of endodermal cells. The stele includes all of the tissues inside the cortex, including the pericycle and vascular tissues. The pericycle produces branch roots. The narrow zone of soil surrounding a root is called the rhizosphere. Many microbes live in and affect the rhizosphere.

Do you think plants with fibrous roots or with taproots would be better adapted to sandy, unstable soils such as those at beaches? Why do you think so?

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FIGURE 7.14

The interior of the rhizotron at the University of Michigan Biological Laboratory. The underground laboratory's windows contain removable glass panes that provide researchers with direct access to the soil. Roots that press against the glass panes can be studied relatively easily.

FIGURE 7.14

The interior of the rhizotron at the University of Michigan Biological Laboratory. The underground laboratory's windows contain removable glass panes that provide researchers with direct access to the soil. Roots that press against the glass panes can be studied relatively easily.

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