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Plant Structures

Introduction and Summary

Table of Contents

Terms

The parts of the plant are divided into two basic sections, the root and the shoot. The root is comprised of all the structures below the soil, and the shoot is composed of the structures above. Included in the shoot of seed plants are the stem, the leaves, and the seeds. Additionally, angiosperms contain flowers as part of their shoots. Each of these structures is vital in different ways to the plants existence.

The seed, which develops from an ovule after fertilization has occurred, surrounds the plant embryo and protects it from desiccation. Each seed consists of an embryo, food source, and protective outer coat, and can lie dormant for some time before germinating. Angiosperm seeds (the seeds of flowering plants) are contained in protective ovaries (that later become fruit), which help to protect the seeds from drying out and aid in their dispersal.

The roots of a plant function in the storage of nutrients, the acquisition of water and minerals (from the soil), and the anchoring of the plant to the substrate. Different plants have different kinds of roots, ranging from a taproot (dicots) to a fibrous root system (monocots) to adventitious roots (vines). Tiny root hairs, which extend from the root surface, provide the plant with a huge total absorptive surface and are responsible for most of the plant's water and mineral intake.

Plant stems (or trunks, as they are called in trees) function primarily to transport nutrients and provide physical support. Transport is achieved through the vascular system (composed of xylem and phloem), which carries water, minerals, and the products of photosynthesis all over the plant body. The tissues within the stems of monocots and dicots are arranged differently, with discrete vascular bundles in monocots and continuous rings of vascular tissue in many dicots.

The leaves of the plant contain chlorophyll and are the major sites of photosynthesis. Because of this important function, leaves are the site of gas exchange in plants, and small pores (stomata) on the surface of the leaf allow carbon dioxide in and oxygen (a byproduct of photosynthesis) out into the surrounding air. These stomata are regulated by guard cells, which open and close depending on the availability of moisture in the environment and protect the plant from losing too much water from evaporation (a phenomenon called transpiration).

Flowers contain the reproductive organs of angiosperms. Each flower is composed of four whorls, each of which contains one of the main structures of the flower. The calyx contains the sepals and the corolla contains the petals; together, the calyx and corolla comprise the perianth, or non- reproductive portion of the flower. The androecium contains the stamens. Stamens, the male reproductive organs, each contain an anther (pollen-production site) and filament. The gynoecium, at the very center of the flower, contains the pistils (sometimes called the carpels), the female reproductive organs. Each pistil is made up of a stigma, style, and ovary.

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