Transport in Plants

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Root Diagram

Root ,organ of higher plants, usually subterranean and having several functions, including the absorption and conduction of water and dissolved minerals, food storage, and anchorage of the plant in the soil. The root is distinguished from the stem by its structure, by the manner in which it is formed, and by the lack of such appendages as buds and leaves. The first root of the plant, known as the radicle, elongates during germination of the seed and forms the primary root. Roots that branch from the primary root are called secondary roots. In many plants the primary root is known as a taproot because it is much larger than secondary roots and penetrates deeper into the soil. Beets and carrots are examples of plants with very large taproots. Some plants having taproots cannot be transplanted easily, for breaking the taproot may result in the loss of most of the root system and cause the death of the plant.

Root (botany), organ of higher plants, usually subterranean and having several functions, including the absorption and conduction of water and dissolved minerals, food storage, and anchorage of the plant in the soil. The root is distinguished from the stem by its structure, by the manner in which it is formed, and by the lack of such appendages as buds and leaves. The first root of the plant, known as the radicle, elongates during germination of the seed and forms the primary root. Roots that branch from the primary root are called secondary roots. In many plants the primary root is known as a taproot because it is much larger than secondary roots and penetrates deeper into the soil. Beets and carrots are examples of plants with very large taproots. Some plants having taproots cannot be transplanted easily, for breaking the taproot may result in the loss of most of the root system and cause the death of the plant.

Under normal conditions the growth of roots is influenced chiefly by gravity and by the presence of water. Roots tend to grow downward into soil, unless water is more readily available at the surface. In addition to the primary growth in length occurring at the apex of the root, a secondary growth occurs that adds xylem, or wood, to the inside of the root and phloem toward the outside. Phloem produced in this manner becomes involved in the formation of bark, which covers old roots as well as old stems. Old roots often are virtually identical therefore with old stems.

Because in many plants roots can be formed from a cut end of a stem, cuttings may be used for plant propagation. Some plants, such as the willow or geranium, root quite easily, whereas others, such as the conifer, rarely root without special treatment. Root formation can be stimulated on cuttings of many plants by the application of the so-called root hormones, substances found naturally in the plant when new roots are formed. Most commercial preparations of root hormones contain indoleacetic acid, one of the most common root-stimulating substances. Occasionally roots may be formed from leaves, as in the African violet, which may be propagated by rooting the cut end of a leaf base in water. In some plants roots may give rise to shoots. For example, the stems that are formed at various distances from the base of a Lombardy poplar arise from roots.

Transpiration

Transpiration:

Transpiration, evaporation of water particles from plant surfaces, especially from the surface openings, or stomata, on leaves. Stomatal transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the surfaces of the epidermal cells of the leaves. The effects of air currents (wind), and the variation of temperature, humidity and light intensity on 

transpiration rate is obvious. Their increase will increase rate of Transpiration, except for humidity, its increase will decrease the rate because, humidity will not allow more water to enter in atmosphere, for it is saturated in water.

Vascular Bundle, (Xylem, Phloem)

Xylem:

Xylem, woody tissue, found in higher plants, that conducts water and inorganic salts throughout the plant and provides it with mechanical support. In leaves, flowers, and young stems, xylem is present in conjunction with phloem in the form of conducting strands called vascular bundles. In roots there is a central core of xylem. Xylem that derives from the shoot and root-growing points is called primary xylem. In addition, new xylem, called secondary xylem, may be added by the activity of the cambium, which actively divides cells situated between the xylem and phloem. This division gives rise to new xylem cells toward the center in roots and toward the outside in most stems. Some plants have little or no secondary xylem, in contrast to woody plants in which indefinite amounts of secondary xylem is the botanical term equivalent to wood. See Stem.

Xylem may contain three types of elongated cells: tracheids, vessel elements, and fibers. At maturity, when functioning in conduction, all of these cells are dead. Tracheids are elongated cells with thick walls characterized by small, sharply defined thin areas known as pits. Vessel elements are specialized tracheids in which the end walls have one or more pores; a vertical series of vessel elements forming a continuous tube is known as a vessel. Fibers, which are specialized tracheids with much-thickened walls, function only slightly in conduction, but serve to increase the strength of xylem.

The xylem of plants that are earlier than most in evolutionary development, such as ferns and conifers, consists of tracheids. In most flowering plants, the xylem also contains well-developed vessels and fibers. Because sequences in the specialization of all these tissue elements can be observed quite clearly, the study of xylem provides important clues to the evolutionary pathways of higher plants.

Phloem:

Phloem, in higher plants, vascular tissue that conducts sugars and other synthesized food materials from the regions of manufacture in the plant to those of consumption and storage. Phloem is found in the vascular bundles, the longitudinal strands of conductive tissue, in association with the water-conducting tissue, or xylem. The vascular bundles constitute major structural units in herbaceous stems and are the veins in leaves. In the vascular cylinder traversing the center of the buttercup root, for example, the xylem forms a star-shaped central core, and bands of phloem are present in the grooves of this core. Typically, the xylem is on the side of the vascular bundle closest to the pith, although other arrangements are not uncommon. In the older portions of a plant the soft cells of the phloem are crushed as new phloem is formed in the growing process and pushed outward. This new phloem is formed by the action of the cambium, or growing zone, a layer of cells that separates the xylem and phloem and produces phloem cells toward the outside of the plant.

Phloem consists of two types of conducting cells, the characteristic type known as sieve-tube elements and another type called companion cells. Sieve-tube elements are elongate cells that have end walls perforated by numerous minute pores through which dissolved materials can pass. Such sieve-tube elements are connected in vertical series known as sieve tubes. Sieve-tube elements are alive at maturity, although their nuclei disintegrate before the element begins its conductive function. Companion cells, which are smaller, have nuclei at maturity and are living; they are found adjacent to the sieve-tube elements and are believed to control the process of conduction in the sieve tubes.

Phloem may contain bast fibers. These fibers are very strong and in certain plants are the source of such commercial fibers as flax and jute, used to make linen fabric and burlap and sacking.

Transpiration Pull:

Water is constantly lost by transpiration in the leaf. When one water molecule is lost another is pulled along by the processes of cohesion and tension, it is called transpiration pull.

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Capillary action (sometimes capillarity, capillary motion, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity, cohesion.

The capillary action is enhanced in trees by branching, evaporation at the leaves creating depressurization, and probably by osmotic pressure added at the roots and possibly at other locations inside the plant, especially when gathering humidity with air roots.

Translocation:

Translocation is the movement of food in plants, in more detail it is the movement of soluble materials within a plant.Common examples are the movement of food materials from the leaves to storage organs, and the movement of dissolved minerals upward from the roots. Mainly Sugar in leaves is converted to starch for storage, & for transfer, its converted to sucrose, then again to target storage organs like tubers, roots, cortex etc it is converted back to starch. Then when needed, utilized as glucose in respiration.