Plants

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monocot

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one of two major groups of flowering plants (angiosperms) that are traditionally recognized, Dicotyledons or dicots being the other. Monocots have been recognized at various taxonomic ranks, and under various names.

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abscisic acid

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also known as abscisin II and dormin, is a plant hormone. It was once thought to be pivotal in abscission and in bud dormancy. Currently, the hormone is thought to act mainly to inhibit growth, to be perhaps only one of the hormones involved in bud dormancy and not the one involved in enforcing it throughout the winter, and help the plant tolerate stressful conditions, particularly water stress.

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phloem

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complex tissue in the vascular system of higher plants that consists mainly of sieve tubes and elongated parenchyma cells usually with fibers and that functions in translocation and in support and storage

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vascular tissue system

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a complex tissue found in vascular plants, meaning that it is composed of more than one cell type. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant.

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tropisms

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involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation.

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indeterminate growth

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growth that is not terminated in contrast to determinate growth that stops once a genetically pre-determined structure has completely formed. Thus, a plant that grows and produces flowers and fruit until killed by frost or some other external factor is called indeterminate. For example, the term is applied to tomato varieties that grow in a rather gangly fashion, producing fruit throughout the growing season, and in contrast to a determinate tomato plant, which grows in a more bushy shape and typically produces a single harvest.

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gravitropism

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turning or growth movement by a plant or fungus in response to gravity. Charles Darwin was one of the first Europeans to document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull (i.e., downward) and stems grow in the opposite direction (i.e., upwards). This behaviour can be easily demonstrated with a potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, bending (biologists say, turning; see tropism) upwards.

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stem

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one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence (flowers), cones or other stems etc.

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node

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Nodes are areas of great cellular activity and growth, where auxiliary buds develop into leaves or flowers.

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internode

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area between nodes

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axillary bud

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lies at the junction of the stem and petiole of a plant. As the apical meristem grow and form leaves, a region of meristematic cells are left behind at the node between the stem and the leaf. These axillary buds are usually dormant, inibited by auxin produced by the apical meristem, which is known as apical dominance. If the apical meristem was removed, or has grown a sufficient distance away from an axillary bud, the axillary bud may become activated (or more appropriately freed from [hormone] inhibition). Like the apical meristem, axillary buds can develop into a stem or flower.

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apical dominance

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he phenomenon whereby the main central stem of the plant is dominant over (i.e., grows more strongly than) other side stems, and on a branch, the main stem of the branch is further dominant over its own side branchlets.

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parenchyma cell

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hin-walled cells of the ground tissue that make up the bulk of most nonwoody structures, although sometimes their cell walls can be lignified. Parenchyma cells in between the epidermis and pericycle in a root or shoot constitute the cortex, and are used for storage of food. Parenchyma cells within the center of the root or shoot constitute the pith. Parenchyma cells in the ovary constitutes the nucellus and are brick-like in formation.

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collenchyma cell

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Collenchyma tissue is composed of elongated cells with unevenly thickened walls. They provide structural support, particularly in growing shoots and leaves. Collenchyma tissue composes, for example, the resilient strands in stalks of celery. Its growth is strongly affected by mechanical stress upon the plant. The walls of collenchyma in shaken (to mimic the effects of wind etc) plants may be 40%-100% thicker than those not shaken. The name collenchyma derives from the Greek word "kolla", meaning "glue", which refers to the thick, glistening appearance of the walls in fresh tissues.

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dicot

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a name for a group of flowering plants whose seed typically contains two embryonic leaves or cotyledons. There are around 199,350 species within this group [1]. Flowering plants that are not dicotyledons are monocotyledons, typically having one embryonic leaf.

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xylem

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one of the two types of transport tissue, phloem being the other one. The word "xylem" is derived from classical Greek ξυλον (xylon), "wood", and indeed the best known xylem tissue is wood, though it is found throughout the plant. Its basic function is to transport water.

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cuticle

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protective waxy coverings produced by the epidermal cells of leaves, young shoots and all other aerial plant organs. The main structural components of plant cuticles are the unique polymers cutin and/or cutan, impregnated with wax.

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leaf abscission

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the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal.

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root hairs

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fine outgrowths or appendages on plants. These are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae.

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indoleacetic acid (IAA)

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ndole-3-acetic acid, also known as IAA, is a member of the group of phytohormones called auxins. IAA is generally considered to be the most important native auxin.

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acid-growth hypothesis

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Explains phototropism by suggesting that increased acidity in the walls of certain cells (stimulated by the hormone auxin) increases their flexibility and expandability, so that more water can diffuse into the cells and cause cell elongation.

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vessel elements

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one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are typically found in the angiosperms but absent from most gymnosperms such as the conifers. Vessel elements are the building blocks of vessels, which constitute the major part of the water transporting system in the plants where they occur.

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determinate growth

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growth that stops once a genetically pre-determined structure has completely formed.

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gibberellins

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plant growth substances (phytohormones) involved in promotion of stem elongation, mobilization of food reserves in seeds and other processes. Its absence results in the dwarfism of some plant varieties.

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apical meristem

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a tissue in all plants consisting of undifferentiated cells (meristematic cells) and found in zones of the plant where growth can take place.

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zone of cell elongation

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areas of rapid cell elongation usually just proximal to the zone of cell division.

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zone of cell differentiation

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[Template--this is for a B cell] The process whereby a B cell in the spleen acquires the specialized features of a marginal zone B cell. Marginal zone B cells are localized in a distinct anatomical region of the spleen that represents the major antigen-filtering and scavenging area (by specialized macrophages resident there). It appears that they are preselected to express a BCR repertoire similar to B-1 B cells, biased toward bacterial cell wall constituents and senescent self-components (such as oxidized LDL).

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simple tissue

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consisting of a single cell type

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dermal tissue system

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The outer layer of the apical meristem gives rise to the epidermis of the primary plant body

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ethylene

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chemical compound with the formula C2H4. It is the simplest alkene. Because it contains a double bond, ethylene is called an unsaturated hydrocarbon or an olefin. It is exceedingly important in industry and even has a role in biology as a hormone. Ethylene is the most produced organic compound in the world; global production of ethylene exceeded 75 million metric tons per year in 2005.

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fibrous root system

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he opposite of a taproot system. It is usually formed by thin, moderately branching roots growing from the stem. A fibrous root system is universal in monocotyledonous plants and ferns, and is also common in dicotyledonous plants.

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ground tissue system

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Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients.

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phototropism

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directional plant growth in which the direction of growth is determined by the direction of the light source. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism (or Skototropism). Most plant shoots exhibit positive phototropism, while roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth.

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procambium

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The band consists of the long, narrow cells of a meristem called a procambium, and as they continue to divide, some of their progeny cells will develop into vascular tissues -- xylem and phloem.

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cytokinins

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any of various plant growth substances (as kinetin) that are usually derivatives of adenine

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rootcap

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a protective cap of parenchyma cells that covers the terminal meristem in most root tips

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terminal bud

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occurs on the end of a stem and lateral buds are found on the side. A head of cabbage (see Brassica) is an exceptionally large terminal bud, while Brussels sprouts are large lateral buds.

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zone of cell division

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areas of mitotic division including the root meristem and the root cap division.

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sclerenchyma cell

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ard and brittle (as you might expect from the root: scler-. The cells develop an extensive secondary cell wall (laid down on the inside of the primary wall). This wall is invested with lignin, making it extremely hard. Lignin, plus suberin and/or cutin make the wall waterproof as well. Thus, these cells cannot survive for long as they cannot exchange materials well enough for active (or even maintaining) metabolism. Functions for sclerenchyma cells include discouraging herbivory (hard cells that rip open digestive passages in small insect larval stages, hard cells forming a pit wall in a peach fruit), support (the wood in a tree trunk, fibers in large herbs), and conduction (hollow cells lined end-to-end in xylem with cytoplasm and end walls missing).

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complex tissue

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multicellular tissue, such as vascular tissue

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stress hormone

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the hormone called abscisic acid (ABA) plays a role in how plants respond to weather stresses, such as cold and drought; plants normally produce an enzyme that breaks down Abscisic Acid (ABA).

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taproot system

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derives directly from the first root that emerge from a seed (the radicle or primary root) that enlarges and forms a prominent central root that is called the taproot. The taproot is larger in diameter than the lateral roots. Lateral roots branch off from the taproot, and subsequent lateral roots can branch off other lateral roots. Taproots generally grow more deeply into the soil than do fibrous roots. It often become a modified storage organ for food reserves such as carbohydrate or for reaching water deep in the ground.

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auxin

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a class of plant growth substance (often called phytohormones or plant hormones). Auxins play an essential role in coordination of many growth and behavioral processes in the plant life cycle.

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sieve plates

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perforated end walls separating the component cells (sieve elements) that make up the phloem sieve tubes in vascular plants. The perforations permit the flow of water and dissolved organic solutes along the tube and are lined with callose. The plates are readily blocked by further deposition of callose when the sieve Tube is stressed or damaged.

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protoderm

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lies around the outside of the stem and develops into the epidermis.

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petiole

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the stalk of a leaf, attaching the blade to the stem; petiolate leaves are ones where the tendril connects to the leaf before its apex

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tracheids

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longated cells in the xylem of vascular plants, serving in the transport of water. The build of tracheids will vary according to where they occur.

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perennial

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a plant that lives for more than two years. Perennial plants are divided into two large groups, those that are woody and those that are herbaceous.

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ground meristem

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Ground meristem develops into the pith. It produces the cork cambium, another secondary meristem.

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procambium

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ies just inside of the protoderm and develops into primary xylem and primary phloem. It also produces the vascular cambium, a secondary meristem.