With this development comes changes in bones, nerves, and muscles, and the underside loses its colour. As an adult, the flounder lives on the sea bottom with the eyed side on top.
flour Finely ground cereal grain or other starchy portions of plants. Flour, especially wheat flour, is a basic ingredient of baked goods (see baking). In the production of refined flour, the starchy endosperm is separated from the other parts of the kernel by milling through rollers. In the production of whole-wheat flour, all parts of the kernel are used. Following milling, the particles of endosperm (called semolina) are ground to flour and often bleached to imitate natural aging. Flour grades are based on the residual amount of branny particles. When flour is mixed with water to make dough, its protein content is converted to gluten, an elastic substance that forms a continuous network throughout the dough and is capable of retain¬ ing gas, thus causing the baked product to expand, or rise.
flow See DEFORMATION AND FLOW, LAMINAR flow, TURBULENT FLOW
flow meter Device that measures the velocity of a gas or liquid. It has applications in medicine as well as in chemical engineering, aeronautics, and meteorology. Examples include pitot tubes, venturi tubes, and rotame¬ ters (tapered graduated tubes with a float inside that is supported by the flowing fluid at a level that depends on the flow rate). Ultrasonic flow meters, in which reflecting ultrasound off a flowing liquid leads to a Dop¬ pler shift (see Doppler effect) that is calibrated to provide the flow rate of the liquid, have important industrial applications and have also been used to measure arterial blood flow.
flowchart Graphical representation of a process, such as a manufac¬ turing operation or a computer operation, indicating the various steps
taken as the product moves along the production line or the problem moves through the computer. Individual operations can be represented by closed boxes, with arrows between boxes indicating the order in which the steps are taken and divergent paths determined by variable results.
flower Reproductive portion of any flowering plant (angiosperm). Popu¬ larly, the term applies especially when part or all of the reproductive structure is distinctive in colour and form. Flowers present a multitude of combinations of colour, size, form, and anatomical arrangement. In some plants, individual flowers are very small and are borne in a distinctive cluster (inflorescence). Each flower consists of a floral axis that bears the essential organs of reproduction (stamens and pistils) and usually acces¬ sory organs (sepals and petals); the latter may serve both to attract pol¬ linating insects (see pollination) and to protect the essential organs. Flower parts are arrayed usually in whorls, but sometimes spirally. Four distinct whorls are common: the outer calyx (sepals), the corolla (petals), the androecium (stamens), and, in the centre, the gynoecium (pistils). The sepals are usually greenish and often resemble reduced leaves; the petals are usually colourful and showy. Pollen is produced in the stamens. A pollen-receptive stigma rests atop each pistil. The pistil, made up of one or more carpels, encloses an ovary that contains the ovules, or potential seeds. After fertilization, the ovary enlarges to form the fruit. Flowers have been symbols of beauty in most civilizations of the world, and flower giv¬ ing is still among the most popular of social amenities.
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The life cycle of a flowering plant. (1) A pollen grain is released from the anther and settles on the stigma. (2) A pollen tube forms and grows through the style toward the ovule opening (micropyle). (3) Two of the nuclei (polar nuclei) in the ovule's embryo sac migrate to the centre to form a single cell. Three cells migrate to the micropyle, and one enlarges to become the egg. Two sperm that have formed from mitotic division of the pollen grain's generative cell enter the embryo sac through the micropyle. (4) One sperm fuses with the egg, resulting in a fertilized egg (zygote), which develops into an embryo. The second sperm fuses with the two polar nuclei to form the endosperm nucleus. (5) This nucleus divides to form a tissue (endosperm) that provides nutrients for the developing embryo.
© MERRIAM-WEBSTER INC.
Flounder ( Platichthys )
F. GREENAWAY-NATURAL HISTORY PHOTOGRAPHIC AGENCY/EB INC.
© 2006 Encyclopaedia Britannica, Inc.
flowering plant ► flux I 685
flowering plant Any of the more than 250,000 species of angiosperms (division Magnoliophyta) having roots, stems, leaves, and well-developed conductive tissues (xylem and phloem). They are often differentiated from gymnosperms by their production of seeds within a closed chamber (the ovary) within the flower, but this distinction is not always clear-cut. The division is composed of two classes: monocots and dicots (see cotyledon). Monocots have flower parts in threes, scattered conducting strands in the stem, and usually prominent parallel veins in the leaves, and they lack a cambium. Dicots have flower parts in fours or fives, conducting strands arranged in a cylinder, a net-veined pattern in the leaves, and a cambium. Flowering plants reflect an immense diversity in habit, size, and form; they account for more than 300 families growing on every continent, including Antarctica. Flowering plants have adapted to almost every habi¬ tat. Most reproduce sexually by seeds via the specialized reproductive organs that are present in all flowers.
flu See INFLUENZA
fliigelhorn Brass musical instrument, a valved bugle. It has three valves and a wider bore than the cornet and is usually pitched in B-flat. The fliigelhorn was invented in Austria in the 1830s. It has maintained its identity—particularly its bore and its squat shape—better than has the formerly very similar cornet. Long used in European military bands, it is now also used in jazz and popular music.
fluid Any liquid or gas that cannot sustain a shearing force when at rest and that undergoes a continuous change in shape (see flow) when sub¬ jected to such a stress. Compressed fluids exert an outward pressure that is perpendicular to the walls of their containers. A perfect fluid lacks vis¬ cosity, but real fluids do not.
fluid mechanics Study of the effects of forces and energy on liquids and gases. One branch of the field, hydrostatics, deals with fluids at rest; the other, fluid dynamics, deals with fluids in motion and with the motion of bodies through fluids. Liquids and gases are both treated as fluids because they often have the same equations of motion and exhibit the same flow phenomena. The subject has numerous applications in fields varying from aeronautics and marine engineering to the study of blood flow and the dynamics of swimming.
fluke or trematode Any member of almost 6,000 species of parasitic flatworms. Flukes are found world¬ wide and range in size from about 0.2 to 4 in. (5-100 mm) long. They most commonly parasitize fish, frogs, and turtles, but also humans, domestic animals, and invertebrates such as mollusks and crustaceans.
They include external parasites (ectoparasites), internal parasites (endoparasites), and semi-external parasites (those that attach to the lin¬ ing of the mouth, to gills, or to the cloaca). Most flukes are flattened and leaflike or ribbonlike and have muscular suckers on the bottom surface, as well as hooks and spines, for attachment to the host. Fluke infestations may cause illness (e.g., schistosomiasis) or death in humans.
fluorescence Emission of electromagnetic radiation, usually visible light, caused by excitation of atoms in a material, which then reemit almost immediately (within about 10 -8 seconds). The initial excitation is usually caused by absorption of energy from incident radiation or particles, such as X-rays or electrons. Because reemission occurs so quickly, the fluores¬ cence ceases as soon as the exciting source is removed, unlike phosphores¬ cence, which persists as an afterglow. A fluorescent lightbulb is coated on the inside with a powder and contains a gas; electricity causes the gas to emit ultraviolet radiation, which then stimulates the tube coating to emit light. The pixels of a television or computer screen fluoresce when elec¬ trons from an electron gun strike them. Fluorescence is often used to ana¬ lyze molecules, and the addition of a fluorescing agent with emissions in the blue region of the spectrum to detergents causes fabrics to appear whiter in sunlight. X-ray fluorescence is used to analyze minerals.