In animals, fertilization is the fusion of a sperm cell with an egg cell. The penetration of the egg cell by the chromosome-containing part of the sperm cell causes a reaction, which prevents additional sperm cells from entering the egg. The egg and sperm each contribute half of the new organism's genetic material. A fertilized egg cell is known as a zygote. The zygote undergoes continuous …
A fertilizer is any substance applied to land to increase plant growth and produce higher crop yield. Fertilizers may be made from organic material, such as animal manure or compost, or it may be chemically manufactured. Manufactured fertilizers contain varying amounts of inorganic nitrogen, phosphorus, and potassium, all of which are nutrients that plants need to grow. Since the 1950s crop produc…
Fetal alcohol syndrome (FAS) represents a preventable pattern of clinical abnormalities that develop during embryogenesis (the developmental stages shortly after conception) due to exposure to alcohol during pregnancy. FAS is currently the leading cause of birth defects and developmental delay, with as many as 12,000 babies born affected in the United States each year. Although the prevalence of F…
In everyday speech, f eudal can mean "aristocratic" (in contrast to democratic), "sumptuous," "reactionary," "hierarchic" (as opposed to egalitarian), "primitive," "medieval," or simply "despotic" or "oppressive" when speaking about political, social, or economic regimes. Since the ninet…
American physicist Richard Feynman's (1918–1988), work and writings were fundamental to the development of quantum electrodynamic theory (QED theory). With regard to QED theory, Feynman is perhaps best remembered for his invention of what are now known as Feynman diagrams, to portray the complex interactions of atomic particles. Moreover, Feynman diagrams allow visual representation …
Optical fiber is a very thin strand of glass or plastic capable of transmitting light from one point to another. Optical fiber can also be called an optical waveguide, since it is a device that guides light. Optical fibers consist of a light-carrying core and a cladding surrounding the core. There are generally three types of construction: glass core/cladding, glass core with plastic cladding, or …
A field is the name given to a pair of numbers and a set of operations which together satisfy several specific laws. A familiar example of a field is the set of rational numbers and the operations addition and multiplication. An example of a set of numbers that is not a field is the set of integers. It is an "integral domain." It is not a field because it lacks multiplicative inverse…
Figurative numbers are numbers which can be represented by dots arranged in various geometric patterns. For example, triangular numbers are represented by the patterns shown in Figure 1. The numbers they represent are 1, 3, 6, 10, and so on. Figurative numbers also include the square numbers which can be represented by square arrays of dots, as shown in Figure 2. The first few square numbers are 1…
Filtration is the process by which solid materials are removed from a fluid mixture, either a gas or liquid mixture. One of the most familiar kinds of filtration is that which students of chemistry encounter in their early laboratory experiences. In these experiences, suspensions of a solid precipitate in water are passed through filter paper supported in a glass funnel. The filter paper traps sol…
Finches are species of arboreal, perching birds that make up the large, widespread family, the Fringillidae. There are three subfamilies in this group, the largest being the Carduelinae or cardueline finches, a geographically widespread group that contains about 122 species. The subfamily Fringillinae or fringillid finches consists of three species breeding in woodlands of Eurasia, while the Drepa…
The true firs are about 40 species of conifer trees in the genus Abies, occurring in cool-temperate, boreal, and montane forests of the northern hemisphere. Firs are members of the pine family (Pinaceae). Firs are characterized by flattened needles, usually having two white lines running the length of the leaf. Firs do not have a petiole joining the needles to the twigs, and after the foliage is s…
More than three quarters of Earth's surface is covered by salt water; in addition, large areas are inundated with freshwater in the form of lakes, rivers, canals, swamps, and marshes. It is therefore not surprising that animals and plants have undergone a wide radiation in such habitats. One of the most successful groups of animals that have evolved to fill all of these habitats is the fish…
Flagella are long, thread-like appendages which provide some live single cells with the ability to move, motility. Bacteria which have flagella are either rod or spiral-shaped and are known as bacilli and spirochetes, respectively. Cocci, or round bacteria, are almost all nonmotile. Animal sperm cells also have flagella. However, prokaryotic cells (such as bacteria) have flagella made up of the pr…
Allowing analysis of the light (photons) from excited atoms, flame analysis is a form of atomic emission spectroscopy (AES). German chemist Robert Bunsen's (1811–1999) invention of the Bunsen burner—a tool now commonly used in modern chemistry laboratories—also spurred the development of flame analysis. Working with Gustav Kirchhoff (1824–1887), Bunsen helped to …
Flamingos are five species of large, colorful, very unusual-looking wading birds that encompass the family Phoenicopteridae. The flamingo lineage is ancient, with fossils of these birds being known from the early Tertiary. These birds occur in tropical and temperate regions of Africa, Madagascar, India, southern Europe, Caribbean coasts, highlands of the Andes in South America, and on the Galapago…
Flatfish are a group of mostly saltwater, carnivorous, bottom-dwelling fish in which both eyes are located the same side of the head. The under side of a flatfish is white while the upper side with the two eyes may be brightly colored. Many of these fish can change color to match their surroundings, making them hard to detect. When flatfish hatch, the eyes are located normally on each side of the …
Flatworms are small, multicelled animals with elongated bodies that have clearly defined anterior (front) and posterior (rear) ends. These worms are bilaterally symmetrical, meaning that their two sides reflect each other. They usually have a recognizable head, which houses gravity and light-receptive organs, and eye spots. They lack circulatory and respiratory systems and have only one opening th…
The flax plant, genus Linum, family Linaceae, is the source of two important commodities. Linen is a historic, economically important cloth made from the fiber of flax. Linseed oil is obtained from the pressed seeds of the plant. There are about 200 species of Linum. The species that is cultivated most extensively is L. usitatissimum, an annual plant grown for its fiber and seed. Varieties of L. u…
Flies belong to the order Diptera, a group that also includes mosquitoes, gnats, and midges. Flies make up the fourth largest order of insects, with about 100,000 species recognized. Dipterans are amongst the most advanced insects in terms of morphology and biological adaptations. Their versatility and extreme range of anatomical and behavioral adaptations have enabled them to thrive in almost eve…
Ratites are flightless birds that lack the keel (high ridge) on the breastbone to which the flight muscles of flying birds are attached. Instead, the entire breastbone looks rather like a turtle's shell. It has also been described as a raft, which gives this group of flightless birds its name, Ratitae (Ratis means raft in Latin). Ratites have heavy, solid bones, while flying birds have ligh…
Flooding, although it usually carries a negative connotation, is quite a natural process and is simply the response of a natural system (a river system) to the presence of too much water during an interval of time. Rivers and streams are governed by a simple equation, Q = A × V, where Q is discharge (amount of water), A is area of the river channel, and V is velocity. When excess discharge …
Flora is a word used to describe the assemblage of plant species that occurs in some particular area or large region. Flora can refer to a modern assemblage of plant species, or to a prehistoric group of species that is inferred from the fossil record. The zoological analogue is known as a fauna, although this word is usually used in reference to a large region. More locally, "vegetation&#x…
Fluid dynamics is the study of the flow of liquids and gases, usually in and around solid surfaces. The flow patterns depend on the characteristics of the fluid, the speed of flow, and the shape of the solid surface. Scientists try to understand the principles and mechanisms of fluid dynamics by studying flow patterns experimentally in laboratories and also mathematically, with the aid of powerful…
Fluid mechanics is the study of gases and liquids at rest and in motion. Fluid statics studies the behavior of stationary fluids and tells us, for instance, how much air to put in our tires and whether a boat in a lake will float or sink. Fluid dynamics studies the flow behavior of moving fluids. Both global weather patterns and the flow of water from a faucet are governed by the laws of fluid dyn…
Fluorescent in situ hybridization (FISH) is a powerful technique for detecting RNA or DNA sequences in cells, tissues, and tumors. FISH provides a unique link among the studies of cell biology, cytogenetics, and molecular genetics. Fluorescent in situ hybridization is a technique in which single-stranded nucleic acids (usually DNA, but RNA may also be used) are permitted to interact so that comple…
Fluorescent light is the most common type of electrical light found in the United States; it is used for practically all commercial lighting, i.e. offices, factories, stores and schools, and it is estimated that there are 1.5 billion fluorescent lamps in use nationwide. Fluorescent lighting is popular due to its high efficacy, i.e. it produces between three to five times more light than an incande…
Flying fish belong to the family Exocoetidae in the bony fish order Atheriniformes. They are close relatives of the needlefish, halfbeaks, and sauries. Flying fish are characterized by a low lateral line, soft fins without spines, and a caudal fin with the lower lobe larger than the upper lobe. The lower jaw of the young flying fish has an extended filament longer than the body, which becomes deta…
Focused ion beams have been used since the 1960s to investigate the chemical and isotopic composition of In addition to precise imaging, FIB technology can be used in a variety of manufacturing environments requiring high levels of precision and accuracy. The image above, using time-lapse, shows a computer-controlled ion beam helping shape a mirror for the Keck telescope. © Roger Ressmey…
Fog is caused by the condensation of water at or near Earth's surface. The atmosphere is obscured—essentially by cloud formation—near the surface and fog conditions are generally characterized as existing when atmospheric visibility is reduced to about one-half mile (approximately 0.8 km). Precipitation fog is a type of evaporation fog that happens when relatively warm rain or…
A fold is a bend in a body of rock or sediment that forms due to a change in pressure. Wave-like folds are composed of layers of the earth's crust that bend and buckle under enormous pressure as the crust hardens, compresses, and shortens. Folds form much the same way as a hump arises in a sheet of paper pushed together from both ends. Folds may be softly rolling or severe and steep, depend…
Food irradiation refers to a process where food is exposed to a type of radiation called ionizing radiation. The high-energy of the radiation, which can come from a radioactive or a non-radioactive source, breaks apart the genetic material of microorganisms that are on the surface of the food. Microorganisms and other surface contaminants, including insects, are killed as a result. This scrutiny o…
Food poisoning refers to an illness that is caused by the presence of bacteria, poisonous chemicals, or another kind of harmful compound in a food. Bacterial growth in the food is usually required. Food poisoning is different from food intoxication, which is the presence of preformed bacterial toxin in food. There are over 250 different foodborne diseases. The majority of these are infections, and…
The term food preservation refers to any one of a number of techniques used to prevent food from spoiling. It includes methods such as canning, pickling, drying and freeze-drying, irradiation, pasteurization, smoking, and the addition of chemical additives. Food preservation has become an increasingly important component of the food industry as fewer people eat foods produced on their own lands, a…
The food pyramid was developed by the U.S. Department of Agriculture (USDA) as a nutrition guide for healthy persons over the age of two years. The guide stresses eating a wide variety of foods from the five major food groups while minimizing the intake of fats and sugars. The daily quantity of foods from each group is represented by the triangular shape. The pyramid is composed of four levels. Th…
Foot and mouth disease is caused by a particular type of virus. The disease affects cloven hooved animals; that is, animals with hooves that are split into two main segments. Examples of domestic cloven hooved animals include cattle, sheep, pigs, and goats. Wild cloven hooved animals that are susceptible to foot and mouth disease include elephants, hedgehogs, and rats. Foot and mouth disease occur…
Force is the term used for an outside influence exerted by one body on another which produces a change in state of motion or state of configuration. This limited meaning in science compared to our everyday usage is most important because of the specific results of this out-side influence. Force producing a change in state of motion gives a body acceleration. If forces acting on a body produces no …
Forensic science reflects multidisciplinary scientific approach to examining crime scenes and in examining evidence to be used in legal proceedings. Forensic science techniques are also used to verify compliance with international treaties and resolutions regarding weapons production and use. Forensic science techniques incorporate techniques and principles of biology, chemistry, medicine, physics…
The metaphysical notion of form (eidos, morphe, Gr.; idea, forma, species, Lat.), as it emerged in the works of Plato, must be carefully distinguished from the everyday notion from which it derived, namely, the shape or outer appearance of a thing as it presents itself to the eyes. The outer appearance of a mannequin, for instance, may be deceptively similar to that of a human being, yet, the form…