Thursday, June 28, 2007
chemical reaction
A chemical reaction is a progression that results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants. Chemical reactions are characterized by a chemical change, and they yield one or more products which are, in general, unlike from the reactants. Classically, chemical reactions include changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformation of elementary particles, as well as nuclear reactions. On the classical meaning, therefore, there are only two types of chemical reaction redox reactions and acid-base reaction. The former involve the motion of lone electrons and the latter of an electron pair.
Different chemical reactions are used in combinations in chemical synthesis in order to get a preferred product. In biochemistry, series of chemical reactions aided by enzymes form metabolic pathways, since straight synthesis of a product would be energetically impossible in situation within a cell. Chemical reactions are also divided into organic reactions and non-living reactions.
Different chemical reactions are used in combinations in chemical synthesis in order to get a preferred product. In biochemistry, series of chemical reactions aided by enzymes form metabolic pathways, since straight synthesis of a product would be energetically impossible in situation within a cell. Chemical reactions are also divided into organic reactions and non-living reactions.
Friday, June 22, 2007
Vehicles
Vehicles are non-living means of moving. They are most repeatedly man-made (e.g. bicycles, cars, motorcycles, trains, ships, and aircraft), although some other means of transportation which are not made by man can also be called vehicles; examples include icebergs and balanced tree trunks. Vehicles may be propelled by animals, e.g. a chariot or an ox-cart. However, animals on their own, though used as a earnings of transportation, are not called vehicles. This includes humans transport another human, for example a child or a disabled person.
Vehicles that do not pass through on land are often called crafts, such as watercraft, sailcraft, aircraft, hovercraft and spacecraft. Movement lacking the help of a vehicle or an animal is called locomotion. The word vehicle itself comes from the Latin vehicular.
Vehicles that do not pass through on land are often called crafts, such as watercraft, sailcraft, aircraft, hovercraft and spacecraft. Movement lacking the help of a vehicle or an animal is called locomotion. The word vehicle itself comes from the Latin vehicular.
Thursday, June 07, 2007
Pawpaw
Pawpaw (Asimina) also known as a prairie banana or Ozark banana, is a genus of eight or nine species of small trees with large leaves and fruit, native to southeastern North America. The genus includes the largest edible fruit native to North America. They are understorey trees of deep fertile bottomland soils. The name, also spelled paw paw, paw-paw, and papaw, probably derives from the Spanish papaya, perhaps due to the superficial similarity of their fruit. Pawpaw is in the same family Annonaceae as the custard-apple, cherimoya, sweetsop, and soursop, and it is the only member of that family not confined to the tropics.
The pawpaws are shrubs or small trees, reaching heights of 2 to 12 m tall. The leaves are alternate, simple ovate, entire, 20 to 35 cm long and 10 to 15 cm broad. The northern, cold-tolerant common pawpaw is deciduous, while the southern species are often evergreen. The fetid flowers are produced singly or in clusters of up to eight together; they are large, 4 to 6 cm across, perfect, with six sepals and petals (three large outer petals, three smaller inner petals). The petal color varies from white to purple or red-brown. Pollinated by scavenging carrion flies and beetles, the flowers emit a weak scent which attracts few pollinators, thus limiting fruit production. Larger growers sometimes locate rotting meat near the trees at bloom time to increase the number of blowflies. Asimina triloba is the only larval host of the Zebra Swallowtail Butterfly.
The fruit is a large edible berry, 5 to 16 cm long and 3 to 7 cm broad, weighing from 20 to 500 g, with numerous seeds; it is green when unripe, maturing to yellow or brown. It has a flavor somewhat similar to both banana and mango, varying significantly by cultivar, and has more protein than most fruits.
History
The earliest documentation of pawpaws is in the 1541 report of the de Soto expedition, who found Native Americans cultivating it east of the Mississippi River. The Lewis and Clark Expedition depended and sometimes subsisted on pawpaws during their travels. Chilled pawpaw fruit was a favorite dessert of George Washington, and Thomas Jefferson was certainly familiar with it as he planted it at Monticello.
The pawpaws are shrubs or small trees, reaching heights of 2 to 12 m tall. The leaves are alternate, simple ovate, entire, 20 to 35 cm long and 10 to 15 cm broad. The northern, cold-tolerant common pawpaw is deciduous, while the southern species are often evergreen. The fetid flowers are produced singly or in clusters of up to eight together; they are large, 4 to 6 cm across, perfect, with six sepals and petals (three large outer petals, three smaller inner petals). The petal color varies from white to purple or red-brown. Pollinated by scavenging carrion flies and beetles, the flowers emit a weak scent which attracts few pollinators, thus limiting fruit production. Larger growers sometimes locate rotting meat near the trees at bloom time to increase the number of blowflies. Asimina triloba is the only larval host of the Zebra Swallowtail Butterfly.
The fruit is a large edible berry, 5 to 16 cm long and 3 to 7 cm broad, weighing from 20 to 500 g, with numerous seeds; it is green when unripe, maturing to yellow or brown. It has a flavor somewhat similar to both banana and mango, varying significantly by cultivar, and has more protein than most fruits.
History
The earliest documentation of pawpaws is in the 1541 report of the de Soto expedition, who found Native Americans cultivating it east of the Mississippi River. The Lewis and Clark Expedition depended and sometimes subsisted on pawpaws during their travels. Chilled pawpaw fruit was a favorite dessert of George Washington, and Thomas Jefferson was certainly familiar with it as he planted it at Monticello.
