Malic acidMalic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L- and D-enantiomers), though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates. The malate anion is an intermediate in the citric acid cycle. The word 'malic' is derived from Latin 'mālum', meaning 'apple'.
Human tooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and permanent teeth begin to form in the twentieth week. If teeth do not start to develop at or near these times, they will not develop at all, resulting in hypodontia or anodontia.
Beginning of human personhoodThe beginning of human personhood is the moment when a human is first recognized as a person. There are differences of opinion as to the precise time when human personhood begins and the nature of that status. The issue arises in a number of fields including science, religion, philosophy, and law, and is most acute in debates relating to abortion, stem cell research, reproductive rights, and fetal rights. Traditionally, the concept of personhood has entailed the concept of soul, a metaphysical concept referring to a non-corporeal or extra-corporeal dimension of human being.
WeekA week is a unit of time equal to seven days. It is the standard time period used for short cycles of days in most parts of the world. The days are often used to indicate common work days and rest days, as well as days of worship. Weeks are often mapped against yearly calendars, but are typically not the basis for them, as weeks are not based on astronomy. The modern seven-day week can be traced back to the Babylonians, who used it within their calendar.
Vitamin KVitamin K is a family of structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation (K from koagulation German for "coagulation") or for controlling binding of calcium in bones and other tissues. The complete synthesis involves final modification of these so-called "Gla proteins" by the enzyme gamma-glutamyl carboxylase that uses vitamin K as a cofactor.
OsteonIn osteology, the osteon or haversian system (həˈvɝ.ʒən; named for Clopton Havers) is the fundamental functional unit of much compact bone. Osteons are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Their length is often hard to define, but estimates vary from several millimeters to around 1 centimeter. They are present in many bones of most mammals and some bird, reptile, and amphibian species. Each osteon consists of concentric layers, or lamellae, of compact bone tissue that surround a central canal, the haversian canal.
Names of the days of the weekIn many languages, the names given to the seven days of the week are derived from the names of the classical planets in Hellenistic astronomy, which were in turn named after contemporary deities, a system introduced by the Sumerians and later adopted by the Babylonians from whom the Roman Empire adopted the system during Late Antiquity. In some other languages, the days are named after corresponding deities of the regional culture, beginning either with Sunday or with Monday.
ChitinChitin (C8H13O5N)n (ˈkaɪtᵻn ) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially filamentous and mushroom forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms.
Space Shuttle thermal protection systemThe Space Shuttle thermal protection system (TPS) is the barrier that protected the Space Shuttle Orbiter during the searing heat of atmospheric reentry. A secondary goal was to protect from the heat and cold of space while in orbit. The TPS covered essentially the entire orbiter surface, and consisted of seven different materials in varying locations based on amount of required heat protection: Reinforced carbon–carbon (RCC), used in the nose cap, the chin area between the nose cap and nose landing gear doors, the arrowhead aft of the nose landing gear door, and the wing leading edges.
