Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells in an effort to produce energy, maintain life, or stimulate growth.
Historically, people secured food through two methods: hunting and gathering, and agriculture. Today, most of the food energy consumed by the world population is supplied by the food industry.
Worldwide more human beings gain their livelihood from agriculture than any other endeavor; the majority are self-employed subsistence farmers living in the tropics]citation needed[. While growing food for local consumption is the core of tropical agriculture, cash crops (normally crops grown for export) are also included in the definition.
When people discuss the tropics, it is normal to use generalized labels to group together similar tropical areas. Common terms would include the humid-tropics (rainforests); the arid-tropics (deserts and dry areas); or monsoon zones (those areas that have well defined wet/dry seasons and experience monsoons). Such labeling is very useful when discussing agriculture, because what works in one area of the world will normally work in a similar area somewhere else, even if that area is on the opposite side of the globe.
A staple food, sometimes simply referred to as a staple, is a food that is eaten routinely and in such quantities that it constitutes a dominant portion of a standard diet in a given population, supplying a large fraction of the needs for energy-rich materials and generally a significant proportion of the intake of other nutrients as well. Most people live on a diet based on just a small number of staples.
Staple foods vary from place to place, but typically they are inexpensive or readily available foods that supply one or more of the three organic macronutrients needed for survival and health: carbohydrates, proteins, and fats. Typical examples of staples include tuber- or root-crops, chicken, grains, legumes, and other seeds. The staple food of a specific society may be eaten as often as every day, or every meal. Early agricultural civilizations valued the foods that they established as staples because, in addition to providing necessary nutrition, they generally are suitable for storage over long periods of time without decay. Such storable foods are the only possible staples during seasons of shortage, such as dry seasons or cold-temperate winters, against which times harvests have been stored; during seasons of plenty wider choices of foods may be available.
A banana equivalent dose (abbreviated BED) is a nonstandard unit of radiation exposure, defined as the additional dose a person will absorb from eating one banana.
The concept is based on the fact that bananas, like most organic materials, naturally contain a certain amount of radioactive isotopes—even in the absence of any contamination due to human nuclear endeavors. The banana equivalent dose was meant to express the severity of exposure to radiation, such as resulting from nuclear power, nuclear weapons or medical procedures, in terms that would make sense to most people.
In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms. They form potassium-selective pores that span cell membranes. Furthermore potassium channels are found in most cell types and control a wide variety of cell functions.
In excitable cells such as neurons, they shape action potentials and set the resting membrane potential.