Provitamin A carotenoids are found in green leafy vegetables (e.g. spinach, amaranth, and young leaves from various sources), yellow vegetables (e.g. pumpkins, squash, and carrots), and yellow and orange non-citrus fruits (e.g. mangoes, apricots, and papayas).
Red palm oil produced in several countries worldwide is especially rich in provitamin A.
Some other indigenous plants also may be unusually rich sources of provitamin A:
- palm fruit known in Brazil as burití, found in areas along the Amazon River (as well as elsewhere in Latin America),
- fruit known as gac in Viet Nam (used to colour rice).
A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.
There are millions types of viruses, ~ 5,000 virus species have been described in detail. Viruses are found in almost every ecosystem and are the most abundant type of biological entity. The origins of viruses in the evolutionary history of life are unclear.
While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles, virions, which consist of the genetic material made from either DNA or RNA, a protein coat, and in some cases an outer coat of lipids. Virion is about one one-hundredth the size of a bacterium.