Virus

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.

Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 virus species have been described in detail, although there are millions of types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology, a sub-speciality of microbiology.

While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. These viral particles, also known as virions, consist of two or three parts: (i) the genetic material made from either DNA or RNA, long molecules that carry genetic information; (ii) a protein coat, called the capsid, which surrounds and protects the genetic material; and in some cases (iii) an envelope of lipids that surrounds the protein coat when they are outside a cell. The shapes of these virus particles range from simple helical and icosahedral forms for some virus species to more complex structures for others. Most virus species have virions that are too small to be seen with an optical microscope. The average virion is about one one-hundredth the size of the average bacterium.

Harry Potter

Harry Potter is a series of seven fantasy novels and one play written by British author J. K. Rowling. The series chronicles the life of a young wizard, Harry Potter, and his friends Hermione Granger and Ron Weasley, all of whom are students at Hogwarts School of Witchcraft and Wizardry. The main story arc concerns Harry's struggle against the Dark wizard Lord Voldemort, who aims to become immortal, overthrow the Ministry of Magic, subjugate non-magic people and destroy anyone who stands in his way.

Since the release of the first novel, Harry Potter and the Philosopher's Stone, on 30 June 1997, the books have gained immense popularity, critical acclaim and commercial success worldwide. They attracted a wide adult audience, and have remained one of the preeminent cornerstones of young adult literature. The series has also had some share of criticism, including concern about the increasingly dark tone as the series progressed, as well as the often gruesome and graphic violence depicted in the series. As of July 2013, the books have sold more than 450 million copies worldwide, making the series the best-selling book series in history, and have been translated into 73 languages. The last four books consecutively set records as the fastest-selling books in history, with the final instalment selling roughly 11 million copies in the United States within the first 24 hours of its release.