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Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). These act as sex cells (gametes – each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes) resulting from genetic recombination during meiosis. Cell features[edit] Eukaryotic cells are typically much larger than those of prokaryotes. Internal membrane[edit] Detail of the endomembrane system and its components A 3D rendering of an animal cell cut in half. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out. Vesicles may be specialized for various purposes.

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Crown eukaryotes Crown eukaryotes are an artificial group of eukaryotic organisms found at the top of molecular phylogenetic trees including both eukaryotes and prokaryotes. They were originally thought to represent a late step of eukaryotic evolution (somewhat similar to a crown group) because they include multicellular and macroscopic lifeforms that represent the majority of the biomass of the planet while accounting for less than 1% of the genetic diversity. However, they are in fact the result of an artificial clustering of eukaryotic organisms with slowly evolving gene sequences. They are thus not a crown that excludes simpler eukaryotes, but correspond roughly to the initial radiation of eukaryotes. All eukaryotic lineages branching below the "crown" in phylogenetic trees are misplaced because of the long branch attraction phenomenon.

A Universe in a Nutshell: The Physics of Everything, with Michio Kaku Transcript My name is Professor Michio Kaku. I’m a professor of theoretical physics at the City University of New York and I specialize in something called string theory. Mitochondrion Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy History[edit] The first observations of intracellular structures that probably represent mitochondria were published in the 1840s.[13] Richard Altmann, in 1894, established them as cell organelles and called them "bioblasts".[13] The term "mitochondria" itself was coined by Carl Benda in 1898.[13] Leonor Michaelis discovered that Janus green can be used as a supravital stain for mitochondria in 1900.

Cyanobacteria By producing oxygen as a gas as a by-product of photosynthesis, cyanobacteria are thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. According to endosymbiotic theory, the chloroplasts found in plants and eukaryotic algae evolved from cyanobacterial ancestors via endosymbiosis. Ecology[edit] Scientists have discovered the largest known solar system Astronomers have found the largest known solar system, linking together a star and what was thought to be a free-floating 'lonely planet' in orbit some 1 trillion (1 million million) kilometres away from its sun. The planet, known as 2MASS J2126–8140, and its star, called TYC 9486–927–1, were both identified within the past decade, but the massive distance between them meant no one had ever considered that the pair might be related. 2MASS J2126–8140 is a gas giant about 12 to 15 times the mass of Jupiter, located about 100 light-years away from Earth. "This is the widest planet system found so far and both the members of it have been known for eight years, but nobody had made the link between the objects before," said Niall Deacon of the University of Hertfordshire in the UK. "The planet is not quite as lonely as we first thought, but it's certainly in a very long distance relationship."

Prokaryote Cell structure of a bacterium , one of the two domains of prokaryotic life. The division to prokaryotes and eukaryotes reflects two distinct levels of cellular organization rather than biological classification of species. Prokaryotes include two major classification domains: the bacteria and the archaea . Huronian glaciation The Huronian glaciation (or Makganyene glaciation) extended from 2400 Mya to 2100 Mya (~300 million years), during the Siderian and Rhyacian periods of the Paleoproterozoic era. The Huronian glaciation followed after the Great Oxygenation Event (GOE), a time when increased atmospheric oxygen decreased atmospheric methane. It is the oldest known ice age, occurring at a time when only simple, unicellular life existed on Earth. Name origin[edit]

Physicists are about to test a hypothesis that could rewrite the textbooks An international team of physicists is about to test a "sacrilegious" hypothesis about protons - one of the basic building blocks of the Universe - and the results could force a literal rewrite of nuclear physics textbooks. The experiments, which are now underway in the US, aim to demonstrate that the structure of protons can change inside the nucleus of an atom under certain conditions. If that's found to be the case, a whole lot of experiments are going to have to be reassessed. "For many scientists, the idea that the internal structure of protons might change under certain circumstances can seem absurd, even sacrilegious," said one of the researchers, Anthony Thomas, from the University of Adelaide in Australia. "To others like myself, evidence of this internal change is highly sought after and would help to explain some of the inconsistencies in theoretical physics."

Bacteria Bacteria ( Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory.[10] The study of bacteria is known as bacteriology, a branch of microbiology. Etymology Origin and early evolution