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Eukaryotic cells have a variety of internal membrane-bound structures, called organelles, and a cytoskeleton which defines the cell's organization and shape. The nucleus stores the cell's DNA , which is divided into linear bundles called chromosomes ; [ 19 ] these are separated into two matching sets by a microtubular spindle during nuclear ...
Cells are broadly categorized into two types: eukaryotic cells, which possess a nucleus, and prokaryotic cells, which lack a nucleus but have a nucleoid region. Prokaryotes are single-celled organisms such as bacteria , whereas eukaryotes can be either single-celled, such as amoebae , or multicellular , such as some algae , plants , animals ...
Eukaryogenesis, the process which created the eukaryotic cell and lineage, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis , in which an archeon and a bacterium came together to create the first eukaryotic ...
Mitochondria and chloroplasts, two organelles found in many eukaryotic cells, contain ribosomes similar in size and makeup to those found in prokaryotes. [48] This is one of many pieces of evidence that mitochondria and chloroplasts are descended from free-living bacteria.
The salt-tolerant Haloarchaea use sunlight as an energy source, and other species of archaea fix carbon (autotrophy), but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria, no known species of Archaea form endospores.
Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus. Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10 to 100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells.
Haeckel's Monera included not only bacterial groups of early discovery but also several small eukaryotic organisms; in fact the genus Vibrio is the only bacterial genus explicitly assigned to the phylum, while others are mentioned indirectly, which led Copeland to speculate that Haeckel considered all bacteria to belong to the genus Vibrio ...
An autogenous model of the origin of eukaryotic cells. Evidence now shows that a mitochondrion-less eukaryote has never existed, i.e. the nucleus was acquired at the same time as the mitochondria. [22] Biologists usually distinguish organelles from endosymbionts – whole organisms living inside other organisms – by their reduced genome sizes ...