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Whether or not viruses should be considered as alive is controversial. [ 33 ] [ 34 ] They are most often considered as just gene coding replicators rather than forms of life. [ 35 ] They have been described as "organisms at the edge of life" [ 36 ] because they possess genes , evolve by natural selection, [ 37 ] [ 38 ] and replicate by making ...
In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells.
Still life patterns are common in Life without Death: if there is no dead cell with three live neighbors, a pattern will remain unchanging for all future time steps. . However, because a cell, once alive, remains alive, the set of live cells grows monotonically throughout the evolution of a pattern, and there can be no oscillators (patterns that cycle through a repeating sequence of shapes ...
Among the most commonly used cell lines are HeLa and Jurkat, both of which are immortalized cancer cell lines. [4] These cells have been and still are widely used in biological research such as creation of the polio vaccine, [5] sex hormone steroid research, [6] and cell metabolism. [7] Embryonic stem cells and germ cells have also been ...
The cell on the left is going through mitosis and its chromosomes have condensed. Cell nucleus: A cell's information center, the cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur.
Today, where a definition of the moment of death is required, doctors and coroners usually turn to "brain death" or "biological death" to define a person as being dead; [27] people are considered dead when the electrical activity in their brain ceases. [28] It is presumed that an end of electrical activity indicates the end of consciousness. [29]
Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. [1] [2] All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and functioning of organisms. [3] Cell biology is the study of the structural and functional ...
The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like mitochondria and chloroplasts are remnants of ancient symbiotic oxygen-breathing bacteria and cyanobacteria , respectively, where at least part of the rest of the cell may have been derived from an ancestral archaean prokaryote ...