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A large fraction of the chemical elements that occur naturally on the Earth's surface are essential to the structure and metabolism of living things. Four of these elements (hydrogen, carbon, nitrogen, and oxygen) are essential to every living thing and collectively make up 99% of the mass of protoplasm. [1]
Biological processes are regulated by many means; examples include the control of gene expression, protein modification or interaction with a protein or substrate molecule. Homeostasis: regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature
Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.5–4.1 billion years ago. [1] [2] Although some prokaryotes live in colonies, they are not specialised cells with differing functions. These organisms live together, and each cell must carry out all life processes to survive.
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis , organisation , metabolism , growth , adaptation , response to stimuli , and reproduction .
In biology, a biological life cycle (or just life cycle when the biological context is clear) is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offspring in the form of a new zygote which then itself goes through the same series of stages, the ...
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The average lifespan of a red blood cell is approximately 120 days. During this maturation process, there is nuclear extrusion – i.e. mature erythrocytes have no nucleus. Nucleated red blood cells present in a sample of bone marrow can indicate the release of incompletely developed cells.
The process of adaptation contributes to this "success" by impacting rates of survival and reproduction, [2] which in turn establishes an organism's level of Darwinian fitness. [5] In life history theory, evolution works on the life stages of particular species (e.g., length of juvenile period) but is also discussed for a single organism's ...