Extinction is the term describing the dying-out of a group or taxon, usually a species. ĭeath is the permanent termination of all biological processes which sustain an organism, and as such, is the end of its life. New lifeforms have evolved from common ancestors through hereditary variation and natural selection, and today, estimates of the number of distinct species range anywhere from 3 million to over 100 million. Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale, but it has also adapted to survive in most ecosystems and conditions. Ībiogenesis, also known as the origin of life, is the natural process of life arising from non-living matter, such as simple organic compounds. Other definitions sometimes include non-cellular life forms such as viruses and viroids, but they are usually excluded because they do not function on their own rather, they exploit the biological processes of hosts. Organisms, or the individual entities of life, are generally thought to be open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve over multiple generations. Cells reproduce through a process of cell division, in which the parent cell divides into two or more daughter cells and passes its genes onto a new generation, sometimes producing genetic variation. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. The gene is the unit of heredity, whereas the cell is the structural and functional unit of life. Biology is the science that studies life. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from matter that does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy transformation, and reproduction.
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