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An organism is defined in a medical dictionary as any living thing that functions as an individual. [1] Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been proposed to define what is an organism.
v. t. e. A microorganism, or microbe, [a] is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells . The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from sixth century BC India.
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea.
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (/ ˌ æ n ɪ ˈ m ɑː l j ə ˌ-i. ə /), With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development.
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations.
Eukaryotes are organisms that range from microscopic single cells, such as picozoans under 3 micrometres across, [7] to animals like the blue whale, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long, [8] or plants like the coast redwood, up to 120 metres (390 ft) tall. [9]
A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. [1] All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.
A colony of Escherichia coli [111] Unlike in multicellular organisms, increases in cell size ( cell growth) and reproduction by cell division are tightly linked in unicellular organisms. Bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction. [112]