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Protoplasm (/prt?(?)?plaz(?)m/, plural protoplasms) is the living part of a cell that is surrounded by a plasma membrane.
In some definitions, it is a general term for the cytoplasm (e.g., Mohl, 1846), but for others, it also includes the nucleoplasm (e.g., Strasburger, 1882). For Sharp (1921), "According to the older usage the extra-nuclear portion of the protoplast [the entire cell, excluding the cell wall] was called "protoplasm," but the nucleus also is composed of protoplasm, or living substance in its broader sense. The current consensus is to avoid this ambiguity by employing Strasburger's [(1882)] terms cytoplasm [coined by Kölliker (1863), originally as synonym for protoplasm] and nucleoplasm ([term coined by van Beneden (1875), or] karyoplasm, [used by] Flemming [(1878)])". The cytoplasm definition of Strasburger excluded the plastids (Chromatoplasm).
Like the nucleus, whether to include the vacuole in the protoplasm concept is controversial.
Besides "protoplasm", many other related terms and distinctions were used for the cell contents over time. These were as follows:
The word "protoplasm" comes from the Greek protos for first, and plasma for thing formed, and was originally used in religious contexts. It was used in 1839 by J. E. Purkinje for the material of the animal embryo. Later, in 1846 Hugo von Mohl redefined the term (also named as Primordialschlauch, "primordial utricle") to refer to the "tough, slimy, granular, semi-fluid" substance within plant cells, to distinguish this from the cell wall and the cell sap (Zellsaft) within the vacuole.Max Schultze in 1861 proposed the "Protoplasm Doctrine" which states that all living cells are made of a living substance called Protoplasm.Thomas Huxley (1869) later referred to it as the "physical basis of life" and considered that the property of life resulted from the distribution of molecules within this substance. The protoplasm became an "epistemic thing". Its composition, however, was mysterious and there was much controversy over what sort of substance it was.
In 1965, Lardy introduced the term "cytosol", later redefined to refer to the liquid inside cells.
By the time Huxley wrote, a long-standing debate was largely settled over the fundamental unit of life: was it the cell or was it protoplasm? By the late 1860s, the debate was largely settled in favor of protoplasm. The cell was a container for protoplasm, the fundamental and universal material substance of life. Huxley's principal contribution was to establish protoplasm as incompatible with a vitalistic theory of life. Attempts to investigate the origin of life through the creation of synthetic "protoplasm" in the laboratory were not successful.
The idea that protoplasm of eukaryotes is simply divisible into a ground substance called "cytoplasm" and a structural body called the cell nucleus reflects the more primitive knowledge of cell structure that preceded the development of electron microscopy, when it seemed that cytoplasm was a homogeneous fluid and the existence of most sub-cellular compartments, or how cells maintain their shape, was unknown. Today, it is known that the cell contents are structurally very complex and contain multiple organelles, the cytoskeleton and biomolecular condensates.
Protoplasm is physically translucent, granular slimy, semifluid or viscous. In it, granules of different shapes and sizes are suspended in solution. It may exist in two interchangeable states which are more liquid-like sol state and more solid-like gel state which is like jelly. The constituent molecules are free to move in sol state, while in gel state, the constituent molecules are compactly arranged. Protoplasm becomes opaque when it is heated. It also coagulates on heating. It occurs everywhere in the cell. In eukaryotes, the portion of protoplasm surrounding the cell nucleus is known as the cytoplasm and the portion inside the nucleus as the nucleoplasm. In prokaryotes the material inside the plasma membrane is the bacterial cytoplasm, while in Gram-negative bacteria the region outside the plasma membrane but inside the outer membrane is the periplasm.
^Strasburger, E. (1882). Ueber den Theilungsvorgang der Zellkerne und das Verhältnis der Kernteilung zur Zellteilung. Arch Mikr Anat, 21: 476-590, BHL.
^Beneden, E. van (1875). La maturation de l'oeuf, la fécondation et les premières de développement embryonnaire des Mammiferes d'après les recherches faites chez le lapin. Bull. Acad. Bel. Cl. Sci. 40, 2 sèr.: 686-736, BHL.
^Flemming, W. (1878). Beiträge zur Kenntniss der Zelle und ihrer Lebenserscheinungen. Arch. f. mikr. Anat., 16: 302-436, p. 360, BHL.
^Parker, J. 1972. Protoplasmic resistance to water deficits, p. 125-176. In: Kozlowski, T. T. (ed.), Water deficits and plant growth. Vol. III. Plant responses and control of water balance. Academic Press, New York, p. 144, .
^Vines, S. H. (1877). An account of Prof. Strasburger's observation on protoplasm. Quart. J. Micr. Sc., Lond., 1877, n. s., 17, pp. 124-132. link.
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^Van Beneden, E. Recherches sur la composition et la signification de l'oeuf. F. Hayez, Bruxelles, 1870 (Extrait du tome XXXIV des Mém. cour. des savants étrangers, publiés par l'Académie royale des sciences, des lettres et des beaux-arts de Belgique). link.
^ abBeale, L. S. (1872). Bioplasm. London: J. & A. Churchill.
^Kupffer, K. W. 1875. Ueber Differenzierung des Protoplasmas an den Zellen tierischer Gewebe. Schriften des Naturwissenschaft, Vereins für Schleswig-Holstein, 1 (3), 229-242, link.
^Velten, W. 1876. Die physikalische Beschaffenhoit des pflanzlichon Protoplasmas. Sitzber. Akad. Wiss. Wien, Math.-Nat. Kl., 73: I 131-151, .
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^Flemming, W. (1882). Zellsubstanz, Kern, und Zelltheilung. Vogel, Leipzig, .
^Bütschli, O. 1892. Untersuchungen über mikroskopische Schäume und das Protoplasma. Leipzig, .
^Schütt, F. (1895). Die Peridineen der Plankton Expedition. Ergebnisse der Plankton-Expedition des Humbold-Stiftung, Bd IV, p. 1-27, Lipsius & Tischer, Kiel. link.
^Seifriz, W. (1931). The structure of protoplasm. Science 73, 648-649. link.
^Munson, J. P., 1899 The Ovarian Egg of Limulus. Athenaeum Press, Boston, Massachusetts
^Bargmann, W. (1956). Über einige Probleme und Ergebnisse des elektronen-mikroskopischen Studiums der Zelle. Dtsch. med. Wschr. 81 (28): 1109-1125.
^Szymonowicz, L. (1901). Lehrbuch der Histologie und der mikroskopischen Anatomie. Stuber, Würzburg. link.
^Szymonowicz, L. (1902). Textbook of histology and microscopic anatomy of the human body, including microscopic technique. Philadelphia, Lea Bros. link.
^ abLardy, H. A. 1965. On the direction of pyridine nucleotide oxidation-reduction reactions in gluconeogenesis and lipogenesis. In: Control of energy metabolism, edited by B. Chance, R. Estabrook, and J. R. Williamson. New York: Academic, 1965, p. 245, .
^Brain, R.M. "Protoplasmania: Huxley, Haeckel, and the Vibratory Organism in Fin de Siècle Visual Cultures", in The Art of Evolution: Darwin, Darwinisms, and Visual Cultures, F. Brauer and Larson, B. University Presses of New England, 2009, pp. 92-123, .