Protoplasm is the living content of a cell that is surrounded by a plasma membrane.
Contents
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).
As for the nucleus, the inclusion or not of the vacuole in the protoplasm concept is also controversial.
History
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. 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. Its composition, however, was mysterious and there was much controversy over what sort of substance it was.
In 1872, Beale created the vitalist term "bioplasm", to contrast with the materialism of Huxley. In 1880, term protoplast was proposed by Hanstein (1880) for the entire cell, excluding the cell wall, and some authors like Julius von Sachs (1882) preferred that name instead of cell.
In 1965, Hardy introduced the term "cytosol", later redefined to refer to the liquid inside cell.
Other related terms are: Urschleim (Oken, 1802, 1809), sarcode (Dujardin, 1835, 1841), Grundsubstanz (ground substance, Cienkowski, 1863), enchylema/hyaloplasma (Hanstein, 1880), paramitome (Flemming, 1882), inter-filar substance (Velten, 1876) and inter-alveolar substance (Bütschli, 1892).
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.
Description
Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and polysaccharides. In eukaryotes the protoplasm surrounding the cell nucleus is known as the cytoplasm and that 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.
Protoplasm was said to exist in two forms: a liquid-like sol state or a jelly-like gel state.