Protoplasm Theory

Long before anyone had identified individual organelles, biologists were already convinced that a cell's living material - whatever it was made of - deserved a name and a theory of its own. Corti was the first to actually observe this living substance. In 1835, Felix Dujardin studied the living, jelly-like content inside animal cells and called it 'Sarcode'. In 1839, Jan Purkinje coined the separate term 'protoplasm' for the equivalent living sap found inside a plant cell. Hugo von Mohl, in 1846, argued for just how important this substance really was to the life of the cell. The two names were finally connected in 1861, when Max Schultze showed that 'Sarcode' (in animal cells) and 'Protoplasm' (in plant cells) were essentially the same kind of material, and proposed a unifying idea that Oscar Hertwig later, in 1892, formally named the 'Protoplasm Theory'. Thomas Huxley, in 1868, gave the concept its most famous description, calling protoplasm the 'physical basis of life' - the idea that this one substance, in whatever cell it is found, is what actually makes that cell alive. Chemically, protoplasm was later shown (by Fisher in 1894 and Hardy in 1899) to behave as a complex colloidal system: mostly water, carrying dissolved solutes of real biological importance (glucose, fatty acids, amino acids, minerals, vitamins, hormones, enzymes), some of which are true, freely soluble (crystalloid) substances and some of which form colloidal (insoluble, suspended) mixtures - most notably the proteins and lipids. This colloidal protoplasm can exist in either a semisolid, jelly-like 'gel' state or a more fluid 'sol' state, and it constantly shifts between the two (solation turning gel to sol, gelation turning sol back to gel), a switching behaviour that underlies much of the cytoplasm's mechanical activity, including the three classic protoplasmic movements: Brownian movement, amoeboid movement, and cytoplasmic streaming (cyclosis). Protoplasm is translucent and odourless, has a viscosity of 2-20 centipoises and a refractive index of about 1.4, sits at a pH of roughly 6.8, and is around 90% water (dropping to only about 10% in dormant seeds). Of the roughly 34 elements detectable in protoplasm, only 13 (carbon, hydrogen, oxygen, nitrogen, chlorine, calcium, phosphorus, sodium, potassium, sulphur, magnesium, iodine and iron) are considered its main, universal elements, with carbon, hydrogen, oxygen and nitrogen alone making up about 96% of the total. Protoplasm is neither a strongly good nor a strongly poor conductor of electricity, forms a delimiting memb …