In physics, to put the definition very simply, plasma is a fourth state of matter that comes after solid, liquid, and gas. This state of matter is achieved when gas is heated to the extent that the atoms of the gas lose all electrons. The resultant quasi-gas is a collection of nuclei and electrons that are free. The nuclei which has lost all the electrons are deemed to be ions, that is, they are electrically charged, to a substantial extent. The entire collection is thus, electrically charged and conductive.
The basic process that takes place in formation of plasma is quite simple. When heated, energy gets pumped into the gas. This causes that gas to disassociate itself from its molecules and take the form of atoms, which further lose their negatively charged electrons. The atoms themselves retain positive charge and are thus deemed to be positive ions.
Plasma in Physics
Plasma, thus, cannot occur naturally, i.e, in free environment on earth. It needs a controlled environment of electromagnetic field to survive without reacting. Stars, which are existent in space, are the best example. The vacuum of space prevents them from reacting. Scientists have laid down certain parameters that define plasma. These parameters include the approximation of ions and electrons, the frequency and volume of iterations, size, lifetime, density, temperature, and magnetic fields.
As mentioned before, naturally-existing plasma occurs in stars or lightning, while artificially-produced plasma is included in applications such as neon signs and television displays. Coincidentally, in 1928, Irving Langmuir named the phenomenon 'plasma', owing to the fact that it strongly resembled blood plasma.
Plasma in Biology
In biology, the term is more properly indicated as blood plasma, as in animals such as mammals, it consists of about 55% of the total blood that is present in the body. It has a whitish-yellow appearance and is the medium which hosts all our blood cells. It is separated by a membrane from the organs of the cell.
Plasma is made of, well, 90% water. The remaining portion is proteins, glucose, clotting factors, mineral ions, hormones, and carbon dioxide. Some other substances are also included in plasma. The concept plasma transfusion came in really handy in the World wars. Plasma can be administrated to the severely wounded, to revive their energy levels, boost healing, curb blood loss and finally, enhance blood clotting.
The term plasma, when used in the biological context, is always accompanied with the prefix blood. The term blood serum (plasma minus fibrinogen) is also used, though its meaning and use is different. Blood plasma is the major material in human blood, whereas plasma in physics is the largest material substance in the universe.