In this article we will discuss about:- 1. Meaning of Living Matter 2. Forms of Living Matter 3. Properties.
Meaning of Living Matter:
Biology seeks to explain the structure and properties of living matter in terms of physics and chemistry. It is, therefore, necessary to be acquainted with the fundamentals of the two sister sciences. Matter is defined as anything which occupies space.
It exists in three different states—Solid, Liquid and Gas. Matter is indestructible. This is the law of conservation of the matter, and is applicable to all substances whether living or non-living. Matter may, however, change from one state to another without suffering any loss of weight. Thus water may be frozen into a mass of ice or vaporized into steam.
Forms of Living Matter:
Matter may exist in a number of different forms. An element in chemistry is a substance which cannot be split up into substances different from itself. Carbon, Oxygen, Nitrogen and Hydrogen are the common elements composing the living matter.
Elements are often found in free state, but in nature, most matters exist in the form of a mechanical mixture or a chemical compound. Air is a mixture of nitrogen and oxygen. A mixture is made up of two or more substances each of which retains its own properties. The composition of a mixture is variable and -the ingredients may occur in any proportion.
Elements may combine to form compounds. A compound is a substance composed of two or more elements combined in definite proportion. It is more or less stable but can be broken up into its component elements by ordinary chemical means. Thus, water, which can be decomposed into the elements hydrogen and oxygen, is a compound.
It must be noted that the properties of a compound are entirely different from those of the elements composing it. Elements and compounds exist as molecules. The molecule is the smallest particle of a matter which retains all the properties of the original substance. If a molecule of a compound is decomposed the resulting parts no longer exhibit the characteristic chemical properties of the original molecule.
A molecule is, in turn, composed of atoms. An atom may be defined as the smallest particle of an element which takes part in chemical reaction. A molecule of helium is composed of only one atom, but a molecule of oxygen contains two atoms. According to modern idea, the atoms of all the different chemical elements are built up with only three kinds of particles called protons (+), electrons (—) and neutrons (±).
The protons carry positive electric charge, the electrons are negatively charged and the neutrons have no charge. The nature of these particles are identical in all kinds of matter. It is the number and arrangement of these particles that determine the kind of element composed by them.
Properties of Living Matter:
We shall close this section with a short discussion of the properties of matter in the colloidal state, because many of the substances of which the plants and animals are composed exist in the living cell as such. In fact, protoplasm owes most of its characteristic physico-chemical properties to the colloidal state of the substances composing it.
If a little sucrose (can sugar) or sodium chloride (common salt) is shaken up with water the resulting system will be a true solution. If, on the other hand, some fine river-bottom silt is stirred up with water in a test tube, a different sort of system will result.
The silt particles do not dissolve but simply become dispersed throughout the watery medium. The suspended particles are large enough to be detected under a microscope.
This is a colloidal suspension. It is not stable, because after a time the particles of silt gradually settle down and the system becomes separated into its original components in contrast to the true solution, which is absolutely stable.
The particles of a colloidal solution are incapable of passing through the pores of a fine parchment membrane in contrast to those of the true solution which readily pass through it. This phenomenon, known as dialysis, was originally devised by Graham to separate the colloids from the crystalloids yielding true solution, from which they can be recovered in the form of crystals.
This division of matter into colloids and crystalloids, depending upon their ability to pass through the pores of a parchment membrane, is not accepted today, because most of the substances can, by suitable means, be brought into the colloidal state.
Thus sodium chloride, when shaken up with petroleum ether yields a colloidal solution although it forms a true solution when the dissolving medium is water. The size of the molecules in a colloidal solution is very large or they exist in a state of aggregation; that is why they cannot pass through the fine pores of a dialysing membrane.
A colloidal solution may either be a suspensoid (silt in water) or an emulsoid (starch or proteins in water). The essential features of both forms are that they are systems consisting of two phases, the dispersed phase and the continuous phase.
In a suspensoid the continuous phase is generally a liquid and the dispersed phase is a solid. But in an emulsoid both the phases are liquid. Milk and latex (milky juice exuding from the cut surface of certain plants like the India rubber plant) are the two natural emulsions.
Emulsions are much more stable than the suspensoids, because they are stabilized by the presence of a third component. These are the emulsifiers. If olive oil and water be vigorously shaken up in a test tube the resulting system will be an unstable emulsion but if a little soap or gum be added to the mixture previous to shaking, it will yield a stable emulsion from which the components do not easily separate out.
Milk is an emulsion of fine droplets of fat in water stabilized by a protein which plays the role of an emulsifier. Butter, on the other hand, is an emulsion of fine drops of water dispersed through a medium of fat. Thus the continuous phase of milk has become the dispersed phase in the butter and vice versa.
It must be remembered that the colloidal solution is, only a state and not a form of matter. Substances in colloid state do not constitute a definite class by themselves, since sodium chloride which is a definite crystalloid when the continuous phase is water, yields a colloidal solution when the continuous phase is changed into petroleum ether.
In true suspensions the components separate out only very slowly and the stability is ensured by the interaction of particles of the dispersed phase, which perform erratic, zigzag movement being bombarded from all sides by the particles of the continuous phase.
This is known as the Brownian movement. It is one of the factors which stabilises a true suspension. It may be pointed out here that the continuous phase may not be always liquid. In some cases it may be solid, liquid or gas. The following examples will exhibit certain interesting colloidal combinations.
