Essay on Protoplasm

The physical material that constitutes living systems is called protoplasam. It is typically a more or less viscous, translucent kind of material that is a complex mixture of many substances, although there is variations in it physical and chemical composition. It may contain material which is not, within itself, a necessary accompaniment of life, such as fat or starch particles.

Whenever, the term protoplasm is used, however, it refers to a given quantity of matter in which the chracteristics of life are manifested. By means of special techniques, much has been learned about the nature and organization of this material.

Such knowledge has shed considerable light on certain fundamental life processes. Furthermore, many important problems which are the concern of modern biology involve the physics and chemistry of protoplasm.

From the chemical standpoint, it might logically by supposed that should contain rare or unusual elements which are completely absent from nonliving matter. This is not the case. The most abundant elements found in protoplasm are also among the most abundant in the nonliving world.

These trace elements are highly variable quantitatively in different protoplasmic systems. They constitute only a small fraction of 1 per cent of the total matter in any given living system. It should be pointed out that “average” or “typical” protoplasm does not exist, since protoplasmic systems vary so widely.

However, the approximations listed above give us some idea of the relative abundance of these substances in protoplasmic systems and may generally be considered typical. From the foregoing discussion, it might be inferred that the most outstanding feature of protoplasm is its chemical make-up. Although it is true that some highly unique materials such as enzymes and nucleic acids go far toward making this a valid assumption, there is another side to the story.

The compounds and elements of protoplasm might be mixed together in the exact proportions found in a given unit of protoplasm, but the resulting material would not be alive. After a unit of protoplasm has died, it is no longer protoplasm by correct definition.

The ingredients are still all present, but the organization is lacking. The one factor that renders such a chemical mixture living, therefore, is the physical relationship which the various components bear to each other. A protoplasmic system is a multiphasic system, that is, it consists of molecular aggregates and particles of various sizes all of which are contained in a liquid medium.

Multiphasic systems may be classified on the basis of the size of the particles involved. If the particles are sufficiently small to form a homogeneous dispersion throughout the medium, they are said to be in solution.

If their size is such that they settle out of the medium in response to gravity, they are said to be in suspension. Finally, if the particles in such a system are intermediate in size, that is, too large to go into solution and too small to settle out, they are said to be colloidal the range in size of colloidal particles is 0.001 to 0.1. Thus particles as small as 0.001 or smaller go into solution, while those as large as 1 or larger settle out. Particles of intermediate size are dispersed in the medium, forming a colloidal system.

A protoplasmic system is a combination of several substances in solution and several types of particles in suspension. The solvent, of course, is water, and it is also the liquid medium or phase in which colloidal particles are dispersed. It is beyond the scope of our treatment here to discuss the various types of colloidal systems which may exist in protoplasm.

It is sufficient for our purposes to understand that protoplasm is a colloidal system involving solids and liquids dispersed within a liquid. In such a system, many reactions occur at the surfaces of particles or aggregations rather than between individual molecules.

Furthermore, the direction or rate of such reactions depends to a great degree upon the electrical charges at the surfaces of the highly polarized particles, as well as depending upon the size and shape of each of them.

Many of the characteristics of protoplasm, including the formation of large macromolecular complexes called organelles, may at least partially be explained on the basis of the characteristics of a colloidal system.

However, it would probably be a mistake to assume that all properties of protoplasm can be duplicated by any test-tube colloidal complex. Let us return to our earlier statement that physical relationships within protoplasmic systems are ultimately responsible for those characteristics which we summarize by the term living.

Perhaps an analogy will clarify this point. Suppose a master watchmaker invents a clock whose parts are so intricately arranged that only he knows the secret of its operation. Suppose further that he dies, and the clock is given to a novice.

Upon observing the clock and its parts, this second person might well conclude that the clock operates successfully because it is composed of certain wheels and gears. In a sense, of course, this is true. It could hardly operate without them.

However, many things are composed of wheels and gears that do not keep time, and in the final analysis, it is the physical relationship which these parts bear to each other that makes the instrument a clock. There is yet another point to be made from this analogy.

When the master craftsman origin all made the clock, he put a great deal of his “genius” into it. Does this mean that there is some mysterious influence, indefinable in physical and chemical terms, still floating around inside the clock? Not at all. His genius is measurable by its results, and we understand that the word is used as a literary one.

Only within recent decades have biologists as a group come to view protoplasmic systems from this clock, or mechanistic approach. The mechanistic point of view is a conceptual scheme within whose framework we have found it possible to launch other conceptual schemes, thus fulfilling the highest requirements of science.

Let us can our analogy of the clock one step farther. Suppose the novice to whom the clock was given has great difficulty in taking it apart in order to observe its inner workings. In exasperation, he finally takes a sledge hammer and smashes the clock.

Because of this drastic action, a random dispersal results. The task of the novice in understanding the inner structure of the clock is now complicated by the fact that it is greatly distorted. Although this may be straining an analogy, we are faced with something of the same difficulty in studying protoplasm.

In getting at the contents of cells, drastic treatments are usually necessary to br,eak them down to their component parts. Thus, when we make either a chemical or a physical analysis of protoplasm, we cannot get a very accurate picture of the actual relationships which exist in the functional or living state.

Because the machinery of protoplasmic systems is quite intricate, there are formidable barriers which stand in the way of understanding it very well, to say nothing of the immense task of putting it together synthetically.

Hence, most biologists are not overly optimistic that either the goals of complete understanding or the artificial production of living protoplasm are near accomplishment. Although great strides have been made toward both. Thus far life seems to come only from previous life in an unbroken chain, at least under conditions which prevail at present on earth.

We can, however, come to some understanding in regard to a few of the physical principles governing the organization of protoplasm, although many which are known require for their understanding a knowledge of concepts and principles that are beyond the scope of this text.