Atom is a Greek word which means a thing that cannot be cut or broken. It is the smallest particle of matter. It is no longer undivided and unbroken. The scientists have broken it into further smallest particles. They are called electrons, protons and neutrons. They release great power and energy. It was Albert Einstein who began to work on the theory of producing energy from atom in 1905. He explained many things. First, he showed that matter and energy are different forms of the same thing. In other words, matter can be converted into energy and vice versa. Second, a small amount of matter produces a great amount of energy. The discovery of atomic energy is one of the wonders of the modern science.

Atomic energy is a double-edged weapon. It can be utilized for destructive as well as peaceful purposes. The scientists, first of all, used it for destructive purposes. They prepared atomic bombs, hydrogen and cobalt bombs which could destroy cities and towns within the twinkling of an eye. It was in 1945, that a single atom bomb destroyed Hiroshima and Nagasaki. It killed thousands of men and women and destroyed vast areas of land. Now all the big powers possess much more atomic and dangerous hydrogen bombs. They can raze the world to ground if they are carelessly used.

Atomic energy can also be used for the welfare of mankind. The scientists in U.S.A, England, France, Canada and Germany are at work for peaceful use of energy. An atom for Peace conference was held at Geneva to think over the use of Nuclear Energy. The U.S.A has already started to use this energy to propel submarines and space rockets. The Russians have also harnessed it for space travel. At present, electricity is produced from the atomic energy in advanced countries like U.S.A, Russia and Britain. Our scientists are also trying to generate electricity from atomic energy. The scientists are also trying to find ways of using atomic power as fuel in ships, aeroplanes, motor cars etc. At present atomic reactors for boiling water exists in different countries.

Atomic energy is safely used to conquer many fatal diseases. Radium is used in the treatment of cancer. Radio-therapy is an important branch of medical science. It is used to destroy the overgrown cells of our body. The isotopes of sodium, potassium, bromine and iodine are used to known the origin of disease. The atomic energy is of immense help to alleviate human sufferings.

Nuclear energy has also brought a revolution in the field of industry. Petrol and coal are well known sources of energy and power. The supply of these two sources of power is coming to an end. The world is in search of another source of power. It is the nuclear energy. Electronic machines and computers are being used in our industry. They are used in the plastic, glass, paper, textile, rubber and cement industry.

Atomic energy is also of great help in agriculture. The barren lands can be tilled into smiling fields with the help of computerized tractors and machines. Crops can be ripened within a very short time. The yield of crops per acre can also be multiplied. In this way, the scientists are trying to solve the food problem. We can say that atomic energy can be used with full advantage for the welfare of mankind.

What is the Alternation of Generation and its Significance?

ALTERNATION OF GENERATIONS:

• In the life history of liverworts, mosses and hornworts there are two distinct multicellular phases or generations.

• These generations are haploid gametophyte and diploid sporophyte, which regularly alternate with each other.

• The gametophyte is the dominant generation because it is more conspicuous.

• It produces gametes called spermatozoids and eggs, therefore called gamete producing generation.

• A haploid spermatozoid fuses with a haploid egg to produce a diploid oospore.

• The oospore does not produce the gametophyte directly but produces a totally different plant called the sporophyte.

• The sporophyte is a less conspicuous generation, which is usually differentiated into foot, seta and capsule (also called sporogonium).

• Spores develop within the capsule by reduction division (meiosis) from spore mother cells.

• The sporophyte produces spores and is, therefore, called spore-producing generation.

• The spore on germination does not develop into a sporophyte but gives rise to the gametophyte.

• Thus in the life history of a bryophytic plant, the two generations, the gametophyte and the sporophyte, regularly alternate with each other.

• The phenomenon of alternation of gametophyte and sporophyte in the life history of a plant is called alternation of generations.

• It should be noted that the gametophyte or haploid stage begins within spores and ends at gametes, whereas the sporophyte being with oospore and ends at spore mother cell.

THE SIGNIFICANCE OF ALTERNATION OF GENERATIONS:

• During the formation of spores from a spore mother cells by meiotic division reshuffling of genes occurs.

• As a consequence, a great variety of spores with different genetic make-up are produced.

• These spores, in turn, produce gametophytes with different genetic combinations.

• The gametophytes with better genetic make-up will have a better chance of survival in the environment where they occur.

• On the other hand, the gametophytes with less advantageous characteristics will be eliminated.

• There is no reshuffling of genes during gametogenesis in the gametophyte as gametes are produced after mitosis.

• The oospore developing after fertilization now has a new genetic make-up as compared to the parent.

• This genetic variation passes to the new sporophyte which on maturity once again produces further genetic recombination which is transferred to the gametophyte.

• In this natural process, the sporophyte thus provides a large amount of genetic variability and nature selects the best genetic combinations.

• In the long run, this will allow the populations to become increasingly better adapted to their environment.