Here is an essay on life.
‘Life’ is abstract. It has, perhaps, no objective reality apart from the living body and, hence, evades definition. Aristotle (304-322 B.C.), the ancient Greek naturalist and father of modern biology (Fig. 2), recognised plants and animals as living objects, but failed to put forward a precise definition of life.
Though life has not been accurately defined even today, yet the presence of life can easily be inferred from the activities of the organisms.
Life has been compared to the flame of a candle which is produced by the burning of the candle substance. Burning or oxidation is a chemical change that induces a rise of temperature in the surrounding invisible medium. Heated particles are thrown into violent vibrations which are manifested in the form of the flame emitting heat and light energies.
It is to be noted that the flame has no separate existence apart from the candle, and that it persists as long as the burning or oxidation goes on. Life, similarly, finds expression in the various activities of plants and animals and it has no real existence outside the living body.
The flame flickers out when the candle substance supplying energy to it is exhausted. Life ceases to exist when the store of energy in the living body is totally spent up.
Life, then, involves a continuous expense of energy just comparable to the constant loss of heat and light by the candle flame. Energy is defined as the capacity for doing work. It exists in two principal forms—potential and kinetic. Energy capable of doing work, such as that stored in the living body or the candle substance is known as potential energy. It is energy at rest.
Kinetic energy is the dynamic variety. It is the energy which is manifesting itself, that is, which is actually at work. Life is a ceaseless conversion of the potential energy into the kinetic form. Activities of a living organism are constantly manifested in the conversion of the potential energy stored in its body into the kinetic variety.
These find expression in movement, production of heat, light and electricity which are utilised by the organism for its own benefit. Everyone is familiar with the locomotion, found in the animals.
They swim actively, or fly easily or run about swiftly either in search of food or to avoid the enemy. Plants, too, are capable of producing motion. The lotus opens its petals at sunrise to close them up again at sunset. The leaves of the Venus’s flytrap come together when touched by an insect to enclose the unfortunate creature in a fatal grip (Fig. 3).
Heat energy is evolved from germinating seeds and from the body of a busy bee. The glow-worm emits light energy to find its way in the darkness of the night. The sea-fishes have phosphorescent patches along their sides glowing with light like the portholes of an ocean-going liner (Fig. 4).
They live at a depth of three to four thousand feet—a cheerless dark place where sun’s rays fail to penetrate. The electric eels of the Amazon basin and the electric rays of the Indian ocean (Fig. 5) are capable of producing electricity in specialised electric organs. This is utilised by the fish to electrocute their enemies and stun their prey.
The earlier Greek observers believed that living things originated spontaneously out of lifeless inorganic substances. Maggots were thought to be born of decaying carcasses and mice originating from river beds. Belief in spontaneous generation of the living things (Abiogenesis) prevailed throughout the dark ages of biology after the death of Aristotle in the fourth century B.C.
It persisted even in the nineteenth century when eminent people firmly believed that at least the microbes are formed spontaneously. The first serious objection to the conception of “spontaneous generation” came from the Italian, Redi, who in 1860 proved that fly-maggots did not originate by abiogenesis, but from eggs of fly.
During the later the later part of nineteenth century, Tyndall, in England, demonstrated that bacteria cannot generate by themselves in any infusion unless the latter is infected with their spores Pasteur (Fig. 15) in France, established the principle of sterilisation by heat or chemicals for guarding off and destroying the microbes.
This is largely applied in modern surgery for presenting wound infection and also for protecting water, food and milk for public use from pollution by bacteria. In 1861 Pasteur confirmed the theory of ‘Biogenesis’ which states that new life comes only from pre-existing parent individuals (OMNE VIVUM EX VI). Biogenesis is effected by reproduction and is the only means for the continuity of life.
