Living beings have many processes in common. Among all the common processes there is one very interesting and wonderful process which is called as reproduction. It means all the living beings reproduce. What is reproduction ? It is a complex physiological process through which new living beings are reproduced. This process increases the number of individuals in a species.
Reproduction is not necessary for the maintenance of life of an individual organism. So it is not called as Life Process. Nutrition, Respiration, Excretion, and Transport etc. processes maintain life. Reproduction is not necessary for the survival of an organism. So these are called as Life Processes.Inside cells, different chemical processes are involved to produce copies of DNA. These copies are not always exactly similar and some changes are bound to occur. These changes cause changes in organisms. Thus, it is clear that variations in organisms are produced spontaneously and these variations are basics of evolution. Here, it is also clear that during reproduction living organisms don’t become able to reproduce their exact copies of individuals.
Variations may be beneficial to a species but not necessarily to an individual. How? It is due to variations that different types of individuals are produced. It keeps up the existence of a species. So, these are essential for a species but not for an individual.
Importance of variations
Variations help an organism in changing conditions of environment. Every organism lives in a specific area which is called as its niche. Every organism is adapted to the conditions of its niche. However if conditions of niche change its organisms get into trouble. At this stage only those organisms can survive who have maximum number of variations.
When conditions of environment change, a large number of organisms perish. These are variations alone that keep some organisms alive. Thus, a species remains alive during adverse conditions due to variations or adaptations of its individuals.
MODES OF REPRODUCTION BY SINGLE ORGANISM
There are two types of reproduction –
(i) Asexual Reproduction
(ii) Sexual Reproduction
In asexual reproduction sex organs don’t take part. Hence, single organisms usually reproduce by asexual methods. For sexual reproduction activities of both the male and the female sex organs together is essential. Hence, two organisms- male and female are essential for sexual reproduction. Now let us study some basic methods of reproduction in single organisms.
When a cell gets fully matured, its nucleus divides into two. Each one of the two nuclei takes its half share of cytoplasm, forms a membrane around and gets separated as a new cell. Each new cell is called as a daughter cell. This method of asexual reproduction is called as fission or binary fission. In Baker’s yeast and amoeba asexual reproduction takes place by this method.
Multiple Fission
The malaria parasite (Plasmodium sp.) covers itself with a cyst in adverse conditions. The cyst breaks when favourable conditions occur. Before the breaking out of the cyst the nucleus of the cell divides many times to form innumerable nuclei. Each new nucleus takes its share of cell material and becomes round ready to perform like a new cell. When cyst breaks numerous new cells with proper nuclei come out and develop to form a number of organisms. This method of asexual reproduction in a single organism is called as multiple fission.
Multiple Fission
Fragmentation
Usually filaments of spirogyra- an alga get broken by mechanical reasons. Afterwards each of the broken pieces develops into a new spirogyra. This process is called as Fragmentation.
Regeneration
The word ‘regeneration’ is made up of two parts re- and –generation which means ‘originate again’. If any part of the body of an organism (say tail of a lizard) is cut in an accident, it develops again to its full length within a time period. This process is called as regeneration. Body construction, repair and development continue in organisms but these are not similar in all the organisms. Some examples –
(i) Replacement of dead and injured cells into new ones
(ii) Healing of wounds
(iii) Development of new organs
(iv) Development of a new organism from any part of the body
Above mentioned developments occur in many different organisms and are examples of regeneration. Asexual processes of repair of injured or useless organs of a body, origin of a new organ from any part of the body of an organism that occurs automatically in the body of an adult organism is called as regeneration.
DO YOU KNOW?
The process of regeneration was discovered by Trembly in 1740 through an experiment on Hydra. Later, this process was gradually discovered in different organisms by different scientists. Some examples are here –
(i) If the whole body of a sponge is destroyed except few living cells that remain alive, these living cells can now develop into a new sponge.
(ii) In some segments in the anterior or posterior part of the body of an earthworm are cut, they are again regenerated to form a complete body.
(iii) Some arthropods like prawn can develop new appendages if they are lost.
(iv) If anyone of the arms of a starfish is cut down, it can again develop into a new arm.
(v) If the body of a Planaria is cut into pieces, each piece can develop into a new planaria.
Budding
In this method of asexual reproduction, a bulb like growth starts somewhere on the outer layer of the body. The nucleus of the cell producing bulb divides in two parts and one part is retained inside the bulb. This bulb like bud may produce other bulbs or may get detached and fall down. The development of this bud into an individual is called as budding. Example: Yeast cell and the multicellular organism Hydra reproduce asexually through this method.
Vegetative Propagation
When a new plant is developed or caused to develop through stem, root or leaf the method is called as vegetative reproduction. In other words, vegetative reproduction means- reproduction through anyone of the vegetative parts of the plant.
I. Methods of vegetative propagation
There are two methods of vegetative propagation- (a) Natural Methods, and (b) Artificial Methods
(a) Methods of Natural Vegetative Propagation
(1) Vegetative Propagation through roots as in Guava, Sesam, Sagwan etc. Roots of these plants have buds that develop into new plants under favourable conditions.
(2) Vegetative propagation through stems as in Pistia, Eichornia, doob (Cynodon), Underground stems (Potato, Ginger, Turmeric, Banana etc.).
(3) Vegetative Reproduction through leaves- as in ferns, Bryophyllum etc.
(b) Methods of Artificial Vegetative Propagation
In the modern world of science man has got astonishing success in horticulture through artificial ways. Some of the popular methods of artificial propagation in plants are listed below-
(1) Grafting as in Citrus, Grape etc.
(2) Cutting as in Sugarcane, Tea, Bougainvillea, Rose, Cactus etc.
(3) Layering as in Chameli, Juhi etc.
(4) Budding as in rose plant.
