There are 2 methods of reproduction

1. Asexual Reproduction
2. Sexual Reproduction

• In asexual reproduction, certain body cells of the parent organism undergo repeated mitotic cell divisions to form two or more new organisms of the same kind

Asexual reproduction takes place by 6 different methods:

1. Fission
2. Budding
3. Spore Formation
4. Regeneration
5. Fragmentation
6. Vegetative Propagation

In the process of fission, a unicellular organism splits to form 2 or more new organisms

There are 2 types of fission

1. Binary fission
2. multiple fission

Binary fission

• The unicellular organisms like Amoeba, Paramecium, Leishmania, bacteria, etc. reproduce by binary fission.

Amoeba

Amoeba reproduces by binary fission by dividing its body into two parts

• when the amoeba cell has reached its maximum size of growth, then first the nucleus of amoeba lengthens and divides into 2 parts.
• After that the cytoplasm of amoeba divides into two parts, one part around each nucleus.

In this way, one parent amoeba divides to form two smaller amoebae.

Paramecium

Paramecium is a unicellular animal having short thread like structures called cilia over its surface.

• A fully grown paramecium divides its body into two parts to form two smaller paramecia.
• This happens by the division of nucleus followed by the division of cytoplasm.

Leishmania

Leishmania is a unicellular animal (which is a protozoan).

Leishmania has a greater degree of organization in its body, having a whip-like structure called flagellum.

Leishmania

• In leishmania, the splitting of parent cell during fission takes place in a definite plane (longitudinally) with respect to flagellum at its end.

• Sometimes (particularly during unfavorable conditions), a cyst or protective wall is formed around the cell of a single-celled organism (like that of plasmodium).
• inside the cyst, the nucleus of cell splits or divides several times to form many smaller nuclei called daughter nuclei.
• little bits of cytoplasm collect around each daughter nuclei and thin membranes are formed around them.
• in this way, many new daughter cells are formed from a single parent cell within the cyst.
• when the favorable conditions arrive, the cyst breaks open and the many daughter cells present in it are released, each forming a new organism.

Plasmodium

Plasmodium is a protozoan which reproduces by the asexual method of multiple fission.

• about 1000 daughter cells are produced by the multiple fission of one plasmodium cell.
• plasmodium is the malarial parasite which produces malaria disease in human beings.
• malarial parasite plasmodium is carried by female anopheles mosquitoes from one person to another thereby spreading the malaria disease

Hydra

Hydra is a simple multicellular animal. Hydra reproduces by the process of budding.

• In hydra, first a small outgrowth called 'bud' is formed on the side of its body by the repeated mitotic divisions of its cells.
• this bud gradually grows to form a small hydra by developing a mouth and tentacles.
• and finally the tiny new hydra detaches itself from the body of parent hydra and lives as a separate organism.
• the bud formed in a hydra is not a single cell, its a group of cells.

Yeast

Yeast is a tiny, unicellular, non-green plant (which is a fungus).

• In yeast first a bud appears on the outside of the cell wall
• the nucleus of parent yeast cell then divides into two parts and one part of the nucleus moves into the bud.
• ultimately the bud separates off from the parent yeast cell and forms a new yeast cell.

• Reproduction by spore formation takes place in plants
• most of the fungi, bacteria and non flowering plants such as ferns and mosses reproduce by the method of spore formation.
• The common bread mold is a fungus plant whose scientific name is Rhizopus

Rhizopus

• If we keep a moist slice of bread aside for a few days, then the spores of bread mold plant present in air settle on the moist bread and germinate to form new fungus plants.
• the bread mold plants first look like a white cottony mass covering the bread slice which later on turns black.
• The common bread mold plant consists of fine thread-like projections called hyphae and thin stems having knob-like structures called sporangia.
• each sporangia contains hundreds of minute spores enclosed in a spore case.
• when the spore case bursts, the tiny spores are dispersed in air.
• these spores are the asexual reproductive units which can produce more bread mold plants under suitable conditions.

Planaria.

Planaria is a flatworm which is found in freshwater ponds and slow moving streams.

• The Planaria worm somehow gets cut into three pieces.
• after a certain time, each cut piece of the body of planaria worm grows into a complete planaria worm.

The regeneration of an organism from its cut body part occurs by the process of growth and development.

• The cells of cut body part of the organism divide rapidly to make a 'ball of cells'.
• the cells present in the 'ball of cells' move to their proper places within the ball where they have to form various organs and body parts of the organism.
• the cells then change their shapes to form different types of tissues. these different tissues form various organs and body parts of the organism.

Spirogyra

Spirogyra is a green, filamentous algae plant which is found in ponds, lakes and slow moving streams.

• spirogyra filament simply breaks into two or more fragments on maturation, and each fragment then grows into a new spirogyra.

• vegetative propagation usually involves the growth and development of one or more buds present on the old part of the plant to form a new part.
• these buds are in the dormant state (inactive state) in the old part of the plant to form a new plant.
• when provided suitable conditions, these buds grow to form new plants.

Bryophyllum

Buds are present on the stems as well as the leaves of the bryophyllum plant which can develop into new plants.

• The leaves of a bryophyllum plant have special type of buds in their margins.
• these buds may get detached from the leaves, fall to the ground and then grow to produce new plants.
• sometimes even before a leaf drops off from the bryophyllum plant, we can see new plantlets already growing on it.

Money Plant

• Cut a piece of stem of money plant in such a way that it contains at least one leaf on it.
• dip one end of this stem in water. after a few days we will find that new roots appear at the point where leaf was attached.
• the piece of stem will gradually grow into a new money plant

The tuber has a number of buds (called eyes). each bud of the tuber grows into a new plant when the old tuber is planted in the soil in the next growing season.

There are 2 types of tubers:

1. stem tubers
2. root tubers

Potato

potato tuber is an underground stem of the potato plant.

• a potato tuber had many buds on its body.
• these buds act as organs for vegetative propagation.
• when a potato tuber is planted in the soil, then the various buds of the potato tuber start growing to form new potato plants.

There are 3 common methods of artificial propagation:

1. cutting
2. layering
3. grafting

• In this method, a cutting of the parent plant having some buds on it is taken and its lower part is buried in the moist soil.
• after a few day, the cutting develops roots and shoot and grows into a new plant.
• cuttings are a means of asexual reproduction in plants.
• The plants like rose, bougainvillea, chrysanthemum, grapes, sugarcane, bananas and cactus etc., can be grown by means of cuttings.

Plants like strawberry and raspberry are propagated by the natural layering method.

• the natural layering occurs because these plants form runners (soft horizontal stems running above the ground).
• wherever the ends of such runners touch the ground, new plants are formed at those places.

• The cut stem of a plant having roots is called stock. stock is the lower part of a plant having the roots
• the cut stem of another plant is called scion. scion is the upper part of a plant which may have leaves on it.

The process of tissue culture for producing new plants:

• a small piece of plant tissue is taken from the growing point of the plant and placed on a sterile jelly which contains nutrients and plant hormones. the hormones make the cells in the plant tissue divide rapidly producing many cells which form a shapeless lump of mass called 'callus'
• the callus is then transferred to another jelly containing suitable plant hormones which stimulate the callus to develop roots.
• the callus with developed roots is then put on a yet another jelly containing different hormones which stimulate the development of shoots
• the callus having roots and shoots separate into tiny plantlets. in this way, many tiny plantlets are produced from just a few original plant cells
• the plantlets thus produced are transplanted into pots or soil where they can grow to form mature plants.

The tissue culture technique is being used increasingly for the production of ornamental plants like orchids, dahlia, carnation, chrysanthemum etc. the production of plants by the method of tissue culture as micropropagation.

Asexual reproduction usually results in the production of genetically identical offsprings, the only genetic variation arises as a result of occasional inaccuracies in DNA replication at the time of cell division.