2. Budding:

ٍٍSome unicellular organisms as well as some multicellular ones reproduce by budding.

In unicellular organisms:

As Yeast fungus, the bud arises as a lateral projection from the original cell, while the nucleus divides mitotically into 2 nuclei. One of them remains in the mother cell, while the other moves towards the bud. It grows gradually, and may remain connected with the mother cell till it full growth. Then it separates or continue in connection with the mother cell forming cellular colonies with other growing buds.

In multicellular organisms:

Such as Sponges, and Hydra the bud grows as a cellular protrusion form one side of the body due to division of the interstitial cells and their differentiation to a bud. This grows gradually to resemble the mother entirely. It usually separate to start its independent life. It is to be mentioned that Sponges and Hydra reproduce also sexually besides their capacity for regeneration.

3. Regeneration:

This method is common in many plants and some animals as Sponges and Hydra, some worms, and sea star (starfish). They are able to regenerate the lost parts of their bodies due to an accident or rupture. If the body of some animals is cut into several parts, each part can grow to a new individual.

The capacity for regeneration decreases in higher animals. In some Crustaceans and Amphibians, it is limited to restoration of the cut parts only. In higher vertebrates regeneration never exceeds healing of wounds especially those located in skin, blood vessels, and muscles.

Regeneration in Planaria:

Planaria is a fresh water flat worm that regenerates even if cut into several transverse pieces or 2 longitudinal parts each will grow into a new individual.

Regeneration in Hydra:

Hydra is able to regenerate if it is cut into several transverse pieces. Each part will grow into a new individual.

Regeneration in Sea Star:

Sea star feeds on the Pearl mussels since it can devour about 10 of these mussels daily including the pearl. Breeders of those mussels in pearl farms were collecting Sea stars, tearing them up to pieces and then throw them back into the sea. They tried to get rid of them; but were unintentionally helping their reproduction. One of the star’s arms with a piece of its central disc can regenerate to a full star within a short time.

4. Sporogony:

Some primitive plants reproduce by means of single cells called spores that are adapted for direct growth into complete plants. A spore is formed of cytoplasm with little amount of water, a nucleus and a thick coat. When the spore matures, it liberates from the mother plant to be disseminated into air. Upon reaching to a suitable medium for growth, its coat ruptures while it absorbs water and divides several times by mitosis and grows to a new individual. Many Fungi such as Bread mould, Mushroom and some Algae and Ferns reproduce by Sporogony.

Advantages of reproduction by Sporogony:

a. Quick propagation.

b. Tolerance to hard conditions.

c. Distribution to distant regions.