Class 12th, Chapter-1, Reproduction in organism, Lecture-3

Asexual reproduction in protists and monerans:-

#In protists and monerans, the organisms or the parent cell divides into two to give rise to new individual. This, in these organisms cell division is itself a mode of reproduction.

#many single celled organisms reproduce by binary fission where a cell divides into two two halves and each rapidly grows into an adults example Amoeba ,Paramecium.

#In yeast the division is unequal and small buds are produced that remains attached initially to the parent cell which, eventually gets separated and matures into new yeast organisms ( cells).

#Members of kingdom fungi and simple plants such as algae reproduce through special Asexual reproductive structures.

a) Zoospores :- These are microscopic flagellated and motile spores produced inside the zoosporangia. These are without resistant covering (naked) are dispersed by swimming . These are formed in certain algae example ulothrix, and fungi e.g. Albugo and chlamydomonas.

b) Conidia:- Conidia are non motile spores produced  singly or in chains by the constrictions of tips of special hyphal  branches called conidiophores. These are dispersed by wind. After dispersal, conidia germinate by giving out germ tubes. These are formed in Aspergillus and Penicillium.

c) Buds:- An outgrowth or ingrowth or a bud develop on a parent body which after attaining specific size detaches and grows independently. 

Example :- sponges ,coelenterates (Hydra) , Annelides (syllis), Tunicates (salpa) and yeast and fungi.

Budding is of two types:-

1. Exogenous budding

2. Endogenous budding

1) Exogenious budding:- When the bud grows on outer surface of the parent body. In Hydra the bud arises from the body surface as an outgrowth. It  enlarges and develops tentacles. The fully formed bud separates from parent body and starts an independent life.

2) Endogenous budding:- 

# When the bud is formed inside the parent body.

Example - Spongilla (fresh water sponge).

#Number of buds called gemmules are formed inside the body.

#Each gemmule is formed as a mass of undifferentiated archaeocytes surrounded by a protective coat of spicules. When the sponge body degenerates during unfavourable conditions, archaeocytes come out through micropile and organise to form the sponge.

While in animals and other simple organisms the term asexual is used unambiguously , in plants the term vegetative reproduction is frequently used. In plants, the units of vegetative propagation such as runners, rhizomes , suckers,  tuber,  offset, bulb are all capable of giving rise to new offspring. These structures are called vegetative propagules. Obviously, since the formation of these structures does not involve two parents, the process involved is asexual.