(i) Process of formation of new organism by an organism of same species without involvement of gametes is called as asexual reproduction.
(ii) Types of asexual reproduction in unicellular organisms:
(a) Binary fission:
(i) In this process, the parent cell divides to form two similar daughter cells.
(ii) Binary fission occurs either by mitosis or amitosis. e.g. Prokaryotes (bacteria), Protists (Amoeba).
(b) Multiple fission:
(i) Asexual reproduction by multiple fission is performed by Amoeba.
(ii) Amoeba stops the formation of pseudopodia whenever there is lack of food.
(iii) It becomes rounded and forms protective covering around plasma membrane. Such encysted amoeba is called as cyst.
(iv) Many nuclei are formed by repeated nuclear division in the cyst.
(v) It is followed by cytoplasmic division and thus many amoebulae are formed.
(vi) They remain encysted till there are adverse conditions. Cyst breaks open on arrival of favourable conditions and many amoebulae are released.
(c) Budding:
(i) Sexual reproduction occurs by budding in yeast cells.
(ii) Yeast cells produces two daughter nuclei by mitotic division.
(iii) A small bulge appears on the surface of parent cell. This is called as bud.
(iv) One of the two daughter nuclei enters this bud.
(v) After sufficient growth, bud separates from the parent cell and starts to live independently as a daughter yeast cell.