Reproduction and Life Cycles – Protozoan

Asexual reproduction occurs in all protozoan through fission, budding and cyst formation. In this method the organism reproduces to form its own type without forming gametes. The parent organism transfers an entire set of diploid chromosome to the daughter cell.

       Figure: Binary fission in protozoan a) In a flagellate trypanosoma b) In a ciliate, Paramecium.

Sexual reproduction involves meiotic nuclear divisions that give rise to haploid gametes from the diploid nucleus and the union of gametes then restores diploidy. It may involve gametes from different parents in which case it is called amphimictic or may involve gametes that may arise from the same parent i.e. automictic. The uniting gametes may be the whole organism or only the nuclei. Where the whole organisms unite the process is termed syngamy and where only the nuclei unite the process is termed conjugation. Syngamy occurs in all groups where sexual reproduction occurs except in ciliates where conjugation occurs.