Types of Life Cycles - Practice Questions & MCQ

Haplontic life cycle

• The haplontic life cycle is also known as a monogenic life cycle. In this type of life cycle, haploid generation dominate over the diploid generation
• The plant body is gametophyte (haploid) and sporophyte (diploid) stage is represented only by Zygote. 
• The gametophytic plant develops hap­loid gametes in the gametangium. 
• The fusion between gametes results in the formation of a zygote, the only diploid stage i.e., sporophytic phase of the life cycle.
• The zygote undergoes meiotic division and forms four meiospores. 
• These meiospores develop into haploid plants. The alternation of generations can be interpreted by chromosome number.
• This type of life cycle is found in the majority of Chlorophyceae like Chlamydomonas, Ulothrix, Oedogonium, Spirogyra, Chara etc. and all members of Xanthophyceae.

Diplontic life cycle:

• The plant body is sporophyte that develops sex organs. 
• Sex organs produce gametes by meiosis. 
• The gametes represent the only gametophytic stage in the life cycle. 
• The gametes undergo fertilization immediately and form a zygote. 
• The zygote gives rise to the new sporo­phytic plant body.
• This type of life cycle is found in the majority of the members of Bacillariophyceae, some mem­bers of Chlorophyceae like Cladophora. Fucus and Sargassum of Phaeophyceae also show this type of life cycle. Gymnosperms and angiosperms are the best representatives of the diplontic life cycle.

Haplodiplontic life cycle:

• In this life cycle, haploid and diploid phases are equally prominent and are represented by two distinct vegetative individuals. 
• They differ only in chromosome number and function. 
• The haploid gametophytic plant reproduces by sexu­al method, while diploid sporophytic plant by the asexual process.
•  In this life cycle alternation of two vegetative individuals occurs by sporogenic meiosis and fusion of gametes.