Life cycle patterns in plants: Alternation of Generation: Alternation of generation is common in all plants. Alternation of the haploid gametophytic phase (n) with diploid sporophytic phase (2n) during the life cycle is called alternation of generation. Following type of life cycles are found in plants:
(a) Haplontic life cycle: Gametophytic phase is dominant. photosynthetic and independent, whereas sporophytic phase is represented by the zygote. Zygote undergoes meiosis to restore haploid condition.
Example: Volvox and Spimgyra.
(b) Diplontic life cycle: Sporophytic phase (2n) is dominant, photosynthetic and independent. The gametophytic phase is represented by the single to few celled gametophyte. The gametes fuse to form zygote which develops into sporophyte. e.g., Fucus, gymnosperms and angiosperms.
(c) Haplodiplontic life cycle: This type of life cycle is found in Bryophytes and pteridophytes which is intermediate between haplontic and diplontic type. Both the phases are multicellular, but they differ in their dominant phase.
In Bryophytes dominant independent phase is gametophyte and it alternates with short – lived multicellular sporophyte totally or partially dependent on the gametophyte. In Pteridophytes sporophyte is the independent phase. It alternates with multicellular saprophytic or autotrophic, independent, short lived gametophyte (n).
