Gametophyte forms gametes by mitosis and gametes after fertilization forms zygote. Zygote(2n) develops into sporophyte (2n) which forms spores by undergoing meosis. Then spores again forms gametophyte by mitosis. In case of algae after zygote is formed, it directly undergo meosis to form spores which further forms gametophyte, in algae sporophyte is not formed.
*** Algae and bryophytes has haploid plant body whereas pteridophytes, gymnosperms and angiosperms has diploid plant body.
1} Haplontic :- Gametophyte(n) stage is dominant, free living and photosynthetic. eg. :- Chlamydomonas, volvox , spirogyra and other algae
2} Diplontic :- Sporophyte (2n) stage is photosynthetic, free living and dominant. Algae Focus also shows diplontic life cycle in which gametophytic phase is single to few celled. But in angiosperm and gymnosperms which also shows diplontic life cycle has gametophyte few to multicelled
3} Haplodiplontic :- Bryophytes shows this, in which haploid gametophyte (n) dominant, independent, photosynthetic, thalloid/erect and sporophyte is shortlived, multicellular and dependent.
4} Diplohaplontic :- Pteridophytes shows this life cycle in which sporophyte (2n) is dominant, independent, photosynthetic, vascular and Gametophyte (n) is multicellular, saprophytic/Autotrophic, independent and short lived.
*** Algae like Polysiphonia, Ectocarpus and Kelp shows haplodiplontic nature of life cycle.
Here complete plant kingdom has been completed. All important NCERT lines has been covered in simple words.
