Question

In which entity sporophytic generation is represented by zygote?

Answer 1

Alternation of generation is commonly observed in organisms belonging to the plant kingdom. The life cycle of plants include haploid and diploid multicellular stages. Haploid generation is the gametophyte (n), which produces the gametes while diploid generation is the sporophyte (2n) which produces spores.

Complete answer:
Alternation of generation is the conversion of gametophyte generation into the sporophyte generation and vice versa. Gametophytes undergo mitosis, whereas in sporophytes meiosis is seen.
Based on the dominant phase of their life cycle, plants are characterized into three types-
1. Haplontic life cycle- The dominant stage is haploid gametophyte. Diploid sporophyte is represented by zygote only, which is not independent. Zygote undergoes meiosis to produce haploid cells which divide mitotically to produce haploid organisms. Eg- Green algae like Chlamydomonas.
2. Diplontic life cycle- Diploid sporophyte is the dominant stage and shows gametic meiosis. Haploid gametophyte is reduced and dependent on sporophyte generation. Eg- Gymnosperms and Angiosperms.
3. Haplo-diplontic life cycle- Both haploid and diploid stages are multicellular. In some, gametophyte is dominant and free-living and the sporophyte is small and short lived and dependent on gametophyte. Eg- Bryophytes. While in others sporophytes are the independent and free-living dominant stage which alternates with the short lived gametophyte. Eg- Pteridophytes and some algae like Kelps.
From the foregoing discussion, we can conclude that in Chlamydomonas , green algae, sporophytic generation is represented by zygote.

Note:
Chlamydomonas is a green algae belonging to class chlorophyceae. It has a gametophytic plant body i.e. it is haploid. It reproduces sexually by isogamous gametes, which unite to form a zygote. Zygote represents the only sporophytic generation in Chlamydomonas and divides meiotically to produce haploid cells which undergo mitosis to give rise to haploid organisms.