Question

The life cycle of algae, such as Spirogyra is
A. Haplontic
B. Diplontic
C. Haplo-diplontic
D. Diplo-haplontic

Answer 1

The dominant phase is the gametophyte which is a free –living phase that forms the male and female gametes. Haploid spores are formed by the meiotic division of zygote that gives rise to the gametophyte on germination.

Complete answer:
A life cycle is a period involving one generation of an organism through means of reproduction. Haplontic life cycle is the primitive type of life cycle characterized by dominant gametophyte and zygotic meiosis. The zygote undergoes meiosis to form haploid spores. Each spore germinates to form gametophyte (divide mitotically). The haploid life cycle is very common in single celled organisms like algae, either planktonic or filamentous. Haplontic life cycle found in many algae, like volvox, spirogyra, ulothrix, green algae like chlamydomonas etc. There are three types of cycles.

Haplontic life cycle: The zygote undergoes meiosis and gametophyte is a dominant phase. The sporophytic phase is represented by single-celled zygotes called zygospores.
Diplontic life cycle: Gametes undergo meiosis and diploid sporophytes are the dominant and independent phase. Gametes are haploid and called a gametophyte.
Haplo diplontic: in haplo diplontic the mitosis occurs in both diploid and haploid cells. Bryophytes show gametophyte stage and later they show sporophytic stage. They are multicellular and often free living.
Sporic meiosis, on the other hand, has two mitosis events (diplobiontic) one in each phase.

Note: All algae goes through a haploid life cycle of development, starting with a diploid zygote, or spore and ending up with a fully mature alga plant. There are three main classification of algae: Rhodophyta, Cholorphyta, Heterokonphyta.