Question

What is a haplontic life cycle? Give an example.

Answer 1

Haplontic life cycle:

1. The haplontic life cycle refers to the life cycle of organisms, which is dominated by the haplontic stage or a stage characterized by a single set of chromosomes.
2. Alage shows haplontic life cycle.
3. Alternation in the generation is shown by algae and plants.
4. As they reproduce sexually they show alternation with the haplontic gametophytic stage and diplontic sporophytic stage.

Biological cycles can be of 3 types:

1. Diplontic life cycle- diploid zygote formed through fertilization of gametes is independent and thus gives rise to the new plant by dividing mitotically. example- angiosperms, gymnosperms.
2. Haplontic life cycle- the free-living independent stage is haploid cells that divide to give rise to a new organism. example- green algae.
3. Haplo-diplontic life cycle- here both gametophyte and sporophyte are multicellular and can depend on each other. example- bryophyte.

Haplontic life cycle:

• Dominant stage - Haploid gametophyte is free-living, photosynthetic, and independent.
• A gametophyte is a single-celled or multicellular gamete containing a structure having a single set of chromosomes.
• Haploid divides through mitosis to give rise to new organisms without undergoing fertilization.
• Diploid zygote (sporophyte) is not free-living or independent.

Process of the haplontic life cycle:

1. A diploid zygote is formed through the embryo.
2. The zygote divides meiotically to form haploid cells.
3. These haploid cells divide mitotically to form independent gametophytes.
4. The mature gametophyte represents the free-ling dominant stage of the haplontic life cycle.

Example of the haplontic life cycle:

Green algae like Chlamydomonas, Spirogyra, Volvox, Ulothrix, etc show haplontic life cycle. Most of the fungi and protists also show the haplontic life cycle