Haplontic vs Diplontic vs Haplo-Diplontic Life Cycles

Look at which body is the big, free-living plant. In haplontic, the haploid gametophyte (n) is the main plant and the only diploid cell is the zygote. In diplontic, the diploid sporophyte (2n) is the main plant and the only haploid cells are the gametes. In haplo-diplontic, BOTH the sporophyte and the gametophyte are multicellular plant bodies that alternate. So it is really a question of 'which stage forms the visible plant', not just ploidy.

Both show the haplontic life cycle. The green alga you see is haploid (n). Two gametes fuse to make a diploid zygote, but the zygote is the ONLY diploid cell. It divides by meiosis right away (zygotic meiosis) to make new haploid plants. This is why 'most algal genera are haplontic' in NEET statements.

Fucus is a brown alga but it is DIPLONTIC, not haplontic. Its main plant body is the diploid (2n) sporophyte. Meiosis happens just before making gametes (gametic meiosis), so the gametes are the only haploid cells. NEET loves this trap: not all algae are haplontic. Ectocarpus (another brown alga) is haplo-diplontic, but Fucus is diplontic.

Both are haplo-diplontic. Two multicellular bodies alternate. In bryophytes the haploid gametophyte is the dominant, leafy, photosynthetic plant and the sporophyte is smaller and partly dependent on it. In pteridophytes it flips: the diploid sporophyte (the fern plant) is dominant and the gametophyte (prothallus) is small and independent. Both still count as haplo-diplontic because both bodies exist.

All seed plants are diplontic: gymnosperms and angiosperms (flowering plants). Their body is the diploid sporophyte, and the gametophytes are microscopic and dependent, not free-living. The brown alga Fucus is the classic non-seed-plant example of diplontic. Human and animal life cycles are also diplontic, but for NEET Plant Kingdom, remember seed plants + Fucus.

In haplontic, meiosis happens in the zygote (zygotic meiosis) as soon as it forms. In diplontic, meiosis happens during gamete formation (gametic meiosis). In haplo-diplontic, meiosis happens in the spore mother cells to make spores (sporic meiosis). Matching the meiosis type to the life cycle is a common NEET question, so link them together.

Haplontic = the free-living plant is haploid (n) and only the zygote is diploid; diplontic = the free-living plant is diploid (2n) and only the gametes are haploid.

No. Most algae are haplontic, but Fucus is diplontic and Ectocarpus is haplo-diplontic. This exception is a favourite NEET trap.

Haplo-diplontic. In mosses (and all bryophytes) both a gametophyte and a sporophyte exist, with the haploid gametophyte being the dominant, leafy plant.

All angiosperms and gymnosperms are diplontic. The plant body is the diploid sporophyte and the gametophytes are microscopic and dependent.

Haplontic goes with zygotic meiosis, diplontic goes with gametic meiosis, and haplo-diplontic goes with sporic meiosis.