What it does
Plants live a double life. One generation, the sporophyte, is diploid (2n: two sets of chromosomes) and makes spores by meiosis. The spores grow into the other generation, the gametophyte, which is haploid (n) and makes gametes. Two gametes join at fertilisation to make a diploid zygote, which grows into the next sporophyte. This is alternation of generations.
What changes from algae to flowering plants is how big and independent each generation is. This page draws each group’s life cycle as a wheel: blue segments are haploid, orange are diploid, and markers show where meiosis (M) and fertilisation (F) happen. Step round with Next stage, or tap a segment, to read what each stage is and why it has that ploidy.
- Green alga (Chlamydomonas, Spirogyra): haplontic. Only the zygote is diploid.
- Bryophyte (moss): haplo-diplontic, and the green plant is the gametophyte; the sporophyte lives on it.
- Pteridophyte (fern): haplo-diplontic, but the big plant is the sporophyte; the tiny prothallus lives on its own.
- Gymnosperm (pine) and angiosperm (flowering plant): the sporophyte is everything you see; the gametophytes shrink to a few cells in the pollen and the ovule. School books call this pattern diplontic.
- Human: truly diplontic: meiosis makes the gametes directly.
It fits the Class 11 biology chapter on the plant kingdom (algae to angiosperms, and plant life cycles), and links to sexual reproduction in flowering plants in Class 12. Revise meiosis with cell division first; the flower that makes the pollen and the ovule is in the floral formula maker.
How to use it
- Tap a group. The wheel, the pattern and the facts change.
- Press Next stage (or Back), or tap any segment. The current segment is outlined, its ploidy shows in the middle, and the line under the wheel explains it, including what happens next.
- The facts list the pattern, the main plant body, whether sperm need water to reach the egg, and how much of the wheel is haploid and diploid.
- The table at the bottom compares all the groups at once.
Worked example
The page opens on the bryophyte (moss). Stage 1 is the leafy gametophyte, haploid (n): “The green moss plant you see is the haploid gametophyte.” Step on: sperm and egg (n), then the F marker: fertilisation, n + n → 2n. Stage 3, the zygote, and stage 4, the sporophyte (foot, seta, capsule), are orange (2n), and the note says the sporophyte depends on the gametophyte for food. After the M marker, meiosis in the capsule gives haploid spores (stage 5), which grow into the protonema (stage 6) and a new leafy plant. The facts say: haplo-diplontic, main body gametophyte (n), water needed, wheel share n 74 %, 2n 26 %.
Switch to Angiosperm: the wheel is now mostly orange (2n 86 %), the gametophytes are a pollen grain and an embryo sac, and the note under the wheel adds that endosperm is triploid (3n).
FAQ
Why are seed plants called diplontic when they still have gametophytes? Their gametophytes are reduced to a few cells inside the sporophyte’s tissues and never live on their own, so the life cycle looks like the diplontic one of animals. Strictly, they still alternate generations, which is why the wheel shows a thin haploid stage.
Do the wheel shares mean time? No. They are rough, to show which generation dominates. A fern prothallus may live for weeks; the fern for years.
Is anything stored? No. Everything runs in your browser. fibub is not part of NCERT; the topics follow the syllabus, but the words and pictures are our own.
Where the numbers come from
- Alternation of generations, ploidy of each stage, and the haplontic, diplontic and haplo-diplontic patterns are standard botany. The wheels, their wording and the rough shares are fibub's own; no textbook text, figures or diagrams are copied.
- A teaching model: the share of the wheel each stage takes is a rough picture of which phase dominates, not a measured time.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.