Plant Kingdom
Alternation of generations
A plant's life swings between two separate bodies — a diploid one that makes spores and a haploid one that makes gametes — each producing the other.
The diploid sporophyte (2n) makes haploid spores by meiosis. Each spore grows into a haploid gametophyte (n), which makes gametes by mitosis. Two gametes fuse into a zygote — and you're back to a sporophyte.
Which body dominates depends on the group: in mosses the gametophyte is the main green plant; in ferns and higher plants the sporophyte takes over.
Where students slip up
It is NOT one plant changing its ploidy midway. The sporophyte and gametophyte are two distinct, genetically separate generations that take turns.
Where this connects
Line up a moss, a fern and a flowering plant and you can watch evolution shift the balance, handing dominance from the gametophyte to the sporophyte. The same cycle, tilted a little further at each step.
Quick check
In a moss, the dominant free-living green phase is the:
- ASporophyte (2n)
- BGametophyte (n)
- CZygote
- DSpore