Alternation of Generations in Plants

Study Notes

Plants have a unique life cycle, known as Alternation of Generations, where they alternate between two different stages of life: diploid (sporophyte) and haploid (gametophyte) stages.
Each generation of the plant looks like its grandparent, not its parent.
The diploid sporophyte stage produces spores through meiosis, which are genetically unique and contain half the number of chromosomes as the parent.
Spores develop into haploid gametophytes through mitosis, which produce gametes (sex cells).

Haploid stage (gametophyte) has one set of chromosomes, while diploid stage (sporophyte) has two sets of chromosomes.
In plants, both haploid and diploid stages can be independent, multi-celled organisms.
In animals, only sperm and egg cells are haploid, and they are single-celled and don't live outside the organism's body.

Bryophytes have a dominant haploid gametophyte stage, which is the large body of moss.
The sporophyte stage in bryophytes is temporary and grows directly from the gametophyte body.
In bryophytes, the gametophyte stage produces gametes, which fuse to form a zygote that grows into a new sporophyte.

In these plants, the sporophyte stage is the dominant stage, which is the visible plant body.
The gametophyte stage in these plants is small and temporary, and provides nutrients to the growing sporophyte.
As plants have evolved from bryophytes to complex angiosperms, the gametophyte stage has become smaller and less long-lived.

The gametophyte stage is haploid, begins as a spore, and produces gametes through mitosis.
The sporophyte stage is diploid, grows from the fusion of male and female sex cells, and produces spores through meiosis.
Spores created through meiosis are haploid and contain one set of chromosomes.