1. Alternation of Generations: Seedless plants have a unique life cycle that alternates between two distinct generations:
* Sporophyte generation: This is the dominant generation, the one we usually see (like ferns and mosses). Sporophytes produce spores in structures called sporangia.
* Gametophyte generation: This generation is much smaller and less noticeable. Gametophytes produce gametes (sperm and egg) that fuse to form a zygote, which develops into a new sporophyte.
2. Spore Production:
* Sporophytes produce spores through meiosis, a type of cell division that reduces the chromosome number by half.
* These haploid spores are released from the sporangia and can be dispersed by wind or water.
3. Gametophyte Development:
* Spores germinate and develop into gametophytes, which are small, independent plants.
* Gametophytes produce gametes (sperm and egg) in structures called antheridia (for sperm) and archegonia (for egg).
4. Fertilization:
* Sperm from antheridia swim to the egg in archegonia, and fertilization occurs.
* The fertilized egg (zygote) develops into a new sporophyte.
Examples of Seedless Plants:
* Ferns: Ferns have large, prominent sporophytes with fronds (leaves). Spores are produced on the underside of fronds in structures called sori.
* Mosses: Mosses have small, leafy gametophytes that dominate their life cycle. Sporophytes are short, stalk-like structures that grow out of the gametophyte.
* Liverworts: Liverworts are similar to mosses but have flat, lobed structures called thalli.
* Hornworts: Hornworts are characterized by long, horn-shaped sporophytes that grow out of their gametophytes.
Key Differences from Seed Plants:
* Seeds: Seedless plants don't produce seeds, while seed plants do.
* Dispersal: Spores are much smaller and lighter than seeds, allowing for wider dispersal by wind and water.
* Gametophyte Dependence: Seedless plants have independent gametophytes, while seed plants have much reduced gametophytes that rely on the sporophyte for nutrients.
