Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems.
A seed consists of an embryo and nutrients surrounded by a protective coat.
The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte.
What human reproductive organ is functionally similar to this seed?
Seeds and pollen grains are key adaptations for life on land
In addition to seeds, the following are common to all seed plants:
Gametophyte / sporophyte relationships in different plant groups
Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition
Reduced, independent (photosynthetic and free-living)
Reduced, dependent on gametophyte for nutrition
Mosses and other nonvascular plants
Ferns and other seedless vascular plants
Seed plants (gymnosperms and angiosperms)
Microscopic female gametophytes (n) inside ovulate cone
Microscopic male gametophytes (n) inside pollen cone
Microscopic female gametophytes (n) inside these parts of flowers
Microscopic male gametophytes (n) inside these parts of flowers
The ancestors of seed plants were likely homosporous, while seed plants are heterosporous.
Megasporangia produce megaspores that give rise to female gametophytes.
Microsporangia produce microspores that give rise to male gametophytes.
An ovule consists of a megasporangium, megaspore, and one or more protective integuments.
A fertilized ovule becomes a seed.
Gymnosperm megaspores have one integument.
Angiosperm megaspores usually have two integuments.
From ovule to seed in a gymnosperm
(a) Unfertilized ovule
Immature female cone