Practice question

Heterospory describes production two distinct spore sizes differing resource allocation: numerous small microspores from microsporangia giving rise to male gametophytes pollen grains with few cells, and fewer larger megaspores with abundant reserves from megasporangia developing into female gametophytes embryo sacs retained. This division labor contrasts with homospory where single spore type yields bisexual free-living gametophyte like most ferns and bryophytes. Evolution toward heterospory in progymnosperms like Archaeopteris enabled retention of megagametophyte within sporophyte tissues, protection via integuments, reduction in gametophyte size and eventual origin seed habit enhancing survival under arid terrestrial conditions reducing water dependence.