Question

Isomorphic alternation of generation is found in
A) Ulva
B) Spirogyra
C) Sargassum
D) Oedogonium

Answer 1

Hint: Alternation of generations is the alternation of a sexual phase and an asexual phase in the life cycle of an organism. The two phases, or generations, are often morphologically, and sometimes chromosomally, distinct.

Complete answer:
To answer this question first we need to understand what is an isomorphic alternation of generations. In this type of alternation of generation, the sporophyte and gametophyte are morphologically similar or identical; whereas in a heteromorphic alternation of generations they are dissimilar.
1) Ulva comprises sea lettuces. The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. In ulva the haploid zoospores give rise to the gametophytes. Both kinds of plants are morphologically identical and therefore ulva shows an isomorphic alternation of generations.
2) In Spirogyra, the sexual reproduction involves a cycle alternation between a haploid vegetative filament (gametophyte plant) and a diploid zygospore, towards the end of growing season the Spirogyra filament produce aplanogametes in vegetative cells called gametangia. The gametes fuse to form a zygospore (2n) gametophyte. But they are morphologically different and therefore ulva shows a heteromorphic alternation of generations.
3) The life cycle of Sargassum is a diplontic type and there is no alternation of generation. The gametes only are haploid structures in the life cycle. After fertilization a diploid zygote is formed which divides to make a diploid sporophyte thallus.
4) Oedogonium is a genus of green freshwater, filamentous macroalgae. The filaments set it apart from other types of macroalgae, due to its rings of cells. Like many algae, Oedogonium exhibits a haploid life cycle. And thus, shows no alternation of generation.

Thus, the correct answer is option A (Ulva).

Note:The dominant generation in vascular plants showing alternation of generation is the sporophyte, while in the non-vascular plants is the gametophyte.