Question

The prothallus represents
A. Gametophyte of fern
B. Sporophyte of angiosperm
C. Sporophyte of gymnosperm
D. Sporophyte of fern

Answer 1

Hint: Pteridophytes are considered as the first true land plants. They do not reproduce via seeds. Instead, they reproduce via spores. They are vascular cryptogams, seedless and display true alternation of generations. Also, pteridophytes are classified into lycopodiopsida and polypodiopsida. In pteridophytes, meiosis occurs at the time of spore formation.

Complete answer
Pro means forward and thallus means twig. It is homosporous.
In pteridophytes, the spores are released and fall into the ground. Then, they develop into prothalluses. This is the gametophyte stage of pteridophytes. The prothallus produces archegonia and antheridia. The prothallus is flat, green, exosporic, autotrophic and cordate (heart-shaped), short-lived. Besides, it is multicellular, small, reduced, dorsiventral, free living, independent and non-vascular.
The spores formed due to meiosis germinate and give rise to inconspicuous, small, multicellular, free-living, photosynthetic thalloid gametophytes called prothallus. Prothallus is representative of the gametophyte stage in pteridophytes.
The diploid sporophyte represents a dominant, independent, photosynthetic and vascular plant body. Haploid gametophyte is prothallus, which is multicellular, saprophytic/autotrophic, independent, short-lived, called prothallus. This pattern is called haplodiplontic lifestyle, which is displayed by all pteridophytes.
Option A Gametophyte of fern: Based on the above points, prothallus is a gametophyte of fern.
Option A is correct
Option B Sporophyte of angiosperm: Angiosperm is unrelated to prothallus
Hence, Option B is not correct
Option C Sporophyte of gymnosperm: Prothallus is not related to gymnosperm.
So, Option C is not correct
Option D Sporophyte of fern: Prothallus is a gametophyte and not sporophyte.
Option D is correct

Therefore, Option A is the correct answer

Note:
Heterospory is present in pteridophytes. Two types of spores are produced, microspores and megaspores. Microspores are smaller in size and megaspores are larger in size. Microspores and megaspores give rise to male gametophytes and female gametophytes respectively. This heterospory has evolutionary significance as there is precursor exists for seed habit in higher plants.