Question

Selaginella and Salvinia are considered to represent a significant step toward the evolution of seed habit because
A. The female gametophyte is free and gets dispersed like seeds.
B. Female gametophytes lack archegonia.
C. Megaspores possess endosperm and embryo surrounded by a seed coat.
D. The embryo develops in a female gametophyte which is retained on the parent sporophyte.

Answer 1

Selaginella and Salvinia are heterosporous Pteridophytes. This means that they produce two different kinds of spores. These spores are formed within their respective sporangium and after fertilization, the embryo is formed inside the archegonium.

Complete answer:Selaginella and Salvinia are the members of the Kingdom Plantae, and the phylum Pteridophyta. Selaginella and Salvinia are heterosporous plants, which means that they produce two different kinds of spores. Due to this the formation of the seeds or the seed habit is the most significant step towards sexual reproduction and evolution.
The two different kinds of spores produced in Selaginella and Salvinia are –
a. Microspores: Microspores are the small-sized spores that give rise to the male gametophyte or the antheridium.
b. Megaspores: Megaspores are the large-sized spores that give rise to the female gametophyte or the archegonium.
The male and the female gametes fuse and the zygotes are formed. The zygote develops further into the embryo. The formation and the development of the embryo take place within the female gametophyte. This female gametophyte is retained on the parent sporophyte for a considerable period of time. This step is somewhat similar to the process of gamete formation, fertilization, and seed formation in the higher vascular plants. Due to this reason, it is considered an important precursor for evolution.
Thus, based on the above information, we can conclude that Selaginella and Salvinia are considered to represent a significant step toward the evolution of seed habit because the embryo develops in a female gametophyte which is retained on the parent sporophyte.
Hence, the correct answer is option (D).

Note: Pteridophytes are broadly classified into two types, based on the kind of spore formation that occurs. These two types are Homosporous and Heterosporous. Homosporous Pteridophytes are those plants that produce similar kinds of spores. Examples of Homosporous Pteridophytes are Lycopodium, Pteris, Dryopteris, etc.