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Step 1: Understanding the Context
In the life cycle of plants, the transition from the gametophyte (haploid) stage to the sporophyte (diploid) stage is a key evolutionary milestone. Bryophytes (mosses and liverworts) typically have dominant gametophytes, whereas gymnosperms and angiosperms show dominant sporophytes. In pteridophytes, although the sporophyte is also the dominant stage, the female gametophyte is retained for a period on the parent sporophyte, leading to an important evolutionary development.
Step 2: Retention of the Female Gametophyte
In pteridophytes, the mature sporophyte produces spores that germinate into gametophytes (prothalli). The female gametophyte (bearing archegonia) remains attached to or in close association with the parent sporophyte for some time. This retention allows the zygote formed within the archegonium to remain protected and nourished on the parent plant.
Step 3: Evolutionary Significance
The retention of the female gametophyte and the development of the embryo within it mark a significant step toward a seed habit. In later groups like gymnosperms and angiosperms, these processes evolve further to form actual seeds, where the embryo is securely protected by seed coats and provided with stored nutrients. Thus, what is observed first in pteridophytes represents an earlier evolutionary stage that paves the way for true seed formation in higher plants.
Conclusion
Since pteridophytes are the first group in which the developing young embryo remains with the female gametophyte on the parent sporophyte for some time, they represent the correct answer. This feature is an essential milestone in plant evolution, eventually leading to the emergence of seeds.
