This question involves understanding the alternation of generations in plant life cycles, specifically comparing the dominance and relationship between the sporophyte (diploid) and gametophyte (haploid) phases in different plant groups.

Key Concepts:

In plants, the life cycle alternates between a diploid sporophyte (which produces spores via meiosis) and a haploid gametophyte (which produces gametes via mitosis). The relative dominance and independence of these phases vary among plant groups:

• Bryophytes (e.g., mosses): The gametophyte is the dominant, photosynthetic, and independent phase. The sporophyte is physically attached to and nutritionally dependent on the gametophyte (semi-parasitic).
• Pteridophytes (e.g., ferns): The sporophyte is the dominant, independent phase. The gametophyte (prothallus) is a small, independent, free-living structure.
• Gymnosperms (e.g., conifers): The sporophyte is the dominant, independent phase. The gametophyte is highly reduced and is not a free-living generation; it is produced within and retained inside the sporophyte (specifically, within the cones).

Step-by-Step Analysis:

Step 1: Analyze Plant I
Observation: "Shows dominant gametophyte, sporophyte semi-parasitic on parent gametophyte."
This description perfectly matches Bryophytes. The gametophyte is the main plant you see, and the sporophyte grows out of it and relies on it for nutrition.

Step 2: Analyze Plant II
Observation: "Shows reduced gametophyte, dominant sporophyte. Both phases are independent."
This describes Pteridophytes. The sporophyte (e.g., the fern plant) is large and independent. The gametophyte (a small prothallus) is also free-living and independent, though it is much smaller and reduced compared to the bryophyte gametophyte.

Step 3: Analyze Plant III
Observation: "Shows reduced gametophyte, dominant sporophyte. Gametophyte is produced within the sporophyte and not as separate generation."
This is a key characteristic of Seed Plants (Gymnosperms and Angiosperms). The gametophyte is microscopic and develops entirely within the sporangia of the dominant sporophyte (e.g., pollen grains and ovules in cones). It is not an independent generation at all.

Final Answer:
The correct sequence is: Plant I: Bryophyte, Plant II: Pteridophyte, Plant III: Gymnosperm.

Related Topics & Formulae:

Related Theory: The trend in plant evolution is a reduction in the size and independence of the gametophyte and an increasing dominance of the sporophyte. Bryophytes represent the most primitive condition with a dominant gametophyte. Pteridophytes show a shift towards sporophyte dominance but still have an independent gametophyte. Gymnosperms and Angiosperms represent the most advanced condition, with a highly reduced, dependent gametophyte.

Key Formulae/Concepts: While no complex equations are involved, understanding the ploidy levels is crucial: $\mathrm{Sporophyte}\leftrightarrow \left(2n\right) \to \mathrm{Meiosis} \to \mathrm{Spores} \left(n\right) \to \mathrm{Gametophyte} \left(n\right) \to \mathrm{Mitosis} \to \mathrm{Gametes} \left(n\right) \to \mathrm{Fertilization} \to \mathrm{Sporophyte} \left(2n\right)$ This cycle continues, alternating between haploid (n) and diploid (2n) stages.