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Difficulty: HardThallophytes, Bryophytes, and Pteridophytes

A terrestrial cryptogam exhibits an independent, vascularized dominant sporophyte phase alongside a tiny, photosynthetic prothallus that relies on a film of water for swimming sperm. Based on these anatomical and life cycle features, to which plant division does this specimen belong, and how does its dominant generation compare to that of bryophytes?

  1. Pteridophyta, possessing a dominant diploid sporophyte generation, whereas bryophytes have a dominant haploid gametophyte generation.Answer
  2. B
    Bryophyta, possessing a dominant haploid gametophyte generation equipped with true lignified xylem vessels for transport.
  3. C
    Thallophyta, possessing an undifferentiated cellular thallus that translocates manufactured food bidirectionally through xylem.
  4. D
    Pteridophyta, possessing a dominant sporophyte phase that relies on extracellular saprophytic digestion for mineral absorption.

Answer

The plant belongs to Pteridophyta, possessing a dominant diploid sporophyte generation, unlike bryophytes which feature a dominant haploid gametophyte generation.
Pteridophytes are vascular cryptogams whose dominant, prominent life cycle stage is the diploid sporophyte (2n2n). Bryophytes, on the other hand, lack true vascular tissues and are dominated by the haploid gametophyte (nn) stage. Both groups remain reliant on free water for motile flagellated sperm during sexual reproduction.

Step-by-Step Solution

1
Analyze the structural and reproductive characteristics described in the stem.
The presence of true vascular tissue (xylem and phloem) and an independent sporophyte phase eliminates Thallophyta and Bryophyta, identifying the plant as a Pteridophyte.
Among cryptogams, only Pteridophytes possess true vascular bundles and an independent diploid sporophyte phase.
2
Compare the dominant phase of alternation of generations between Pteridophytes and Bryophytes.
Pteridophytes feature a dominant diploid (2n2n) sporophyte, whereas Bryophytes feature a dominant haploid (nn) gametophyte.
Evolutionary trends in land plant adaptation demonstrate a transition from gametophyte-dominated life cycles in bryophytes to sporophyte-dominated life cycles in pteridophytes.

Key Concept

Alternation of generations and vascular differentiation in plant cryptogams (Thallophytes, Bryophytes, and Pteridophytes)
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Topics

Thallophytes, Bryophytes, and Pteridophytes

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