Question

What is common between Pteris and Sphagnum.
A. Dominant haploid stage
B. Vascular diploid stage
C. Dependent diploid stage
D. Haploid independent stage.

Answer 1

Hint: Bryophyte (Sphagnum) and pteridophytes (Pteris) both are said to show alteration if generation in which the haploid and diploid phase of their life cycles are said to alternate one another and so they are said to have a haplodiplontic life cycle.

Complete answer:
Sphagnum is a bryophyte while Pteris is a pteridophyte.
1. They show different life cycles and alternation of generation is also seen.
In the case of Sphagnum, the independent mature stage is haploid in nature, it is also known as the gametophyte stage.
2. The gametes are formed by means of mitotic or educational division forming a diploid zygote which forms the diploid sporophyte.
3. This sporophyte is dependent on the gametophyte. In the case of pteridophytes also the sporophyte that is produced from the fusion of haploid gametes is also diploid in nature.
4. The dominant phase is sporophytic in the case of pteridophytes.
5. Both cycles have a dependent diploid stage in their life cycles.

Additional information: In most diplonts, mitosis happens only in the diploid phase, i.e. gametes generally form quickly and fuse to form diploid zygotes.
In the whole cycle, gametes are the only haploid cells, and mitosis occurs only in the diploid phase.

Hence, the correct option is (C), Dependent diploid stage.

Note: Organisms exhibiting alteration of generation, the sporophyte which is the diploid phase is dependent upon the gametophytic stage, as seen in both bryophytes and pteridophytes.