Question

Which of the following statements is true about the alternation of generation in pteridophytes?
(a) Diploid generation is followed by a triploid generation.
(b) Haploid generation is followed by a diploid generation.
(c) Triploid generation is followed by a haploid generation.
(d) Diploid generation is followed by the haploid generation.

Answer 1

Hint: In pteridophytes, the gametophyte results in the sporophyte by the process of syngamy, and the sporophyte results in the gametophyte by the process of meiosis.

Complete step by step answer:
Pteridophytes exhibit a regular feature of alternation of generations. During sporogenesis, the reduction division results in the formation of haploid spores representing the first stage of the gametophyte generation followed by fertilization resulting in the formation of a zygote representing the first stage of sporophyte generation. The gametophyte takes part between meiosis and syngamy whereas the sporophyte takes part between syngamy and meiosis. The gametophyte is haploid (n) and the sporophyte is the diploid phase (2n). These two phases follow one another in regular succession resulting in the regular alternation of generation.
The antherozoids (male gametes) are produced from antheridia in numbers. They are flagellated and can swim in the water. The spheres (female gametes) are produced in flask- shaped archegonia singly. These are non- motile. The fusion between an egg cell and an antherozoid results in a zygote (diploid) having the combined nuclear material of the two gametes. The zygote undergoes mitotic divisions and develops into the sporophyte (diploid). The spore mother cells of the sporangia undergo meiosis resulting in non- motile spores (haploid). These spores undergo mitosis and result in gametophyte (haploid) thus completing the life cycle.
So, the correct answer is ‘(c) Diploid generation is followed by a haploid generation’.

Note:
- The term “Alternation of generation” was used by Hofmeister in 1851.
- The gametophytic phase is sexual and the sporophytic phase is asexual.
- The dominant phase of their life cycle is known to be the sporophytic phase.