Chapter 19, Problem 31A

Summary Introduction

To analyze:

The relationship exhibiting between the sporophyte and gametophyte generations in the alternation of generations.

Introduction:

The life cycles that have an alternation of generations undergo regular alternation of the gametophyte and sporophyte generations. These two phases follow each other rigidly. It is also referred to as haplo-diplontic life cycle as it possesses well developed multicellular haploid and diploid phases.

Explanation of Solution

Different groups of algae complete their life cycle in different patterns. A group of Algae undergoing alternation of generations takes two generations, which are a gamete bearing haploid gametophyte and a spore-producing diploid sporophyte, to complete their life cycle. The gametophyte is a multicellular haploid generation that alternates with sporophyte that is a multicellular diploid generation.

The gametophyte is haploid (n) and produces gametes by mitosis. The gametes fuse and form a diploid zygote that develops into the sporophytic thallus. The sporophyte is diploid (2n) and produces spores or reproductive cells by undergoing meiosis. The haploid spores germinate to produce haploid gametes.

  

Conclusion

Thus, in the alternation of generation, there is a sequential recurrence of two well developed haploid gamete producing gametophyte and a diploid spore-producing sporophyte.