Question

Compare and contrast the life cycles of the Ectocarpus sp. and Laminaria sp. In your answer you should include a description clearly stating the similarities and differences in these life cycles.

Answer 1

Ectoparus and Laminaria are both brown algae.

Ectoparus is filamentous brown alga. Laminaria is large and sporophyte is diferentiated in to holdfast, stipe and blade.

Ectoparus includes morphologically identical sporophyte and gametophyte Isomorphic alternation of generation. Where as the Laminaria has sporophytic stage more dominant than the gametophyte and heteromorphic alternation of generation

Diploid sporophytic stage has two types of sporagia, plurilocular and unilocular. Unilocular sporangia produce biflagellate meiospores. On germination these produce haploid gametophytes. Laminaria produce unilocular sporangia.

Gametophyte of ectoparus is monoecoius producing both male and female gametes. In case of Laminaria, male gametophyte and female gametophyte are different and hence they are dioecious.

Fertilization of the egg occurs partially extruded from Oogonium and zygote develops insitu to form sporophyte

Similarities--

Both show alternation of generation. Sporophyte is well formed in both of them. Basic similarities in life cycle. Sporophyte produces spores by meiosis. The zoospores are flagellated and heterokont flagella.

Both have haplo-diplontic life cycle.

Sporophyte is diploid , producing spores by meiosis, gametophyte is haploid producing gametes. Fusion of gametes results in sporophyte repeating the life cycle. This is haplodiplontic life cycle. It is intermediate between haplontic and diplontic life cycle.