Reproduction of Algae

Generalized reproduction

                A.            Asexual:  spore formation - from mitosis (called mitospores)

                B.            Sexual:  spore formation - from meiosis (called meiospores)

                                1.             Sporophyte:  diploid plant

                                2.             Meiocytes:  cells that undergo meiosis

                                3.             Gametangia:  where gametes are produced

                                                a)            Antheridium:  sperm-producing gamete

                                                b)            Oogonium:  egg-producing cell

                                4.             Sexual life cycles - algae have representatives in each

                                                a)            Typical algae & fungi - zygotic (most life is haploid)

                                                b)            Plants - sporic (half of life is haploid)

                                                c)             Animals - gametic (most life is diploid)

More on reproduction

                A.            Asexual - can be vegetative or by spores

                B.            Generalized sexual:  gametes ==> diploid zygote ==> meiosis - meiospores ==> gametophyte ==> gametes in gametangia

                                1.             Isogamy - gametes are identical (what you see is the same)

                                2.             Anisogamy - gametes are not identical (can "see" the difference)

                                3.             Oogamy - antheridia produce sperm and oogonia produce egg

                C.            Types of life cycles

                                1.             Algae typically show zygotic (Chlorophyta); gametic (Chromophyta / Chrysophyceae) - diatoms); and sporic (Chromophyta / Phaeophyceae)

                                2.             In zygotic, the zygote is the only diploid cell (example - green algae)

                                3.             In gametic, meiotic division directly leads to formation of gametes (diatoms)

                                4.             In sporic, there is alternation between haploid and diploid generations (example - a brown alga - Fucus)

                                                a)            Haploid generation is a bunch of cells, diploid generation is big (conspicuous)

                                                b)            Thallus (diploid) - has cavities called conceptacles

                                                c)             Conceptacles have microsporangia and megasporangia

                                                d)            Meiosis forms haploid microgameteophyte and megagametophyte - these gametophytes are distinct haploid "plants"

                                                e)             They divide some more, reproduce, and release fertilized eggs