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Reproduction of Algae

1. Asexual Reproduction
One individual can produce copies of itself

  • Cellular bisection: many unicellular algae, longitudinal or trans-verse cell division
  • Zoospores / Aplanospores: Zoospores are flagellated reproductive cells from which a new individual/colony can grow; sometimes the spores begin to develop within the mother cell and lack flagella: aplanospores; aplanospores can develop into zoospores
  • Autospores: Nonmotile spores that cannot develop into zoospores
  • Autocolony formation: In coenobia, each cell goes through several divisions to form a mini-colony
  • Fragmentation: colonies or filaments break into two to several pieces that continue to grow
  • Akinetes: Enlarged vegetative cell with thick wall and storage products; survival of harsh conditions rather than additional copies

2. Sexual Reproduction
  • Plasmogamy, the fusion of haploid cells (gametes), preceeds karyogamie (nuclear fusion) to form a diploid zygote
    • Gametes look like vegetative cells or very different
    • Isogamy: both gametes look identical
    • Anisogamy: male and female gametes differ morphologically
    • Oogamy: One gamete is motile (male), one is nonmotile (female)
    • Monecious: both gametes produced by the same individual
    • Diecious: male and female gametes are produced by different individuals
    • Homothallic: gametes from one individual can fuse (self-fertile)
    • Heterothallic gametes from one individual cannot fuse (self-sterile)
    • Three different types of life cycle, depending on when miosis occurs, the type of cells produced, and if there is more than one free-living stage present in the life-cycle
    • Life-cycle I: major part of life-cycle (vegetative phase) in haploid state, with meiosis upon germination of the zygote (zygotic meiosis) 

    • also referred to as haplontic life cycle, a single, predominant haploid phase

    • Life-cycle II: vegetative phase is diploid, with meiosis upon formation of gametes (gametic meiosis)

    • also referred to as diplontic life cycle, a single, predominant diploid phase

    • Life-cycle III: three multicellular phases, the gametophyte and one or more sporophyte(s)

    • Gametophyte: typically haploid, produces gametes by mitosis
      Sporophyte: typically diploid, produces spores by meiosis
      Isomorphic: sporophyte and gametophyte look alike
      Heteromorphic: sporo- and gametophyte look different