Multicellular algae - are organisms with complex and varied life cycles (figure 97). The lower multicellular Thallophyta plants, which lack the vasc

Life cycle of algae

Multicellular algae — are organisms with complex and varied life cycles (figure 97). The lower multicellular Thallophyta plants, which lack the vascular system — is one of the most difficult groups of multicellular organisms to classify. They belong to two subkingdoms and 11 departments. Not by chance they have the most different life cycles.

In multicellular green algae life cycle can be simple or complex, but usually a combination of these two types. What does it mean? Simple life cycle takes place with the participation of asexual reproduction and haploid organization of the thallus cells (so-called body of multicellular algae and fungi), when in individual cells haploid spores form, directly from which haploid multicellular organisms germinate. The complex life cycle is associated with the alternation of asexual and sexual reproduction, diploid and haploid phases. In the latter case, form spores that do not differ externally, having only two flagella. They copulate, forming a diploid zygote, in which by meiosis haploid spores are formed, giving rise to new thalli.

However, in some cases the situation may be more complex, as not only an alternation of generations occurs, but also a change of life cycles type. For example, in the spring takes place only asexual reproduction, and in summer the cycle of asexual reproduction alternates with sexual. Taken from http://worldofschool.org

Diagram 97. The life cycle of green algae Ulothrix: A — sexual reproduction; B — asexual reproduction; 1 — haploid multicellular organism with a filamentous body; 2 — the formation of gametes; 3 — exit of gametes to the outside; 4 — copulation; 5 — a zygote; 6 — the beginning of the development of a multicellular organism from the spore, which was formed as a result of meiotic divisions; 7 — the formation of spores; 8 — exit of spores to the outside; 9 — spores with four flagella

In brown algae may also occur the alternation of haploid and diploid development phases. However, in many species of brown algae is observed, as in most animals, a simple life cycle with sexual reproduction. Thallus of brown algae, unlike in green consists of diploid cells. On it are formed male and female reproductive organs where ova and sperm are formed. Copulation of gametes occurs in the aquatic environment and new algae develop from the resulting zygotes.

Categories:
Questions:
  • The life cycle of what algae — green or brown — is very similar to the life cycle of most animals?