Life History Chapter 6

Reproduction Complex in seaweeds Asexual or vegetative reproduction is common Fragments of thallus can often grow into new individuals Some seaweeds produce spores – Cells specialized for dispersing to new locations or persisting through unfavorable conditions Some have flagella and are known as zoospores

Sexual Reproduction Not common in unicellular marine algae Fusion of gametes Red algae male gametes lack flagella – They may be released in strands of slime Male and female gametes may be formed in the same thallus – Fusing gametes will be from separate thalli

Spores Seaweed cells divide by mitosis Seaweeds also produce haploid spores or gametes by meiosis 4 Types of life histories

Alternation of Generations Most common type among all three groups of seaweeds 2 types of thalli – 1) diploid (2N) sporophyte generation through meiosis produces gametes (1N) – haploid spores – 2) haploid (1N) gametophyte generation and produces haploid gametes Some species- separate male and female thalli Some species- both types of gametes are produces by every thallus

Alternation of Generations A life history with two generations, a sporophyte and gametophyte In some algae the sporophyte and gametophyte are structurally identical In some algae the large plant (sporophyte generation) is what we see and the gametophyte generation is barely visible.

Alternation of (3) generation Unique to red algae A bit more complex – A third generation A diploid carposporophyte results from the fusion of gametes – Carpospores- diploid spores produced by the carposporophyte and develop into sporophytes

No alternation of generations Similar to that of animals 1 thallus and it is diploid (2N) Thallus produces haploid (1N) gametes by meiosis After fertilization the zygote develops into a new thallus (2N) This reproduction method is observed in some brown and some green algae

Haploid dominant Occurs in some green algae Dominant thallus is haploid and produces haploid gametes Dipolid zygote forms from fusion of gametes In the zygote meiosis takes place and results in haploid spores Each spore develops into haploid individual

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