How Do Algae Multiply?

Asexual Reproduction

• Algae reproduce asexually by sporulation and daughter colony formation. Sporulation is the formation of zoospores within the cell walls of strands of algae called filaments. Multitudes of zoospores each form filaments identical to their parents through mitosis. To complete the process, these filaments release their own zoospores. In daughter colony formation, the cells of parent colonies contain daughter colonies until released to form new colonies. The daughter colonies are exact replicates of their parent colonies. Flagella allow them to swim through spinning to go on and form their own colonies.

Sexual Reproduction

• Sexual reproduction in algae occurs in two ways: isogamy and heterogamy. Isogamy produces two identical gametes, one male and one female. The gametes unite to form a zygote. Inside the zygote, zoospores form, are released and form a new colony. Some are mobile, swimming with flagella, and others float through water on currents until finding their host. Heterogamy produces two different gametes, male and female. The male is small and mobile while the female is large and immobile. The zoosporangium, not the zygote, produces zoospores, which go on to form a new colony.

Alternation of Generations

• Algae alternate between sexual and asexual reproduction. In order for algae to enter its sporophyte phase, they must start in their gametophyte phase. Meiosis produces the haploid spores, which then spawn gametes during mitosis. These gametes become diploid sporophytes, then form a zygote -- and the cycle repeats. The majority of other plants also rely on the alternation of generations for reproduction.

Algae Colonies

• The ability for algae to form colonies was a major evolutionary change, occurring approximately 1 billion years ago. Individual cells, when grouped, specialized in one task such as swimming. Others do nothing but reproduce. They can not do this on their own because they have to perform all the functions. With their grouping, they increased in size as well and were more difficult to eat, being larger than any protozoan. Blue-green bacteria is sometimes mistaken for algae due to its similar appearance and ability to photosynthesize. It does however, with algae, comprise 90 percent of all cells using sunlight today.