Algae are one of the most diverse species of plant life. They are photosynthetic, like most other plants, but lack most of the structures of terrestrial plant life, such as stalks, leaves and rhizomes. All algae goes through a haploid life cycle of development, starting with a diploidzygote, or spore, and ending up with a fully mature alga plant. There are three main classifications of algae: Rhodophyta, Cholorphyta and Heterokontophyta.
The first step in the development process takes place when the diploid, or immature spore cell, goes through a cellular division process known as meiosis. Before this process, the diploid is actually known as a diploidzygote. Afterward, it’s called a haploid spore.
During meiosis, the single diploidzygote transforms from a single cell into four distinct and separate cells or spores. These haploid cells are now sexually mature and ready to mate. The male and female haploids fuse together to form gametes.
After fusion, the gametes form new diploid cells and the process begins again.
Lifespans differ for each species of algae, with an average life expectancy ranging from a few days to a year or two.
Algae can reproduce in one of two ways, either asexually by mitosis or sexually, with the fusion of the gametes. Asexual reproduction can happen much more quickly, but diversity is limited. Sexual reproduction allows for greater diversity but is considerably slower.
Algae have adapted to live in many different aquatic environments, from freshwater ponds and lakes to oceans. Algae blooms occur when water conditions are hospitable for reproduction, usually as the colder water begins to warm in the late spring and early summer, and where the water is nutrient-rich. Large algae blooms can become hazardous to other aquatic life, such as fish and other plants, by robbing the water of dissolved oxygen and nutrients.
The haploid life cycle is very common in single-celled organisms like algae, either planktonic (free floating) or filamentous (anchored). The process occurs thousands of times a day and is dependent on a number of factors for its success, including water temperature, sunlight availability, nutrient content of the water and water pH. If these conditions are ripe, the algae will thrive. If they are not, the algae cannot reproduce.
Green algae has a special adaptation. Volvox, a species of green algae, produces a zygospore after syngamy, which is a zygote (diploidzygote) that is encrusted in a protective shell that protects it from harsh conditions, making it much hardier and less dependent on perfect aquatic conditions to be successful in reproduction.