Algaearea varied categoryof all non-plant photosyntheticorganisms.
Algaeplaya significant roleinmarine,freshwater and terrestrial ecosystems.
Seaweedsareenormoustypesof marinealgae.Phycologyisthestudyof algae.
Algae are classified as unicellular, colonial, or multicellular. Some algae, such as diatoms, are extremely tiny.
Other algae, such as kelp, can grow to be the size of trees. Some algae, known as phytoplankton, float in the water. Other algae, known as epiphytic or benthic algae, attach themselves to rocks, docks, plants, and other solid things.
Classification
Green algae, diatoms, red algae, brown algae, and dinoflagellates are the five primary groups of eukaryotic
algae. They areclassified as protozoa. Cyanobacteria areanother typeof blue-green algae. Someauthors do not regard blue-greenalgaeasreal algaesincetheyareprokaryotesrather thaneukaryotes.
Green algae. Green algae are the most closely linked to plants. They have the same colors as plants (chlorophyll a, b, and carotenoids), the same molecules in their cell walls (cellulose), and the same storage product (starch).
Green algae can be unicellular or produce filaments nets, sheets, spheres, or intricate mosslike formations.
There are both freshwater and marine species. Some green algae species dwell on snow, among lichens, or alongsideother algae.
GreenAlgae Green algae are the most closely related to plants. They have the same colors (chlorophyll a, b, and carotenoids), cell wall components (cellulose), and storage product (starch) as plants. Green algae can be unicellular or multicellular,including filaments,nets,sheets,spheres,or complexmosslikeformations.
There are freshwater and saltwater species. Some green algae species live on snow, as lichens, or in symbiotic relationships with sponges or other aquatic creatures. Chlorella and sea lettuce are examples of edible green algae.Thereareat least 17,000different typesof greenalgae.
Diatoms
Diatomsarefrequentlyrecognized asthemost attractivealgae.
Each diatomhas a glass cell wall with a species-specific pattern of dots and lines carved into it. The patterns ondiatomcell wallsaresoaccuratethat theyhavebeenused totest theopticsof newmicroscopesfor years.
Diatoms are also the most numerous algae in the open ocean, accounting for almost one-quarter of all oxygen gas generated on Earth each year. In the spring, diatom populations commonly bloom in lakes, providing a significant food sourcefor zooplankton and constituting thebaseof theaquaticfood chain. There areabout a hundred thousand diatomspecies.
RedAlgae
Many edible and commercially significant species of red algae, such as nori and laver, are virtually entirely marine. Carageenan and agar, which are utilized as food thickeners and stabilizers, are similarly derived from red algae.Themajorityof red algaearebig,sophisticated seaweeds. Therearebetween4,000and 6,000species.
BrownAlgae
Brown algae, which comprise the biggest and most complex seaweeds, are virtually entirely marine. Kelp for example, may grow to be more than 60 meters (200 feet) tall and can create dense underwater forests off the coast of California. Rockweed and Sargassum, after which the Sargasso Sea is named, are two more major brownalgae.Therearearound 1500speciesof brownalgae.
Dinoflagellates
Dinoflagellates are unicellular algae with cellulose armor and flagella that spin as they swim. Dinoflagellates live in both freshwater and saltwater habitats. When disturbed, certain dinoflagellate species create an unusual bluelight knownasbioluminescence.
Other dinoflagellates are poisonous and are to blame for red tides and shellfish poisoning epidemics. Dinoflagellatesrangeinnumber from2,000to4,000species.
Life Cycles
The life cycles of algae are highly diverse. Some algae members exhibit practically any form of life cycle that can be imagined. Individuals reproduce in an asexua life cycle by separating. The asexual division is the primary modeof reproduction for certain dinoflagellates. Threeforms of sexual lifecycles requirethefusing of gametesat somepoint:gameticmeiosis,zygoticmeiosis,and sporadicmeiosis.
GameticMeiosis
Meiosis creates the gametes in the gametic meiosis life cycle (used by humans); hence, the gametes are the only haploid cells in the life cycle. The person seen is made up of diploid cells. Gametic meiosis occurs in diatoms.
ZygoticMeiosis
The zygote undergoes meiosis during zygotic meiosis making it the sole diploid cell. The organism's other cells areall haploid.Manygreenalgae,including sea lettuce,gothroughzygoticmeiosis.
SporadicMeiosis
Within the life cycle of sporadic meiosis, there exist both haploid and diploid individuals. Meiosis generates haploid spores, which split to form a person composed completely of haploid cells. Mitosis is the process throughwhichthisindividual generatesgametes.Adiploid zygoteisformed whentwogametescombine.
The zygote splits into an individual composed completely of diploid cells. To finish the cycle, this person generatessporesvia meiosis. Thelifecycleisreferred toasthe"alternationof generations" becauseit contains two generations of humans, a haploid generation and a diploid generation. Sonicmeiosis occurs in plants and manygreen,red,and brownalgae.
The manufacturing of nori is a billion-dollar-a-year industry in Japan, Korea, and China, but because the two generations in the nori life cycle look radically different, the second generation was not identified until the earlytwentieth century. Thisfinding significantlyenhanced humans' capacityto cultivatenori, and a memorial park inJapanhonorstheBritishscientist whofound it,KathleenDrewBaker.
EconomicandEcologicalImportance
Algae are the foundation of the aquatic food chain. Many forms of algae are also consumed by humans. For almost two thousand years, the sea algae nori and kelp have been collected in China. Spirulina, a blue-green algaehighinproteinand vitaminB,isgathered inAfrica'sLakeChad.
Algae photosynthesis is critical to the biosphere because it decreases the quantity of carbon dioxide in the atmospherewhileincreasing theamount of oxygen.
Some algae can cause environmental issues, including red tides and fishy-tasting water. These issues are typically caused by excessive nitrogen discharge from agriculture, sewage, and other human activities. Overflowing sewage lagoons, for example, have been connected to an epidemic of the nerve-toxin-producing Pfiesteria (a dinoflagellate)ontheAtlanticcoast Responsive
