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Algae Aquatic photosynthetic eukaryotic organisms.
Kingdom Protista

Cell structure: Eukaryotic.

Categories: Algae are grouped into seven categories.

Phototrophic: uses energy from sunlight to synthesize organic compounds for nutrition.

Pigments: Chlorophyll a, Chlorophyll b, Chlorophyll c, Carotenoids(β-carotene), Phycobilins and other accessory pigments that absorb light of different wavelengths.


Asexual reproduction: some employ mitosis, while others undergo fragmentation of cells from colonies or from multicellular aggregates or by produce spores that develop into mature organisms.

Sexual reproduction: involves meiosis, they produce haploid gametes that combine to form diploid zygotes, a process that results in greater genetic variation.

Important Algae types

Golden algae: contains Chlorophyll c and carotenoid called fucoxanthin that give them a yellowish brown color.

Fire algae: consists of the dinoflagellates, unicellular algae that also possess chlorophyll c. This algae have capability to produce oil droplets, but also store energy as starch. Dinoflagellates are known for their tendency to form algal blooms.

Yellow green Algae(Xanthophyta): They are unicellular and contain chlorophyll c.

Red algae: Phycobilins a form of photosynthetic pigments can capture green and blue light that penetrates deep into the water, allowing the red algae to survive at greater depths than other algae.  Some red algae have cell walls made of calcium carbonate and play a role in building coral reefs.

Brown and red algae together constitute seaweed. Some brown algae can reach up to 100 feet in length.

Niche Aquatic system: Plays the prominent role as primary producers.
Ecological Significance

Ecosystem: They produce most of the planet’s oxygen.

Human food chain: Major source of iodine and protein for many human societies.


Sudden increase in nutrients leads to overgrowth of algae in waterbodies(eutrophication) and disturbs the food webs.

Increased decomposition of algae results in overconsumption of  oxygen in the waterbodies, resulting in the death of

other microorganisms in the ecosystem and increase in BOD.

Red tide: A phenomenon of discoloration of seawater caused by a bloom of toxic red dinoflagellates calledGymnodinium breve. During the spring and fall, the waters of the shores of the Pacific, Gulf Coast, and New England states churn, carrying an abundance of nutrients to the surface. These conditions allow Gymnodinium breve to thrive, giving the water a reddish appearance. The algae secrete products that are toxic to fish and other marine organisms and that concentrate in shellfish. Though the toxin is harmless to shellfish, it can be harmful to humans who ingest it, causing neuromuscular problems such as numbness.

Economic significance
Algae Benefits
Gelidium and Gracilaria Important sources of agar, a substance that microbiologists use to thicken culture media and also to produce the gelatin capsules that contain drugs or vitamins.
Purple seaweed Produces Carrageen, a substance used in food production, cosmetics, and pharmaceutical industries.
Red and Brown algae

Used as food source.

Kelps(brown algae) - a good source of Iodine. Also produces algin, a gelling agent used in many foods such as ice cream and in substances such as toothpaste. Seaweeds also contain many vitamins and minerals.

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