Algae, Diatoms, Agar, and Protozoa: Comprehensive Study Notes

Algae

Photosynthetic organisms related to cyanobacteria and modern terrestrial plants, characterized by cellulose in their cell walls.

Cellulose

A shared feature linking algae to plants, found in their cell walls.

Agar

A polysaccharide derived from red seaweed, used to solidify microbiological media (petri dishes, solid tubes). Dissolves at about 90^{\circ}C and solidifies at about 40^{\circ}C.

Carrageenan and Alginate

Common seaweed-derived thickeners used in foods and other industries; alginates are also used in medicine.

Spirulina

Technically a cyanobacterium (not a true alga) marketed as a 'superfood' due to its essential amino acids and vitamins.

Diatomaceous Earth (DE)

A very fine, abrasive white powder formed from the silica remains (silicaceous frustules) of dead diatoms. Used as an abrasive, filtering agent, and pest control.

Global Oxygen Production

Approximately 70\% of atmospheric oxygen comes from algae and cyanobacteria; terrestrial plants contribute roughly 30\%.

Eutrophication

Excessive algal growth on the water surface caused by abundant nutrients (nitrogen and phosphorus), leading to light limitation, decomposition, and oxygen depletion in aquatic systems.

Red Tide

Algal blooms often caused by dinoflagellates, which can tint the water red and produce toxins that concentrate in shellfish, leading to shellfish poisoning.

Amnesic Shellfish Poisoning (ASP) and Paralytic Shellfish Poisoning (PSP)

Illnesses caused by consuming shellfish that have filtered toxins from certain algal blooms, with toxins being somewhat resistant to heating.

Algal Biofuel

A potential energy source from algae that accumulate high lipid content (up to about 50\% of dry weight), which can be extracted for biodiesel, with remaining biomass used as animal feed.

Protozoa

Predominantly unicellular, non-photosynthetic heterotrophic organisms belonging to the kingdom Protista, lacking cell walls and often classified by motility.

Trophozoite

The active, feeding form of protozoa that exists in favorable conditions.

Cyst

A resting, often non-metabolic or low-metabolic form of protozoa that can survive harsh environmental conditions and enables transmission.

Apicomplexa (Sporozoa)

A group of non-motile intracellular parasitic protozoa with complex life cycles, often requiring more than one host (e.g., Plasmodium spp. causing malaria).

Plasmodium spp.

Apicomplexan protozoa that cause malaria, transmitted by Anopheles mosquitoes.

Toxoplasma gondii

An apicomplexan protozoan with cats as the main reservoir; can pose fetal risk to pregnant women and is tested for in the TORCH panel.

Cryptosporidium

An apicomplexan protozoan whose cysts are highly resistant to chlorination, making it a major waterborne disease concern, especially for immunocompromised individuals.

Mastigophora (Flagellates)

Protozoa that move using one or more flagella (e.g., Giardia lamblia, Trypanosoma spp., Leishmania spp., Trichomonas vaginalis).

Giardia lamblia

A flagellated parasite that causes giardiasis ('Giardia diarrhea'), commonly associated with contaminated water.

Trypanosoma spp.

Flagellate protozoa that cause African sleeping sickness (e.g., T. gambiense) and Chagas disease (T. cruzi).

Leishmania spp.

Flagellate protozoa that cause cutaneous and visceral leishmaniasis, transmitted by sandflies.

Sarcodina (Amoeboids)

Protozoa that move via pseudopods (false feet), typically bottom-dwelling in moist environments (e.g., Entamoeba histolytica, Naegleria fowleri).

Entamoeba histolytica

An amoeboid protozoan that causes amoebic dysentery, a common intestinal parasite.

Naegleria fowleri

The 'brain-eating amoeba' that causes primary amoebic meningitis (PAM), often fatal and associated with nasal exposure to warm freshwater.

Acanthamoeba spp.

Amoeboid protozoa that can cause encephalitis and keratitis, associated with contact lens use and contaminated water.

Ciliophora (Ciliates)

Protozoa characterized by numerous cilia used for locomotion and feeding (e.g., Balantidium coli).

Balantidium coli

A ciliate protozoan and the only known ciliate that commonly infects humans, primarily associated with pigs (zoonotic parasite).

Bacterial Diarrhea vs. Protozoal Diarrhea

Bacterial diarrhea from contaminated water typically begins within about 1 day, while protozoal diarrhea (e.g., Giardia) often presents later (2–4 days) and can be more severe or prolonged.