Introduction to Microorganisms: Algae, Viruses, Helminthes

Written by:  J.Sace • Edited by: DaniellaNicole
Updated Oct 22, 2009
• Related Guides: Carbon Dioxide | Computer Viruses

Although we cannot see microorganisms with our naked eye, their ecological importance is immense. Life on earth would be difficult without them. In part 1 of this series, we learned about a brief biology of Bacteria, Archaea, and Fungi. Now let us learn about Protozoa, Algae, Viruses, and Helminths


Algae (singular:alga) are eukaryotes with the ability to produce their own food through the process of photosynthesis. There are unicellular (e.g. planktons) and multicellular (e.g. seaweeds) algae found in freshwater (e.g. lakes and rivers), marine (e.g. sea) and terrestrial (e.g. moist pavements) habitats. Unicellular algae are the interests of researchers in the field of microbiology. Algae are similar to terrestrial plants with respect to the “cellulose" composition of their cell walls (Madigan 2006).

Because algae undergo photosynthesis to produce their food, they require carbon dioxide from the environment; therefore they play the role as a global sink of carbon dioxide. The oxygen they release in photosynthesis supplies enough oxygen for fishes and invertebrates. A type of carbohydrate extracted from the cell wall of red algae (Rhodophyta) is the main ingredient of agar. Agar is widely used as a culture media of various bacterial species especially the medically and pathologically important ones. Bacteria sampled from a patient must first be cultured in nutrient agar for study, evaluation, and identification so that doctors will be guided on how they will treat the patient (Madigan 2006).

An example of medically important alga is the dinoflagellate of the Phylum Dinoflagellata. Red tide which is the result of a massive buildup of dinoflagellates in the sea, poses threat to human health. Dinoflagellates produce toxins that are not poisonous to fishes and shellfishes that eat them. However, those toxins are fatal to humans that eat the infected fishes and shellfishes. Poisoning could be “diarrhetic, paralytic, and neurotoxic (Refer to Encarta Yearbook, 1995)."


Viruses differ from other microbial groups discussed in this series because they are “acellular" or “not cellular". They are so tiny that a powerful microscope like electron microscope is needed just to observe and study them. You possibly cannot see them using an ordinary light microscope. The basic structure of a virus is composed of a core, a protein coat, and a lipid membrane envelope (may be absent to others). The viral core is made up of either DNA or RNA but not both. The protein coat surrounds the core for protection. Sometimes the protein coat is surrounded by a lipid membrane called envelop for added protection. Viruses can only reproduce inside the cell of their host organism (either a plant or animal). They utilize the cellular machinery of their host to produce the needed materials or organic molecules to produce their offspring; this makes them great parasites. Viruses are considered to be living when they multiply inside the host cells they infect. They are considered nonliving when they are outside of living hosts (Madigan 2006; Nester 2007).

Popular viruses are the HIV virus, influenza virus, Hepatitis virus, and many more. You could read more about pathogenic viruses on medical books and websites.

Multicellular Animal Parasite

Multicellular animal parasites are actually not microorganisms, technically speaking, but they share similar characteristics to microorganisms. They are small that a microscope (at least) is needed to observe them. Their pathogenesis in the human body has some similarities to other microbes. The most common multicellular animal parasites are the helminthes which involve the flatworms and roundworms (Madigan 2006). These worms could block blood vessels when they grow in number and size causing illness to infected individuals. They can also secrete toxins that damage body tissues and internal organs. They also compete with human in the absorption of nutrients in the small intestine; this results to the malnourishment and vitamin deficiency to the infected individual (Ingraham 2002).


Encarta Yearbook. High Tide for Red Tide. August 1995.

Madigan, Michael. 2006. Brock Biology of Microorganisms. Upper Saddle River, N.J. : Prentice Hall/Pearson Education.

Nester, Eugene. 2007. Microbiology: a human perspective. New York: McGraw-Hill Higher Education

Ingraham, John. 2002. Introduction to Microbiology. Pacific Grove, Calif.: Brooks/Cole Pub.

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