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Characteristics of Protozoa
Protozoa are single-celled eukaryotic organisms. These microscopic organisms measure 10 to 52 micrometers but can grow as large as 1 mm. They can move using their specialized appendages such as cilia and flagella. They feed on organic matter and other microorganisms through phagocytosis. There are also protozoans that produce their own food (autotrophs) through the process of photosynthesis. They reproduce via binary fission or multiple fission.
There are over 30,000 different species of protozoa documented by scientists; this makes protozoa one of the most diverse organisms in the planet. Protozoans are found in almost any place in the biosphere. They can be found in oceans, lakes, rivers, glaciers, ponds, hot springs, and terrestrial environments. They can survive harsh conditions (extreme heat or cold) by transforming into dormant cysts.
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Types of Protozoa
Protozoa are classified according to the type of cellular appendage they use for locomotion. Ciliates are protozoans that use cilia (thread-like projections) for movement. Amoeboids are protozoans that create temporary projections called pseudopodia (false feet) to move. Protozoans that use flagellum (long thin tapering outgrowths of the cell) for motility are called flagellates. Lastly, sporozoans are non-motile protozoans that reproduce through spores. Other than movement, protozoans have some animal-like characteristics that intrigue evolutionary biologists. Modern biologists are studying the role of protozoa in animal evolution. They are also studying the ecological importance of protozoa. Below are some of the important roles played by protozoa in the environment.
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Ecological Importance of Protozoans
The major ecological importance of protozoa is its role in food chain.Many aquatic animals feed on protozoa. For example, giant whales screen seawater to get tons of protozoa for food. Many fishes and invertebrates rely on protozoa as major sources of protein.
Protozoa help control the population of bacteria as well as other protozoans by feeding on them. Controlling the population of other organisms is important in maintaining ecological balance and diversity.
Like bacteria, aquatic and terrestrial protozoa hasten the decomposition of the remains of dead plants and animals. Decomposition is a very important ecological process because important nutrients and minerals are returned back into the environment. Protozoa feed on organic matter released by decaying plants and animals.
Many species of protozoa are in mutual relationship with other animals. For example, zooxanthellae are photosynthetic flagellate protozoa and intracellular symbionts of corals. Zooxanthellae provide corals with a continuous supply of carbohydrates produced during photosynthesis. Ninety percent of coral’s energy requirement is provided by zooxanthellae. In exchange for carbohydrates, corals provide zooxanthellae home and protection.
Protozoa are ecologically important organisms in carbon cycling. The ocean is the largest sink for atmospheric carbon dioxide – the major greenhouse gas. Photosynthetic protozoa absorb carbon dioxide for photosynthesis. Carbon dioxide is the major raw material in the production of carbohydrate during photosynthesis. By recycling carbon dioxide, protozoa contribute in the mitigation of global warming.
Protozoa can also be used as bioindicators. Biological indicators are organisms used to monitor the health and integrity of an environment. The presence or absence of a specific protozoon in an environment (e.g. river) can indicate either ecological integrity or disturbance (e.g. pollution). Protozoans sampled from a particular environment can be analyzed for the presence of toxic substances. Protozoans are good in accumulating environmental toxins. In addition, the cellular structures of the sampled protozoans can also be studied for any damage or abnormality caused by pollution.
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- Sigee, David C. Freshwater Microbiology. University of Manchester.
- Image Source: http://upload.wikimedia.org/wikipedia/commons/6/6e/Oxytricha_trifallax.jpg