Protozoa are single-celled, animal-like, eukaryotic organisms found in aquatic and terrestrial environments. They are larger than bacteria, measuring 10 micrometers to as large as one millimeter. They also possess more advance characteristics than bacteria: enclosed genetic material; more advance appendages for locomotion (cilia and flagella), and; more advance cellular structures and organelles. Having more than 30,000 different species, protozoa are among the most diverse organisms in the planet. They consume their food via phagocytosis (engulfing and ingesting foreign particles). Protozoa that possess chloroplasts can produce their own food through the process of photosynthesis. Protozoan reproduction involves binary fission or multiple fission. Protozoa are found anywhere, as long as there is water or moisture. They can be found in stagnant water, ponds, rivers, lakes, oceans, and damp soil. Interestingly, protozoa can survive in extreme environments (extreme cold or heat) such as Antarctic water and hot spring. They transform into dormant cysts when they sense harm from their environment or food scarcity.
People’s familiarity with protozoa is not that stronger compared to bacteria. In fact, most people don’t know that protozoa exist. Protozoa are small indeed, but their ecological importance is immense. Let us look at the different ecological roles that protozoa play in the environment.
In aquatic ecosystem, protozoa are important components of the food chain. Food chain is simply the feeding relationships among organisms; it’s a hierarchy of different living things, each of which feeds on the one below.
Protozoa are found at the bottom of the food chain. They are consumed by larger organism such as invertebrates and fishes. Protozoa are good sources of proteins and minerals for aquatic organisms.
Many species of protozoa consume bacteria. In fact, bacteria are main components of protozoan diet. Protozoa control the population of bacteria by feeding on them. Controlling their number is highly important in maintaining ecological stability.
Do you know that protozoa also contribute in the mitigation of global warming? Photosynthetic species of protozoa act like trees. They use carbon dioxide to manufacture carbohydrates during photosynthesis. (Take note that carbon dioxide is a major greenhouse gas that causes global warming.)Photosynthetic protozoa use carbon dioxides dissolved in the ocean – the largest sink for atmospheric carbon dioxide produced by man.
Oxygen molecules released by protozoa during photosynthesis are used by aquatic animals. Adequate dissolved oxygen in aquatic environments is important to the survival of aquatic animals. Oxygen is a basic life necessity; it is needed in respiration or energy production.
Protozoa joins bacteria as major decomposers in the food chain. Decomposers are organisms that break down organic matter from complex to simpler form. Through decomposition, minerals and nutrients are returned back to the environment. Organic matter from decaying plants and animals are used by protozoa as food. Protozoa consume organic matter via phagocytosis.
There are protozoa that live in symbiotic relationship with higher organism. These protozoa provide their host with food. In exchange for food, the host provides protozoa home and protection.
Protozoa can also be used a biological indicators (bioindicators). Bioindicators are organism used to monitor the health of a particular environment (e.g. river). Protozoa can be sampled and analyzed in the laboratory for the presence of toxic substances. Protozoa are good accumulators of toxic compounds such as lead and mercury. When toxic compounds are found in protozoa, it is likely that the environment where the protozoa were sampled is polluted. The sampled protozoa can be further analyzed to detect DNA damages as well as other structural damages.
It is also reported that protozoa can help in wastewater treatment by feeding on bacteria and organic matter found in the wastewater.