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What are protozoans?
Protozoans are single-celled (unicellular) eukaryotes (cell has nucleus) so small that they can only be viewed with the aid of a microscope. They are found in almost all bodies of water and in damp places. They live freely in the environment or as parasites to various animal hosts. These animal-like organisms are able to move using their specialized appendages like flagella and cilia. Some protozoans behave like plants by undergoing the process of photosynthesis or the conversion of light energy into carbohydrates. Protozoans are ecologically important organisms by acting as decomposers in the food web. They are also important medically by acting as pathogen in various animal and human diseases.
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Why students should see protozoans under a microscope?
Protozoans are ecologically and medically important organisms that students should have knowledge of. Students may not be aware that these tiny organisms exist because they are not visible to their naked eye. They may have read something about protozoans in books, magazines, T.V. programs, internet articles, or somewhere else but they are not enough to catch the appreciation and interest of students to these organisms. Thus, it would be nice to perform an experiment where students can view moving protozoans under a microscope. Real life experience with the protozoan is a fantastic activity that students will surely enjoy.
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Types of protozoa
There are about 30,000 species of protozoa identified but this figure is growing as scientists are rapidly discovering new species in different regions of the planet. Most of the protozoans in record are classified on the basis of their locomotion. The types of protozoa are the following:
Flagellate: protozoan that uses a long thin cellular appendage called flagellum to move (e.g. Giardia sp.)
Amoeboid: protozoan that uses temporary projections called pseudopodia to move (e.g. Entamoeba histolytica)
Ciliate: protozoan that uses tiny threads (cilia) projecting from its body to move (e.g. Paramecium sp.)
Sporozoa: non-motile protozoan that produce spores (e.g. Plasmodium)
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Before the Experiment
The teacher tells the students to read informative articles on protozoa in the internet or in books. Tell them to familiarize themselves on the basic characteristics (e.g. shapes, motility, morphology, diet, habitat, etc.) of the different types of protozoa. Instruct them to bring pictures of protozoa with labels during the experiment.
The students should know how to use the microscope properly before performing this experiment.
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Materials for the Experiment
- Medium sized bottle
- Pond water
- Dried leaves
- Dropper or pipette
- Microscope slides and cover slips
- Microscope (and knowledge of its use)
- Pencil and coupon bond/ drawing pad
- Pictures of protozoa with labels
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The teacher divides the class into groups. A group of three members is recommended. Each group shall prepare a pond water culture one week before the experiment. To prepare the water culture, fill a medium-sized bottle with pond water. Then add dried leaves to the bottle which will serve as additional food source for the protozoans. Cover the bottle with a thin cloth so that oxygen can enter the culture. Place the pond water culture in a warm area directed with sunlight for a week.
After one week, the protozoans in the pond water culture have already multiplied in number. To start viewing them on the microscope, get small water sample in the culture using a dropper or pipette and then place a drop to a slide. Slowly cover the water drop with the cover slip. Put the slide in the microscope stage for viewing. Focus the protozoans both in low and high power objectives. Observe the shapes and movements of the organisms found in the water sample. Draw the organisms in a coupon bond and try to label their distinguishing structures (e.g. flagellum, cilia). Take note all your observations on the organisms that you have drawn.
Using the pictures of protozoans that you brought in class, try to identify the protozoans that you saw in the microscope. Are there flagellates, amoebas, ciliates, or sporozoans in your slides?
It may be possible that you cannot see any protozoa in your slide; if this happens, view more water drops under the microscope until you spot any protozoa. According to people who have already performed this experiment, protozoans thrive in the bottom of the bottle so try to get your sample there using a long pipette. Moreover, check your microscope if it’s functioning properly because there may be a problem in your microscope that prevents you from seeing the tiny organisms.
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Ecological and Medical Importance of Protozoans: A Follow-up Discussion
The experiment should be followed by a discussion on the ecological and medical significance of protozoans.
Protozoans act as decomposers by feeding on dead plants and animals in the environment. Decomposers like the protozoans are important components of the food chain; their disappearance will cause imbalance of nature.
Protozoans help regulate the population of bacteria in the environment by feeding on them.
Protozoans serve as food of many animals. Fishes, marine mammals (e.g. whales), mollusks, insects, and other animals depend on protozoans for survival.
Protozoans are medically important because they cause various human diseases. For example amebiasis is caused by the flagellate Entamoeba histolytica and malaria is caused by sporozoan Plasmodium falciparum.
Protozoans are agriculturally important because they inflict diseases to poultry and livestock. For example veterinary diseases such as coccidiosis, babesiosis, anaplasmosis, and trypanosmosis are all caused by pathogenic protozoans.