Lesson Plan - Get It!
If you went to a creek or stream and grabbed a handful of dead leaves from the water’s edge and looked at them under a microscope, what would you see?
In this lesson, you will learn about two of the four main groups of protozoans in the Protista Kingdom.
Protozoans are animal-like protists that are unicellular heterotrophs. Do you recall how unicellular heterotrophs get nutrition? In the previous Related Lesson in this Kingdom Protista series, found in the right-hand sidebar, you learned that heterotrophs are organisms that cannot make their own food and must get their nutrition from an outside source.
Protozoans feed on dead organic matter, like the dead leaves you may find at edge of a pond or stream. They are a very diverse group and are classified in two manners. They are classified by the way they move and whether they are parasitic.
If you would like to see a chart of all the phylum in the Protista kingdom, check out the website, Protists, on Mr. Hitt's Science Class webpage.
Protozoans can move in many different ways. Some move in the same manner as bacteria with cilia or flagella, while others send out cytoplasm containing membranes called pseudopodia to move and eat. In the picture above, there is an example of an amoeba (far left) that moves with pseudopodia. The protozoan in the center is an example of a flagellate, which uses a flagellum to move. Third, the protozoan on the right is an example of a ciliate that uses hair-like cilia to move. Check out this fascinating video on Movement in Protozoa from KCSE ONLINE to see the three ways they move (NOTE: The video is silent):
Amoebas are hundreds of species of shapeless protozoans that belong to the phylum Rhizopoda. They move and eat with pseudopodia that they form and have no cell wall. As an amoeba approaches its food, it forms pseudopodia around it, which create a food vacuole. A vacuole is a membrane-bound storage sac or bubble-like structure. Digestive enzymes break down the food, and the nutrients are absorbed into the cytoplasm.
Amoebas like moist environments and are found in salt water, fresh water, moist soil, and even among wet patches of moss. They are able to absorb the nutrients directly from water through their cell membranes.
Amoebas reproduce by asexual reproduction. A single parent produces an offspring by dividing into two new cells.
The phylum Ciliophora has about 8000 members, known as ciliates. They move about using the tiny little hairs called "cilia" that surround the cell. They feed mainly on bacteria that is swept into their oral groove that is also lined with cilia. The food vacuoles break down the food, which is then absorbed into the cytoplasm.
Ciliates can live in every kind of aquatic habitat, including lakes, rivers, oceans, and even sulfuric springs. The contractile vacuole pumps out excess water that constantly enters the cell because they live in aquatic environments.
Ciliates reproduce by asexual reproduction. A single parent produces an offspring by dividing into two new cells.
Flagellates belong to the phylum Zoomastigina, and they move using one or more flagella. As they whip their flagella side to side, flagellated protists are able to move throughout their environment. Some flagellates have chloroplasts, organelles that photosynthesize light, like the euglena in the picture below. They are able to produce their own food through photosynthesis like plants. However, euglenas have been found with and without chloroplast.
Some flagellates are parasites that cause diseases like the African sleeping sickness in humans, while others are very helpful. The flagellates that live in the guts of termites help digest food by converting the cellulose in the wood into carbohydrates.
Flagellates reproduce by asexual reproduction. A single parent produces an offspring by dividing into two new cells.
Protozoans make up a very diverse group of organisms. All of those above are unicellular heterotrophs, meaning they cannot produce their own food. The euglena genus is an autotroph and can produce its own food if chloroplast is present. The amoebas, ciliates, and flagellates are grouped together because of the way they move.
Discuss with a parent or teacher the three different ways the protozoans you just learned about move, and the environments they are found in.
In the Got It? section, you will be drawing a model of each type of protozoan you just learned about, and will make a presentation to your teacher or parent.