Protozoa
5 Minutes
Protozoa classification and amoeba cell structure for students, explaining movement, feeding, and reproduction. An English science lesson.
- Four groups of protozoa based on movement: amoeboid to sporozoans
- Parts of an amoeba including pseudopodia and two types of vacuoles
- How amoebas feed and reproduce through fission and sporulation
What this lesson teaches
Protozoa are single-celled eukaryotic microorganisms belonging to the kingdom Protista that depend on other living things for food. Measuring between 20 and 200 microns in size, these heterotrophs live in water bodies such as lakes and ponds, as well as inside plant and animal tissues, and their study is called protozoology.
Classification based on movement
- Amoeboids move by extending finger-like projections called pseudopodia, or false feet, as seen in amoebas.
- Ciliates are covered with tiny hair-like structures called cilia that propel the cell, as in Paramecium.
- Flagellates move through their surroundings using a thread-like structure called a flagellum.
- Sporozoans are parasites that do not move, and Plasmodium is an example of this group.
Cell structure of an amoeba
An amoeba is protected by an outer cell membrane made of proteins and lipids, which controls the movement of substances into and out of the cell. Its cytoplasm has two distinct parts: a clear, gel-like outer layer called ectoplasm, and an inner region called endoplasm. The endoplasm houses the nucleus, organelles, and two kinds of vacuoles. The food vacuole digests nutrients, while the contractile vacuole expands and contracts to pump water and waste materials out of the cell.
How an amoeba feeds
When an amoeba senses food nearby, it extends its pseudopodia to surround the food particles and pull them inside the cell body. Once inside, the food vacuole breaks down complex materials and supplies the absorbed nutrients to the cytoplasm. Any remaining waste that the amoeba cannot use is forced out of the cell through the contractile vacuole.
Two ways amoebas reproduce
- Fission takes place under favorable conditions, where the nucleus and cell body of a mature amoeba split in two to produce another amoeba.
- Sporulation begins when the membrane surrounding the nucleus breaks open.
- Chromatin spills out into the cell, and new nuclear membranes form around these pieces to create multiple nuclei.
- The parent amoeba bursts open, releasing all of the newly formed nuclei as separate amoebas.