Protojoa

\( \newcommand\) • • • • • • Animal-Like Protists: Protozoa Animal-like protists are commonly called protozoa (singular, protozoan). Most protozoa consist of a single cell. They are animal-like because they are heterotrophs, and are capable of moving. Although protozoa are not animals, they are thought to be the ancestors of animals. Ecology of Protozoa Protozoa generally feed by engulfing and digesting other organisms. As consumers, they have various roles in food chains and webs. Some are predators. They prey upon other single-celled organisms, such as bacteria. In fact, protozoa predators keep many bacterial populations under control. Other protozoa are herbivores. They graze on algae. Still others are decomposers. They consume dead organic matter. There are also parasitic protozoa that live in or on living hosts. For example, the protozoan that causes malaria lives inside a human host. Protozoa are also important food sources for many larger organisms, including insectsand worms.

The taxonomic kingdom Protista is a collection of single-celled organisms that do not fit into any other category. Protists are a group made up of protozoa, unicellular algae, and slime molds. We will concentrate on the animal portion of this group: the protozoa (proto = first, zoa = animals). Protozoa are the oldest known group of heterotrophic life that consume and transform complex food particles into energy. Although protozoans are only made up of a single cell, these organisms manage to perform all the basic tasks of life. The protozoa are divided into four major groups: the ciliates, the flagellates, the heliozoans, and the amoebas. Ciliates:Ciliophora Structure in this group is fairly diverse, but almost all species retain a few basic characters that help to identify them as ciliates. The first character is the presence of cilia on at least one developmental stage of the organism. Modifications from the full body covered norm include a single ring of cilia, grouped ciliary organelles called cirri, and restriction of cilia to feeding tentacles. Most species also bear toxicysts that are most likely used to capture and stun prey. These toxicysts can be found around the mouth, along the length of tentacles or anywhere else on the surface of the cell body. Amoebas:Sarcodina Amoebas can reach a maximum size of 2 mm in diameter. These protozoans are constantly changing shape; they look and move much like balloons half filled with water. When manipulating a water balloon yo...

The term protozoa implies ‘first animals’. As the primary hunters of the microbial world, protozoa help in continuing the equilibrium of bacterial, algal and other microbial life forms. Protozoa also means ‘little animal’. They are named so because many species act like small animals. They search for and collect other microbes as food. Previously, protozoa were specified as unicellular protists possessing animal-like characteristics such as the capability to move in water. Protists are a class of eukaryotic microorganisms which are a part of the kingdom Protista. The term ‘protozoan’ has become debatable. Modern science has shown that protozoans refer to a very complex group of organisms that do not form a clade or monophylum. This has led scientists to give up the term protozoa. Hence, the sub-kingdom Protozoa is not used today. Currently, protozoa are defined as single-celled, heterotrophic, or colonial eukaryotes possessing non-filamentous structures. Characteristics of Protozoa Protozoa do not have a cell wall and therefore can have a variety of shapes. Nevertheless, some of the protozoans have a pliant layer, a pellicle, or a stiff shell outside the cell membrane. Protozoa vary in size and shape. Their sizes range from 10 to 55 micrometers, but they can be as large as 1 mm. The largest protozoa are called xenophyophores, which can measure up to 20 centimeters in diameter. Protozoa prefer living in moist and aquatic habitats. Their cysts can be found in the bleakest pa...

amoeba, also spelled ameba, plural amoebas or amoebae, any of the microscopic unicellular protozoans of the rhizopodan order Amoebida. The well-known type species, Amoeba proteus, is found on Entamoeba histolytica causes amebic dysentery. Two related free-living genera of increasing biomedical importance are Acanthamoeba and Naegleria, strains of which have been recognized as disease-causing parasites in several vertebrates, including humans. Amoebas are identified by their ability to form temporary cytoplasmic extensions called