The protozoa are one-celled animals and the smallest of all animals. Most of them can only be seen under a microscope. They do breathe, move, and reproduce like multicelled animals. They live in water or at least where it is damp. Animals in this group include the paramecium, the euglena and the ameba.
Some protozoans are harmful to man as they can cause serious diseases. Others are helpful because they eat harmful bacteria and are food for fish and other animals.
Below is a link to a description of three types of protozoa.
A protozoa has no inner or outer skeleton. They move a variety of ways. The ameba has a false foot that extends as it moves. The paramecium is covered with hairs and the euglena has a whip-like tail to move.
Digestion A protozoa takes in food via the water and stores the food in sacs called vacuoles. They eat tiny algae and bacteria.
Nervous A protozoa has a very low level reaction to the world around it and does not have a brain per se. They can react to light and temperature changes.
Circulation A protozoa has water flow in through the pores. The water contains the food and oxygen the protozoa needs.
Respiration A protozoa takes in oxygen through the cell membrane and gives off carbon dioxide through the cell membrane.
Reproduction A protozoa reproduces by splitting in half. This is called fission.
Excretion A protozoa has sacs called vacuoles that take in and get rid of water.
Symmetry A protozoa is usually asymmetrical.
Coloration A protozoa is very microscopic and is pale in color generally.
The effect of rumen protozoa on the urinary excretion of purine derivatives in goats
Urinary purine derivative (PD) excretion was estimated to examine the effect of rumen protozoa on total PD excretion in goats fed hay and a concentrate diet. The effect of increasing protozoa number in the rumen on nitrogen (N) balance and urinary PD excretion was determined after inoculation. Protozoa increased slowly until 4 days after inoculation, and on the 5th day after inoculation rapidly, finally (10 days) reaching 4·1×105/ml of rumen contents similar to that before defaunation. Urinary N excretion showed a small (non-significant) decrease. Urinary PD excretion did not change until the 7th day, and then the level decreased on the 8th day after faunation presumably due to the effect of increased protozoa in the rumen. The mean urinary total PD excretion significantly (P<0·05) decreased in the defaunated group compared with that in the faunated group. Comparable changes were not seen in plasma PD level of faunated and defaunated groups.
The degree to which natural levels of UV exposure are deleterious to protists is species-specific and varies substantially - even between closely related species. The freshwater heterotrophic flagellate, Bodo saltans, and two marine flagellates, Paraphysomonas bandaiensis and P. imperforata, had reduced motility and feeding when exposed to UV-A radiation (Ochs 1997; Sommaruga et al. 1996). B. saltans and B. caudatus also accumulated greater DNA damage after exposure to UV-B than did chrysomonad or cryptomonad flagellates (Sommaruga and Buma 2000). The ciliate Stentor coerulus was sensitive to UV-B exposure (Häder and Häder 1991), but S. araucanus showed no difference in the proportion of survivors when treatments were shielded from UVR (Modenutti et al. 1998). During in situ incubations of arctic ciliate populations, UV-B had strong negative effects on Askinasia sp. and Bursaridium sp., moderate negative effects on Halteria sp. and Strombidium sp., and no apparent effect on Urotricha sp. (Wickham and Carstens 1998). Our research on the protozoa isolated from the UV-transparent Lake Giles - ciliates Cyclidium sp. and Glaucoma sp., and the heterotrophic flagellate Paraphysomonas vestita - also indicate a wide range of sensitivities to UV-B exposure