PROTOZOA

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.

Amoeba Moving With Its False Feet (Pseudopodia) System TypeProtozoas SystemMuscular- SkeletalA 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. DigestionA protozoa takes in food via the water and stores the food in sacs called vacuoles. They eat tiny algae and bacteria. NervousA 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.CirculationA protozoa has water flow in through the pores. The water contains the food and oxygen the protozoa needs.RespirationA protozoa takes in oxygen through the cell membrane and gives off carbon dioxide through the cell membrane. ReproductionA protozoa reproduces by splitting in half. This is called fission.ExcretionA protozoa has sacs called vacuoles that take in and get rid of water. SymmetryA protozoa is usually asymmetrical.ColorationA protozoa is very microscopic and is pale in color generally.

System TypeProtoz oas SystemMuscular- Skeletal 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.

The ameba is one of the simplest of the protozoa. It can be found in ponds and rivers and on the surface of the leaves of water plants. It looks like a grayish blob under a microscope. Its shape is constantly changing as it moves along. One characteristic of the ameba is its false feet, that scientists call pseudopodia. The false feet extend out and then the rest of the body follows the false feet along. The ameba eats little animals and plants. It sends out its false feet to surround the plant or animal and then pops it right into the cell! The ameba has tiny sacs in its body called vacuoles. Some of the vacuoles have food in them. Others collect water and squeeze the extra water out.

Oxygen enters the ameba through its thin covering called a cell membrane. The carbon dioxide leaves the ameba through the cell membrane as well. The ameba avoids light but swims faster in warmer temperatures. The ameba reproduces by splitting in half. This is called fission. The ameba's nucleus or center splits in half and goes to opposite ends of the cell. Then the cell narrows and splits in half.

If paramecium encounters an obstacle, it reverses the ciliary beat and moves back. It then changes direction slightly and moves forward. It will do this repeatedly until it gets past the obstruction. This reaction also shows that paramecium is sensitive to stimuli (in this case, the stimulus of touch).

Paramecium Reproduction Paramecium reproduces, like amoeba, by binary fission. The ciliate stops moving and both mega- and micronucleus divide and move to opposite ends of the organism. The cytoplasm then divides at right angles to the long axis and the daughter paramecia separate. Binary fission may take place 2 or 3 times each day.

Paramecium can take in food only at the cytostome. The cilia in the oral groove create a current of water which wafts the food organisms up to the cytostome where they are ingested in a food vacuole. This food vacuole then follows a specific route through the cytoplasm. On its travels, enzymes are secreted into the vacuole and the food is digested. The digested substances are then absorbed into the cytoplasm.

Vorticella has a stalk which attaches it to pondweed or pond debris and which can retract if the protozoan is disturbed. The cilia do not cover the body but are restricted to a double row on the upper margin. The cilia create a feeding current which wafts food particles into the oral groove.