What Are Protists?• A group of one-celled organisms with well

defined nuclei

• All protists live in moist surroundings

• Many protists possess both plant-like and animal-like features

• Animal like protists are called PROTOZOAN

We will take a close look at four protists that are similar in some respects and are also very different in others.

Similarities:

All have cytoplasm surrounded by a protective covering

All have a well-defined nucleus

All reproduce asexually by cell division (binary fission)

All have vacuoles

All move about their environment

Amoeba• The amoeba is a tiny, one-celled organism

• The name amoeba comes from the Greek word amoibe, which means change

• They are legendary as the ultimate shape shifters

• Amoeba are quite hard to find

Amoeba • An amoeba consists of a single

blobby cell surrounded by a porous cell membrane.

• The amoeba "breathes" using this membrane

• Amoebas move by changing the shape of their body, forming pseudopods (temporary foot-like structures).

• The word pseudopod means "false foot."

• The pseudopodia movement that enables the amoeba to capture prey.

• Usually the pseudopods form a kind of dome that makes escaping impossible.

• They must have some sort of chemical detection since they notice a prey without having to touch it.

These two images of Amoeba proteus shows how a fast moving ciliate is surrounded by quick developing pseudopodia.

Paramecium

• The paramecium is larger than the amoeba

• Shaped like a slipper, its name comes from the Greek word for “oval”

• It is common in ponds throughout the world • Paramecium is a good example of cell complexity.

• The paramecium has two nuclei, a big and small one

• The big one operates as the director of the cell's activities, rather like a little brain

• The smaller one is used for reproduction

• It is covered with tiny hairs called cilia that help it move

• The paramecium is able to move in all directions with these cilia

• The cilia also propels the food into a tiny mouth called the oral groove

Euglena

• The euglena is unique because it is sort of like a plant and also like an animal

• It is pear shaped

• It has a whippy tail called a flagellum that allows it to move through the water

• The euglena is able to make its own food like a plant when it is in the sunlight

• When it is in darkness, however, it can find food like an animal

• It takes in tiny plants and animals much like the amoeba and paramecium.

Interesting Fact

• When it is too hot or cold for a euglena, it forms a protective casing called a cyst around its body that protects it until conditions outside the cyst become better.

Volvox• Volvox is a green algae • It exists as a grand spherical colony• The bright green spheres within are "daughter

colonies"

The individual algae are connected by thin strands of cytoplasm.

The individual alga also have small red eye spots.

Each little alga within the colony bears two flagella, whip-like hairs.

• The volvox resembles a little planet

• In the northern region the eyespots are more developed

• This differentiation of cells make Volvox quite unique

Sometimes we can find inhabitants within the colony. There is a small rotifer, called Proales parasita that lives inside Volvox and feeds on the cells.

One of the 7 Wonders of the Micro World