Protozoans.

Protozoa are single-celled eukaryote animals from the group Protista. There are many different types of Protozoa, divided into such groups as: Sarcodines, which include the blobby, crawling amebas; Mastigotes, or flagellates, which have one to several long "tails" to swim with; and Ciliates, which include some of the most complicated cells anywhere and which have many small projections called cilia that move them along, usually acting together in a very coordinated pattern. There's also a group that are all tiny parasites, but we are not going to look at those in this lab. Here you will gain some experience identifying and classifying these groups.

 

PROCEDURE:

Part One.

Get one of the available slides of preserved, stained protozoans. Find a good specimen at an appropriate magnification. Be aware that preservatives can distort the appearance of these animals, and objects dyed by stains may be invisible on living specimens, just as some living structures do not stain. In the box on the answer sheet, sketch your specimen, labeling everything present from the Protozoan Structures sheet. Under the sketch, place the name (genus) of the organism, and what lens was in place for the sketch (this is important - similarly-shaped protozoans may be very different sizes).


Part Two.

There are specimen jars available, labeled with letters. Listen to the instructions as to whether you can take them directly from the jars. Note that instructions for using cover slips are also at the jar stations - some organisms can be crushed by cover slips, and some are so small that you'll need high power (where you must have a cover slip) to see them properly. Don't use the oil immersion (100X) lens!! Look for movement of fairly large or very numerous things - most of these protozoans are big, but may have tiny food animals in with them. They may be attached or swimming amongst debris from the specimen jars.

Each live specimen should correspond to a preserved specimen that you've drawn in Part One, although there may be some differences from distortion, staining, or this being the same genus but a different species. Use key features to decide which Part One protozoan your live one is, and put the Part Two answers and sketch with the Part One protozoan. Draw and label the live animal, placing the letter and lens used beneath the drawing. The answer the questions in the place provided. If you have not contaminated your specimen, you can return it to the jar it came from and get another.


Questions for Each Live Specimen:

1. Describe in some detail how your protozoan moves. 

Different movement patterns can provide clues to what group the animal belongs to. Amebas crawl very slowly by "flowing" into cell extensions called pseudopods. Flagellates are often being moved by a flagellum so large in comparison to the cell that the cell shakes as it moves. Ciliates are being moved by many small coordinated cilia, and so seem to glide along.


2. How fast is the protozoan moving? This is a relative judgment, based on how easy it is for you to keep up with the animal.


3. Can you see any kind of activity outside or inside the protozoan? Describe what you can see. Creative uses of the iris diaphragm (and, sometimes, sticking your finger in above the light source to create a shadow edge) can reveal movements. You may not really be able to see anything, but give it a try.



4. Describe the appearance of the cytoplasm. Any feature could be important - color, graininess, whether there seem to be different zones, whatever.


5. Decide - to which group (the amebas / Sarcodines, the flagellates / Mastigotes, or the Ciliates) does this Protozoan belong?

 

 

Protozoans. Answer Sheet. Name _____________________

Part One Labeled Drawing.



















Name:                                Lens:

 Part Two Labeled Drawing.



















Letter:                                     Lens:

1. Movement Pattern:

2. Relative speed:
3. Activity:
4. Cytoplasm:
5. Group:

Part One Labeled Drawing.












Name:                                 Lens:

 Part Two Labeled Drawing.












Letter:                                      Lens:

1. Movement Pattern:

2. Relative speed:
3. Activity:
4. Cytoplasm:
5. Group:

Part One Labeled Drawing.



















Name: Lens:

 Part Two Labeled Drawing.





















Letter: Lens:

1. Movement Pattern:

2. Relative speed:
3. Activity:
4. Cytoplasm:
5. Group:

Part One Labeled Drawing.













Name:                                    Lens:

 Part Two Labeled Drawing.













Letter:                                  Lens:

1. Movement Pattern:

2. Relative speed:
3. Activity:
4. Cytoplasm:
5. Group:

Protozoans - Structure List for Sketch Labels.

Structures in italics are characteristic of certain groups.

Outside Structures:

CELL MEMBRANE. This is the fatty outside barrier around any cell. Protozoans very rarely have cell walls. In amebas, the shape is quite changeable; in flagellates and ciliates, the shape usually stays fairly constant.

PSEUDOPOD. This feature of amebas (and sometimes stranded flagellates) is a fairly fat projection pushed out by an apparent flow of cytoplasm. If the protozoan "decides" to go that way, it fastens the pseudopod to the surface and flows the rest of the cell into it.

FLAGELLUM. (Plural, flagella) Found only in flagellates, this long cell projection, too thin to pick up stain in preserved specimens, is used as a propellor to move the cell along. There often is just one - protozoan species with more than 12 are very rare.

CILIA. (Singular, cilium) Found only in ciliates, these numerous small projections may vary in size on the same specimen. They move in a coordinated fashion, and often aren't visible on stained specimens.

ORAL GROOVE. Only found in ciliates (but not all ciliates have them), this is a dent-like "mouth" where food particles are swept and placed in digestive food vacuoles. The cilia here are often longer than elsewhere on the animals.


Inside Structures:

CYTOPLASM. This jellyish material fills a cell from the nucleus to the cell membrane.

NUCLEUS. (Plural, nuclei) A round or oval structure found in amebas and flagellates. It usually stains deeply, but may be clear or invisible in live specimens.

MACRONUCLEUS. Only found in ciliates. This is the "working" nucleus, and may be a large circle or oval or appear like a string of beads.

MICRONUCLEUS. Only found in ciliates. This is where the "master copy" of the cell's DNA is stored. It is small and may not be distinguishable from other parts of the cell.

CHLOROPLASTS. These small, green, dot-like structures are found in all plants and some protozoans. They are often too small to resolve - the green of a plant-like protozoan is localized in these structures, but just looks like an even color.

STIGMA. Some plantlike protozoans use this orangish-red structure to keep them near the light at the water's surface. It's paired with a shadow-casting device (that isn't visible) to help the animals swim toward the light.

FOOD VACUOLE. When food particles are taken in, they are confined to these membrane "bubbles." Often invisible in live specimens, the food inside may stain in preserved protozoans.

CONTRACTILE VACUOLE. Fresh water protozoans must pump out the water that enters them by osmosis - they fill these membrane "bubbles" and then squeeze the water out. These are very difficult to see - preserved specimens often empty theirs when they contact the preservative chemicals, and live specimens have so many structures that picking this one out is difficult. If you see what you think is a contractile vacuole, watch it for size changes - it will get bigger and bigger, then shrink quickly down to almost nothing.

 

First Written 1990;  Last Update 2001;  Web Version 2001,  M. McDarby

 

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