Hay! Isn't That a Protozoan?

GRADE: 6

CLUSTER: Diversity of Life

TIME: 2-5 days, 45 minutes per day

SPECIFIC LEARNING OUTCOMES

• STSE 104.05, 104.08
• Initiating and Planning 204.06, 204.08
• Analysis and Interpretation 206.01
• Knowledge 300.19, 302.12

KEY WORDS

Objective:

Students will learn that...

• protozoa are one-celled microscopic animals.
• protozoa use cilia, flagella, or pseudopodia to move; some don't move at all.
• protozoa need food and water to live and grow. If there's no food or water, they can form a cyst around themselves and wait until the conditions improve.
• some protozoa cause disease.

Background Information:

There are 60,000 known species of protozoa - simple one-celled animals too small to be seen with the naked eye. You'll find protozoa wherever you find water.

Like other animals, protozoa need food and water to grow. If conditions dry out, or if food supplies diminish, some protozoa can enclose themselves in cysts. A cyst is a protective casing that keeps the animal from drying out and keeps the temperature relatively constant. When favourable conditions return, a protozoan emerges from the cyst and begins feeding and reproducing again.

Protozoa move by beating tiny hairlike structures called cilia, or whipping long tail-like structures, called flagella. Some protozoa move by making their inner fluids (cytoplasm) flow in a certain direction. This makes one part of them (called a pseudopodium) extend in one direction; the rest of the cell follows. Other protozoa don't move at all.

Some protozoa cause disease. One protozoa causes malaria and is transmitted to humans through the bite of an infected mosquito; another causes sleeping sickness in people bitten by the tsetse fly. Fortunately, most protozoa are harmless to humans.

After making this hay infusion and culturing some protozoa, you and your students will have your own personal supply of protozoa to observe and study.

Activity Materials:

One 1-litre jar with lid Dried timothy grass A few dried leaves A jar of pond water containing scum (you can also use the salt water from a nearby salt marsh) A small amount of silt or mud-like soil from the bottom of the pond (or salt marsh)

Uncooked rice Hand lenses Glass slides and cover slips Eyedroppers Clean culture dishes Microscopes Small pieces of cotton

Questions to Begin:

1. Does anyone know what protozoa are? Has anyone ever seen a protozoan? Where do they live?
2. Are protozoa plants, animals or something else?

Procedure:

1. Take the class outside on a leaf-gathering mission. Ask the students to find a few dried leaves on the ground and bring them back to the class. If you have a pond nearby, they can also collect samples of pond water and mud to bring back to the class. If you don't have a pond nearby, you'll have to make a special trip with the class or by yourself ahead of time.

2. Fill a litre jar one-fourth full of pond water, pond scum and mud. Add a few spears of hay and the leaves. Cover the jar and put in warm place, out of direct sunlight. You can ask for volunteers to help you with this step. Let the jars sit for 2-5 days.

3. At the end of that time, add a few grains of uncooked rice to the mixture. Don't be alarmed if the water turns a dark colour and begins to stink. Inside the jar, the hay and leaves are decomposing, making a prime environment for protozoa to grow.

4. After the protozoa have had a few days to grow, give each student (or team) a clean culture dish. Open the jar, and with an eyedropper collect a sample of the water from the top. Be careful not to disturb the mud. Place the water in the culture dish.

5. Have the students observe their water samples with a hand lens. They'll probably see the larger protozoa, such as Paramecium, swimming around.

6. Next, have each student observe the protozoa in their culture dishes through the microscopes. Place a drop of water on a clean, dry glass slide. Cover the drop with a cover glass by placing one edge down first to avoid trapping air bubbles beneath the glass. If the protozoa are moving around too much, try placing a few fibres of cotton on the slide before adding the drop of water. This should trap the protozoa. Try observing first under low power, then gradually move to strong power.

7. Have each student draw the animals they see and if possible, identify how each is moving. Does it have cilia, or one or more flagella? Does it move at all?

8. Repeat the process, this time with a sample of water from the bottom of the jar. Be careful not to stir up or collect the mud. Again, have the students draw the protozoa they see and identify how each is moving.

9. Close with a discussion of the class' findings.

Questions to Close:

1. Where did the protozoa come from?
2. How did the protozoa in your sample move? Using cilia? Flagella? Some other way? Not at all?
3. Were the protozoa at the top of the water the same or different than the ones at the bottom?
4. What do you think protozoa eat?
5. Can you think of anything that might eat protozoan?