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LABORATORY EXERCISES #4 PART I: OBSERVING LIVING PROTISTS: LETS PLAY LEEUWENHOEK
LABORATORY EXERCISES #4
PART I: OBSERVING LIVING PROTISTS: LETS PLAY LEEUWENHOEK
INTRODUCTION
Today you will have the opportunity to observe cells which are actually individual organisms-- unicellular or colonized Eukaryotes. These organisms, which are members of the kingdom Protista, come in many shapes and sizes and exhibit diverse behaviors. As a student scientist, you will practice your observational and microscope skills as you investigate the activities of these creatures. The 17th-century observation Anton van Leeuwenhoek is most known for is his identification of these tiny creatures that he called animalcules using a simple compound light microscope he built himself. This lab should give you a sense of what he witnessed in his studies.
STUDENT OBJECTIVES
1. Prepare and observe wet-mount slides of mixed protists.
2. Improve microscope technique.
3. Improve observation skills.
PRE-LAB QUESTION:
You will be working with Paramecia, Euglenoids, and, hopefully, Amoebae, in this lab.
1. Identify the name of the phylum for each, and the primary mechanism of locomotion for each at the beginning of your summary question and drawing sheets that you must bring to the lab session along with these instructions.
MATERIALS:
Slides, coverslips, methyl cellulose, toothpicks, mixed protist cultures, paper towels.
PROCEDURE
1. Make a wet-mount slide of a mixed protist culture by using the following technique:
a. Clean the slide and coverslip with a small piece of paper towelling. NO SMUDGES, PLEASE.
b. Hold the dropper and squeeze out all the air bubbles (not all the air though) before you put it into the culture.
c. Gently lower the dropper into the fluid and draw up no more than 3 cm of the fluid. DO NOT DIG INTO THE AGAR AT THE BOTTOM OF THE CULTURE DISH.
d. Gently expel 1 drop onto the slide.
e. Place the coverslip on the slide at an angle, wet the edge with the liquid on the slide and lower it. If there are bubbles, use the tip of your pencil to gently force them out.
f. Observe the slide under LOW power. If the protists are moving too fast, you can make another slide. Wipe off the slide with paper towel. Place 1-2 drops of methyl cellulose (Detain) on the slide and 1-2 drops culture fluid. Stir gently with a toothpick and place a coverslip on top. You may have better success without the Detain, though.
2. Observe the Protista under low and then high power. Draw in pencil two organisms in the space on your worksheet, clearly labeling the overall magnification underneath each (for example, 40X) as well as identifying the cell membrane and the nucleus for each with a line pointing to the structure.
Chilomonas
Chlamydomonas
Gonium
spirostromum Pond Critters: These line drawings should be use as models for your own drawings.
From //www.microscope-microscope.org
Click onto any protist to find out more
Euglena
Colpidium
Stentor Volvox
paramecium species
euplotes
peranema Pelomyxa,
chaos-chaos
didinium eudorina
pandorina
difflugia Vorticella
Blepharisma
Arcella
top and side view Actinosphaerium
Bruseria truncatella
Amoeba proteus
PART II: HOW DOES THE STRUCTURE OF A PARAMECIUM ENABLE IT TO FUNCTION IN ITS ENVIRONMENT?
INTRODUCTION
Paramecia are familiar organisms in the biology laboratory. They are often used as representative Protists. Many of their activities and structures are similar to other members of their Kingdom. Locomotion, feeding, and defense are three behaviors which you will readily observe today. As you make your observations, keep in mind the importance of the relationship between structure and function.
STUDENT OBJECTIVES
1. Observe the structure of paramecia.
2. Relate structure of paramecia to their functions and behaviors.
3. Improve microscope technique.
4. Improve observation skills.
PRE-LAB QUESTION: See Part I.
MATERIALS
Slides, coverslips, methyl cellulose, toothpicks, congo red yeast, acidified ink, paramecium cultures, paper towels.
PROCEDURE
1. Clean a slide and a coverslip.
2. WITHOUT INTRODUCING BUBBLES INTO THE CULTURE, use the dropper to pick up about 2 ml of fluid from the culture. Place a drop on the slide and return remaining culture back to the culture dish.
3. Add 1 drop of methyl cellulose (Detain) to the slide and mix the drops with a toothpick. Slowly place the coverslip on the culture and try to avoid trapping any air bubbles under the coverslip.
4. Observe some Paramecia under LOW power. Move your slide around and observe freely swimming paramecia. You might find some that are feeding on clumps of green food.
5. Observe the way the swimming paramecia move forward. Contrast this with their motions when they are feeding or bumping into material from the culture fluid.
6. Switch to HIGH power. Observe the cilia along the parameciums body and how they help propel it. Note the position of the oral groove, which is surrounded by cilia. The beating contractile vacuole, helpful in getting out excess water from within the cell, may also be evident within the cytoplasm of the cell as an asterisk-like, pulsating structure.
7. CONGO RED and YEAST Take your slide off the microscope stage. Place one drop of the congo red yeast (food) next to one drop of the living ciliate culture. (Congo red is a pH indicator which means its color will change as the pH changes). Gently mix with a toothpick, and gently cover with a coverslip.
8. Focus under LOW and then HIGH power. Observe the yeast as it is swept up by the paramecium. As it ingests the yeast, food vacuoles are being filled up with the stained yeast. Watch the food vacuoles and observe their movement and any changes in their color over time. Draw in pencil a fed paramecium, as indicated on your worksheet.
9. INDUCTION OF TRICHOCYSTS: Clean and dry the slide and coverslip. Place 1 drop of ciliate culture on the slide. Next to the culture, place 1 drop of acidified blue ink. Gently place the coverslip on the drops WITHOUT MIXING. Observe the slide under LOW then HIGH power. As the two different fluids diffuse into one another, observe how the paramecia react by discharging their trichocysts. Draw in pencil a trichocyst-induced paramecium as indicated on your worksheet.
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