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Preying Protozoa Lab Instructions

Discipline: Life Science, Environmental Science

Grade Level: Middle/High School

Overview: In this activity students observe, compare and contrast
feeding behaviors of two carnivorous species of protozoa.



Materials Required

Cultures of Bursaria, Didinium or Chaos

2 species are included in the Preying Protozoa set. The cultures contain
Paramecia as a prey source

Compound light microscope

Glass slide

Coverslips

Dropping pipettes

Optional: additional Paramecium multimicronucleatum culture as a prey species

Optional: Protoslo® Quieting solution


Activity Procedure

  1. Place a drop of one of the cultures you wish to examine on a clean, dry microscope slide.
  2. Optional: To enhance feeding response, add a drop of Paramecium multimicronucleatum to the slide before adding the cover slip.
  3. Gently lower the coverslip onto the slide.
  4. Observe the activity of the organisms using appropriate magnification on your compound light microscope.
  5. If feeding activity is difficult to observe, add a drop of Protoslo® Quieting Solution to your slide.
  6. An alternative way to view feeding it to place the culture jar on the stage of a dissecting scope and view the jar using appropriate magnification. Note: Protoslo® cannot be used when using this method.
  7. Have students compare and contrast the feeding methods they observe.

Results/Summary

Bursaria truncatella is a one of the largest known ciliates. This organism’s digestion can be easily studied. Bursaria truncatella are oval in shape with a rounded posterior and shortened anterior end. The buccal cavity of the organism is surrounded by cilia and extends midway into the central part of the cell. This unique anatomical feature allows the Bursaria truncatella to digest large food particles.

Didinium nasutum is a voracious ciliate predator that feeds almost exclusively on Paramecium. Didinium are barrel shaped organisms. Their bodies are encircled by 2 bands of cilia called pectinelles. Didinium use the pectinelles to move through the water. Protruding from the anterior end of the organism is a cone shaped structure that serves as a mouth opening for capturing prey.

Note: Both Bursaria and Didinium will encyst by turning into a hard-shelled sphere when prey is scarce. Encysted forms will persist until food is available again.

Chaos (Pelomyxa carolinensis) is a species of sarcodine protist closely related to Amoeba. Like Amoeba, Chaos may settle to the bottom of the culture jar. When taking samples for examination, be sure to take samples from the bottom of the jar to ensure that sufficient numbers of organisms are collected. Chaos feeds by extending pseudopods around prey items and digesting them by phagocytosis. Chaos do not have a mouth and ingest their food inside on enzyme filled vacuoles, absorbing extracted nutrients across the cell membrane.

Prey Protozoan Species

Paramecium multimicronucleatum is a ciliate commonly used for classroom study because of its relatively large size. This species is commonly studied in feeding behavior and simple response studies.






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