An Investigation of the Structure, Survival, and Function of Protists

Title: An Investigation on the Function, Structure, and Classification of Protists

Purpose:

This lab was performed in order to educate the participants on protists, and helped further the class' knowledge of what occurs constantly on in a world smaller than can be seen with a naked eye. Classification, structure, food source, reproduction, and movement of protists were all covered in an attempt to instruct the students on the kingdom protista, an often-overlooked category of organisms that are many times forgotten in favor of kingdom animalia or kingdom plantae.

Materials:

• Colored pencils
• Living slides of Stentor, Amoeba, Paramecium, Euglena, and Volvox
• Protoslo
• Stentor/Amoeba/Chilomonas/Paramecium/red stained yeast/Euglena/Volvox live cultures
• Microscope slides
• Coverslips
• Compound light microscope
• Latex gloves

Results:

See microscope drawings in lab packet (to be submitted in class)

Discussion:

Although the kingdom protista includes the most diverse collection of eukaryotic organisms, varying in means of movement, obtaining food, and body structures, protists do have some similarities. All protists have mitochondria, live in moist environments, and are eukaryotic, meaning they have a nucleus. Protists almost exclusively exist in moist or aquatic environments but can live in plants or animals as parasites. In ciliates, the mouth pore opens into a gullet, which forms food vacuoles that move throughout the cytoplasm. Enzymes in the vacuoles digest food into smaller organic molecules that enter the cytoplasm. Undigested materials move to the anal pore, which contracts and expels them. Excretion also occurs with contractile vacuoles, saclike organelles that expand to collect excess water and contract to squeeze the water out of the cell, and help with osmoregulation. Ciliates can reproduce both asexually and sexually. Asexual reproduction in ciliates occurs by binary fusion, where the micronucleus divides by mitosis and the macromolecule simply elongates and splits in half (one half goes to each new cell). Sexual reproduction in ciliates involves conjugation, where two cells join and their macronuclei disintegrate. Each diploid micronucleus then undergoes meiosis, producing four haploid micronuclei. In each cell, all but one micronucleus disintegrates. The remaining micronucleus divides by mitosis, producing two identical haploid micronuclei; the two cells then exchange one micronucleus and the two micronuclei in each cell then fuse to form one diploid micronucleus. The two cells separate, and a macronucleus forms in each cell from products of mitotic divisions of the micronucleus. Although the cells exchange genetic material during conjugation, they produce no new cells. After conjugation, the two cells divide, forming four offspring. Animal-like protists perform respiration through gas exchange of oxygen and carbon dioxide through the cellular membrane. Animal-like protists perform circulation through its enzymes transporting food around the cell, and nervous control is maintained through their cellular membrane, which preserves a steady, pleasant temperature for the protist inside the organism. Cilia, singular cilium, are short, hair-like cytoplasmic projections that line the cell membrane that enable movement. Flagella, singular flagellum, are long, whip-like structures that are made up of microtubules and used for movement. Pseudopodia, singular pseudopod, are large, rounded cytoplasmic extensions that function both in movement and feeding, and a pseudopodium forms when the cytoplasm flows forward to create a blunt arm-like extension. Animal-like protists are classified into phylum Protozoa (protozoans), phylum Ciliophora (ciliates), phylum Sarcomatigophora, and phylum Apicomplexa. Plant-like protists are classified into seven phyla based on type of pigments, forms of food storage, body form, and cell wall composition. The seven phyla are phylum Chlorophyta (green algae), phylum Phaeophyta (brown algae), phylum Rhodophyta (red algae), phylum Bacillariophyta (diatoms), phylum Dinoflagellata (dinoflagellates), phylum Chrysophyta (golden algae), and phylum Euglenophyta (Euglenoids). Colonies of cells are many cells of the same species that function together as a group, although the cells may have specialized functions. Taxonomists have classified Euglena as an animal-like Protist and a plant-like Protist at different times because Euglena is both plant- and animal-like. Many are autotrophic, like plants, but they lack a cell wall and are highly motile, like animals. Euglenoids also contain chlorophylls a and b and carotenoids.

Conclusion:

This lab achieved its purpose in educating the class on protists. Through the actual lab, the students were able to observe the structure, movement, and nutrition for the protists under the compound light microscope, and through exploration of the discussion questions, they developed a further understanding of their classification and means of reproduction of all protists. Any sources of error could only have derived from under the microscope. It is possible that some of the specimens could have died before being viewed, but it seemed that all of the organisms did show movement and the majority were observed feeding, attributes which could not be completed unless the protists were still alive. Even though each specimen observed in the lab looked very different and had some defining qualities, similarities could be seen between all of the protists, both animal- and plant-like.