Idea Transcript
BIO170 General Biology Freeman/Mac Leod FMCC
PROTISTS Objective: After completing this exercise, you should be able to do the following: Describe the diversity of protists. Describe the key characteristics of 4 of the major eukaryotic lineages (Amoebozoa, Excavata, Alveolata and Stramenopila). Identify representative organisms in those 4 major eukaryotic lineages. Identify prominent morphological structures of each organism observed. Introduction: Unicellular eukaryotic organisms originated over 2 billion years ago, and today they are found in every habitable region of Earth. The enormous diversity of organisms, their numerous adaptations, and their cellular complexity reflect the long evolutionary history of eukaryotes. The protists have been called a “catch-all group” in the domain Eukarya. They included not only the unicellular eukaryotes but also their multicellular relatives, like the giant kelps and seaweeds.
Figure 1: 3-Domain Tree of Life System
The most familiar groups of protists, commonly called algae and protozoans, have been well studied since the earliest development of the microscope. Therefore, one might assume that the taxonomic relationships among these groups are well understood. However, their phylogeny (evolutionary history) has been difficult to determine from comparisons of cell structure and function, nutrition and reproduction. Recent molecular and biochemical research, particularly the
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BIO170 General Biology Freeman/Mac Leod FMCC ability to sequence ribosomal and transfer RNA genes, has provided strong new evidence for reconstructing the evolutionary relationships among the protists. The three-domain system is a biological classification introduced by Carl Woese in 1977 that divides cellular life forms into Archaea, Bacteria, and Eukarya domains. Domains are further divided into major lineages separated by morphology. In this lab, you will become familiar with 4 of these lineages: Amoebozoa, Excavata, Alveolata, and Stramenopila. The protists range in size from microscopic to macroscopic. Some of the large brown algae can be 60 m long. Many protists have a characteristic overall form, organelles with distinctive features, or both. All eukaryotes alive today, including all living protists, have a nucleus and endomembrane system, mitochondria or genes that are normally found in mitochondria, and a cytoskeleton. As you examine the diverse samples notice how this taxon ranges from heterotroph to autotroph, and from structurally simple (unicellular) to complex (multicellular). Autotrophic organisms are able to convert the sun’s energy to organic compounds. Heterotrophic organisms must ingest organic compounds via ingestion (uptake of large particles or whole organisms by pinching inward of the plasma membrane). Traditionally, autotrophic protists are called algae and heterotrophic protists are called protozoa. Some protozoa, euglenoids for example, are mixotrophic, capable of photosynthesis and ingestion. As you work through this lab, look for characteristics of each protist that are shared with animals, plants and/or fungi. Most evolutionary biologists believe the remaining multicellular kingdoms arose from protist ancestors. Determine the nutritive mode of each organism. Note morphological characteristics of each example studied. Determine which characteristics are found in the same clade and which are shared with other clades. What means of locomotion does each organism possess? What role does it play in the ecosystem? Where does it live? What taxon does each organism belong to and why?
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BIO170 General Biology Freeman/Mac Leod FMCC
Figure 2: Phylogenetic Tree of Eukarya
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BIO170 General Biology Freeman/Mac Leod FMCC In this lab you will study the examples of groups of protists shown in Table 1. Table 1: Groups of protists investigated in this lab exercise Major Lineage Major subgroup Procedure Excavata
Euglenida
A
Example Genus Euglena
Alveolata
Ciliata
B
Paramecium
Dinoflagellata
C
Peridinium
Diatoms
D
Thalassiosira
Diatoms
D
Mixed diatoms
Lobose amoeba
E
Amoeba
Stramenopila
Amoebozoa
THE EXCAVATA Key features of the lineage Excavata are 1) A feeding groove on one side of the cell (the “excavation”). 2) Lack of mitochondria (evolutionarily, mitochondria were lost). SUBGROUP EUGLENIDA One sub group of this lineage is the Euglenida. These are aquatic organisms (both freshwater and marine) that lack a cell wall. The cell membrane is supported by a unique set of proteins that form a pellicle. Some are autotrophic (via photosynthesis) but most ingest their food. They reproduce asexually. The organism you will observe belongs to the genus Euglena. These organisms move by use of a long flagellum (also possess a second flagellum), are unicellular, are mixotrophic and can be found in fresh and salt waters. Procedure: 1. Refer to Photo atlas p.18 as you do this exercise. 2. Obtain a prepared slide of Euglena and observe it using scanning, low and high powers of the compound microscope. 3. Draw your specimen (indicate magnification) in your notebook and label clearly using Fig 3 as a guide only (do not just copy): flagellum, chloroplasts, nucleus, eyespot, pellicle (thin layer supporting the plasma membrane).
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BIO170 General Biology Freeman/Mac Leod FMCC
Fig. 3: Diagram of Euglena sp.
B. THE ALVEOLATA Key features of the lineage Alveolata are 1) The presence of alveoli (small sacs located under the plasma membrane). You will study 2 sub-groups of this lineage: the Ciliata and the Dinoflagellata
SUBGROUP CILIATA: The Ciliata have cilia that cover their body. They require water to survive and so are found in aquatic and wet terrestrial habitats (like wet soil). They have two nuclei: a large macronucleus and a small micronucleus. Ciliates obtain food by ingestion. They reproduce asexually though they also can exchange genetic material during the process of conjugation. The organism you will observe belongs to the genus Paramecium. Procedure: 1. Refer to Photo Atlas page 22. 2. Using the compound microscope, examine a living Paramecium. Place a drop of water from the bottom of the culture on a clean slide. Add small drop of Protosol and then the coverslip. 3. Observe your specimen using scanning, low and high powers 4. Describe the movement of your specimen. Is it directional or random? 5. Draw your specimen in your notebook (indicate magnification) and label clearly using Fig 4 as a guide only (do not just copy): Oral groove, food vacuole, macronucleus, cilia
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BIO170 General Biology Freeman/Mac Leod FMCC 6. Observe your specimen feeding by adding a drop of yeast stained with Congo red to the edge of the coverslip (it will diffuse around the paramecia). Watch as the yeast moves into the oral groove, gullet and food vacuole
Fig 4: Diagram of Paramecium caudatum
SUBGROUP DINOFLAGELLATA Swirl your hand through tropical ocean waters at night and you may notice a burst of tiny lights (bioluminescence). Visit a warm, stagnant inlet and you might notice that the water appears reddish and dead fish are floating on the surface. Both of these phenomena may be due to activities of dinoflagellates. The subgroup Dinoflagellata is characterized by cellulose plates that contribute to their characteristic shape. They have two flagella. One extends from the organism and the other is found in a groove around the body of the organisms. The two perpendicular flagella help the organism move through their environment.
Procedure: 1. Refer to Photo atlas p.21. 2. Obtain a prepared slide and prepare a wet mount of Peridinium. 3. Focus the slide using scanning power. You may have to switch to a higher power objective to see them clearly 4. Detect locomotion in your living specimen 5. Observe the intricate geometric patterns using the prepared slide 6. Draw your specimen in your notebook (indicate magnification) and label clearly using Fig 5 as a guide only (do not just copy). Flagella, nucleus, sulcus
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BIO170 General Biology Freeman/Mac Leod FMCC
Fig 5: basic structure of Peridinium
C. THE STRAMENOPILA Key features of the lineage Stramenopila are 1) The presence of hairs that cover the flagellum. This is present in at least one stage of their life cycle. SUBGROUP DIATOMS One subgroup of the Stramenopila is the Diatoms. These organisms have silica rich “glassy” cell walls that can be very ornate. They gain energy through photosynthesis and are the most important photosynthesizers in cold marine waters. Their cell wall deposits are mined as diatomaceous earth and have numerous economic uses (swimming pool filters, abrasive in toothpastes and silver polish). Diatoms reproduce both asexually and sexually. Diatom cells are either elongated, boat-shaped, bilaterally symmetrical pennate forms or radially symmetrical centric forms. The cell wall consists of two valves, one fitting inside the other, in the manner of the lid and bottom of a petri dish. You will observe organisms from the genus Thalassiosira as well as “mixed” species of diatoms. Procedure: 1. Refer to Photo atlas p.20 2. Prepare a wet mount of Thalassiosira and observe it using the compound microscope. Are you able to detect locomotion? Can you see chloroplasts?
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BIO170 General Biology Freeman/Mac Leod FMCC 3. Draw your specimen in your notebook (indicate magnification) and label clearly your photo atlas as a guide only (do not just copy) and indicate its shape. a. Cell wall, chloroplast 4. Obtain a prepared slide of diatoms and observe it using the compound microscope. 5. Observe the intricate geometric form using the prepared slide Are they centric, pennate or both? 6. Draw your specimen in your notebook (indicate magnification) and label clearly using your photo atlas as a guide only (do not just copy) and indicate its shape. a. Cell wall, chloroplast
D. THE AMOEBAZOA Key features of the lineage Amoebozoa are 1) The lack of a cell wall. 2) The presence of pseudopodia (used for ingestion and movement). SUBGROUP LOBOSE AMOEBA Most Amoebozoa are unicellular and are common in soils and aquatic habitats. One subgroup of the Amoebozoa is the Lobose amoeba. These organisms produce lobose pseudopods; blunt extensions of the organism that are characterized by a clear ectoplasm and granular endoplasm. The species Amoeba proteus will be observed in this lab exercise. Amoeba proteus occupies freshwater environments and feeds on algae, rotifers, and even smaller amoebae. Due to the presence of phytochrome (pigment) A. proteus may appear in a variety of colors under the microscope. Procedure: 1. Refer to Photo atlas p.22 2. Obtain a prepared slide of Amoeba proteus and observe it using the compound microscope. 7. Draw your specimen in your notebook (indicate magnification) and label clearly using Fig 6 as a guide only (do not just copy). a. cytoplasm, ectoplasm, endoplasm, pseudopodium, nucleus, food vacuole, plasma membrane
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BIO170 General Biology Freeman/Mac Leod FMCC
Fig. 6 Anatomy of an amoeba courtesy of Wikipedia
Synthesis 1. Complete the following Table (on the next page). Cut it out. Tape or paste it into your notebook.
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BIO170 General Biology Freeman/Mac Leod FMCC
Comparison Table of Protists: Major Lineage
Major Subgroup
Defining characteristics
Examples from lab
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BIO170 General Biology Freeman/Mac Leod FMCC Major Lineage
Major Subgroup
Defining characteristics
Examples from lab
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