The Protists (This was a lab- Ignore lab-related comments)

INTRODUCTION

 Members of the  Protista are a diverse group with so little in common that it's unlikely they share a common evolutionary relationship. While some are photosynthetic, for example, the nutrition of others is more similar to that of animals or fungi. Even among the photosynthetic protists, different combinations of photopigments, various schemes for storing food, and a variety of reproduction schemes makes it unlikely that many of these are related.

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EXERCISE 1 Animal-like Protists.

 The animal-like protists (protozoans) are differentiated from one another by their mode of locomotion: by pseudopodia, flagella, cilia, or no mobility. None are photosynthetic (although in some older texts you will find Euglena included among the flagellate protozoans).

Figure 1. Sarcodine diversity. (A) Amoeba, (B) Radiolarian, and (C) Foraminifera.

1- Phylum Sarcodina (false-foot protists). Sarcodines move and feed with temporary appendages called pseudopodia ("false feet"). Taxonomy of the group is based on the type of pseudopodia and test (shell), if present.

·         Order Amoebina (observations of live specimens)- Use the supplied pipette to remove some material from the bottom of an Amoeba culture. Transfer to a depression slide, apply a cover slip and observe under the low power of your compound microscope. Adjust your illumination to low and follow the activities of an Amoeba (Fig 1A). The outer surface of the organism is surrounded by a cell membrane. The cytoplasm is divided into an outer non-granular ectoplasmand an inner granular endoplasm. The endoplasm holds the various cellular organelles (nucleus, vacuoles, etc). The nucleus is not well-defined in living Amoeba (use a prepared slide). Locate the contractile vacuole (a clear oval space in the cytoplasm) and make a note of its size and position. Since the interior of an Amoeba is hypertonic to the surrounding fluid, water tends to enter the cell by osmosis. The contractile vacuole of Amoeba and other fresh water protists serves as a temporary storage space for this excess water. As the vacuole fills it moves toward the "posterior" end of the Amoeba and eventually contracts to expel its fluid. Contractile vacuoles help to regulate the internal osmotic environment and are therefore examples of osmoregulatory organelles. You have probably already noticed the pseudopodia used for locomotion. Amoeba extend these false feet and then flow into the newly-created appendages. This peculiar mode of locomotion is called amoeboid movement. ­Sketch several successive stages of pseudopod extension and movement.­ Pseudopodia are also used to surround and capture food in a temporary stomach (forming a food vacuole). Identify the food vacuoles in the endoplasm of your organism. If your Amoeba is feeding, call this to the attention of your instructor and classmates. ­Has the ­vacuole gained or lost water since you began your ­­observations? What do you think would happen if you added a drop of ­­distilled water to your slide. Test your hypothesis and explain. Sketch ­­and label representatives and record your observations in the results ­section.

·         Order Amoebina (Prepared slides)- Compare and contrast the prepared slides of Amoeba and Chaos (Pelomyxa). Note differences in size and the presence of multiple nucleii in Chaos.

·         Order Radiolaria- Radiolarians secrete a porous silicon dioxide test (shell) from which feeding pseudopodia extend (Fig 1B). Examine the prepared slide depicting diversity among the radiolarians. Note the regularity and glass-like appearance of their shells (pseudopodia are not usually present on prepared slides).

·         Order Foraminifera- Foraminiferans also form skeletons, but theirs are constructed from calcium carbonate. The shell is pitted with small pores (foramina) from which feeding pseudopodia extend (Fig 1C; pseudopodia will not be seen on prepared slides). ­Examine the prepared slide of and compare the morphology of the foramin shell to that of radiolarians. ­

2- Phylum Mastigophora (flagellated protozoans). Mastigophorans move with whip-like appendages called flagella (which may occur singly, in pairs, or in larger quantities). Examine the prepared slide of Trypanosoma sp. under medium and high magnification. Trypanosoma is a blood parasite and is the causitive agent of African sleeping sickness. The parasite is carried by the tsetse fly, whose bite injects Trypanosoma into the host's circulation. Note the circular red blood cells and the spindle-shaped parasites. Under low illumination and with careful focusing, you can also identify the flagellum attached to an undulating membrane running along the length of the organism. Locate the nucleus. ­Make a drawing of your in the results section (include a few blood cells for scale). ­

3- Phylum Ciliophora (the ciliates). Ciliates are covered with numerous short hair-like structures called cilia that can be used for locomotion and/or as food-gathering devices. In addition, members of this phylum have two or more nucleii (a small generative- and larger vegetative nucleus). The ciliates are among the most ecologically diverse of the protozoan phyla; with members found in fresh water, salt water, in symbiotic relationships, and as internal or external parasites. Classification within the phylum is based mainly on the structure of their feeding appendages.

Figure 2. Ciliate diversity. (A) Structure of Paramecium and (B) Vorticella.

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Plant-like Protists and Algae.

 The algal protists are photosynthetic organisms that serve as the base of many food chains. Like other members of this kingdom, little joins the group together (other than being photosynthetic).

PROCEDURE:

1- Division Pyrrhophyta (dinoflagellates). Dinoflagelates are found in both marine and fresh water environments. Marine blooms of some species are responsible for the so-called "red tides" that cause destruction of fisheries (caused by powerful nerve toxins). Carotenoids and pigments peculiar to this division mask the usual chlorophylls and are responsible for red color of many dinoflagellates. Some species can supplement photosynthetic activities by ingesting solid food. Examine the prepared slides of the following species under your compound microscope. ­Sketch and a few representative individuals. ­

2- Division Chrysophyta (Diatoms). Diatoms are characterized by glass-like silicified shells that bear a striking similarity to Petri dishes (with interlocking top and bottom valves). This, along with the sculpting of the shells, makes them among the most beautiful of all microorganisms. They are found in both marine and freshwater habitats and are often seen as a brownish coating on rocks in running streams. Depending on the species, unicellular, filamentous and colonial forms are found and they may be be either spindle- or disc-like in shape. Diatoms are plentiful in the fossil record and have built up in thick mineral deposits that are mined as diatomaceous earth (their abrasive properties are useful in many industrial processes). Observe the diversity of diatom forms in your sample and ­make a drawing depicting some of the more diatoms.

3- Division Euglenophyta (Euglenoids). Euglenoids are flagellated single-celled photosynthetic organisms that may be included in the discussions of mastigophorans in some texts. Examine the living Euglena or prepared slides and identify as many structures as possible (Figure 3A).

4- Division Chlorophyta (Green algae). Green algae are a highly diverse group that inhabit marine, fresh water, and terrestrial habitats. They include unicellular, colonial, and multicellular forms.

Single-celled algae- Chlamydomonas. Make a wet mount of Chlamydomonas (or examine the prepared slides) and identify the structures depicted in figure 3B. Chlamydomonas is a motile green algae (with two flagella) in fresh water habitats and the soil. They have a single large chloroplast (that may hide the nucleus in your specimen). Depending on the species, the chloroplast may be urn-shaped, H-shaped, or stellate. Note also the food-storing pyrenoid(s) and a red pigment body near the flagellar end (the eye spot or stigma). Although usually seen as single individuals, you may find one or more colonial groupings in your sample.

Figure 3. Diversity within the euglenoids and green algae. (A) Euglena, (B) Chlamydomonas, and (C) Volvox.

Colonial algae- Pandorina and Volvox. Although not true multicellular organisms, the colonial algae Pandorina and Volvox offer glimpse of what early multicellular organisms might have been like. Mature colonies of Pandorina usually consist of 16 cells arranged as a solid sphere within a common matrix. Volvox colonies, on the other hand, are hollow and composed of several thousand cells (large enough, if fact, to be seen with the naked eye). Like Pandorina, the individual Volvox cells share a common matrix. If available, make a wet mount of Volvox (in a depression slide) and examine their rolling motion for signs of coordinated activity. Under high magnification and low illumination, you may be able to make out the matrix of protoplasmic connections. among the cells that aid coordination during swimming and the paired flagella attached to each cell. You may also note smaller colonies within the parent colony. Small colonies with similar morphology to the parent colony were produced asexually by an infolding of the parent colony's surface (the daughter colonies; Fig 3C). Dark spheres may be also be present within your organism. If so, these are zygotes (produced sexually through fusion of eggs and sperm). ­Examine prepared slides of Volvox both modes of reproduction (make sketches in the results ­section). Compare the structure of Volvox to that of Pandorina .­

Filamentous green algae. Examine the display material depicting the following filamentous algae.

·         Ulothrix filaments are unbranched and grow in fresh water attached to rocks and other substrata. The cells are similar to one another (except for the basal cell, which is modified as a holdfast). Each cell has a single nucleus and several chloroplasts. Under magnification you may find that some cell casings are empty. If so, these cells have released zoospores (containing flagellated cells that resemble Chlamydomonas). When liberated from the parent plant, the zoospores swim around for a while, and then settle on a substratum. They then lose their flagella and, through elongation and division, produce the filamentous form.

·         Ulva filaments branch in two directions (but within a single plane) to produce broad, leaf-like structures. Compare the pattern of branching in Ulva to that you just saw in Ulothrix.

·         Spirogyra is a filamentous algae with an unusual spiral chloroplast.

Siphonous green algae. Acetabularia is the best-known of the siphonous algae. It is umbrella-shaped and can reach a height of 9 cm. Despite its size, it is considered to be a single cell filled with thousands of nucleii. Owing to their large size and the mass of shared cytoplasm, this unusual organism has been the focus of studies concerned with morphogenisis and developmental biology. Grafts can be made between dissimilar species, for example, to study the role of the nucleus vs. cytoplasm in genetics and development. Examine the preserved specimens of Acetabularia on display.

From your observations, describe the feeding, locomotion and general behavior

of Amoeba, Paramecium, and Stentor in the following table. For each, indicate if you actually saw feeding or are making assumptions based on the structure. Under general behavior, include any traits that struck you as interesting.