Kingdom Protista
(single-celled organisms )


Although there is some disagreement, most biologist agree that members of the kingdom Monera were the evolutionary forerunners of the kingdom Protista who in turn were the evolutionary forerunners of the other three kingdoms Plantae, Fungi, and Animalia. Because of this situation a study of a few phyla in this kingdom will serve as a starting point in our evolutionary survey of Animal Biology.

The protistans are conventionally divided into three categories: protozoans (animal-like), algae (plant-like), and slime molds (fungus-like). However, these categories are not evolutionarily related. We will now examine a few protozoan phyla, and one phylum of algal protistans. Currently recognized protozoan phyla are: Rhizopoda (amoebas), Actinopoda (radiolarians and heliozoans), Foraminifera (foraminiferans), Apicomplexa (former sporozoans), Zoomastigophora (flagellates), and Ciliophora (ciliates).

PROTOZOA (single-celled animal-like)

Phylum Rhizopoda: (root-like feet) e.g. Chaos (Pelomyxa), Amoeba, and similar unicellular animals. This group was formerly called the Sarcodina. These organisms have no definite shape or form. They move by pseudopods (false feet) temporary extensions of the cell - in any direction. They also use these to feed by engulfing the prey and incorporating it into their cytoplasm. The prey remains inside a vacuolar structure called a food vacuole within which food gets digested and absorbed into the cytoplasm. The undigested food is left behind. Excess water enters the cell by osmosis, as well as during the feeding process; this water accumulates in a spherical, clear contractile vacuole which contracts intermittently to release the water to the surroundings. Amoebas reproduce asexually by binary fission.

Prepare a wet mount of Pelomyxa by using a dropper to remove a drop of water from the bottom of the culture container and placing that drop on a slide. Do not stir the culture media during this procedure! Also, do not attempt to place a cover slip on this slide! Locate the organism under low power (it will look like a white speck to the eye), and observe under medium power. Observe using very low light intensity! Sketch an amoeba a few times, at different stages of movement, indicating by means of arrows the direction of cytoplasmic flow.

Try to observe the amoeba during feeding and locate a food vacuole. Observe the filling and subsequent contraction of a contractile vacuole. Incorporate these features and the pseudopodia in a drawing of the amoeba. Also label the ectoplasm, and the granular endoplasm.

Phylum Ciliophora: (ciliates) e.g. Paramecium
This is a highly diverse group of protozoans, characterized by the cilia that are used for movement, feeding, or both. The cilia may occur in rows, longitudinal or spiral, or may occur in tufts. The highly coordinated movement of the cilia contributed to the evolutionary success of this group.

Paramecium, unlike the amoeba, has a definite shape. Their spindle-shaped body has anterior and posterior ends, although they dart backwards or forwards very swiftly. Their movement can be slowed down by an anaesthetic or a viscous liquid.

Prepare a mount of Paramecium by placing two drops of DetainTM solution on a slide along with a drop of culture medium. Then add a drop of yeast suspension stained with Congo red (the yeast will serve as a food source; the Congo red is a pH indicator). Place a cover slip over this without trapping an air bubble. Observe the movements of the Paramecium under medium power, then under high power. Note the ciliary movement, and the anterior and posterior ends. Locate the gullet, followed by the oral groove; also note the cilia lining both of these. Now observe the food vacuole. Observe the contractile vacuoles on both ends of the organism. Make a sketch of the Paramecium, labeling all of the above features. Observe the darting movement of the animal by placing some obstruction in its path. Describe this movement. You may also look for the nucleus. In these organisms there are two nuclei – the macronucleus and the micronucleus – which may not be apparent in the live specimen.

Examine a prepared slide of Paramecium conjugation. Conjugation is a mode of sexual reproduction in which two individuals of different strains exchange micronuclear materials through a conjugation tube. Make a sketch of the conjugation identifying the appropriate features.

Phylum Foraminifera
These "hole bearers" are relatives of the amoebas, and are largely marine in habitat. They secrete calcium carbonate to produce their own shells which are pierced by many tiny holes. It is through these holes that the animal extrudes its pseudopodia to act like raptorial appendages (predatory in function).

Phylum Actinopoda: Radiolarians - marine forms; Heliozoans - freshwater forms
These possess radiating needle-like pseudopodia - "ray feet." Their skeletons or shells are made up of silicates.

Phylum Apicomplexa; formerly called Sporozoans
These are parasitic animals with complex forms at different stages of growth. They form spores and oocysts. Both vertebrate and invertebrate hosts might be involved. Included in this phylum are Plasmodium, which causes malaria in humans. Observe the demonstration slide, if available.

Phylum Zoomastigophora: the flagellates
Movement in these organisms is brought about by the whip-like flagella. Many are solitary but some colonial forms are also found. Some are free-living and some are parasitic or symbiotic. Trichonympha inhabits the gut of termites aiding the digestion of cellulose. Trypanosoma is parasitic in humans, causing disease like African sleeping sickness and Chagas disease. Observe the slides of Trypanosoma (blood smear slide) and draw on at high magnification.

ALGAL PROTISTS

These are photosynthetic organisms, containing chlorophyll a. Many of these are flagellates.

Phylum Chlorophyta: e.g. Volvox
Volvox is a colonial flagellate. Observe and draw the Volvox colony (from the "mixed protozoa" slide). Note that the colony is made up of many zooids (individuals) organized in a hollow ball. Some division of labor exists within the colony.


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