Protista

hyperthermophiles that live in extremely hot environments above 176 degrees Fahrenheit. There is even a strain that can reproduce above the boiling temperature of water. There is a strain called Picrophilus torridus that can grow at the remarkable pH of 0.

There is speculation that, in extreme outer space environments, these microbes might be the only form of life that is possible. They reside in high enough concentrations in the ocean to affect the ecology of the ocean; however, as many of these are just being discovered, it is no known how they play a role. They may partly play a role in the nitrogen cycle of the ocean by virtue of being able to undergo nitrification.

PROTISTA

Protista is a kingdom among the eukaryotes that has not yet been discussed in this course. This is a heterogeneous group that consists mostly of unicellular or simple multicellular forms. There are many different types of organisms in this kingdom, including algae, protozoa, molds, and slime. They will have both sexual and asexual reproduction and can be sessile (nonmotile) or can move via cilia, pseudopodia, or flagella.

The different subdivisions include diatoms, brown algae, green algae, slime molds, amoebas, flagellates, ciliates, foraminiferans, radiolarians, heliozoans, and apicomplexans (sporozoans). Many ingest food rather than synthesize food as is seen in plants. The major classifications depend on their methods of locomotion. Figure 34 shows some of the different types of Protista:

Amoebas have pseudopodia as their major means of transportation. These are used for both feeding and for locomotion, giving them their characteristic irregular shape (although there are shelled forms of these organisms). They reproduce solely asexually but do not have regular mitosis like other eukaryotes. The pseudopodia move via the coordinated action of microfilaments that push out the cell membrane; they do not have cell walls. There may be many pseudopodia at once, depending on the circumstances.

Amoebas have a two-part cytoplasm. There is an inner endoplasm, which is granular, and an outer ectoplasm, which is clear. The nucleus contains most of the cell’s DNA and there are contractile vacuoles that excrete water in order to maintain a proper osmotic equilibrium within the cell. They use phagocytosis to get food, by sending out pseudopodia to engulf the food. They also participate in pinocytosis or cell-drinking.

The foraminiferans are related to the amoeba but form a calcareous shell around themselves. These are marine animals that do not engage in motility and live on the ocean bottom. They die off, leaving behind a shell that forms an ooze that will become sedimentary rocks. Foraminifera are members of a phylum that includes amoeba. Figure 35 shows the different shapes of these organisms:

The tests consist of different shapes and materials of shells. There are chitin tests and tests consisting of calcium carbonate. Most of these organisms reside in the ocean, although a few are found in soil or other aquatic environments. Most are microscopic, although there are very large species that are as large as 20 centimeters in diameter. There are 10,000 living species of foraminifera and four times that many existing in fossil form.

The radiolarians or Radiolaria or Radiozoa are radially symmetrical organisms that secrete spherical skeletons made from silicates. They are unicellular organisms that reside in aquatic environments. Figure 36 shows a picture of the radiolarian species:

These radiolarians are small protozoa that have a central capsule that divides the cell into its inner and outer endoplasm and ectoplasm. They are part of the zooplankton seen in the ocean, their skeletons forming an ooze on the bottom of the ocean floor that ultimately forms rock. They have multiple thin pseudopods supported by microtubular bundles that help the organism be buoyant. Many have engulfed symbiotic algae that provide the energy for the organism. Aside from the shell, they are related to the amoeba and Foraminifera. Within their group, there are many organisms that have different structural features.

Flagellates (the singular of which is flagellate) are unicellular organisms that have at least one flagellum. The flagella are made from a characteristic “nine plus two” arrangement, which is nine fused pairs of microtubules surrounded by two central singlets of microtubules. They arise from a basal body at the edge of the organism. Some will have a cytostome, which is another term for mouth, in which food is taken in. The structure of the flagella will determine the classification of the organism. The Euglena is a type of flagellate that uses the flagella for locomotion. There is one facing forward and one that faces backward. Figure 37 shows what a euglena looks like:

It is believed that flagellates are a primitive classification of organisms believed to have evolutionarily given rise to all other protozoans, fungi, higher plants, and even animals. Most are commensal organisms that live within the body structures of other organisms. They can have sexual or asexual reproductive capabilities.

The trypanosomes, for the most part, live commensally within a host organism and are known for a complex life cycle. The genus of these organisms is called Trypanosoma, which is a type of parasitic flagellated protozoan. They often require more than one obligate host to complete their life cycle, many having some type of vector to transmit disease to higher animals and humans. In humans, they are responsible for African sleeping sickness and Chagas disease—both tropical diseases. Figure 38 shows the life cycle of the organism that causes Chagas disease:

Ciliates are the type of Protista that includes the paramecium. This is an oblong organism with numerous cilia covering the organism. They range in size from 50 to 330 micrometers in length and are oblong in shape. There is an elastic membrane called a pellicle and multiple cilia around the organism that act in movement of the organism in a single direction. There is an area that is called the oral groove that is responsible for “eating” and an area called the cytoproct that is an “anal pore”, where excretion occurs.