The submission form for the protist portion of this week's lab is off the BB lab section. Read below to get background on the protists.

Learning Objectives:

	Describe differences between 2 major groups of protists (animal-like and plant-like).
	Gain an appreciation of the diversity of organisms found in this kingdom.
	Understand some of the different methods of feeding and movement in protozoa.
	Explain the key role that protists play in supporting life in aquatic communities, as well as sustaining human life on the planet.

Introduction

Some of the simplest eukaryotic organisms belong to the Domain Eukarya, Kingdom Protista. If only one word could be used to describe this kingdom, it might be the word diversity. Members of this very large kingdom (approximately 100,000 species) show considerable variation in their forms, habits, lifecycles, habitats, and methods of obtaining nutrients. The kingdom can be divided into two groups: the animal-like protists or protozoa, and the plant-like protists or algae. Today in lab we will be examining selected species from this kingdom.

The Protozoa

The protozoa are the animal-like protists. Since organisms in the Kingdom Animalia are heterotrophic and motile, we would expect protozoa to also be heterotrophic and motile. Indeed, they are. The prefix "proto-," as in prototype, means the first or before, and the suffix, "-zoa," represents "zoo" for animals. So, the word protozoa means sort of "the first animals."

Protozoa are single-celled, heterotrophic organisms. They are distributed worldwide and inhabit both terrestrial and aquatic environments. They are complete organisms that possess all the necessary tools for performing the same metabolic functions that humans perform: ingest food, digest food, expel waste, and obtain oxygen. In protozoa, this is all accomplished within a single cell. Many protozoa have forged symbiotic relationships with other organisms (living with them), and some are responsible for causing some of humankind's most dreaded diseases. Structurally, most protozoa are enclosed in a simple cell membrane, covered by a layer of protein called the pellicle. Some groups of protozoa manufacture a hard outer covering, or test, composed of calcium carbonate or silica; it is called a test to distinguish it from the notion of a cell wall, which would sound plant-like. Protozoa may reproduce asexually (no exchange of genetic material between two individuals), or sexually (exchange of genetic material between two individuals). Taxonomists classify protozoa according to their method of movement, and it is the mode of locomotion that we will base our study of the protists today.

Ciliated Protozoa

The ciliates are a large group of protozoa that move and obtain food by means of short, hair-like structures called cilia. A cilium (singular) is an extension of the cell membrane and contains bundles of microtubules within it. Cilia are used to sweep smaller protists, bacteria, and non-living organic matter into an oral groove. At the distal end of the oral groove a food vacuole will be formed. Cilia are very abundant and cover the entire cell surface. Ciliates occupy a variety of habitats including freshwater, soil and as symbiotes in the guts of vertebrates. The photo above is of a ciliate called Blepharisma, which has a slightly pink coloration making them good to see (but still small); the oral groove on the Blepharisma in the photo surfaces at the bottom, in the middle of this cell.

You will be examining a HUGE ciliate in lab-- Stentor coeruleus. He is my favorite protist, because he is so big and easy to see.

Amoeboid Protozoa

The amoeboid protozoa move by means of amoeboid movement, or pseudopodia. Pseudopodia are protoplasmic extensions that move the organism in a particular direction. The organism uses these "false feet" for locomotion and food capture by endocytosis. The best-known members of this group are the amoebas. Amoebas are widely distributed organisms of mostly freshwater environments. They occur commonly on undersides of vegetation in slow-moving streams or ponds. Some species of Amoeba inhabit soil, salt water, and a few are important endoparasites of humans and other animals.

Flagellated Protozoa

Flagellated protozoa locomote my means of a long, whip-like flagellum. We are not looking at any of these specifically in lab, because the ones we might have chosen to look at are too small to see well with our microscopes. Peranema is an example of this type of protozoan, and is shown in this photo to the right. There are some Peranema that are in the container with Stentor, as food for Stentor. You might see some there.

Peranema uses its flagellum to pull, rather than push, itself through the water. It is pretty fun to watch. Some other flagellated protozoa are not so much fun, because they can cause some human diseases.

The Algae

The algae are the plant-like protists. As such, you would think that algae would have the following characteristics:

	autotrophic (whether it is by chlorophyll or not)
	nonmotile
	cell walls

Many of the algae stick to this list, but, certainly, there are exceptions. Some algae can move using flagella. Some algae don't have cell walls. And one kind of algae can even adopt a heterotrophic life style when stuck in the mud at the bottom of a pond or when there's little sunlight. Here's a more thorough description of the algae...

Algae are autotrophic (photosynthetic) organisms. Like the protozoa, some algae are single-celled. Unlike the protozoa however, many representatives are multicellular, attaining lengths of 100 or more meters, and possess cell walls. Many species are aquatic, with most occupying marine habitats. Terrestrial habitats are not devoid of algae. Certain species can be found in damp soil, building and rock surfaces, and on tree bark. Some are quite at home in the fur of mammals, in swimming pools, birdbaths, flowerpots, and roof gutters of homes. It is safe to say that algae can be generally found anywhere there is an abundance of moisture and sunlight. Over 30,000 species of algae have been described by phycologists (phycology is the study of algae).

Taxonomists use several criteria to classify algae, the most common method being the dominant photosynthetic pigment color found in the chloroplasts of the algal cells. We will use this characteristic to group the algae that we observe. You see, algae can live in all sorts of aquatic environments-- some live at really deep regions of the ocean. Not all wavelengths of light can make it down to the bottom of the ocean. The green light that bounces off our chloroplasts in land plants is great on the land, but not so great in the depths of the ocean. So other wavelengths of light have to be used by algae. You will see green, golden-brown, red, and brown algae.

Although algae can be multicellular, they are not multicellular in the same way as plants are. Plants are complex multicellular organisms. Algae are simple. That means that even though there are many cells in one organism, the cells are all of the same type, or almost all of the same type. Multicellular algae can organize their cells into filaments, colonies, or even tissue-like sheets. The filaments are cells lined up end-to-end, like boxcars. The colonies are spherical clumps of cells. And the sheets are like you see in seaweed.

Euglenoids

We are not looking at euglenoids in our lab, because they tend to be very small. But they are also very cool. These are the organisms I described a bit in the introduction as having characteristics of both protozoa and algae. An example of a euglenoid is Euglena, a freshwater protist. Algal characteristics include the ability to photosynthesize and store starch. Protozoan characteristics include the lack of a cell wall, and the ability to ingest food (which they do when they can't get enough light). Some species of Euglena are very tolerant of polluted waters, and act as water quality indicators for humans when expensive pollution monitoring equipment is not available.

Dinoflagellates

Dinoflagellates are bizarre looking algae. The prefix "dinos-" means whirling. They are freshwater algae, but they exhibit the protozoan characteristic of being able to move using flagella. In fact, they have two flagella that they move independently. These two flagella extend at right angles from each other, so that the dinoflagellate can move along, spinning away using flagellar movement; the spinning, or whirling movements they make, is how they got their name. Dinoflagellates are algae, though, and are able to use photosynthesis. They are surrounded by a cell wall that has an odd appearance, since it looks like a suit of armor. There are some dinoflagellates that contain a red pigment and, when in high enough numbers in the ocean, cause the ocean to have a reddish hue; this is called red tide. The dinoflagellates in the red tide are toxic to many of the ocean organisms, so where the red tide goes, ocean life perishes. Peridinium is not at all harmful.

Green Algae

Green algae are the largest group of algae, consisting of unicellular, colonial, simple multicellular and more complex multicellular members. A few representatives are detailed below.

Some members of the green algae are single-celled organisms. For example, Chlamydomonas is single-celled. Some Chlamydomonas-like organisms have been found fossilized in rock dating back nearly 1 billion years. Each individual is composed of a single chloroplast, nucleus, a light-sensing eyespot (or stigma), a starch storage area called a pyrenoid, and two flagella. We aren't looking at any unicellular green algae, because they are too small.

Other green algae are multicellular. You will be viewing Volvox, Spirogyra, and Ulva. Each one of these has a different arrangement of their cells (colonies, filaments, and sheets, as described above).

Golden-brown Algae

Members of this group possess both chlorophyll and another pigment called xanthophyll. These photosynthetic pigments impart a golden-brown color to the algae. The best-known members of this group are the diatoms. Diatoms are unicellular algae and are found in abundance in both terrestrial, marine, and freshwater environments. Economically they are of tremendous value to humans.

The defining characteristic of diatoms is the presence of their glass-like cell walls composed of silica. The walls are arranged in overlapping halves, much like a candy box or petri dish fits together. Once the organism dies, the protoplast inside decomposes but the glass-like walls remain intact for hundreds or thousands of years. Over thousands of years significant deposits of these may accumulate on the ocean floor. These deposits may be extensive to be commercially mined. This material is better known as diatomaceous earth. Humans use this material in a wide array of products, including paints, cement, fertilizers, toothpaste, polishes, and cleaners. Diatomaceous earth also kills snails and slugs.

Red Algae

The red algae are almost exclusively multicellular and many are marine. Red algae tends to have a very hard cell wall, made of calcium carbonate. This is the same stuff that contributes to the hard shell around shellfish. So, when you step on this seaweed, it hurts more than feels slimy! You are going to be looking at a freshwater red algae, called Callithamnion, just because it is a good one to see under the microscope.

Brown Algae

The brown algae are exclusively multicellular and marine, like the red algae. Characteristic coloration comes from a combination of at least 4 photosynthetic pigments. These algae are most common in cooler marine waters, and range in size from microscopic filaments to giant kelp that may attain lengths of up to 100 meters.

An important representative of the brown algae is Laminaria or kelp. Kelp might seem a bit too complicated to be considered "simple." Yet, it still is truly a simple multicellular organism. All the cells of the leaves (the blades) are basically the same. Each kelp "plant" also has a stalk-like stipe, and an area that is root-like to hold it into the ground (the holdfast). The leaf-like blade is the site of most photosynthesis. Keep in mind that algae are not plants-they lack true stems, leaves and roots. Distributed along the blade may be several or many air bladders that help to keep the blade buoyant.

Kelp may grow in large concentrations or underwater " forests" in certain areas, and are extremely important ecologically in the oceans. Many marine mammals, fish, and invertebrates depend on these kelp forests for protection from storms, hiding places, and as nurseries for young.

Ecological Importance of Protists

While responsible for causing many dreaded human diseases (malaria, African sleeping sickness, and giardiasis to list a few), protozoa also benefit humans tremendously. Protozoa are important nutrient recyclers in natural ecosystems. Without organisms like bacteria, fungi and protozoa, soils would quickly become depleted of nutrients making plant growth impossible. All organisms on earth depend on healthy plant populations for survival. Protozoa also play a key role in wastewater treatment plants by consuming enormous quantities of bacteria, and are important components of food chains.

Algae is much more than simply "seaweed" or "pond scum"--it is a vital component of our biosphere, and the survival of humans would be jeopardized without it. Indeed, algae produced more than 50% of the oxygen molecules that your cells consumed during this laboratory! Algae also form the base of aquatic food pyramids. This algae is primarily microscopic, and is called phytoplankton. Without algae in lakes, rivers, and oceans, there could be no life in these environments since all aquatic life either directly feeds on algae, or feeds on organisms that feed on algae. Humans usually feed at the top of the food pyramid. Without phytoplankton in the oceans, salmon, tuna, cod, shrimp, lobsters and a myriad of other seafood products would not be available to us.

� 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.