BS 120
Field Natural History
Spring
1
LAB 5
KINGDOM PROTISTA
Objectives:
1. To examine some typical examples of the diverse Kingdom Protista which includes all
of the animal–like microorganisms of the Subkingdom Protozoa and of the plant–like
microorganisms of the Subkingdom Algae,
2. To illustrate how complex cells of unicellular Protistans can be.
3. To have you, as a relatively gigantic organism, appreciate some of the special challenges
faced by small unicellular organisms, and the adaptive solutions to these challenges that
they have arrived at.
4. To learn the general differences between the various phyla.
This lab presents a special challenge to you, one that takes practice and patience and a willingness
to live with frustration. You may be ready to observe Euglena or Peridinium for example, but these
highly motile organisms are living their own lives and will not readily stop and pose for you!
Also, because you will be looking at very small organisms, the slides that you prepare from the
stock cultures may not always contain what you are looking for. Sometimes the cultures we obtain
are rich with organisms, other times there doesn’t seem to be as many. You won’t be able to see this
until you put the slide under the microscope. When looking for organisms, be methodical and
thorough, but don’t waste too much time. Go back and make another slide preparation.
Methods:
You are to obtain samples of protists from each of the phyla listed below. Use your survey
handout to verify visible characteristics, and sketch each organism that you see. Some of the living
organisms may require special techniques to prepare, and your instructor will review these in the
pre-lab lecture. You will be responsible for knowing the differences between each of the phyla
listed below by observing the representative species. In addition, you should know the general facts
included in the description of each phyla.
Please note that you should not use the oil immersion [100x] lens on your compound
microscope but rather those capable of lower magnification, starting with the lowest magnification
and working up to the 43x lens.
Locomotory modes- An important criterion used in the classification of Protistans is their means
of locomotion.
Flagellates – Several major groups of Protistans move by means of one or two elongated, whip-like
flagella. Among those that you should see today are Euglena, the dinoflagellate Peridinium and the
Volvox culture. Some groups of flagellates are photosynthetic (autotrophic) , while others absorb
organic nutrients and are non-photosynthetic (heterotrophs).
Ciliates – This large group moves by means of cilia, locomotory structures that are much smaller
than flagella. Each ciliate organism has many cilia, which are coordinated by a “pseudo-nervous”
system that allows the organism to swim in a very controlled fashion. Ciliates are
nonphotosynthetic heterotrophic protistans; many are highly predatory. Ciliates that you will see
today include Stentor, Paramecium, and the predaceous Didinium.
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BS 120
Field Natural History
Spring
2
Cytoplasmic streamers (Sarcodina)– Examples you should see today are Chaos and Difflugia,
Diatoms and Ameoba. Ameobas are nearly transparent and difficult to view. They will be available
as pre-mounted slides. Ameobas move by using a flexible cell membrane, which can be extended
into pseudopods (false feet), by smooth, flowing movements of internal cytoplasm. Diatoms have a
rigid silica skeleton, but there is a longitudinal grove in the motile species, and within this groove
the inner, deformable membrane is in direct contact with the aquatic medium in which the diatom
lives. Cytoplasmic streaming deforms the cell membrane in a coordinated front-to-rear “wave” that
pushes against the water (or fluid medium), moving the diatom forward.
Nonmotile Protistans – Many protistans have no means of locomotion, but are permanently
attached to objects in their environment (the stalked ciliates) or are free-living plankton that are
moved around by water currents. Photosynthetic protistans living in the plankton are utterly
dependent on eddies and vertical water movements to keep them near the surface. Because they are
denser than water, they otherwise would sink out of the well-lit upper layers of lakes and oceans to
depths where it is too dark for them to photosynthesize. Because small organisms of the same
density sink more slower than larger ones, and because small organisms are also more easily carried
upwards by vertical eddy currents, there has been strong selection for small planktonic protistans.
Small size can be viewed as one of the most basic adaptations of planktonic organisms.
The movement of microorganisms through waterThe rapid swimming of organisms like Euglena, Paramecium and Stentor is a remarkable
feat that has captured the interest of not just of biologists, but of engineers specializing in fluid
dynamics. In absolute terms, of course, these microorganisms swim much more slowly than do fish.
But when compared to larger swimmers on a matching scale, Protistan flagellates and ciliates are
far faster:
a) Protists can travel at speeds up to 100 body lengths per second,
b) speedy fishes like tuna can achieve only about 10 body lengths per second
c) the fastest human swimmer can travel just over 1 body length per second.
This may explain why you have difficulty in keeping them in the field of view when they are on the
move!
The swimming speeds of fast protistans are all the more remarkable when one realizes that
organisms of such small mass have negligible momentum. Unlike fish or a human, whose inertial
momentum makes them glide through the water between strokes, a protistan stops dead between
strokes – or it would if it didn’t have some continuous mechanism of propulsion. Fortunately, both
cilia and flagella provide continuous propulsion; the protistan needs this, because without inertial
momentum to carry it forward the viscosity (resistance to movement) of the water would create an
insurmountable obstacle to getting anywhere. “To appreciate the nature of the viscous forces
experience by microorganisms, we would have to swim in a fluid one million times more viscous
than water. Even a pool filled with honey, the relative strength of viscous to inertial forces would be
two orders of magnitude smaller than it is for microorganisms swimming in water, and a more
appropriate fluid would be molasses or even tar” ("How microorganisms move through water. ",
1986 American Scientist, by G.T.Yates –an engineer!). This means that if a protistan had a
discontinuous means of propulsion (like the arm motions of a human swimmer), it would not move
forward at all, but would simply thrash in place.
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BS 120
Field Natural History
Spring
3
THE SUBKINGDOMS AND PHYLA OF THE KINGDOM PROTISTA
The Kingdom Protista includes a variety of organisms that are either unicellular,
multicellular, or in some cases are grouped into colonies. Protistans are divided into the animal–like
Protozoans, which are covered with a cell membrane or pellicle and have specialized organelles
such as contractile vacuoles, cytostomes, mitochondria, ribosomes, and flagella or cilia. The
Subkingdom Algae includes all of the photosynthetic eukaryotic organisms which were separated
from Kingdom Plantae, where they used to be included, due to their lack of tissue differentiation.
The protistan kingdom also includes the slime molds, organisms that are believed to be related to
the fungi, which we may observe during the fungi lab.
The algae may be unicellular, multicellular, or in colonies. They are found in a variety of
habitats such as submerged in water, on soil, on the bark of trees or on the surface of rocks. Algae
have visible nuclei and chloroplasts which contain chlorophyll and other pigments. Typically there
are seven Phyla of algae, and we will examine each today in lab. The Euglenoids are considered by
some to be a mobile form of algae, because they possess chloroplasts, and are therefore autotrophic.
Subkingdom Algae
Phylum Euglenophyta (Euglena): We have prepared slides of Euglena. This Phylum shows the
difficulty in dividing up the protists into protozoa and algae. Why?
Phylum Chlorophyta (green algae): The Chlorophyta are believed to be the ancestors to green
plants. The Chlorophyta contain some examples that exemplify why the Protists are sometimes
considered a “catch-all kingdom.” Although Protists are generally unicellular, many species of
Chlorophyta are colonial or multicellular. In colonial organisms, the cells making up the colony
may be interconnected, and they function as a unit. The Volvox that you will see in lab today is a
hollow ball of colonial cells, and there is a division of labor. Some cells are involved with
reproduction and others are not. The dark green spheres inside are daughter colonies that will be
released when the mother colony breaks apart. There are prepared slides and living samples of
Volvox. Proto-Slo will not be necessary.
In multicellular algae, different cells are specialized for different functions, such as in the large
seaweeds. Some parts of the algae are like large leaves, while the holdfasts that attach to rocks are
like roots.
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Field Natural History
Spring
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Spirogrya (also Chlorophyta) is characterized by a spiral chloroplast in each of its cells. It forms
long filaments. Spirogyra can be found locally in freshwater.
Phylum Bacillariophyta (diatoms): Look at the mixed or marine diatom slide (prepared slide).
Diatoms are enclosed in a “shell” made of silica. They are widely used as abrasives in scouring
powder, and toothpaste, and also in roadsigns and license plates because of their reflective qualities.
Diatoms move by cytoplasmic streaming.
Phylum Dinoflagellophyta (dinoflagellates): Obtain a prepared slide of Peridinium. They have
two flagella that beat within two grooves, one perpendicular to the other. The dinoflagellates are the
primary photosynthesizers in the oceans.
Phylum Phaeophyta (brown algae): look at the sample of kelp (in the jar) (Laminaria) on display.
This species can grow to be 100 meters long.( If this is not available, there will be a jar of Fucus, as
Porphyra and Chondrus crispus.
Phylum Rhodophyta (red algae): examine a sample of Rhodymenia on display (in the test tube).
Red algae is the source of carrageenin which is used to make gelatin harden and ice cream smooth.
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BS 120
Field Natural History
Spring
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Subkingdom Protozoa
All protozoa reproduce asexually by cell division (fission) but a few exhibit some degree of
sexual reproduction. They possess dormant stages, called cysts, which are resistant to drought, heat
and freezing. Locomotion plays an important role in the classification of the protozoans into the
Rhizopoda which move by flowing protoplasmic projections called pseudopodia, the Zoomastigina
that move by flagella and the Ciliates that move by cilia. Other protozoa lack any means of
locomotion (Sporozoa) and are all internal parasites of other organisms.
Phylum Ciliophora (ciliates): prepare a slide of Dindinium/Paramecium using Proto-slo.
Dindinium is a predaceous ciliate that feeds on Paramecium. Also look at the prepared slide if
desired. Look for large, slipper-shaped cells with a groove down the middle. This is the oral
groove, used to direct food into the “mouth” of the protozoan. The ciliates are considered to be the
most complex of the protozoa.
Phylum Euglenophyta (Euglena) – represents the true difficulty in classifying Protists. Euglenoids
are heterotrophic, which means they’re more like animals (Protozoa). But they also have
chloroplasts and are capable of photosynthesis, making them autotrophic, and much more like the
Algae.
Phylum Rhizopoda (sarcodines or amoebae like): prepare a slide of Chaos using a slide with a well.
The rhizopods are amoung the largest unicellular organisms. They move by extending pseudopodia
(false feet), and flowing cytoplasm into them. The pseudopodia can also flow around a food
particle and engulf it.
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BS 120
Field Natural History
Spring
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Phylum Zoomastigina (flagellates): Termite parasites are flagellates in this phylum. The protozoa
are in a mutualistic relationship with the termites.
What does this mean?
To view the termite symbionts (Trichonympha), gently squeeze the abdomen of a termite
until brown goo is projected from the anus. Dab this goo on a slide and add a drop of termite saline
solution. Cover with a coverslip and scan for moving cells at 100X.
Trypanosoma T. cruzi – Chagas disease –recall 1st lecture. Causes swelling of the eye, tiredness,
fever, enlarged liver or spleen, swollen lymph glands, and sometimes a
rash, loss of appetite, diarrhea, and vomiting. Transmitted by true bugs
(Hemiptera)
T. rhodesiense, T. gambiense – African sleeping sickness, transmitted by the Tsetse
fly.
Look for these serpentine shaped protests between the red blood cells.
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