Kingdom Protista
These Eukaryotic life forms possess a nucleus (unlike bacteria and viruses), and are
often placed into a single category, the Protozoa. This kingdom also includes algae.
Protozoans will be the topic of the first Zoology 5 laboratory and various kinds of
protozoans will be observed. Many protozoans form colonies. Individuals making-up a
colony are nearly identical and each performs, with the exception of individuals
specialized for reproduction, the same functions. This is unlike multicellular organisms
where cells have separate functions.
Protozoans are a diverse assemblage of organisms possessing all types of symmetry, a
wide array of structural adaptations, many feeding modes and occur wherever moisture is
available. They are sessile (attached), motile, free-living or parasitic. Studying the
protozoans presents problems because they have been separated into taxonomic groups
based on their mode of locomotion. This is convenient but artificial and has no clear
phylogenetic (evolutionary) bases.
Phylum: Sarcomastigophora
Members of the taxon move by means of flagella, pseudopodia or both. Usually only
one type of nucleus is present and they fail to form spores during their life cycle. When
sex is performed it is syngamous (fertilization of a gamete by another).
Subphylum: Mastigophora
Mastigophorans (sometimes termed Flagellates) are characterized by the presents of
one or more flagella. These are considered to be most primitive protozoans, however
they are believed to be the ancestors of the metazoans (animals). Some mastigophorans
contain chlorophyll and are able to perform photosynthesis. They are called
phytomastigophorans and an example of these plant-like forms is Volvox (see below).
Flagellates without chlorophyll are known as the zoomastigophorans. An example of
these protozoans is Trypansoma, the causative agent in African sleeping sickness.
Volvox is a colonial organism exhibiting a quasi-multicellular condition. It is often
considered a link between multicellular organisms and unicellular life forms. If present
in the classroom, prepare a wet mount of live Volvox colonies using a depression slide to
avoid crushing this beautiful organism. Colonies may reach a size of 5 mm and can be
seen with the unaided eye. While observing Volvox notice its spheroidal shape,
swimming motion and color (why is it green?). Volvox colonies are hollow spheres with
numerous cells embedded in a gelatinous outer wall. Each cell contains a nucleus,
vacuole, a red eyespot, green chloroplasts and two flagella, visible under high power
(400X).
Figure 1. Draw a Volvox colony under low power (40X). Make the drawing 10
cm in diameter. Label and annotate.
Figure 2. Draw a portion of a Volvox colony under high power (400X). make
the drawing 10 cm across. Label and annotate.
Study Questions
1. Define a colony.
2. What are the similarities and differences between plants and animals?
3. Why is Volvox considered as protozoan rather than a metazoan?
Figure
Subphylum: Sarcodina
Sacodinans (also known as the Rhizopoda) usually lack cilia or flagella (usually) and
move via pseudopodia. Amoeba (or Ameba) is representative of this subphylum. They
are commonly found in ponds and streams attached to floating vegetation or debris. They
require oxygen for respiration and must live where other microbes exists as a food
source. The specimen in lab is Amoeba proteus but sometimes Pelomyra carolinensis
(formerly Chaos chaos) is present.
Make a wet mount of amoeba using a depression slide. Your instructor will
demonstrate the technique for placing an amoeba on a glass slide. Amoeba should be just
visible to the naked eye as whitish, nearly transparent spots. First locate them with your
dissecting scope then examine under low power. Reduce the light by closing down the
iris of the microscope diaphragm. Amoeba can be difficult to locate so be patient.
When located, watch and study the moving pseudopodia and cytoplasmic fluid.
Figure. 3 Draw a series of five outline sketches of your specimen showing
successive changes in shape. Make each sketch 2.5 cm across and at a
1-2 minute intervals. Do not select an amoeba that is not moving!
Use arrows to indicate movement and number the five sketches.
Anatomy. The long finger-like projections are called pseudopodia (“false feet”).
Within the cell you will discover a number of structures and organelles. Amoeba are
rather simple protozoans making them ideal organisms for study. Identify and study the
structures within and watch cytoplasmic streaming. Your textbook will be of help in this
study.
Figure. 4 Draw an Amoeba 10 cm across and label all the structures identified.
Label and annotate.
Study Questions
4.
5.
6.
7.
8.
9.
10.
Explain the protoplasmic movement within the amoeba.
What is the outer layer or “skin” of the amoeba called?
How does the amoeba eat?
How does the amoeba ingest food and digest food?
What sex is an amoeba
How does an amoeba reproduce?
Why is the amoeba considered immortal?
Phylum: Ciliophora
Ciliates have organelles of locomotion called cilia. In addition they possess two
distinct types of nuclei and are the most complex unicellular life forms. Their
reproduction is as complex as that of many metazoans. Ciliates are common inhabitants
of aquatic environments and live as commensals in the guts of many animals.
Paramecium is a ciliate often used in life science classes and in the study of microbes.
Paramecium is common in freshwater where there is abundant decaying vegetation and
bacteria abound. They are found world-wide and easy to obtain for laboratories.
Although there are several species ranging in size from120 to 350 microns and differing
in structural detail, P. caudatum is the species usually found in life science classes.
Obtain a sample of a Paramecium culture and make a wet mount slide. Sometimes
culture contains P. multimicronuleatum (120-350 microns) or Spirostomum
ambiguum (1-3 mm) one of the largest protozoans. Observe the organism with the
naked eye or under a dissection microscope with a dark surface under the slide. Notice
that these creatures tend to aggregate near the edges of the drop or around debris.
Although they may seem slow to the unaided eye, under a compound microscope they are
speed demons. To slow them down add a drop of viscous methyl cellulose (Protoslo).
Carefully mix the Protoslo with the drop of Paramecium culture provide. Place a cover
slip over the mixture and observe. Fiber from lens paper can also be used in place of
Protoslo to slow these organisms down.
Figure 5. Draw a Paramecium 20 cm long. Label and annotate all organelles
and structure that you can find.
Study Questions
11.
12.
13.
14.
15.
16.
Which end is front and which end is rear?
Describe locomotion. Does the cell rotate on its axis? Is rotation
clockwise or counterclockwise?
Can Paramecium move backwards? What happens when it meets an
object?
How does a Paramecium maintain water balance?
How does a Paramecium respire?
How does a Paramecium eat?