Laboratory 1 - The Protozoa
While they are not invertebrates, the Protista represent the first eukaryotic organisms to
evolve. The vast majority of the species comprising Kingdom Protista are unicellular, but there
are also aggregate, colonial, and multicellular species. The presence of quasi-multicellular and
true multicellular species among the protists is significant in understanding how a species of
protistan gave rise to multicellular eukaryotes. The principle of continuity states that “any stage
of life’s evolution should originate from some preexisting state(s).” This means that one group
should have the genetic wherewithal to give rise to features seen in groups evolving from that
older form. Hence, the capacity of some protistans to evolve multicellarity provided an avenue
for other multicellular eukaryotes (including humans) to evolve. This evolutionary link is one of
the reasons we study protistans as part of invertebrate zoology – it gives us a perspective of the
steps that started the process of animal evolution.
Another reason we examine the Protista is that even though most of them are unicellular,
they can carry out all of the basic life processes in the housing of a single cell. This means
everything from cellular respiration to reproduction occurs within a single cell. An observation
you want to make during lab is the relative size of the cells of protistans. Some will be quite
large, whereas others will be small. Think about what the minimum size is for a cell and it can
still carry out all life processes. Next, what is it about the protists that have small cell size?
Have they given up some life processes for smaller size or have they acquired something that
allows for smaller size. In later labs, compare the cell size of protists to the cells of multicellular
eukaryotes. Note the magnification you are using to observe protists and draw an image that
reflects what you are seeing using the field of view to provide perspective of scale (hint: the 40X
objective will provide the best view on most, although 10X might be sufficient for the larger
taxa). Always start with the scanning (4X objective) when first trying to find something on a
glass slide.
The third topic of observation in this lab exercise is the complexity and diversity of the
Protista. Note protistan systematics in the lab manual (pp. 2 – 4). This is a complex group
despite their apparently unicellular simplicity. We will use the classification of invertebrate
phyla to understand the relatedness of taxa within each phylum in future labs. This is not the
case for the Protista as the classification is largely man-made (we will discuss this more in
lecture) and it is constantly changing. Still, it provides a perspective of the diversity of this
group and gives a hint at the complexity (think principle of continuity again) that allowed a
protistan ancestor to give rise to the organisms we will be examining for the remainder of the
semester. This means – you will not be responsible for the taxonomy beyond the scientific name
of each organism.
Lab Practicum
You will examine living specimens during lab time. The key is to be sure you are observing the
correct organism (it is hard to keep pure cultures of protists because many protists eat other
protists!). You can use the lab manual as a guide but we are not worried about pieces and parts
in this exercise. Your focus is being able to recognize the different taxa and getting a perspective
on their complexity (mode of locomotion, reproduction, special features). BUT the emphasis
with the live specimens is to observe and think about these unicellular (and a colonial) organisms
as fully functional entities. The other issues (complexity but not taxonomy or pieces and parts)
can be done later in lab and during outside of lab time.
Lab Objectives:
1. Study live specimens to observe mode of locomotion and general behavior. Differences
between ciliate, flagellate, and amoeboid protistans.
2. Consider the question "what is the minimum size of a cell for carrying out all of life's
processes - comparing a protozoan to a metazoan cell.
3. Compare unicellular, colonial, and multicellular protists for organization and complexity.
Follow the procedures outlined in the lab manual. Always start your search for live specimens
using the low-power objective. Move to the high-power objective once you have found the
specimen. You will find that you can make observations on both magnifications (low-power =
movement, behavior; high-power = fine structure).
Live Specimens
Euglena (p.7)1
Volvox (p. 9)2
Amoeba (p.12)
Difflugia or Arcella (p. 14)
Actinosphaerium (p. 19)2
Parameciu (p. 27)1
Stentor (p. 29)1
Vorticella (p. 29)
Bursaria (p. 29)1
1
2
Use proto-slo
Use a depression slide
Preserved Specimens
Preserved specimens are stained to allow for better observation of internal structures. There are
also some taxa on the preserved specimens list because they cannot be observed well as live
specimens.
Ceratium (p. 4)
Stentor
Vortcella
Difflugia
Actinosphaerium
Bursaria
Euglena
Volvox
Amoeba
Paramecium
You do not need to complete the worksheet at the end of Protista Exercise.
Additional Resources:
A Google image search using the genus name for any of these taxa will find good images while
observing the live specimens
Pond Life – video of protistans (and other organisms we will see throughout the semester)
http://micro.magnet.fsu.edu/moviegallery/pondscum.html
Invertebrates in Motion – another good web site with invertebrate motion and images
http://www.eeob.iastate.edu/faculty/DrewesC/htdocs/#non-oligochaetes
Refer to web links on p. 56-57 of lecture text for additional information