Invertebrate Zoology: Protista
How do single celled organisms make a living?
Thomas Sobat, PIE Fellow, Biology Department, Ball State University, Muncie, Indiana 47306
PRIMARY INDIANA STANDARD ADDRESSED:
5.4.2 Observe and describe that some living things consist of a single cell that
needs food, water, air, a way to dispose of waste, and an environment in which
to live.
Inclusions: 5.4.4, 5.4.5, 5.4.6, 5.5.9, 5.5.10, 5.6.4
OBJECTIVES
Students will understand that there are single celled organisms, and that these
organisms are not defined as animals.
Students will know that single celled organisms require food, water, air and an
environment suitable to maintain life.
Students will generate hypotheses regarding the maintenance of protist life in
variable environments.
Students will have a research experience in which they will test their hypotheses
and report their findings
MATERIALS
5 beakers (500-1000 ml)
Aquarium pump
Aquarium hose
4 air stones
1 four-way gang valve
Distilled water
Microscope
Microscope slides and cover slips
Eyedroppers (1/treatment)
Petri dishes (1/treatment)
Single edged razorblade
Club soda or Protoslow
Dark box (to cover “light” beaker)
INTRODUCTION
Background information
The protists (Kingdom Protista) are the simplest eukaryotes, yet they
represent an incredibly diverse group. Most are unicellular, while others are
colonial and closely related to single protist cells. It is the unicellular character
that separates protists from the Kingdom Animalia, whose members are
multicellular by definition. One group of protists, the algae, are autotrophic
(photosynthesizers), while the rest eat bacteria, other protistan cells, or small
organic particles suspended or dissolved in water
As with all eukaryotic cells, protists contain membrane-bound nuclei and
endomembrane systems, as well as numerous organelles. Movement is often
provided by one or more flagella, cilia, or by cellular extension (psudopodia), and
cilia are often present on the plasma membrane as sensory organelles. Unlike
prokaryotes, protistan nuclei contain multiple DNA strands. Although they are
significantly less complex than other eukaryotes, protists can reproduce
asexually, and some are capable of meiosis and sexual reproduction. Cellular
respiration in the kingdom is primarily an aerobic process (with oxygen), but
some protists, including those that live in mud below ponds or in animal digestive
tracts, are anaerobes (without oxygen).
Protists represent an important step in early evolution, evolving from
prokaryotes and eventually giving rise to the entire line of eukaryotes. The first
protists probably evolved over 1.7 billion years ago, 2.3 billion years after the
origin of life, from simple communities of prokaryotic cells.
The Kingdom Protista is divided into three groups, grouped by lifestyle: the
protozoans, the slime molds and algae. Protozoans include all protists that
ingest their food and live in aquatic habitats, such as ponds, drops of water in
soil, or the digestive tracts of animals.
Slime molds have both unicellular and colonial life stages. When sufficient
bacteria (food) are present, cellular slime molds are single cells; however, when
food becomes scarce, they aggregate into slug like colonies, which become large
reproductive structures.
The third group of protists, the algae, contain chloroplasts and
photosynthesize like plants; these can be unicellular or colonial. The algae
inhabit all aquatic environments, and form symbiotic relationships with fungi in
terrestrial environments (lichens).
Lesson information
The premise by which this lesson has been developed involves the
students attempting to determine the requirements of life (oxygen, food, light,
etc.) for these seemingly simple organisms. Initially students should be exposed
to instructional material that describes the distinguishing characteristics within the
protists, and between the protists and the animals. It is imperative that
throughout this lesson students are reminded that protists are single celled
organisms and not animals.
Students will be responsible for developing hypotheses regarding protist
life maintenance, by relating their knowledge of plant and animal life to the
simpler protist analogues (algae and protozoans). Using simple beaker sized
microcosms, students will test their hypotheses with “protist farm” raised mixed
cultures colonized on microscope slides. In the light of good (“fair”) science
students will compare organisms maintained in a control setting to various
treatment groups exploring the effect of single variable manipulations. In keeping
with the scientific method students will report the results of their experiments in
the form of a written manuscript or presentation. This form of assessment will
require them to research the topic organisms, manage data, and develop
graphics.
PROCEDURE
1.) Following the presentation of pertinent introductory material students should
be encourage to develop hypotheses regarding protist life requirements relative
to student observations of the requirements of plants and animals.
2.) Requirements (variables) should be tested individually by comparing the
effects of the absence of one variable in a treatment microcosm to its presence in
the control microcosm following a defined period of time (seven days).
Microcosms will be beaker sized, and the control will include “protist farm” water,
an air stone with air supplied through it, and an ambient light source. Variables
included (water, food, air, and light) are the fundamental requirements for life in
plants, animals and protists, and should be the targets of student hypotheses
(variations on the theme can be attempted).
Experimental design
Each Microcosm (control and treatments) will have one colonized
microscope slide placed inside of it, and allowed to incubate for a given period of
time (in excess of six days).
Microcosms should be set up as follows (see figure):
control - will include “protist farm” water, an air stone with air supplied through it,
and an ambient light source.
Food – to test the effects of the absence of food, place one colonized slide in a
microcosm that contains an air stone and fill it with distilled water.
Light – to test the effect of the absence of light, place one colonized slide in a
microcosm filled with “protist farm” water that contains an air stone, and cover it
with a light restrictive box.
Air - to test the effect of the absence of air, place one colonized slide in a
microcosm filled with “protist farm” water without an air stone.
Water – to test the effect of the absence of water, place one colonized slide in a
microcosm without water
Slide preparation
Slides are to be incubated in a “protist farm” following the design put forth
by Wood (1996) for a period in excess of 10 days, and it is imperative that all
slides are treated equally.
To view colonized slides:
1. Scrape the material from both sides of the slide into a dry Petri dish.
2. Rinse both sides of the slide over the Petri dish using 10 ml of distilled
water and mix thoroughly (steps 1 and 2 may be completed up to 24 hours
in advance).
3. Place one drop of the protist rich mixture on a clean dry microscope slide,
and cover it with a cover slip.
4. Place slide on microscope and view using at least 100x magnification.
3.) Prior to experiment setup one slide should be scraped, viewed and initial
counts should be made. Multiple students can complete this, each making and
counting their own slides. Individual counts can be used as replicates, and be
averaged.
Slide counts should proceed as follows:
1. All counts should be completed using the same magnification.
2. Start at one edge of the cover slip and move to the other edge counting all
organisms in the field of view (the number of passes may vary based on
colonization time. If initial slide counts require x number of passes across
the slide to yield >100 organisms, then all counts should be made using x
passes.).
3. Students should distinguish between green immobile and non-green
mobile cells, and record these counts separately.
4.) After the experiment has been set up and allowed to incubate for a period of
at least seven days. Counts should be made for the control and all of the
treatments (students can be divided into groups where it is the responsibility of
each group to perform counts on a particular treatment). Comparisons can be
made between the initial and the control, and the control and individual
treatments.
5.) Upon completion of counts, all replicate counts should be averaged, and data
should be entered into a Microsoft Excel spreadsheet (this can be done in a
number of ways, 1. use calculators, 2. students can calculate averages using
their math skills, or 3. all data points can be entered into the spreadsheet and
students can use the “CALC AVG” function of the software). Students can
develop graphs using the graphing function associated with the spreadsheet
software (see Excel help). Once graphs have been generated the class should
discuss trends in the data so that students have a clear understanding of their
results prior to writing their reports.
ASSESSMENT
The experiments can be run to a number of different levels, each step could be
considered a unit of assessment. If students are held responsible for
hypotheses, experiments and graphs, points could be assigned for each stage.
Add report writing or a quiz and the level of assessment increases (see attached
quiz).
EXTENSIONS
One variation of this lesson might include adding multiple slides to the control
and treatment microcosms upon setup, and continuing the experiment for an
extended period. Each week an additional series of slides could be processed,
and temporal aspects of this study could be added to the hypotheses.
CONNECTIONS
This lesson would be an outstanding continuation of a microscopy lesson, or a
precursor to curriculum dealing with plants and animals.
References
Wood, T.S. 1996. Aquarium culture of freshwater invertebrates. The American
Biology Teacher. 56(1) 46-50.
Protist Quiz 15 points
Name_____________
Match the following organisms with the proper Kingdom
1.
2.
3.
4.
5.
___Algae
___Mouse
___Protozoan
___Oak tree
___Human
A. Animalia
B. Protista
C. Plantae
True False:
6. ___ Protists are multicellular animals
7. ___ Algae are protists
8. ___ Bacteria are protists
9. ___ Some protists make food using the suns energy
10. ___ Some protists eat bacteria
11. The following are all protists except:
a. Algae
b. Slime mold
c. Protozoans
d. Worms
12. Protozoans can be found in:
a. Ponds
b. Soil water
c. Digestive tract of an animal
d. All of the above
13. Algae
a. eat bacteria
b. get energy from the sun
c. are animals
d. are plants
14. ____________ are unicellular, and animals are _______________
GLOSSARY
Aerobic - requiring the presence of air or free oxygen to sustain life.
Anaerobic - living in the absence of air or free oxygen.
Animalia - the taxonomic kingdom comprising all animals.
Autotrophic - any organism capable of self-nourishment by using inorganic
materials as a source of nutrients and using photosynthesis or chemosynthesis
as a source of energy, as most plants and certain bacteria and protists.
Cilia - short, hairlike, rhythmically beating organelles on the surface of certain
cells that provide mobility, as in protozoans, or move fluids and particles along
ducts in multicellular forms.
Eukaryote - any organism with a fundamental cell type containing a distinct
membrane-bound nucleus.
Flagella - a long lashlike appendage serving as an organ of locomotion in
protozoa, sperm cells, etc.
Invertebrate - a. without a backbone or spinal column; not vertebrate.
b. of or pertaining to creatures without a backbone.
Kingdom - a taxonomic category of the highest rank, grouping together all forms
of life that share fundamental characteristics
Lichen- any complex organism of the group Lichenes, composed of a fungus in
symbiotic union with an alga, most commonly forming crusty patches on rocks
and trees.
Microcosm - a little world; a world in miniature
Organelle - a specialized cell structure that has a specific function; a cell organ.
Prokaryote - any one-celled organism that lacks a distinct membrane-bound
nucleus and has its genetic material in the form of a continuous strand forming
loops or coils: characteristic of monerans.
Protista - a taxonomic kingdom comprising the protists.
Protozoa - any of various one-celled protist organisms that obtain nourishment
by ingesting food particles