Purposes
1 . To study representatives of the various phyla in the
kingdom Protista
2. To learn the life cycles of economically important
protistans
Background
Protists
are eukaryotic organisms. The ancestors of this group were the first to have a
true nucleus, chromosomes, organelles such as chloroplasts, mitochondria, endoplasmic
reticulum, cilia, and cell division by mitosis or meiosis. The ancestral
protists not only gave rise to the modern protists but also three other
kingdoms of life: fungi, plants, and animals. Most protists are unicellular, although
several of the algae are colonial or truly multicellular. Although protists
are often described as being simple organisms, their cellular organization and
metabolism is every bit as complex as those found in the so-called higher
organisms. In fact, higher organisms are often much simpler at the cellular
level because their many cells are specialized to perform particular functions
while single protistan cells perform all functions necessary for life as
independent organisms.
Protists live everywhere there is water: in the ocean, in
freshwater, in puddles, in damp soils, and, as symbionts, in the body fluids
and cells of multicellular hosts. Some are autotrophic, making their own food
materials through photosynthesis, while others are heterotrophic, absorbing
organic molecules or ingesting larger food particles. All protists can
reproduce asexually by mitosis while some are also capable of sexual
reproduction involving meiosis and nuclear exchange. A cyst stage is found in
the life cycle of many protists; it allows the species to lie dormant and
escape harsh temporary conditions.
The boundaries of the kingdom Protista are not well understood. When first proposed in 1969 by Robert Whitaker, the kingdom was defined as containing unicellular organisms but subsequent studies have indicated that some fungi and plants are more similar to the protists than they are to other fungi and plants. Consequently, some multicellular algae, such as the kelps, and some fungi, such as the slime molds and water molds, are considered by some to be protists. About 60,000 species of living protists are known and a similar number have been described from the fossil record. For the purposes of this lab manual the protists will be defined as containing the following phyla. Those that will be studied in this exercise are marked with an asterisk.
Nutrition Primarily by Photosynthesis *Dinoflagellata: brown algae having two flagella;
dinoflagellates
Chrysophyta: golden algae having flagella and colonial forms
*Bacillariophyta: algae with silica shells; diatoms
*Euglenophyta: green flagellates lacking cell walls; euglenoids
*Chlorophyta:
green algae
Phaeophyta:
multicellular brown algae; kelps Rhodophyta: multicellular red algae; seaweeds Nutrition Primarily by Ingestion *Rhizopoda:
naked and shelled amoebas *Actinopoda: amoebas with axopodia and siliceous
skeletons; heliozoans and radiolarians Foraminifera: amoebas
with calcareous shell; forams *Apicomplexa: parasitic protists with complex
life
cycles;
sporozoans
*Zoomastigina:
motility by means of flagella
*Ciliophora:
protists with cilia; ciliates
Protists Resembling Fungi
Myxomycota:
plasmodial slime molds Acrasiomycota: amoeboid cells that aggregate to
form fruiting body; cellular slime molds Oomycota: water
molds; to be studied in Exercise 16
Lab Instructions
In this
exercise you will look at representatives from several, but not all, of the
phyla listed above.
Photosynthetic Protists
Dinoflagellata
These organisms are the primary components of phytoplankton,
forming the basis of marine food chains. About 1100 species have been
described. Red tide is caused by the explosive growth of certain species of
dinoflagellates.
101 Make a wet-mount slide of Peridinium
from the stock culture. This dinoflagellate is common in freshwater lakes
and streams. Note the trispiked appearance of the organisms. These cells have
plates of cellulose called theca that
surround the cell. Two flagella are present and lie in grooves in the wall at
right angles to each other. Peridinium
is photosynthetic and contains chlorophyll a and c, but the
green color is masked by the presence of orange-brown carotenoid pigments. Make
a sketch of Peridinium below.
Bacillariophyta
The 10,000 species of diatoms share a common characteristic:
a cell wall consisting of two valves made of silica. They are often
golden-yellow in color because of an excess of carotenoid and xanthophyll
pigments, which tend to mask the green of the chlorophylls that are also
present. When the diatom cell dies, the siliceous valves do not disintegrate
and accumulate as sediments (fig. 15.1). In
1~ Make a wet-mount slide from the diatomaceous earth
available in the laboratory. Place a drop of water on the slide and then add a
very small amount of diatomaceous earth to the drop. Stir well before adding a
coverslip and viewing.
Note the exceedingly delicate patterns of the diatom
valves. These are the skeletal remains of cells that lived thousands of years
ago. In a top down view, some valves will be round, others triangular, ovoid,
and irregular. When viewed from the side, these same valves appear rectangular
or ovoid.
Figure 15.1 Diatoms
exist in an exquisite variety of geometrical patterns.
The ornamentation of the valves is often used as a test of the
resolution of microscopes. In a poor microscope, only the outline of the valve
will be visible, while in very good microscopes the fine indentations and
perforations will be apparent. Sketch a few different types of diatom valves
below. Indicate the location of the girdle,
the region of overlap between the two valves.
Euglenophyta
This small group of about 800 species contains flagellated,
autotrophic protists that lack cell walls, having instead a flexible outer
covering called a pellicle. Species
are common in waters polluted with organic matter and on the surfaces of wet
soils.
Anatomy of
Euglena
00- Make a wet-mount slide of Euglena from the stock culture and observe through your compound
microscope. If the organisms are swimming too fast to be studied, make a new
slide but add methyl cellulose, a thickening agent, or shred a small piece of
lens paper into the drop to trap the organisms.
Euglena is usually pear-shaped with the blunt end being the anterior.
Does the flagellum push or pull the organism through the water?
1. Watch the organism
closely. What evidence is there that the surrounding pellicle is flexible?
Figure 15.2 Anatomy of Euglena sp.
As you study Euglena, find
the structures indicated in figure 15.2.
What color is the eyespot,
also called the stigma, near the base of the flagellum? How many flagella
does Euglena have?
Excess sugars produced during photosynthesis are converted
into paramylum, a unique form of
storage starch. Is the chlorophyll of Euglena
localized in structures, or spread throughout the cell as in cyanobacteria?
Chlorophyta
The 7000
or so species of green algae can be grouped to create a natural progression
from single cells to multicellularity. Three lines of evolution are apparent:
(1) the formation of colonies, (2) the formation of multicellular filaments,
and (3) the formation of definite multicellular organisms.
Colonial Series
You will examine species from
three genera known as the volvocine series: Chlamydomonas,
Pandorina, and Volvox.
56
Figure 15.3 Life
cycle of the green alga Chlamydomonas.
On the
supply table, two cultures of Chlamydomonas
will be found, one labeled + and the other -. Under favorable conditions
of light intensity, temperature, and nitrogen starvation, Chlamydomonas will undergo sexual reproduction. Place one drop of
each culture side by side on a clean microscope slide, but do not mix. While
looking at the slide through your dissecting microscope, mix the drops and
observe what happens. Add a coverslip and look at the cells under high power of
your compound microscope. Sketch the cells below.
+ Compare your drawing to the life cycle in figure 15.3. Chlamydomonas is capable of asexual and
sexual reproduction. In asexual reproduction, the cells divide by mitosis. In
the initial stages of sexual reproduction, such as you just observed, cells of
different mating types come together and their flagella intertwine. The cells
act as gametes and fuse to produce a zygote. Because the two mating types are
morphologically identical, Chlamydomonas
is described as being isogamous (=
identical male and female gametes). The zygote will eventually develop a thick
wall and go into a period of dormancy, usually overwinter. When dormancy ends,
the zygote will divide by meiosis to produce four cells (zygospores), which
will become typical adult cells. Is an adult cell of Chlamydomonas haploid or diploid? What about the zygote?
Figure 15.4 Volvox: (a)
adult colony with smaller daughter colonies inside; (b) magnification of cells
in colony wall; (c) differentiation of cells in colony for sexual reproduction.
a b
c
Now make a wet-mount slide of the second species in this
series, Protococcus. Observe the
slide with your compound microscope. How does Protococcus. differ from Chlamydomonas? How is it similar?
Illustrate your answer with a sketch.
Now make a slide of Volvox,
but do not add a coverslip. View the slide through your dissecting
microscope with reflected light coming from one side. How does Volvox differ from `Chlamydomonas?
A colony of Volvox consists
of 500 to 50,000 cells. The coordinated stroking of two flagella in each cell,
allows the organism to move in a direction while spinning on its axis. The
cells in the colony are held together by a gelatinous matrix and are connected
to neighboring cells by thin strands of protoplasm.
Figure 15.5 Life
cycle of Ulothrix.
Young colonies produced by either asexual or sexual reproduction
may be contained inside the parent colony (fig. 15.4). In sexual reproduction,
several cells in the colony differentiate into motile sperm and a few others
become nonmotile eggs. Sperm swim to the eggs, and fuse with them to form
zygotes. Zygotes develop into daughter colonies inside the parent colony and
are released when it dies. Because the male and female gametes can be distinguished
from one another, Volvox is described
as being heterogamous (= different
male and female gametes). Because the egg is the larger of the two gametes,
Volvox is also described as being oogamous.
The cells that produce sperm are called antheridia, and those that produce eggs are called oogonia. Because of this
differentiation of cell types and division of labor, the colony has some of the
properties of a truly multicellular organism.
Filamentous
Series
In this series you will study two species in two genera: Ulothrix, which is isogamous, and Oedogonium, which is heterogamous.
lo. Obtain a prepared slide of Ulothrix and look at it with your
compound microscope. This is a common filamentous green algae in streams and
lakes. Each unbranched filament is composed of cylindrical cells joined end to
end
(fig.
15.5). Some filaments have a basal cell that serves as a holdfast. Each cell has a single collar-shaped chloroplast that
surrounds the cytoplasm and the nucleus.
Scan along the filament until you find a cell in which the
contents have divided into 2, 4, 8, or 16 cells inside the cell walls. These
cells are zoospores and are asexual
reproductive cells. When released, they swim away by means of four flagella.
Each cell can divide and produce a new filament.
You should be able to find some cells, called gametangia, in which the contents have
divided into 16, 32, or 64 cells, each with two flagella. These are isogametes and when released will fuse
with other isogametes to form a zygote. The
zygote usually secretes a heavy cyst wall and does not divide until the
following spring. The zygote is diploid and will undergo meiosis to produce
four zoospores, which each can give rise to new vegetative filaments. The
zygote is the only diploid cell in the life cycle. What important process is
happening during fusion and meiosis that is an advantage to the species?
Figure 15.6 Oedogonium:
(a) photomicrograph; (b) life cycle.
a.
®
Obtain a slide of Oedogonium and look at it through your
compound microscope. Scan along the filament and find a vegetative cell, which
should be examined under high power (fig. 15.6). It contains a net-shaped
chloroplast that surrounds the cytoplasm and nucleus.
Some of the cells in the filament will be dark colored and
swollen. These are oogonia and
contain a single egg. In fact, the genus name Oedogonium means enlarged
egg cell. Find other cells in the filament that are short and disk-shaped.
These are antheridia and each
produces motile sperm. Mature sperm have a crown of flagella on the anterior
end and when released swim to and enter the oogonium where fertilization
occurs. Zygotes are identifiable by a thick cell wall that surrounds them
inside of the oogonia. Zygotes eventually divide by meiosis to produce four
microzoospores. When they escape from the oogonium, they form new filaments.
Asexual reproduction occurs when vegetative cells differentiate into large.
Figure 15.7 Conjugation
between mating types in Spirogyra: (a) vegetative cells grow as filaments and
have a spiral-shaped chloroplast; (b) sexual reproduction (conjugation) starts
when tubes grow outward from adjacent filaments; (c) condensed protoplast
leaves male filament and enters female Moment; (d) zygotes are formed when
protoplasts fuse.
(a) (b) (c) (D)
macrozoospores, which leave the filament and give rise to new
filaments. Is Oedogonium isogamous or
heterogamous?
P Before leaving the filamentous green algae, you should
examine one other species. Obtain a prepared slide of Spirogyra.
Also known as green silk, this species is usually found in
cool, clear, running water. Vegetative cells are cylindrical and contain a
single, spiral-shaped chloroplast (fig. 15.7). Spirogyra is isogamous and does not produce motile gametes. Gametes
are transferred by the process of conjugation.
Scan
your slide until you find two adjacent filaments where tubes are growing
outward toward one another (fig. 15.7). One filament is of mating type + and
the other -. When the tubes meet they will fuse, forming a connection between
the two cells. The contents of one cell will move through this conjugation tube
and fuse with the other cell to form a zygote. The zygote overwinters and then
will give rise to four haploid nuclei. Three will degenerate and the fourth
will grow to produce a new filament.
ALGAE LAB 2
DIVISION
CHLOROPHYTA
The Chlorophyta are the green algae. They are an ancient group, possibly extending
back to the origin of photosynthetic, cellular plants. Complex green plants are considered to have
arisen from green algae.
Distinguishing
Characteristics:
1.
Pigments---chlorophyll a and auxiliary pigments, chlorophyll b and
carotinoids (yellow and orange pigments).
2.
Food reserve--true starch.
3.
Cell wall--cellulose..(exceptions)
4.
Flagellation--when present, always
I. Examine the various specimens on
demonstration. Describe one
macroscopic and one microscopic sample on your paper. Use the following terms to help with the description;
Branching, cell shape, color,
chloroplasts..(shape, size, location), filaments, presence of any reproductive
structures, any outer sheath present and anything else you can describe it
with!
DIVISION PHAEOPHYTA
Most brown algae (Phaeophyta) grow in the
intertidal zone. Nearly all are
marine. There are no unicellular
genera. Forms vary from simple branched filaments to giant seaweeds over 60
meters long. Many of the giant species,
especially the kelps, show a high degree of external differentiation into a
root-like HOLDFAST, a short, stem like STIPE, and a long strap-like BLADE. All larger species have air bladders of
various sizes.
Distinguishing
characteristics are:
1. Pigments--chlorophyll a and auxiliary
pigments, chlorophyll c, carotinoids and fucoxanthin (brown pigment).
2.
Food reserve--laminarin and mannitol.
3.
Cell wall of cellulose and algin (a commercially valuable compound).
4.
Reproductive cells with two laterally placed flagella.
5.
Well developed alternation of generations.
II. Examine the various specimens on
demonstration. Describe one
macroscopic and one microscopic sample on your paper. Use the following terms to help with the
description;
Branching, cell shape, color,
chloroplasts..(shape, size, location), presence of any reproductive structures,
any outer sheath present and anything else you can describe it with!
DIVISION RHODOPHYTA
The red algae (Rhodophyta) are relatively
small plants, most species being less than 0.7 meters long. Their growth forms are simple filaments,
highly branched filaments or sheet-like bodies.
They are abundant in warm marine waters. A few are fresh water. They are capable of living at depths greater
than those of any other algae.
Distinguishing characteristics:
1.
Pigments--chlorophyll a and the auxiliary, pigments, chlorophyll d,
phycoerythrin, and phycocyanin.
2.
Food reserve--floridean starch.
3.
Cell wall of cellulose sometimes covered with gelatinous material
commercially known as AGAR.
4.
Absence of any kind of motile cells.
5.
Complex life cycles in many.
III. Examine the various specimens on
demonstration. Describe one
macroscopic and one microscopic sample on your paper. Use the following terms to help with the
description;
Branching, cell shape, color,
chloroplasts..(shape, size, location), presence of any reproductive structures,
any outer sheath present and anything else you can describe it with!
DIVISION
CHRYSOPHYTA
(golden-brown algae (diatoms))
The golden-brown algae
(Chrysophyta) possess evolutionary trends in size increase some of which are
exhibited by filamentous and colonial forms.
We will examine diatoms, either filamentous or unicellular forms. Diatoms are characterized by cell walls
composed of two overlapping halves that fit together in a manner similar to the
parts of a Petri dish.