Biol-302 Botany, Spring 2007
Velma Matthew, TA – Kathy Boothby
Lab 3: Phycology (the study of algae): Cyanobacteria, Unicellular Algae, &
Multicellular Algae.
Prokaryotes
Domain: Bacteria
Division: Cyanobacteria (Blue-green algae)
Phylum: Cyanophyta
Genera: Gloeocapsa, Anabaena, Gloeotrichia, & Oscillatoria
Cyanobacteria are single celled or colonial prokaryotes which have a number of
intriguing characteristics. They are very similar to the first photosynthesizers on the
planet, and underwent endosymbiosis to form chloroplasts in plants. Some can fix
nitrogen, which is an essential source of nitrogen for many plant species. Some form
symbioses with fungi to form lichens. Cyanobacteria can form nuisance algal blooms in
the presence of pollution. Some produce toxic chemicals.
One example is Anabaena, which is capable of causing odor problems even
when its population is very small. The odor is thought to be due to the death and decay
of some of the alga cells. Anabaena is a blue-green alga that can fix its own nitrogen.
Because of its nitrogen-fixing ability, it does not need water that is polluted with high
levels of nitrates or organic matter. Some Anabaena produce a chemical that is toxic to
many species of animals. Blooms of Anabaena have been associated with skin rashes
in humans. Blooms of blue-green algae have also caused the death of livestock drinking
the water and have caused fish kills.
Another example is Oscillatoria, which is considered to be the group of alga that
is the second most tolerant of organic pollution after Euglena (which is not a
prokaryote). It is commonly found with Euglena in lagoons and other water with high
levels of nitrogen. The name of this alga refers to the movement that is characteristic of
living filaments. Filaments slowly oscillate or glide back and forth in the water. You will
have the opportunity to view this and several other types of algae. (source: Phycological
Society of America)
1. Prepare a slide of Gloeocapsa from the culture in class and locate single cells
and colonies of 2-4 cells, enclosed in a gelatinous sheath.
a. Draw a colony of 2-4 cells and label the gelatinous sheath.
b. What is the function of the gelatinous sheath? Attachment
It may also serve a protective function
2. Prepare a slide of Merismopedia from the culture in class. The root “merismos”
means: division on a plane. Therefore, colonies are rectangular and usually one
cell thick.
a. Draw a colony of Merismopedia.
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3. Prepare a slide of Anabaena from the culture in class. These filamentous
bacteria have heterocysts, akinetes, & photosynthetic cells.
a. Draw a filament of Anabaena and label the three structures mentioned
above & the gelatinous matrix.
b. What is the function of heterocysts and why must they be kept separate
from the photosynthetic cells? Nitrogen fixing
Nitrogenase, the enzyme that catalyses the reaction, is sensitive to
oxygen. It only works in an anaerobic environment.
4. Prepare a slide of Gloeothrichia from the culture in class.
a. Draw and label the heterocysts, akinetes, photosynthetic cells, & the
gelatinous matrix.
b. What is the function of an akinete? Survival during harsh conditions
5. Prepare a slide of Oscillatoria from the culture in class. The cells of these
filamentous bacteria are joined only at their walls, so that each cell leads an
independent life.
a. Draw a filament of Oscillatoria and label the individual cells.
b. Are any of the filaments divided in to short fragments or segments?
(segments are differentiated by dark dead cells)
These fragments are called hormogonia (singular: hormogonium); what is the
purpose of the fragments? Produce new filament after it breaks free
from the main filament
Eukaryotes
Kingdom: Protista
Phylum: Euglenophyta
Genus: Euglena
Many authorities consider Euglena as the most tolerant genus of organic
pollution. It is commonly found in farm ponds, lagoons where sewage is treated, and
other bodies of water with high levels of nitrogen (though Euglena will also be found in
clean water). Sometimes a red pigment hides the chlorophyll (Phycological Society of
America), and can turn the water red.
6. Prepare a slide of Euglena from the culture in class. Euglena are unicellular
organisms that contain chloroplast similar to those of green algae; this suggest
that the euglenoid chloroplast were derived from endosymbiotic green algae.
a. Draw a Euglena and label the flagellum, eye spot (stigma), contractile
vacuole, nucleus, and a chloroplast.
What is the color of the stigma? What is its function? In what direction are the
Euglena moving (flagellum end or other end)? Function of the eyespot: It
shades the actual photoreceptor as the Euglena swims.
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Eukaryotes
Kingdom: Protista
Phylum: Bacillariophyta
Family: Bacillariophyceae (Diatoms)
Diatoms, such as Navicula, are often used as indicators of water quality. Clean
water has relatively low populations of many different species of diatoms. As water
becomes polluted, the variety of diatoms decreases, but the population of pollution
tolerant types increases. The silica cell walls of diatoms do not decompose when the
cells die. The remaining skeletons of the cells leave a long fossil record, but can create
problems when they clog the filters at water treatment plants, especially during the
spring and fall when diatoms are most abundant (they prefer cold water). The diatoms
are killed by chlorine, which is added to the water as it enters the treatment plant. The
silica boxes do not break down and must be filtered out of the water.
Diatomaceous earth is composed of the fossilized shells of diatoms. It is found in
areas (such as the Great Basin) that were once covered by oceans but are now dry.
Diatomaceous earth is used by organic gardeners to control insects around plants. The
tiny holes in the silica material absorb moisture, which kills the insects.
7. Look at a prepared slide of Diatoms. Several species may be present on each
slide. Note that some diatoms aggregate into filaments, while others do not.
a. Draw both pennate and centric diatoms.
8. Prepare a slide of Navicula from the culture in class.
a. Draw Navicula.
b. Is this pennate or centric?
9. Prepare a slide of diatomaceous earth from the sample in class.
a. Draw the diatoms that you see.
b. Are these pennate or centric diatoms?
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