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UNIT 2: ALGAE
Botany: An introduction to plant biology, 5th ed. Mauseth. Chapter 19
OBJECTIVES
The authors of the textbook classify living organism into three domains: Bacteria, Archaea,
and Eukarya. The Bacteria and Archaea are Prokaryotic organism whereas the Eukarya are
Eukaryotic organisms. Photosynthetic organisms occur in both Eukaryotic and Prokaryotic
lineages (Domains Bacteria and Eukarya; there are no known photosynthetic members of
Domain Archaea). This lab considers the physical and reproductive characteristics of these
organisms.
Protists are a very large, diverse, and polyphyletic group. In this lab we will consider only
those lineages that contain photosynthetic organisms. At the end of lab you should be able to
identify a prokaryotic cell, and discuss how it differs from a eukaryotic cell. In addition, you
should learn the names of the phyla and the identifying characters of each of the Eukaryotic
groups. You should also be able to recognize by sight the different algal phyla. In addition, you
should be able to identify the genera of green alga you observed in lab and understand their life
cycles.
BACKGROUND
Prokaryotes are those organisms having cell walls, cell membranes, DNA, RNA, and
ribosomes but lacking the membrane bound nucleus and organelles of eukaryotes. Once
thought to all be basically similar, modern molecular biology techniques have shown that there
are two very different groups of prokaryotic organisms, the Bacteria and Archaea. The two
groups are distinguished by cell wall structure, lipid structure, ribosomal RNA (rRNA) sequences,
and the structure of the ribosomes themselves.
The organisms that we will be looking at in lab today are members of the Bacteria. Virtually
all Bacteria are unicellular although the cells may be arranged in chains, filaments, clumps, or
colonies. In all cases each cell functions independently from the others. Bacteria species are
distinguished from each other on the basis of characteristics such as pigmentation, cell shape,
cell wall structure, nutrition requirements and whether they are heterotrophic or autotrophic.
Heterotrophic bacteria obtain some or all of their nutrition through a process called
extracellular digestion. Autotrophic bacteria like Cyanobacteria are photosynthetic and contain
the pigments chlorophyll a and phycocyanin. These pigments give the cyanobacteria their
characteristic blue-green color. Some of the cyanobacteria, such as Gloeocapsa, have single
cells enclosed in a gelatinous sheath. When a cell divides, each "daughter" cell will have its own
sheath but will remain inside the common sheath for a time. This gives the appearance of a
colonial form. Other forms of cyanobacteria, such as Oscillatoria, Anabaena, Lyngbya, and
Nostoc, are filamentous. These chains or filaments are also enclosed in sheaths although their
sheaths are not as obvious as the one in Gloeocapsa.
Like the fungi, the relationships between Eukaryotic organisms as a whole are in a state of
flux. The number of supergroups of Eukaryotes varies from as few as three to as many as 8 (see
http://comenius.susqu.edu/biol/202/taxa.htm for one 4-supergroup model. Although your text
carefully avoids the concept of Supergroups, Raven (the previous Botany text) uses either 5 or 8
groups (Figure 1) depending on how you interpret the clasogram; but in the 10th edition,
Campbell favors four supergroups (Figure 2). Photosynthetic organisms are not found in the
lineage containing animals and amoeboid organisms, and the Supergroup Rhizaria.
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Figure 1. Five or eight supergroups as utilized by Raven.
Figure 2. Four supergroups as utilized by Campbell, 10th ed.
The protists, members of the
former kingdom Protista, are
among the most diverse. They are
comprised of eukaryotic organisms
that are predominantly singlecelled without any cell
specialization. It also includes
some multicellular organisms
whose morphological and
molecular characteristics do not fit
in the parameters used to describe
the other kingdoms. The Protista
has some members that are fungilike (the water molds), some that
are animal-like (the protozoa), and
some that are photosynthetic (the
algae). We will only be
considering the lineages
containing photosynthetic
organisms.
The photosynthetic organisms
range in complexity from singlecelled members to multicellular
members with specialized cells.
Many exist as colonies (groups of
loosely attached cells) or filaments
(chains of cells). Your text divides
the Eukaryotic algae into six phyla
based on phylogeny, pigments,
carbohydrate food reserve,
presence and number of flagella,
and cell wall components (Table
19-2 [page 466] of your text).
Three different types of life
cycle patterns are found in the
algae (see page 469 of your
textbook): zygotic meiosis,
gametic meiosis and sporic
meiosis. In organisms with a
zygotic meiosis pattern (text
Figure 19-14 a-b), haploid
cells/gametes undergo
fertilization to produce a diploid
zygote which immediately
undergoes meiosis to produce
spores. The zygotic meiosis
pattern occurs in all of the fungi as
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well in some algae. In organisms with a gametic meiosis pattern (text Figure 19-14 c-d), the
diploid zygote undergoes mitosis to produce diploid individuals which will then undergo meiosis
to produce haploid gametes. This process is followed immediately by fertilization restoring the
diploid condition. This pattern is found in some algae as well as animals. In organisms with a
sporic meiosis pattern (text Figure 19-15), the diploid zygote undergoes mitosis to produce
diploid individuals which at some point will undergo meiosis to produce haploid spores. The
haploid spores produce haploid gametes by mitosis. Fertilization restores the diploid condition.
A sporic life cycle pattern is referred to as an alternation of generations life cycle and is found in
multicellular algae and in land plants.
In addition to having various life cycles, the algae also have different types of gametes
(Figure 19-16, textbook page 470). Some algae are isogamous, producing morphologically
identical, motile gametes often referred to as “+” and “-”. Anisogamous algae produce gametes
that are similar in morphology, but dissimilar in size. Oogamous algae produce two distinctly
different types of gametes, a small motile sperm and a large nonmotile egg.
We will look at members of all 4 of the supergroups containing photosynthetic organisms:
the Excavata (Euglenophyta), the Alveolata (Phyrrhophyta), the Stramenophiles (Bacillariophyta,
Phaeophyta, and Oomycota; we will not look at Xanthophyta or Chrysophyta), and what
Campbell (and others) call the Archaeplastida (Rhodophyta and Chlorophyta). As you look at
these organisms, fill out the table at the end of this lab exercise.
EXERCISE 1: CYANOBACTERIA
Obtain a prepared slides of Anabaena sp., Nostoc, and Oscillaroria (slides #1-3) Also make wet
mounts of each of the living cyanobacteria cultures provided (Anabena, Nostoc, and Oscillatoria
as well as the mixture provided). These cells are larger and strongly pigmented making them
easy to see. The mixture, which comes with a key, may have other 5 other species in it; use the
key to identify as many of them as possible. If it’s available, get a leaf of the Azolla (a water fern
that we will examine later), and make a “squash” mount. Look for the presence of Anabena.
1. How many different species do you see in the mixture? What are they? Draw them in the
space provided.
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2. Since these living cyanobacteria cells have a blue green coloration are chloroplasts visible in
any of them? (Anabaena, Nostoc, Oscillatoria or any of the species in the mixture? Explain.
3. In the culture of Nostoc there are long chains of cells (filaments) with an occasional cell
much larger than the others (see page 600 in Textbook) . What is the name of the cell and
what is its function? Can you see these cells in your wet mount?
4. When you looked at the live Oscillatoria, could you see any movement? Can you tell how it
moves? See if you can you find out how it moves.
5. Did you find Anabena in the Azolla leaf? How do you know it is Anabena and not just Azolla
cells that you separated from the leaf tissue during the squashing process?
EXERCISE 2: SUPERGROUP EXCAVATA (Phylum Euglenophyta)
Euglenophyta are an exclusively unicellular group. Pigmentation is similar to that of the
green algae (chlorophylls a and b, carotenoids). Euglenophyta do not have rigid cell walls.
Instead, they have a flexible pellicle composed of layers of proteins that lie inside the plasma
membrane.
On the front or side lab bench is a living culture of Euglena; you also have a prepared slide
as well (slide #4). Make a wet mount using a drop of the culture. Answer the following
questions as you look at the specimens.
6. Do Euglena have flagella? How do you know? Can you see them? Why or why not? Can
you see evidence of them? Why or why not?
7. What is the shape of an individual Euglena?
8. EXERCISE 3: SUPERGROUP ALVEOLATA (Phylum Dinophyta)
Dinophyta has starch, peridinin and carotenoids, pigments, and chlorophylls a and c. One
unique characteristic of the dinoflagellates is the internal cellulose armor-like plates. A second
unique character is the two lateral flagella. One flagella coils around the cell in a groove while
the other one acts as a rudder.
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Obtain a slide labeled Dinoflagellates (slide #5). Also make a wet mount of Peridinium sp.
provided by your instructor. These are single-celled dinoflagellates.
9. Can you see the flagella? Why or why not? Can you see evidence of the flagella
EXERCISE 4A: SUPERGROUP STRAMENOPHILA or HETEROKONTS (Phylum Bacillariophyta –
diatoms)
Bacillariophyta have fucoxanthin, a yellowish-brown pigment, in addition to chlorophylls a
and c, and the carotenoids. This gives them a yellowish or brownish color. One unique
characteristic of the diatoms is the cell wall is composed entirely of silica. When a diatom dies,
the cellular contents decay but the siliceous cell wall does not. Instead, it settles to the bottom
of the body of water it is in. In some areas, large amounts of diatom cell walls have been
deposited and are mined as diatomaceous earth.
PART A:
From the jar of mixed diatoms and desmids, obtain a sample and make a wet mount. What
kinds of organisms do you see? Draw some of them.
PART B:
Observe the slide of mixed diatoms (slide #6).
10. In parts A and B, what part of the alga do you actually see?
EXERCISE 4B: SUPERGROUP HETEROKONTA (Phylum Phaeophyta – brown algae)
Phaeophyta are another group of algae that is predominantly marine. Brown algae are
either branched filaments or are multicellular. The brownish color of this phylum is caused by
the presence of pigment fucoxanthin.
On your lab bench or on the front or side bench are prepared slides of Phaeophyta (slide #7
– Fucus). In addition, there are live specimens in the front of the room.
11. Based on your observation of the live specimens, is there any cell specialization within this
phylum? How did you come to this conclusion?
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12. How do these organisms attach to the ocean floor?
13. How does this phylum differ from the other algae phyla you have looked at?
14. Which other phylum has the same pigments as the Phaeophyta?
EXERCISE 4C: SUPERGROUP HETEROKONTA (Phylum Oomycota – Water Molds)
Members of the Oomycota have long been considered fungi. However, the resemblance to
the true fungi was only superficial. The cell walls of the fungus-like protists are made of
cellulose, which is a characteristic of plant cells rather than true fungi. The zoospores of most of
the fungus-like protists are flagellated; fungal spores are not flagellated, and only the Chytrids
produce motile gametes. Some species of fungus-like protists use pseudopodia to engulf food
particles.
You have fresh Saprolegnia to make a wet
mount of as well as a prepared slides of both
Saprolegnia and Achlya (slides 8-9). First, study
the life cycle of Saprolegnia, a water mold as
shown in Figure 3 (left). and then obtain a
prepared slide of Saprolegnia, a water mold and
observe its life cycle under both low (10X) and
high (40X) power objective lenses.
15. What structures do you see that would lead
you to think that this might be a member of
the fungi rather than a protist?
Figure 3. Saprolegnia from Raved, 10th Ed.
16. What structures do you see that would lead you to think that this was a protist and not a
member of the fungi?
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EXERCISE 5A: SUPERGROUP ARCHAEPLASTIDA (Phylum Rhodophyta – The red algae)
The Rhodophyta are most often found in warm, marine waters, although there are
freshwater species. They may be unicellular, filamentous, or multicellular. The reddish color is
caused by the presence of a group of pigments called phycolibins. The cell walls of some of the
red algae include the polysaccharides carrageenan and agar.
You have fresh Polysiphonia as well as prepared slides of Polysiphonia and Nemalion (slides
10-11) to examine.
Examine the life cycle as shown in
Figure 4. You will notice that there are
three different stages in the life cycle.
This is not unusual in members of the
Rhodophyta.
17. Can you see all three stages in the
live material? Why or why not?
18. Can you find all three stages in the
prepared slides? How similar are the
phases of Polysiphonia and Nemalion
to each other?
Figure 4. The life cycle of Polysiphonia from Raven
10th ed.
EXERCISE 5B: SUPERGROUP ARCHAEPLASTIDA (Phylum Chlorophyta – The green algae)
One of the most diverse phyla of the algae is Chlorophyta. The green algae may be
unicellular, filamentous, colonial, or multicellular. They are found in freshwater, seawater, soil,
snow, polar bear hair, and house dust. The green algae are of particular interest to botanists as
they are thought to be among the most closely related to land plants. While no known alga has
all of the characteristics of plants, all of the key plant characteristics are found within the
Chlorophyta. These characteristics include the use of chlorophyll a, chlorophyll b, and
carotenoids in photosynthesis; cellulose cell walls; starch storage; isogamous; anisogamous;
oogamous gamete pairs; zygotic and sporic meiosis.
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On your lab table and at the front of the lab or side table are several cultures of green algae.
Included are unicellular, colonial and filamentous forms. Make wet mounts of each of the
cultures. There are also several prepared slides to examine (slides 11-17). There are both
examples for most taxa. As you observe each of the specimens fill in the table on the
worksheet.
When you make your wet mount of Volvox, be sure to use the deep-well slides. These are
large organisms! When you are finished with the specimens, see if you can “flush” them back
into the jars.
EXERCISE 5C: SUPERGROUP ARCHAEPLASTIDA (Phylum Charophyta – The green algae)
The Charophyta include those species that are believed to be the most recent common
ancestor to land plants. Depending on the analysis, this is either Chara (which we have live
material of) or Choleochaete (which we do not). In fact, some classifications place these
organisms as sister to land plants rather than as algal taxa. These species include unicellular,
colonial, filamentous, and parenchymatous forms. Included within this group are several
species known for their unusual chloroplasts and methods of reproduction: Spirogyra and
Zygnema. While both Coleochaete and Chara show parenchymatous growth, Chara is
distinguished by whorls of leaf-like structures looking very similar to some land plants.
Characteristics shared with land plants (like the Chlorophytes) include open cytokinesis; the
formation of a phragmoplast during cytokinesis; the nodal structure of Chara and the
development of parenchyma.
On your lab table and at the front of the lab or side table is a culture of Chara. In addition,
there are prepared slides of Closterium, Spirogyra, and Chara (slides 18-20). As you observe
each of the specimens fill in the table on the worksheet.
19. How does the reproduction of Spirogyra differ from other algal species? Can you see
conjugation occurring in the live material? What about the prepared slides?
20. How do the archaegonia and antheridia of Chara differ from other algal species? Can you
see these structures on the live material? What about the prepared slides?
After you have examined all of these organisms, fill in the life cycle charts that follow. Be
sure to indicate the type of meiosis pattern (sporic, gametic, or zygotic) and the type of gamete
produced (anisogametes, isogametes, or oogametes). In blanks with an "S" put the name of the
structure indicated and its ploidy (n or 2n). Possible structures include spore, gamete, egg,
sperm, zygotes, and vegetative adult. Blanks with a "P" indicate a process has occurred.
Possible processes include meiosis, fertilization, germination, and mitosis. Blanks with "S/G"
indicate the structure is a sporophyte or gametophyte.
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21. LIFE CYCLE: CHLAMYDOMONAS SP.
MEIOSIS PATTERN: _______________
GAMETE TYPE:___________________
22. LIFE CYCLE: VOLVOX sp.
MEIOSIS PATTERN: _______________
GAMETE TYPE:___________________
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23. LIFE CYCLE: SPIROGYRA SP.
MEIOSIS PATTERN:_____________
GAMETE TYPE:_________________
24. LIFE CYCLE: OEDOGONIUM SP.
MEIOSIS PATTERN:________________
GAMETE TYPE:____________________
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25. LIFE CYCLE: ULVA SP.
MEIOSIS PATTERN:________________
GAMETE TYPE:____________________
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EXERCISE 6: COMPARISON AMONG ALGAE PHYLA
From your observations of Exercise 1 – 5. and Table 19-2 pages 466 of your textbook fill in the table below.
Growth Form
(Unicellular,
Filamentous, or
Multicellular)
26. Euglena sp.
27. Peridinium sp.
28. Heterokonts/
Stramenophiles
a. Diatoms
b. Fucus sp.
c. Saprolegnia sp.
d. Achlya sp.
29. Archaeaplastida
a. Polysiphonia sp.
b. Nemalion sp.
c. Chlamydomonas sp.
d. Oedogonium sp.
e. Volvox sp.
f. Ulva sp.
g. Closterium sp.
h. Spirogyra sp.
i. Chara sp.
Flagella
Color of
organism
Cell wall
component
Carbohydrate
food reserve
Shape of
Chloroplast
Which group does the
organism belong to?
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TERMINOLOGY TO BE FAMILIAR WITH
1. akinetes
27. Dinophyta
2. agar
28. egg
3. algin
29. Euglenophyta
4. alternation of
30. Eukarya
generations
31. eukaryotic or eukaryote
5. anisogametes
32. extracellular digestion
6. antheridium
33. filament
7. antibiotic
34. flagella/ flagellum
8. aplanospores
35. floridian starch
9. Archaea
36. fucoxanthin
10. asexual reproduction
37. gametic meiosis
11. autotrophic or autotroph
38. gametophyte
12. bacillus (plural bacilli)
39. gas vacuole
13. Bacteria
40. genophores
14. bacteriochlorophyll
41. heterocyst
15. Bracillariophyta
42. heterotrophic or
16. carotenoids
heterotroph
17. carrageenan
43. holdfast
18. cellulose
44. isogamous
19. chemosynthetic
45. isomorphic
autotroph
46. laminarin
20. chlorophyll
47. multicellular
21. Chlorophyta
48. nitrogen fixation
22. chrysolaminarin
49. oogamous
23. coccus (plural cocci)
50. paramylon
24. colonial algae
51. pathogenic or pathogen
25. conjugation
52. pellicle
26. cyanobacteria
53. peptidoglycans
54. Phaeophyta
55. phragmoplast
56. photosynthetic
autotroph
57. phycobilins
58. phycocyanin
59. phytoplankton
60. pili
61. prokaryotic or
prokaryote
62. pyrenoid
63. Rhodophyta
64. sexual reproduction
65. silica
66. spirillum (plural spirilla)
67. saprobic or saprobe
68. sperm
69. sporic meiosis
70. sporophyte
71. starch
72. stigma
73. stipes
74. unicellular
75. zoospores
76. zygotic meiosis
77. zygote
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QUESTIONS FOR FURTHER THOUGHT
1. What is the biological role of prokaryotes in the biosphere? Could life on earth continue
without them?
2. You have just found an organism that you do not recognize.
a. What characteristics will determine whether it is a prokaryote or eukaryote?
b. What characteristics will determine if it is heterotrophic or autotrophic? If autotrophic,
what characteristics will determine if it is phototrophic or chemotrophic?
3. Describe the various methods of reproduction in the cyanobacteria. How does this differ
from the reproduction of eukaryotic cells?
4. If prokaryotic cells do not undergo sexual reproduction (meiosis and fertilization), how does
genetic variation arise?
5. What is the significance of the fact that there are no "natural" organic compounds that
cannot be broken down or digested by some organism (usually by a bacterium or fungus)?
6. If an antibiotic were discovered that were capable of killing all bacteria, would this improve
life for all the other organisms on the planet? Why or Why not?
7. Given the relatively few ways to visually distinguish prokaryotic species from each other
(cell shape, color, flagella, etc.), how can over 4000 different species be identified?
8. Are the Archaea or the Bacteria considered to be more closely related to eukaryotic
organisms? Why?
9. The cyanobacteria are sometimes referred to as the blue-green algae. Which pigment is
responsible for their bluish color?
10. What are some economic uses of cyanobacteria?
11. What characteristics are used to separate the algal phyla of the Protista?
12. What are some of the commercial and industrial uses of algae?
13. Given the portion of the earth that is covered by water, how important do you think the
algae are in global photosynthesis and oxygen production?
14. Which phyla of the algae are thought to be the most important in aquatic food chains?
15. Why must the food chains in aquatic habitats begin with algae? Give an example of a food
chain.
16. What are the cellular characters which distinguish the filamentous Cyanobacteria such as
Oscillatoria from the filamentous green algae such as Spirogyra?
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17. Do you think that the filamentous greens are true colonial organisms? What about
Oscillatoria?
18. What is the difference between a spore and a gamete? Discuss their ploidy, origins,
function, and ultimate destiny.
19. Which phylum of algae is thought to be ancestral to plants?
What specific characteristics does this phylum share with plants?
20. What wavelength of light is most likely absorbed by red colored algae? Why do you say
that?
21. What is the ecological significance of this wavelength in relationship to their deep tropical
waters habitat?
22. What are some of the commercial/economic uses of the Rhodophyta?