PBIO 100 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
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General characteristics [For a detailed review of the
Plant
Kingdom, see the site maintained by Cardillo & Samuels]
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Eukaryotic;
placed in Kingdom Protista (also frequently termed
Protoctista)
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Mostly photosynthetic
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Photosynthetic pigments- four different kinds of chlorophyll
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accessory pigments- a variety, including blue, red, brown, golden
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Require moist environments (lack a waxy cuticle found in terrestrial plants)
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May be microscopic and float in surface waters (phytoplankton) or macroscopic
and live attached to rocky coasts (seaweeds)
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Size ranges from size of bacteria (0.5 um) to over 50 m long (1 um = 1/25,000th
inch; 1 m = 39 inches)
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Lack vascular (conducting) tissues- no true roots, stems, or leaves
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Modes of reproduction
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Sexual and asexual
-Have single-celled gametangia (reproductive organs)- no multicellular
reproductive organs
- Life history has 1, 2, or 3 stages (in contrast, plants have 2 stages,
gametophyte and sporophyte)
View of
their phylogenetic relationships
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Representative algae
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Red algae
(Division Rhodophyta)
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Evolution: Red algae are some of the oldest eukaryotic organisms on the planet.
Fossils of red algae have been found that are over 2 billion years old.
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Habitat: There are 4000 different species of red algae.
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They are very abundant in tropical and warm waters, although many are found
in cooler waters.
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Red algae are typically found in marine waters attached to rocks or other
plants in the calmer, deeper waters beyond the tidal zone.
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Some red algae are reef builders in tropical seas, as important or more important
than coral animals.
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The red algae act as habitat and food for some animals.
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Structure: Their size and complexity vary from thin films growing on rocks
to complex filaments or membranes growing to heights approaching 1 meter.
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Their accessory pigments called phycobilins mask the chlorophyll a and give
them their red color. Due to these specialized pigments, red algae are often
able to photosynthesize in deeper water than other algae.
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Red algae do not have flagella at any stage of their life cycle.
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Commercial: Chondrus crispus
(Irish moss)
is a small filamentous red algae found on rocky ledges in the subtidal zone
of the coastal waters.
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The Irish started using small quantities of Irish moss boiled with milk to
produce a jelly dessert that the French later called "blanc mange." The mixture
of a polysaccharide from the walls of the algae with the proteins in milk
produces carrageenan.
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This thick solution or gel is used in ice cream, whipped cream, fruit syrups,
chocolate milk, bread, and macaroni. It is also used in tooth paste,
pharmaceutical jellies, and many kinds of lotions.
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In this country, Irish moss is commercially harvested in Maine.
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The agar used to grow bacteria and other media, such as the bread mold in
the fungi experiment, is derived from red algae.
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Some red algae are eaten by humans.
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Diatoms
(Golden-brown algae; Division Bacillariophyta)
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Largest group of algae but many of its species still undescribed.
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Evolution- A relatively recent group; diatoms did not exist in the age of
the dinosaurs.
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Habitat: cool marine oceans
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Very important in food chains- especially in cooler, marine waters as
phytoplankton
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Structure:
mostly unicellular
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Silica in cell walls (tiny glass houses); cell walls fit like a
Petri dish [slow
to load but worth it!]
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Reproduction- asexual for several generations, then sexual (to restore
size)
Tired of studying real
diatoms? Try
these!
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Kelps (brown algae;
Division Phaeophyta)
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Evolution- Closely related to diatoms and also a young group, but very different
in appearance.
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Habitat: rocky coasts in temperate zones or open seas (cold water algae)
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Structure: multicellular only. Some attain great size- 180 feet and grow
2 feet per day.
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Examples: shoreline: Laminaria; open ocean: Sargassum
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Dinoflagellates
(Division Pyrrhophyta or Dinophyta)
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Evolution
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Habitat: Especially important in food chains in warm, tropical oceans
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Structure: Mainly unicellular.
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Green and colorless forms (some phagotrophic, some parasitic- e.g. fish kills
on the Pokomoke river by
Pfiesteria
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Biflagellate
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Nucleus unusual- chromosomes always visible
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Some bioluminescent forms- light up when water is disturbed
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Reproduction commonly asexual
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Green
algae (Division Chlorophyta)
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Next to the golden-brown diatoms, the green algae are the second largest
group of algae.
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They are also the most diverse of the algae, with at least 7000 species.
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Evolution- almost as old as red algae
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Habitat: They are found mostly in fresh waters and on land. Most species
float in rivers, lakes, reservoirs, and creeks.
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They can also live on rocks, soil, and tree bark.
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A few species, such as sea lettuce (Ulva), live in the salt water
along the coast. Large, thin sheets of sea lettuce often totally obscure
the muddy bottom in sheltered bay and estuary habitats.
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Structure: Green algae are organisms with a variety of body forms including
single cells, filaments, colonies, and thalli (singular - thallus, multicellular
forms that have a leaf-like shape).
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The higher terrestrial plants arose from a green algal ancestor. They possess
the same photosynthetic pigments (chlorophyll a and b) and some green algae
have stiff cell walls composed of cellulose, as do plants.
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Commercial:
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Green algae are an important source of oxygen and food for aquatic organisms.
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Some are consumed as food by humans.
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Examples - fresh water: Volvox, Spirogyra; marine:
sea
lettuce (Ulva)
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Significance to humans
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Beneficial algae
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Base of the aquatic food chain- especially important are the diatoms and
dinoflagellates
a. Seaweeds are not only food, but shelter for aquatic organisms- especially
important are the kelps, which form underwater forests; Sargasso Sea
community
b. Some red algae are reef builders in tropical seas; as important or more
important than coral animals
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Other uses of importance
and their history (e.g., fertilizer, fodder, etc.) and
algal
farming
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Harmful algae- excess growth causes:
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Clogging of waterways, streams, and filters- when water is polluted with
nutrients such as fertilizer or sewage
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A bad taste to water when present in large numbers
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Toxicity to animals (paralytic shellfish poisoning, red tides- both caused
by dinoflagellates)
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Commercial
uses
of algae
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Algin- thickening agent in ice cream, marshmallows- from brown algae;
carrageenan- in foods, puddings, laxatives, toothpaste- from red algae
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Iodine- from brown algae
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Agar- from red algae
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Food- especially reds and browns- important in East Asia
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Diatomaceous
earth- used for filtering, insulating, and soundproofing
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The Future
Other Sites of Interest:
Marimo
balls-Japan
Pfiesteria links
Excellent
review of fungi and algae (and other stuff)
Basic information on
seaweeds
Outline
review: pull down to get to algae section
Detailed
review of protists and origin of eukaryotes
Protist
Image Data: Excellent pictures and information
Diatom Home Page
Summary
of the commercial aspects of algae
Index Nominum
Algarum: Scientific names of algae (technical)
Delwiche
Last revised: August 18, 1998, Straney