BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland


  1. General characteristics [For a detailed review of the Plant Kingdom, see the site maintained by Cardillo & Samuels]
    1. Eukaryotic; placed in Kingdom Protista (also frequently termed Protoctista)
    2. Mostly photosynthetic
      1. Photosynthetic pigments- four different kinds of chlorophyll
      2. accessory pigments- a variety, including blue, red, brown, golden
    3. Require moist environments (lack a waxy cuticle found in terrestrial plants)
    4. May be microscopic and float in surface waters (phytoplankton) or macroscopic and live attached to rocky coasts (seaweeds)
      1. Size ranges from size of bacteria (0.5 um) to over 50 m long (1 um = 1/25,000th inch; 1 m = 39 inches)
    5. Lack vascular (conducting) tissues- no true roots, stems, or leaves
    6. Modes of reproduction
      1. 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
  2. Representative algae
    1. Red algae (Division Rhodophyta)
      1. 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.
      2. Habitat: There are 4000 different species of red algae.
        1. They are very abundant in tropical and warm waters, although many are found in cooler waters.
        2. Red algae are typically found in marine waters attached to rocks or other plants in the calmer, deeper waters beyond the tidal zone.
        3. Some red algae are reef builders in tropical seas, as important or more important than coral animals.
        4. The red algae act as habitat and food for some animals.
      3. Structure: Their size and complexity vary from thin films growing on rocks to complex filaments or membranes growing to heights approaching 1 meter.
        1. 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.
        2. Red algae do not have flagella at any stage of their life cycle.
      4. Commercial: Chondrus crispus (Irish moss) is a small filamentous red algae found on rocky ledges in the subtidal zone of the coastal waters.
        1. 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.
        2. 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.
        3. In this country, Irish moss is commercially harvested in Maine.
        4. The agar used to grow bacteria and other media, such as the bread mold in the fungi experiment, is derived from red algae.
        5. Some red algae are eaten by humans.
    2. Diatoms (Golden-brown algae; Division Bacillariophyta)
      1. Largest group of algae but many of its species still undescribed.
      2. Evolution- A relatively recent group; diatoms did not exist in the age of the dinosaurs.
      3. Habitat: cool marine oceans
        1. Very important in food chains- especially in cooler, marine waters as phytoplankton
      4. Structure: mostly unicellular
        1. Silica in cell walls (tiny glass houses); cell walls fit like a Petri dish [slow to load but worth it!]
      5. Reproduction- asexual for several generations, then sexual (to restore size)
        Tired of studying real diatoms? Try these!
    3. Kelps (brown algae; Division Phaeophyta)
      1. Evolution- Closely related to diatoms and also a young group, but very different in appearance.
      2. Habitat: rocky coasts in temperate zones or open seas (cold water algae)
      3. Structure: multicellular only. Some attain great size- 180 feet and grow 2 feet per day.
      4. Examples: shoreline: Laminaria; open ocean: Sargassum
    4. Dinoflagellates (Division Pyrrhophyta or Dinophyta)
      1. Evolution
      2. Habitat: Especially important in food chains in warm, tropical oceans
      3. Structure: Mainly unicellular.
        1. Green and colorless forms (some phagotrophic, some parasitic- e.g. fish kills on the Pokomoke river by Pfiesteria
        2. Biflagellate
        3. Nucleus unusual- chromosomes always visible
        4. Some bioluminescent forms- light up when water is disturbed
        5. Reproduction commonly asexual
    5. Green algae (Division Chlorophyta)
      1. Next to the golden-brown diatoms, the green algae are the second largest group of algae.
      2. They are also the most diverse of the algae, with at least 7000 species.
      3. Evolution- almost as old as red algae
      4. Habitat: They are found mostly in fresh waters and on land. Most species float in rivers, lakes, reservoirs, and creeks.
        1. They can also live on rocks, soil, and tree bark.
        2. 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.
      5. 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).
        1. 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.
      6. Commercial:
        1. Green algae are an important source of oxygen and food for aquatic organisms.
        2. Some are consumed as food by humans.
      7. Examples - fresh water: Volvox, Spirogyra; marine: sea lettuce (Ulva)
  3. Significance to humans
    1. Beneficial algae
      1. 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
      2. Other uses of importance and their history (e.g., fertilizer, fodder, etc.) and algal farming
    2. Harmful algae- excess growth causes:
      1. Clogging of waterways, streams, and filters- when water is polluted with nutrients such as fertilizer or sewage
        1. A bad taste to water when present in large numbers
        2. Toxicity to animals (paralytic shellfish poisoning, red tides- both caused by dinoflagellates)
    3. Commercial uses of algae
      1. Algin- thickening agent in ice cream, marshmallows- from brown algae; carrageenan- in foods, puddings, laxatives, toothpaste- from red algae
      2. Iodine- from brown algae
      3. Agar- from red algae
      4. Food- especially reds and browns- important in East Asia
      5. Diatomaceous earth- used for filtering, insulating, and soundproofing
  4. 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)

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Last revised: August 18, 1998, Straney