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Plantlike Protists: Unicellular Algae


Taxonomy, or the science of classifying organisms, groups organisms into categories based on various characteristics.


Aristotle’s classification system proposed that if something moves, it is an animal, and if it doesn’t, it is a plant. Of course, sponges were mistakenly taken for plants, and when they threatened the shellfish industry centuries ago, were “killed” by being cut up and tossed back into the sea. To the surprise of the shellfish harvesters, the next year, the number of sponges had increased; the shellfishers were actually helping the sponges reproduce (asexually) by their actions.


Linnaeus proposed naming organisms by a two-name system that we call binomial nomenclature. These were very specific names based on the organism’s characteristics and are the genus and species of today. Note that the genus is always capitalized and the species is not, as in Terrestris americanus, and the entire name is underlined or italicized.


The modern system of classification now contains five major groups called kingdoms. Life on the planet could be seen as analogous to a grocery store. The major consumer item areas, such as produce, dairy, and canned goods, would be analogous to the kingdoms of living things. As with the grocery store, the sub-categories get more and more specific until it is possible to name an item exclusive of all other items in the store. You should know the categories, starting with the largest (the kingdom) and continuing to narrower and narrower groups in the sequence: Kingdom, Phylum, Class, Order, Family, Genus, and Species. In plants, the word “phylum” is replaced with the word “division.” Modern day study has become so detailed that we will now find such categories as sub-genus and super-species. The student is responsible only for the above schema. Most beginning biology students become familiar with the mnemonic—memory device—in a variety of expressions, one being King Phillip Come Out For Goodness Sakes. The first letter of each word, in the order given, is the first letter of each of the major categories in taxonomy.

Kingdom Cell type Organization Nutrition Organisms
Monera Prokaryotic Unicellular-small Absorb, Photsyn., Chemosyn. Bacteria, Cyanobacteria
Protista Eukaryotic Unicellular or colonial Ingest, Photosyn. Protozoa, Algae
Fungi Eukaryotic Multicellular Absorb Fungi, yeast, molds
Plantae Eukaryotic Multicellular Photosyn. Plants
Animalia Eukaryotic Multicellular Ingest. Animals


Canis familiarus

domesticated dog

Felis feline

domesticated cats

Homo sapiens

modern humans


Kingdom Monera

Prokaryotes are single-celled, microscopic prokaryotic cells with no distinct nucleus or other membrane-enclosed organelles.


Bacteria have cell walls composed of peptidoglycan, an amino acid–sugar complex, and circular DNA. Composition of the cell wall provides us with the Gram staining means of identifying certain types

of bacteria. Reproduction of bacteria was outlined in an earlier chapter. Some bacteria possess flagella. While many bacteria are decomposers, some fix nitrogen and other elements in a form usable by organisms, and some are pathogenic.

A. Shapes

Bacteria can be found in three shapes: coccus (round-shaped), bacillus (rod-shaped)—the one the SAT II Biology exam commonly refers to when asking a question about bacteria—and spirillus (spiral-shaped).



B. Types

Aerobic (oxygen-needing) bacteria are the largest group of bacteria. Anaerobic (not needing oxygen) bacteria are found in two groups: those that need an oxygen-free environment (obligate) and those that

do not need a lack of oxygen, but a small amount of oxygen will not kill them (facultative).


Kingdom Protista

Protists belong to the Kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms.

Characteristics of Protists

  • mostly unicellular, some are multicellular (algae)
  • can be heterotrophic or autotrophic
  • most live in water (though some live in moist soil or even the human body)
  • ALL are eukaryotic (have a nucleus)
  • A protist is any organism that is not a plant, animal or fungus

Protista = the very first

Classification of Protists

  • how they obtain nutrition
  • how they move

Animallike Protists - also called protozoa (means "first animal") - heterotrophs
Plantlike Protists - also called algae - autotrophs
Funguslike Protists - heterotrophs, decomposers, external digestion

.Animallike Protists: Protozoans

Four Phyla of Animallike Protists
Classified by how they move

  • Zooflagellates - flagella
  • Sarcodines - extensions of cytoplasm (pseudopodia)
  • Ciliates - cilia
  • Sporozoans - do not move


move using one or two flagella
absorb food across membrane




moves using pseudopodia ( "false feet" ), which are like extensions of the cytoplasm --ameboid movement
ingests food by surrounding and engulfing food (endocytosis), creating a food vacuole
reproducing by binary fission (mitosis)
contractile vacuole - removes excess water
can cause amebic dysentery in humans - diarrhea and stomach upset from drinking contaminated water
Other sarcodines: Foraminferans, Heliozoans




move using cilia
has two nuclei: macronucleus, micronucleus
food is gathered through the :mouth pore, moved into a gullet, forms a food vacuole
anal pore is used for removing waste
contractile vacuole removes excess water
exhibits avoidance behavior
reproduces asexually (binary fission) or sexually (conjugation)
outer membrane -pellicle- is rigid and paramecia are always the same shape, like a shoe



do not move on their own
Malaria is a sporozoan, infects the liver and blood

Plantlike Protists: Unicellular Algae

  • contain chlorophyll and carry out photosynthesis
  • commonly called algae
  • four phyla: euglenophytes, chrysophytes, diatoms, dinoflagellates
  • accessory pigments help absorb light, give algae a variety of colors



live in water
have 2 flagella for movement
use chlorplasts for photosynthesis, but can turn into heterotrophs if they are kept in the dark
has an eyespot used for sensing light and dark
pellicle - like a cell wall, helps maintain their shapes



Chrysophytes yellow-green algae, "golden plants" Diatoms produce thin cell walls of silicon, main component of glass Dinoflagellates Often have two flagella luminescent



Ecology of Unicellular Algae

  • make up the base of aquatic food chains
  • phytoplankton makes up half of the photosynthesis that occurs on earth (oxygen)
  • can cause Red Tides - algal blooms - which are toxic


Date: 2016-01-03; view: 305

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