Objectives:
to gain a broader appreciation for the diversity of the protists
to note similarities and differences between the various groups and how they attempt to solve the same basic problems of daily living
to note the unique relationships that sometimes exist within the groups
Introduction
The Protista are probably the most diverse of the eukaryotic
Kingdoms. Members are unicellular, filamentous, colonial or multicellular. All
require some form of moisture, fresh or saltwater, to survive and
reproduce. They are divided into three categories for ease of classification.
The categories relate to the ways in which nutrition is obtained
by organisms in each category. They may be subdivided as to the manner of locomotion in the case of the protozoans.
Your Photographic Atlas for the Biology Laboratory, 4th Edition, contains pictures and drawing of the various protistan groups starting on page 29.
In the absence of microscopes and slides we will observe the organisms by using the embedded links.
- Animal-like Protists (The Protozoans) - all are heterotrophic and are usually grouped by locomotion type and
feeding means.
- Ameboid (Division Rhizopoda) - free-living (Amoeba
proteus) and parasitic (Entamoeba histolytica) forms are present; some (Foraminiferans and Radiolarians)secrete shells, known as tests, around them. Move by extruding cytoplasm inside of membrane.
- Flagellate (Division Zoomastigophora) - free-living, symbiotic forms such as those found in termite intestines, and parasites such as Giardia lamblia (causative agent of Beaver Fever) and Trypanosoma gambiense (causative agent of African Sleeping
Sickness) abound. Move by means of flagella - typical 9 + 2 microtubule arrangement.
- Ciliate (Division Ciliophora) - mostly solitary, free-living and fresh water groups; reproduce by conjugation. Have two nuclei - large macronucleus controls growth, small micronucleus controls conjugation. Move by means of cilia. Paramecium
caudatum andStentor are examples.
- Sporozoans (Division Apicomplexa) - all members of group are parasitic with one or more intermediate hosts. All lack means of independent locomotion. Plasmodium is an example. This genus causes malaria. Four different species involved and vary with geography and time of onset of symptoms.
- Plant-like Protists (The Algae) - all groups contain members
that are photosynthetic and contain chlorophyll a. They are found in all water venues from the oceans to the rivers, lakes, streams and ponds. The single celled groups are called the phytoplankton and collectively all of the groups are known as the algae.
- Division Euglenophyta - contain light sensitive red
pigment spot (called eyespot) and carry on photosynthesis when
light is available and as heterotrophs otherwise. Lack cell wall and
have pellicle made of protein strips inside of plasma membrane.
Store their food as fats and paramylon (unique polysaccharide) and
contain chlorophylls a & b and carotenoids. Chloroplasts are
probably result of endosymbiosis. Euglena sp. is the common example.
- Division Chrysophyta - contains diatoms (Bacillariophyta) and
golden and yellow green algae. Mostly photosynthetic and
free-living some diatoms are symbiotic with foraminiferans. Groups
contain chlorophylls a & c as well as a golden brown carotenoid
called fucoxanthin. Food molecules produced through
photosynthesis are stored as oils and chrysolaminarin (a polymer of
glucose and mannitol). Cell wall contain silica not cellulose.
- Division Pyrrhophyta or Dinoflagellata - mostly photosynthetic
and marine, pigmentation varies dependent in part on their
endosymbiotic history. Pronounced “deeno” it refers to the twirling
or whirlpool motion these organisms make. Some are
bioluminescent and can be seen on the crest of waves coming in to
shore at night. Algal blooms called red tides can poison animals
including fish and humans as the result of toxin produced. They
contain chlorophylls a & c and store their food as starch.
- Division Rhodophyta - mostly multicelled, and marine, living in
clear tropical waters. Cell walls of some species contain calcium
carbonate. these species are called the coralline algae and
contribute to coral reef formation. Agar and carrageenan as well as
cellulose are found in the cell walls of most. Some species such as
Porphyra nereocystis are used as a wrapping for sushi and are
known as nori. Chlorophylls a & perhaps d are found as are
accessory pigments known as phycobilins which increase the
portion of the spectrum that can be used for photosynthesis
particularly in deep waters. Food is stored as Floridean starch
similar to glycogen.
- Division Phaeophyta - known as the brown algae or kelp. Amongst
the largest of the seaweeds. Contain chlorophylls a & c, carotenoids
and fucoxanthin (also found in diatoms). Food stored as laminarin, a
glucose-mannitol polymer. Food is translocated as mannitol and
amino acids. Cell wall consist of cellulose and alginic acids which
are converted to algin which is used as a stabilizer in paints and an
emulsifier for foods. Sargassum, Fucus, Macrocystis, and
Laminaria are the largest and best known.
- Division Chlorophyta - the green algae are the group from which
the true plants developed. Extremely diverse in structure (single
celled, colonial, filamentous, multicellular) and in types of
reproduction. Contain chlorophylls a & b, and carotenoids; store
food as starch grains inside chloroplasts; cell wall contains
cellulose, pectins and other typical polysaccharides. Found in fresh
water, salt water, bogs, sediments, on land and rocks, tree bark, and
snow. Chlamydomonas and Chlorella are single-celled,
Volvox and Pediastrum are colonial, Spirogyra
and Ulothrix are filamentous, and Ulva and
Codium are multicellular.
- Fungus-like Protists (The Slime and Water Molds)- all
members resemble fungi and were originally classified as such. All groups differ from fungi by producing motile cells during their lifetime. Two major categories:
- Slime Molds (Divisions Acrasiomycota - the
cellular slime molds and Myxomycota the plasmodial slime molds). Cellular slime molds behave like amebas while plasmodial slime molds
stream along as a wallless cytoplasmic mass that resembles slime.
- Water Molds (Division Oomycota) may be free-living or parasitic such as Saprolegnia on fish or downy mildew on grapes or the parasite Phytophthora infestans which was responsible
for potato blight and caused the emigration of many Irish in the late 1840’s.
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