Kingdom Protista – the “Junk Drawer of Taxonomy”
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protists are unicellular (single-celled) organisms
some may form colonies but none form tissues
first appeared in fossil record 1.5 billion years ago
all have a membrane-bound nucleus so are eukaryotic
many act as the major food resource for aquatic organisms
some can cause diseases
they can be plant-like, animal-like, or fungi-like
Plant-Like Protists
 algae are an example of plant-like protists
 all are aquatic
 they contain chloroplasts, chlorophyll and can photosynthesize
o Euglenophyta – have flagella (e.g. Euglena species)
o Chrysophyta – have silica shell (e.g. diatoms)
o Pyrrophyta – dinoflagellates (phytoplankton)
o Chlorophyta – green algae (e.g. Spirogyra and Ulva)
o Phaeophyta – brown algae (e.g. Fucus species and kelp)
o Rhodophyta – red algae (e.g. Porphyra species)
Euglena
 move using a flagellum
 they also have an eyespot which helps them stay in the
light to photosynthesize
 they do not have a cell wall but may have a firm but flexible
covering called a pellicle
 they also contain a special organelle called a contractile
vacuole – this helps the Euglena get rid of excess water if
it enters hypotonic surroundings.
 Euglena divide using binary fission lengthwise
Algae
 Algae can be red , brown, or green.
 Most are multicellular but do not form tissues as seen in
higher plants
 Algae can be found in very wet soils, covering the base of trees, or on rocks.
 kelp (or seaweed) is an example of red or brown algae
 Unicellular algae are called phytoplankton
The Importance of Algae
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algae are primary producers in ecosystems – they form the base of many food
pyramids in the aquatic ecosystems.
they provide about 80% of all of the oxygen around the earth
humans use algae as fertilizer, they can extract agar for use in culture medium, drug
capsules and cosmetics
the millions of years of algae dying and sinking to the bottom of the oceans has
created most of the fossil fuels and crude oil deposits in the earth’s crust
Animal-Like Protists (Protozoa)
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there are many different shapes and sizes of protozoa – the major phyla include:
Sarcodina, Mastigophora, Ciliophora, Sporozoa
all are heterotrophs, and can obtain their food in several ways:
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capturing and eating other organisms
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decomposing dead organisms
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absorbing chemicals from the water
o being a parasite (lives on or inside another living organisms and gets its food
from that organism)
the main method of classifying animal-like protists is by their type of locomotion
o using pseudopods – Sarcodina (e.g. Amoeba species)
o using flagella – Mastigophora (e.g. Trypanosoma aka African sleeping sickness,
symbiotic flagellate in termite gut)
o using cilia – Ciliophora (e.g. Paramecium species)
o no locomotion of their own – (parasitic protozoans) – Sporozoa – use body fluids
of hosts that they parasitize to move around (e.g. Plasmodium species aka
malaria)
Sarcodina
 Amoeba is an example of a Sarcodine
 It is a large cell but is not very complex
 It moves by extending and retracting pseudopods – extensions of the cell membrane
which changes shape constantly as it moves
 The cytoplasm has two layers:
o ectoplasm – the outer protective layer
o endoplasm – the inner layer which contains most organelles
 amoebas feed by phagocytosis – just like a macrophage in your bloodstream!
 They reproduce by binary fission
Ciliophora
 Paramecium is an example of a Ciliophore
 It uses its cilia in a coordinated beating fashion to
move the cell
 Paramecia have an oral groove which leads to a
cavity called a gullet – at the end of the gullet, a food
vacuole can form where it will digest food using
enzymes
 Paramecia can defend themselves using trichocysts –
hundreds of tiny poison-filled barbs can be sent out
towards a predator
 Paramecia have two nuclei – one controls the cell’s
activities and the other controls division.
Sporozoa
 Sporozoans are parasitic.
 They do not have their own method of locomotion – they usually rely on the fluids of
their host to get around
 They are very good at reproducing quickly, using spores
 Spores are reproductive cells with a half-set of chromosomes ( haploid )
 One of the best known examples of a sporozoan is the genus Plasmodium, which
causes malaria in humans
 Malaria kills over one million people every year worldwide, 75 percent of them are
children in Africa.
 Other diseases caused by sporozoans include:
o Entamoeba histolytica – causes dysentery – spread by eating or drinking food
contaminated by cysts – these cysts come from the fecal matter of an infected
person or animal.
o Giardia lamblia – “beaver fever” – caused by drinking water that has been
contaminated by animal activity
o Trichomonas vaginalis – STD – infects the urinary and reproductive tracts
o Trypanosoma – causes African sleeping sickness – transmitted by the Tsetse fly
Fungi-Like Protists
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only one Phylum in this sub-Kingdom
o Gymnomycota – e.g. Dictyostelium species
Also referred to as slime moulds
prefer cool, shady, moist places
are often found under fallen leaves or rotting logs
can move around using amoeboid movement
Dictytostelium lives unicellularly but can converge into a mass plasmodium
This will act like a migrating slug and move into an open area in the light
there it can grow into a fruiting body, produce spores and release them
these coordinated cells are not quite a tissue, but may have been an early step in
the evolution of more complex, multicellular organisms that do have tissues (like
plants and animals)