Animal like Protists

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  • Eukaryotes
  • Found in kingdom Protista
  • Most are unicellular
  • Heterotrophs that ingest small food particles & digest it inside food vacuoles containing digestive enzymes
  • Classified by the way they move (cilia, flagella, pseudopodia…)

  • Microscopic in size
  • 65,000 identified species with almost half extinct
  • Found in freshwater, marine, and moist terrestrial habitats
  • Make up part of the zooplankton & serve as food for animals in marine & freshwater systems
  • First seen by Leeuwenhoek in 1675
  • Many species are free living
  • Some species are parasitic living in the bloodstream of their host & cause malaria, amebic dysentery, or giardiasis
  • Many serve as food for other organisms in aquatic habitats; called zooplankton


  • All reproduce asexually by binary fission (single protozoan divides into two individuals)
  • Some species reproduce by multiple fission producing more than two individuals
  • Some species reproduce sexually by conjugation (opposite mating strains join & exchange genetic material)


  • Eyespots in some protozoans can detect changes in light

  • Many can form harden covering called cyst when conditions become unfavorable (no water, pH or temperature changes, nutrient deficiency, decreased oxygen supplies…)
  • Metabolic activity of protozoans resumes when conditions become favorable again
  • Some protozoans can detect & avoid obstacles and harmful chemicals in their environment
  • Freshwater protozoa have contractile vacuoles to pump out excess water


  • Divided into 4 phyla based on their method of movement — Sarcodina, Ciliophora, Zoomastigina, & Sporozoa
  • Found in the kingdom Protista along with algae, slime molds, & water molds
  • Sarcodinians move by extending their cytoplasm or pseudopodia (fingerlike projections of the cytoplasm)
  • Zooflagellates move by whip like flagella
  • Ciliophorans or ciliates move by hair like cilia move
  • Sporozoans are nonmotile


Phylum Common Name Locomotion Type of NutritionExamples
some parasitic
some parasitic
some parasitic
Sporozoasporozoans(None in Adults)heterotrophic;
some parasitic



Protozoan Evolution:

  • First eukaryotic organism thought to have evolved about 1.5 billion years ago
  • Protozoans possible evolved from the 1st eukaryotes by Endosymbiosis 
  •  Endosymbiosis – process where one prokaryote lives inside another becoming dependent upon each other

Phylum Sarcodina:

  • Includes hundreds of species of amebas
  • Found in freshwater, marine, & moist soil habitats
  •  Usually reproduce asexually
  • Their cytoplasm consists of clear, outer ectoplasm and granular, inner endoplasm
  • Move by extending cytoplasm (cytoplasmic streaming)
  • Cytoplasm extensions are called “false foot” or pseudopods
  • Pseudopods form when the inner cytoplasm or endoplasm pushes the outer cytoplasm or ectoplasm forward to make a blunt, armlike extension
  • Ameba move by cytoplasmic streaming to produce pseudopods; process called ameboid movement

  • Sarcodines also use their pseudopods for feeding by surrounding & engulfing food particles & other protists; called phagocytosis
  • Food is surrounded by a pseudopod & then this part of the cell membrane pinches together forming a food vacuole; called endocytosis
  • Cytoplasmic enzymes enter the food vacuole & digest the food
  • Undigested food & wastes leave by exocytosis

  • Most Sarcodinians have contractile vacuoles to pump out excess water

  • Oxygen & carbon dioxide diffuse through the cell membrane
  • Sarcodinians may form hard, protective, inactive cysts when conditions become unfavorable (drought, lack of nutrients, heat…)
  • React to stimuli such as light
  •  Some Sarcodinians have hard shells called the test made of silica or calcium carbonate
  • Radiolarians found in warm, marine waters have a test made of silica & have sticky pseudopodia to trap food

  • Marine Foraminiferans have a test made of calcium carbonate with holes through which pseudopodia extend

  • Foraminiferan tests build up and form limestone or chalk (e.g. White Cliffs of Dover)
  • Important food source in marine habitats
  • Entameba histolytica cysts in untreated water supplies cause amebic dysentery which can be fatal

Phylum Ciliophora:

  • Called ciliates because they move by short, hairlike cilia lining the cell membrane
  • Cilia may be modified into teeth, paddles, or feet

  • Largest group of protozoans
  • Most found in freshwater, but some are marine
  •  Called plankton & serve as a food source
  •  Form protective cysts to survive unfavorable conditions
  • Members include the Paramecium, Vorticella,  & Stentor
  • Have 2 types of nuclei — smaller micronuclei & larger macronuclei
  • Macronucleus controls asexual reproduction by mitosis
  • Can reproduce sexually by conjugation (two paramecia join together & exchange DNA)
  • Gases diffuse across cell membrane


  • Trumpet shaped protozoan with cilia around the top
  • Attaches to feed & then detaches to swim around


  • Cup shaped protozoan with cilia at the top
  •   Has a coiled stalk to raise & lower the organism
  • Can attach to surfaces

Paramecium caudatum:

  •  Slipper shaped protozoan found in freshwater

  • Clear, elastic covering of cell membrane called pellicle
  • Pellicle made of protein for protection
  • Use cilia to swim & obtain food (algae & bacteria)
  • Have 2 contractile vacuoles to pump out excess water
  •  Cilia sweep food into oral groove where mouth located at the bottom
  •  Food enters short tube called gullet into food vacuoles where it’s digested
  • Wastes leave through anal pore

  • Have trichocysts (tiny, toxic darts to help capture prey or anchor to a surface)
  •  Respond to light & learn by trial & error
  • Reproduce asexually by mitosis & sexually by conjugation

Phylum Zoomastigina:

  • Called Zooflagellates because have one or more whiplike flagella to move
  • Flagella made of bundles of microtubules

  • May be freshwater or marine
  • Some are parasites such as Trypanosoma that destroy red blood cells & causes fatal African sleeping sickness

  • Trichonympha lives symbiotically inside termites & digests cellulose

Phylum Sporozoa:

  • Adult sporozoans have no structures for movement
  • Form spores

  • Most are parasitic using one or more hosts
  • Immature sporozoans are called sporozoites & live in body fluids of hosts
  • Plasmodium is transmitted by mosquitoes & causes malaria
  • Plasmodium sporozoites enter the bloodstream, travel to the liver, divide & form spores called merozoites
  • Merozoites attack red blood cells & later form eggs & sperm that fertilize
  •  New sporozoites migrate to the salivary glands of mosquitoes where they can be passed on to another person
  • Malaria can be controlled by controlling mosquito populations & it is treated with a drug called quinine derived from the Cinchona Tree