Author: Biology Junction Team

 

Protozoa Animal like Protists All Materials © Cmassengale

Characteristics:

• 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

Reproduction:

• 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)

Adaptations:

• 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

Classification:

• 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

 

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

Stentor:

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

Vorticella:

• 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