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PROTOZOA
An introduction
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Protozoan / Protozoa
Protozoology
“First animal”
Eukaryotic protists.
Generally, single-celled.
Size: Between 5 & 250 μm in dia
More than 65,000 described species
across 7 phyla.
Size-wise…
• Leishmania donovani
– Cause of the human disease kala azar
– 1 - 4 μm
• Amoeba proteus measures 600 μm
• Certain ciliates reach 2 mm
• A protective envelope extinct members of
Foraminiferida measure upto 15 cm in dia.
OCCURENCE
• Moist habitats - Sea, Soil & in freshwater
• Even in polar regions & at high altitudes
• Under dry conditions, forms a cyst
– Eg.: Naeglaria, an amoeba.
• Parasitic protozoa
– Eg.: Malarial parasite, Plasmodium
ECOLOGY
• Free-living forms
• Symbiotic protozoa
– Eg.: in the termite gut, beneficial to host
• Parasitic protozoa
– Cause disease.
FREE-LIVING PROTOZOA
Factors which influence their
distribution and population
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Moisture
Temperature
Light
Nutrient availability
Other physical & chemical conditions.
• LIGHT
– Bear chromatophores
– Carry out photosynthesis; requires sunlight
– Few protozoa avoid light.
• pH
– Optimum pH range of 6 – 8 for maximum
metabolic activity.
– Yet, extremities: 3.2 to 8.7
• NUTRIENTS:
– Some protozoa thrive in water rich in oxygen
but low in organic matter (mountain springs,
brooks, or ponds)
– Water rich in minerals
– Water where there is active oxidation &
degradation of organic matter (the majority of
freshwater protozoa, such as the ciliates).
– Water with little oxygen
– Salt & freshwater.
• Anaerobic protozoa
– Spp of Metopus, Saprodinium & Epalxis
• Aerobic protozoa
– Bodo, Paramecium, Aspidisca, and Vorticella.
• Temperature
– Optimum temperature between 16 and 25°C
– Max. between 36 and 40°C
– Rarely, 30 to 56°C of hot springs
SYMBIOTIC PROTOZOA
• Commensalism
– Host is neither injured nor benefited, but
commensal is benefited
– Ectocommensalism
• Protozoa attach themselves to a host’s body.
– Endocommensalism
• Protozoa, inside the host’s body.
• Mutualism
– Beneficial to both
– Eg.: Flagellates in the termite gut digest
woody material eaten by termite to a
glycogenous substance which can be used by
the host cells
PARASITIC PROTOZOA
• Parasite lives at the expense of the other.
• Host may develop pathological conditions.
• Parasite feeds on host cells, cell
fragments, cytoplasm and even nuclei.
• Eg.: Sporozoa
• Hyperparasitism
– Parasitic protozoa that parasitize other
protozoan
In the food chain….
• In marine waters
– Zooplankton: Protozoa that feed on the
photosynthetic phytoplankton
– Light energy  Phytoplankton  Zooplankton
 Carnivores
• Dead bodies of producers & consumers 
Decomposition by fungi & bacteria 
Ingestion of bacteria by protozoa.
(Saprophytic)
PROTOZOAN MORPHOLOGY
INTRA-CELLULAR ORGANELLES
• Protein fibrils - Fibrillar bundles,
myonemes & microtubules: For
contractility
• Cytoplasm:
– Ectoplasm (gel-like) & Endoplasm
(voluminous & fluid)
• Membrane-bound systems in endoplasm
• Endoplasmic reticulum
• Ribosomes
• Golgi complexes
• Mitochrondria
• Kinetosomes or blepharoplasts:
Intracytoplasmic basal bodies of cilia or
flagella.
• Food vacuoles
• Contractile vacuoles, and
• Nuclei
• In the ciliates, two dissimilar nuclei
– One large Macronucleus controls the
metabolic activities and regeneration
processes
– One small Micronucleus for reproductive
activity.
• Cell membrane (plasmalemma)
– Physical protection
– Exchange of substances (semipermeable)
– Site of perception of chemical and mechanical
stimuli
– Establishment of contact with other cells (cell
sensitivity to external factors).
• PELLICLE
– Combinations of membranes
– Eg.: in Euglena, Paramecium
• A diffuse layer of mucopolysaccharides over the
plasmalemma
• For Pinocytosis: Uptake of fluids and soluble
nutrients through small invaginations in the cell
membrane that subsequently form intracellular
vesicles
• THECAE, SHELLS, TESTS, LORICAE
Feeding Structures
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Pseudopodial engulfment of amoebas
Tentacular feeding tubes of suctorians
Cytostome of many ciliates
Oral groove
Peristome
Cytopharynx:
– A region, nutrients pass through & get
enclosed in a food vacuole.
LOCOMOTOR ORGANELLES
• Pseudopodium
– Temporary projection of part of the cytoplasm
when pellicle is absent
– Eg.: Amoebas (Sarcodina)
– For capturing food substances.
• Flagellum
– An extremely fine filamentous extension of the
cell
– Varies from 1 to 8; Usually, 1 or 2
– 2 parts: an elastic filament called an axoneme
and the contractile cytoplasmic sheath that
surrounds the axoneme.
• Cilia
– Locomotor function
– Also aid in the ingestion of food
– Fine & short threadlike extensions from the
cell
– Uniform or different in lengths
REPRODUCTION
• Asexual reproduction
• Sexual reproduction
• Both asexual and sexual processes
– Some parasitic protozoa
• Asexual reproduction
– Cell division
• Binary fission
• Multiple fission
– Budding: A variation of unequal cell division.
BINARY FISSION
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In amoebas
Pseudopodia are withdrawn
Nucleus divides
Organism elongates
Constricts in the center to form 2 daughter
cells.
MULTIPLE FISSION
• Formation of multiple nuclei within the
mother cell
• Corresponding number of daughter cells
• Occurs commonly in the foraminifera, the
radiolaria, and the heliozoa.
• In the sporozoa, malarial parasite
Plasmodium
– Schizogony
BUDDING
• Formation of a new organism by the
protrusion of part of another
• New cell is genetically identical to the
primary one (a clone).
• Exogenous budding:
– Involves formation and separation of the bud
toward the outside.
• Endogenous budding
– In many suctorian species
– Formed inside the mother cell
SEXUAL REPRODUCTION
• Sexual fusion of two gametes (syngamy or
gametogamy)
• Conjugation:
– A temporary union of two individual cells for
purpose of exchanging nuclear material –
found exclusively in ciliates
– After exchange of nuclei, the conjugants
separate
– Each of them gives rise to its respective
progeny by fission or budding.
• When they are unlike in morphology (as well as
physiology), they are anisogametes and can be either
microgametes or ma crogametes. That is, they are like
the spermatozoa and the ova of metazoa, respectively.
Thus microgametes are motile, relatively small, and
usually numerous in comparison to macrogametes.
Anisogametes are common among the sporozoa. For
example, in Plasm odium vivax (a sporozoan that causes
a type of malaria), anisogamy results in the formation of
ookinetes or motile zygotes which give rise to a large
number of sporozoites (long, slender bodies with an oval
nucleus and firm cuticle, capable of producing new
infection).
REGENERATION
• Capacity to regenerate lost parts from
simple forms to those with highly complex
structures.
• The collar functions as a food catching
device.