Protozoan
The name protozoan (Gr protos= first; zoon= animal) come from Goldfuss (1818) who, however,
used the name simply for the lower groups of zoophyta including protozoans, sponges,
coelenterates, rotifer and bryzoon. It was Von Siebold (1845) who recognizing the unicellular
nature of the protozoan, first used and defined the name protozoan in the present sense.
Protozoan are generally microscopic in size, they are found in fresh water, salt water and damp
soil, while some are parasitic symbiotic and commensals. they are called a cellular or noncellular because their bodies are not diffenretiated in cells, part of their bodies are specialized for
various functions; these parts are called organelles in contrast to the organ of metazoan.
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Protozoan may regarded equivalent not to a metazoan cell, but to an entire metazoan
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Protozoans have undergone cytological differentiation, whereas metazoa have undergone
histological differentiation during the course of evolution.
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The term unicellular used for protozoa is unfortunate. Protozoa form heterogeneous
group, the member display an extreme diversity of structure, different types of symmetry
and adaptation to various environments
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Many protozoa are complicated in structure, some form colonies.
A protozoa might be defined as an organism which is made up of a mass of protoplasm not
divided into cells and which carries on all the vital activities of life such as locomotion, feeding,
digestion, egestion, respiration, excretion and reproduction etc. Although it is not divided into
cells, it has specialization and division of labour within its cytoplasmic mass.
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in as much as protozoa are not made up of cells, they represent what a called
protoplasmic level of organization
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about 50,000 species have been named.
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20,000 of them are fossil forms
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the immense number of protozoa have traditionally been separated by their means of
locomotion into four classes
1. Phylum protozoa
(a) class sarcodina with pseudopodia eg. Amoeba
(b) class mastigophora (flagellate) with flagella eg Trypanosoma, Euglena
(c) class ciliate with cilia eg. paramecium
(d) class sporozoa with no organelles for locomotion
Recently the committee on Taxonomy and Taxonomic problem of the society of protozoologists
published a revised classification of the protozoa
(Honigberg et al 1964) who reported that protozoa have been divided into four subphyla
i. Sarcomastigophora
ii. Sporozoa
iii. Cnidospora
iv. Cillophora
Protozoa can look into in two concepts
i. Plant-like
ii. Animal-like this refer to the way the food is gathered plants are typically autotrophic,
meaning that they synthesize their own organic constituents from inorganic
substrates. Animals are typically heterotrophic, meaning that they obtain organic
molecules synthesized by other organisms. Heterotrophic protozoa may ingest their
food in a soluble form or in a particulate form. Particulate food is acquired by
phagocytosis via an infolding or invagination of the cell membrane to surround a
visible food particle. Heterotrophs that feed on visible particles are phagotrophs or
holozoic feeders whereas those that ingest soluble food are osmotrophs or saprozoic
feeder.
A distinction between plant and animal on the basis of nutrition works well for muticellular form
but not unicellular
Autotrophlic protozoa (Phototrophs) use light energy to synthesize their organic molecules, but
they often practice phagotrophs and osmotrophs as well
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A single class Englenoidea (Phylum Euglenozoa) contain some forms that are mainly
phototrophs some that are mainly phagotrophs species of Euglena show considerable
variety in nutritional capability.
The means of locomotion was used to distinguish three of the four classes in traditional phylum
protozoa. Members of a parasitic class once called sporozoa lack distinct locomotory structure,
but share an organelle capable of invading host cells.
Members of the other three traditional protozaon classes differ in means of locomotion.
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Flagellates use flagella/ flagellum
diagram
Amoeba-use pseudopodia to move, typically, a flagellate has a few long flagella, and a ciliate
has many cilia, but no real morphological distinction some investigator called both
undulipodea.…
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A cilium propels water parallel to the surface to which the cilium is attached whereas a
flagellum propels water parallel to the main axis of the flagellum.
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Amoebas are able to assume a variety of body forms due to flowing cells cytoplasm. The
cytoplasm can be extended outward in pseudopodia of a various shape.
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Lobopodia- are blunt tipped,
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Filipodia- are thin and sharply pointed
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Rhizopodia – are branched filaments
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Reticulopodia are branched filament that emerge to form a netlike structure
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Axopodia- are thin, pointed pseudopodia that contain a central longitudinal (axial)
filament of microtubules called an axoneme
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Amebas that make shells are called testate eg. Arcella,
Difflugia, globigerina,
Diagram
General characteristic of the phylum protozoa
1. They are unicellular; some are colonial, and some with multicellular stages in their life
cycles
2. They are mostly microscopic, although some are large enough to be seen with naked eye
3. All symmetries are represented in the group, shape variable or constant. (oval, sphercial
or others.
4. No germ layer present
5. No organ or tissue but specialized organelles are found, nucleus single or multiple.
6. Free living, mutualism, commensalism, parasitism all are represented in the group.
7. locomotion by pseudopodia, flagella, cilia and direct cell movements and some sessil
8. Some provided with simple endoskeleton or exoskeleton, but mostly naked.
9. All modes of nutrition are represented, autotrophic, heterotrophic and saprozoic
10. Some are aquatic while some are terrestrial in habitat
11. Some exhibit free-living mode of life while other are symbiotic
12. Reproduction is asexual by fission, budding and cysts and sexually by conjugation or by
syngamy.
Function and component of protozoa cells
1. Nucleus- As in other eukaryotes, structure whose interior communicates with the
cytoplasm by small pores in the nucleus, the chromosomal materials (chromatin) often
clumps together irregularly relatively clear. This appearance is described as vesicular and
is a characteristics of many protozoa nuclei character such as the persistence of
nucleolous during mitosis are useful in identify protozoan clades (splitting of lineage
branch)
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Ciliates process two kinds of nuclei a germ line nucleus called the micronucleus and a
somatic nucleus called the macronucleus
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Mitochondria- is an organelle used in recovering energy from carbon bonds of fuel
molecules where oxygen serves as the terminal electron acceptor, it contains DNA,
Cristae, the internal membranes of a mitochondrion are of variable form, being flat,
tubular, discoid or branched. This form of cristae is considered a homologous character
and in conjunction with other morphological features is used to describe protozoa.
In a cell without mitochondria, hydrogenous mess may be present hydrogenosomes are
organelles that perform a respiratory function in the absence of oxygen and are assumed to have
evolved from mitochondria derivatives that lack DNA and are collectively called mitosomes.
Golgi apprartus
The golgi appraratus is part of the endomembrane system that participate in cellular secretory
processed and intracellular digestion of ingested food vacuoles Golgi apparatus are also called
dictyosomes.
Plastids – contain of a variety of photosynthetic pigment
Extrusome- This general term refers to membrane bound organelles in protozoans that are used
to extrude something form the cell. The ciliate trichocyst is an extrausome
Nutution- Holozonic nutrition implies phagocytosis in which an unfolding or invagination of the
cell membrane surrounding a food particle as invagination extends father unto the cell, it is
pinched off at the surface. The food particle thus is contained in an extracellular
membrane- bound vesicle, a food vacuole or phagosome, lysosome contain digestion enzymes
fuse with the phagosome and pour their contents into its where digestion begins. As digested
product are absorbed across the vacuolar membrane the phagosome becomes smaller. Any
undigested material may be released into the external environment by excytosis. The site for
phagocytosis is a definite mouth structure the cytostome.
Excretion and Osmoregulation In protozoan, vacuoles can be seen by light microscopy in the
cytoplasm of many protozoa. Some of this vacuole periodically fills with fluid substance that is
then expelled. Evidence is strong that the contractile vacuoles function primarily as
osmorequlator. They are more prevalent and fill and empty more frequently in fresh water
protozoa than in marine and endosymbiosis species where the soundings medium would be
more nearly isosmotic (having the same osmotic pressure) to the cytoplasm. Excretion is entirely
by diffusion. The main endproduct of nitrogen metabolism is ammonia.
Reproduction- sexual phenomena occur widely among protozoa, and sexual process may
proceeds certain phases of asexual reproduction, but embryonic development does not occur,
protozoa do not have embryo.
Different method of reproduction in protozoa include:
1. Fission- The cell multiplication proceed that produces mone individual protozoa to called
cell division in which tow essential identical individual result when a progeny cells is
considerably smaller than the parent and the grows to actual size, the process is called
budding. It occurs in some ciliates.
Multiple fission- division of the cytoplasm (Cytokiness) is preceded by several nuclear
divisions, so that a member of individuals are produce almost simultaneously. Multiple
fission or schizogamy is coming in some Apicomplexa and some ameba, if multiple
fission is proceeded by or associated with union of gametes, it is called sporogony.