Introduction
Biology is the study of living things and their vital processes. Besides the study of plants
and animals, and the study of structure of organisms-morphology and the functions-physiology.
Biology also covers various areas like: cell biology, population biology, ecology, genetics,
biochemistry, molecular biology, and physical anthropology, evolution and behavior,
environmental science and microbiology. Biology also deals with the study of in the molecular
and microscopic level like microbiology. That includes bacteria, viruses, fungi, protozoa and so
on.
This very assignment primarily consists of various modes of reproduction in protozoa.
Secondarily, it also touches few relevant aspects of protozoa in general and its general life-cycle
base on one of the protozoa. Their occurrence, mode of respiration and taxonomical
classification too are included here in this very assignment.
Protozoa are parasites. They are microscopic, unicellular organisms that lack
photosynthetic capability. It is a eukaryotic organism as its cell contains a true nucleus and is
bounded by a nuclear membrane. Generally, they are aquatic. Their mode of reproduction is
asexual and sexual but asexual most often. The mode of locomotion or movement is facilitated
by the specialized structures such as cilia, flagella, or pseudopodia. They are heterotrophic as
they feed on other organisms to obtain the nutrients they need to live.
After the completion of this very assignment I assure that I will be able to convince and
beware any readers and learners of this very assignment as very useful and knowledgeable to
continue and carry out their further studies and reading hereafter.
Protozoa
Protozoa are parasitic protists. Protozoan microscopic, unicellular organisms that lack
photosynthetic capability. Reproduce by asexual fission. Protozoa which belong to the Kingdom
Protista constitute a group of eukaryotic cells. They are eukaryotic protists. They have a
membrane-bound nucleus as well as the other membrane-bound organelles that are characteristic
of higher animals. Protozoa have specialized structures for movement such as cilia, flagella, or
pseudopodia. Their cell posses no rigid cell wall. They are heterotrophic as they are unable to
prepare their own food. They
hunt, digest and store food. They feed on other animals to obtain
the nutrients they need to live. They are mainly found in fresh water & marine habitats, some
found in soil or aerial habitats large number parasitic on man.
Taxonomical classification
Group
Phylum Name
Flagellates
Mastigophora
Ciliates
Ciliophora
Sporozoans
Sporozoa
Rhizopods
Sarcodina
Classification of protozoa shows that they are not a unified group, but appear along the
evolutionary continuum; and the reason that they are lumped together in the group known as
protozoa is because they are all single-celled eukaryotic organisms that lack chlorophyll.
Protozoa are divided into three phyla and these are; Sarcomastigophora, Ciliophora and
Apicomplexa
The phylum Sarcomastigophora is divided into two Sub-phyla, which are Sarcodina or
amoeboid protozoa such as Entamoeba histolytica, and Mastigophora or Kinetoplasta the
flagellated protozoa such as Trypanosoma brucei. Ciliophora are the Ciliophora are the ciliated
protozoa such as Balantidium coli and Apicomplexa are protozoa that form spores such as
plasmodium falciparum ciliated protozoa such as Balantidium coli and Apicomplexa are
protozoa that form spores such as plasmodium falciparum.
Flagellates: These organisms have a trophozoite- vegetative feeding form but also
possess flagella for locomotion and food gathering. All pathogenic species are true parasites,
being unable to reproduce outside the host.
Ciliates: These possess rows of hair-like cilia around the outside of the body for motility
and also to direct food into a primitive mouth termed a cytostome. All ciliates possess two
nuclei: a large polyploid micronucleus and a small micronucleus active only during sexual
reproduction. Some species form cysts- resting form.
Amoebae: These are the simplest of the protozoa and are characterized by a feeding and
dividing trophozoite stage that moves by temporary extensions of the cell called pseudopodiafalse feet. In some species the trophozoite can form a resistant cyst stage able to survive in the
environment. Those that infect the gut are true parasites being unable to reproduce except in a
living host. Others occur naturally in soil and water and are not true parasites. They are termed
‘free-living’ and infect humans as opportunistic pathogens.
Apicomplexa: This is a unique group lacking any visible means of locomotion. They are
all parasitic and most are intracellular, having a life cycle involving both sexual and asexual
reproduction. The common feature of all members is the presence of an apical complex at the
anterior pole in one or more stages of the life cycle.
Occurrences
Mostly aquatic and are found in moist habitats. Mainly found in fresh water & marine
habitats; some found in soil or aerial habitats, large number parasitic on man & other animals.
They are even common in the sea. Free-living protozoa have been found in the Polar Regions
and at high altitudes as well.
Movement
Protozoans move by the use of cilia, flagella, pseudopods or some have no movement
Respiration
Respiration takes place when oxygen diffuses into the cell, where the food molecules
become oxidized. The energy produced and the organic molecules are used for maintenance and
building of the cell. Waste products, carbon dioxide and water diffuse out of the cell.
Nutrition
Since they live in aquatic environments, water, oxygen, and other small molecules readily
diffuse into the cell through the cell membrane. In addition protozoa take in food either by
pinocytosis - ingestion of fluid into a cell forming an internal vesicle or phagocytosis-engulfing
solid food particles and forming a food vacuole as a means of obtaining water and food.
Protozoans hunt, digest and store food. Most are heterotrophs. They feed on other animals to
obtain the nutrients they need to live.
Morphology
Characterized by great morphologic diversity. Some have two nuclei macronucleus contains
many copies of genome controls metabolism, growth, and sexual reproduction and micronucleus
that involved in genetic recombination, sexual reproduction, and regeneration of
macronuclei.All produce Trophozoite which is vegetative stage which feeds upon bacteria and
particulate nutrients. Cyst where some protozoa produce a protective capsule under adverse
conditions (toxins, scarce water, food, or oxygen)
Modes of Reproduction
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).Generally, protozoa multiply or
reproduce by asexual reproduction. In few cases the sexual reproduction is also occurred.
Therefore, protozoa can reproduce asexually and sexually. Some posses asexual phase in one
host and a sexual in another phase. (p.399).
Asexual Reproduction
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).This reproduction occurs by simple
cell division, in which the daughter cells can either be equal or unequal sizes. Under this
reproduction, it can either be binary, multiple fission or budding mode of reproduction. If two
daughter cells are formed it is called binary or transverse fission and if many daughters cells are
formed it is call multiple fission. If there is variation of unequal cell division it is called budding.
The multiple fission is also called schizogony where nucleus undergoes multiple divisions before
the cell divides then cytoplasm forms around each nucleus before division takes place followed
by giving rise to multiple daughter cells.(p.399)
(From https://my.unisa.edu.au/unisanet/Information/12936info/08%20Pod%20%20protozoa.pdf)
Binary fission
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).The simplest form of binary fission is
found in the amoebas. The pseudopodia are withdrawn before the nucleus divides. After the
division of nucleus the organism elongates and constricts in the centre in order to form two
daughter cells.
Amoeba having special protective coverings are more complex in their manner of binary
fission due to the type of the covering they posses. Those with soft coverings, the division are
longitudinal along the axis of the body and covering constricts into two equal halves. In those
having more rigid body coverings, the part of the cytoplasm protrudes from the apertures to
secrete a new covering over the surface. Only after the formation now covering does the nuclear
division occurs.
In flagellates, the fission is longitudinal along the major body axis. Since the flagella
themselves are incapable of division, they must be regenerated from basal bodies called
blepharoplasts which arise in the vicinity of the old basal bodies. Thus multiplication of basal
bodies usually precedes cell division.
The transverse fission is the characteristic of the ciliates. The fission occurs at the right
angle to the long axis of the cell. In the simplest from of transverse fission, an equatorial furrow
appears first which separates the cell surface layer into an interior and a posterior half. A
constriction follows, leading to the separation of the two daughter cells. (p.399-401)
Multiple fission
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).In such fission, a single parental
mother cell divides to form many daughter (final) cells. The division is usually preceded by the
formation of multiple nuclei within the mother cell, which then cleaves rapidly to form a
corresponding number of daughter cells. Multiple fission is not widespread as binary fission it
often takes place in addition tot eh latter processes. In ciliates and flagellates, this type of fission
is found relatively few species. Perhaps the best known examples of multiple fission are found in
protozoa, e.g. in the malarial parasite plasmodium where it called as schizigony and serves to
spread the parasites quickly in the host.(p.401)
Budding
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).It is the varied process by which by
which sessile protozoa produce motile offspring. In such case the mother cell remain sessile and
releases one or more swarming daughter cells. The swarmer differs from the parent cell not only
in a lower degree of differentiation but also in the possession of special loco motor organelles.
Some form of budding is found in all sessile ciliates and is used to disseminate the species while
the mother cell remains in situ.
Budding can either be exogenous or endogenous. The exogenous involves the formation
and separation of the bud towards outside. Definite exogenous are found/seen in suctorians when
a portion or portions of the adult sessile suctorian bud from the parent, develop cilia, and swim
away. In endogenous budding, the swarmer is formed inside the mother cell.( p.401-402)
Sexual Reproduction
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).In such type of reproduction there will
be sexual fusion two gametes that occur in most of the free-living protozoa. Free-living
protozoan normally resort to sexual reproduction only when environmental conditions become
adverse, because this mode of reproduction enhances genetic variation through mechanisms such
as mutation, etc. (p.402)
Process often involves production and fusion of gametes and process of conjugation and
exchange of genetic material between different mating types as in Paramecium.
Conjugation mode reproduction which generally a temporary union of two individuals for
the purpose of exchanging nuclear material, in sexual process found in ciliated protozoa
paramecium. After the exchange of nuclei, the conjugation separate and each of them gives rise
to its respective progeny by fission or budding. When the gamates which are developed form
triphoziotes are morphologically alike, they are called isogamates. If they are unlike they are
called anisogamates.
Conjucation of paramecium
Regeneration
In all the protozoa, from simple to highly complex structure they can regenerate. When a
protozoon is cut into two, the nucleated portion regenerates but anucleted portions degenerates.
In general nucleus in necessary for regeneration. In ciliates/ paramecium, the macronucleus alone
is sufficient to regenerate.
Life-cycle
Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce
sexually, some asexually, while some use a combination. There are few protozoa as in
plasmodium vivax, they reproduce sexually inside the host and asexuallly outside the host and
vice-versa.
Some protozoa have life stages alternating between proliferative stages -trophozoites and
dormant cysts. As cysts, protozoa can survive harsh conditions, such as exposure to extreme
temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen
for a period of time. Being a cyst enables parasitic species to survive outside of a host, and
allows their transmission from one host to another. When protozoa are in the form of
trophozoites they actively feed. The conversion of a trophozoite to cyst form is known as
encystation, while the process of transforming back into a trophozoite is known as excystation.
Generally, the basic mode of life-cycle and reproduction in protozoa are similar.
However, there are few differences that exist amongst the types of protozoa. Here, I have
generally explained the lifecycle based on one of the protozoan which is most common in most
of the protozoa.
Conclusion
Biology, the study of the living things includes all the macroscopic and microscopic
organisms.Despite the practical and real eye-eight of all the microscopic organisms I could learn
and know the microscopic organisms like protozoa through the textbook and cyber references as
macroscopic organisms in naked eyes.
With completion of this assignment, I could learn that not only higher organisms like
animals respire, locomote, feed, reproduce, and so on but also lower organisms too do. However,
the mode of respiration, locomotion, feeding, reproduction, etc. are different from higher
organisms. As in case of lower organisms the mode of reproduction is dissimilar to to higher
organisms where they reproduce asexually and sexually but higher organisms by sexually. The
modes of locomotion too is different from higher organisms unlike limbs but use of cilia,
flagella, pseudopods, etc. unlike us they too don’t respire through nostrils but oxygen diffuses
into the cell, where the food molecules become oxidized. Moreover, unlike other higher
organisms protozoa take in food either by pinocytosis - ingestion of fluid into a cell forming an
internal vesicle or phagocytosis-engulfing solid food particles and forming a food vacuole as a
means of obtaining water and food. Like us it is heterotrophic.
The very assignment basically contains modes of reproduction- asexual and sexual
reproduction. The asexual reproduction which comprises the double and multiple fission, and
budding. But in case of sexual reproduction is the involvement of two gamates for the continuum
of life-cycle.
Doing such assignment as such is very useful and knowledgeable as it requires patient to
read, go through every googling searches, and log in to the different resources in the cyber and
library as well.
References
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August, 2011 from www.unaab.edu.ng/.../455.
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http://www.parasitetesting.com/definition-of-protozoa.cfm
http://mdmedicine.wordpress.com/2011/04/22/protozoa-basic-facts/
http://www.cbv.ns.ca/mchs/diversity/ProtozoanBiblio.html
The Eukaryotic Members of the Microbial World-Protozoa ( n.d.) Retrieved on 30th August 2011
from faculty.evansville.edu/md7/micro02/eukary/eukary_files/eukary.ppt.
Protozoa and protozoan diseases (2009). Self-directed learning. Retrieved on 25th August 2011
from https://my.unisa.edu.au/unisanet/.../08%20Pod%20%20protozoa.pdf
Pelczar, M.J., Chan,E.C.S., and Krieg,N.R.(2008).Microbiology.New Delhi: Tata McGraw-hill
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