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 pseudopodia-false 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.