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Home » Reproduction in Protozoa with Diagram

Reproduction in Protozoa with Diagram

  • Zoology

In this article we will discuss about the reproduction in protozoa with the help of suitable diagrams. Asexual reproduction in protozoa and sexual reproduction in protozoa.

Asexual Reproduction

There is no gamete union in asexual reproduction in protozoa. Only one animal can create new individuals in such a situation. Binary and multiple fission are the most common ways for protozoa to reproduce asexually.

I. Binary Fission

The animal divides and two individuals are produced from one in asexual reproduction in protozoa. A simpler version of mitosis separates the micronucleus into two. Amitosis separates the macronucleus into two halves. A constriction separates the cytoplasm into two equal halves. Individuals who are daughters can re-create structures that they do not receive from their parents. Asymmetrical structures such as the gullet and the peristome of Paramoecim cannot be shared equally by both daughters in asexual reproduction in protozoa.

Types

Transverse fission: The animal divides transversely into two. Examples: Amoeba, Paramoecium, etc.

Longitudinal fission: The animal splits into two along the long axis of the body. Examples: Euglena, Vorticella, etc.

Oblique binary fission: The plane of fission is oblique. Examples: Dinoflagellata, Ceratium, Cochliodinium,. etc.

II. Multiple Fission

One at a time, a large group of individuals are created in asexual reproduction in protozoa. Some amoebae, Euglena, Polystomella, and other organisms are examples.

The animal becomes encrusted, and the nucleus divides repeatedly, producing a huge number of minute daughter nuclei in asexual reproduction in protozoa. The cytoplasm fragments and a little portion of it surround each daughter nucleus, resulting in the formation of many small animals. If the conditions are favourable, the cyst breaks, allowing these little animals to emerge and mature into adults.

Multiple fission is widespread in apicomplexans and sarcomastigophorans. Depending on the period and time of occurrence, the process has been given various names in asexual reproduction in protozoa.

Types

Gamogony: When the results are sex cells, such as Plasmodium microgametocytes. Monocytes are an example.

Scizogony: Agametes or merozoites are the resultant individuals. Plasmodium is a good example.

Sporogony: Sporogony is a condition that happens after sexual fusion. Spores are products that are enclosed by a cyst or a resistant covering. Swarmers, also known as swarmospores, are motile spores.

III. Plasmotomy

By dividing the cytoplasm without nuclear division, the multinucleate individual splits into numerous little multinucleate offspring in asexual reproduction in protozoa. Further nuclear division restores the size of the daughter people and restores the number of nuclei.

IV. Budding

The separation of a piece of the parent organism’s cytoplasm with a daughter nucleus produces new individuals in asexual reproduction in protozoa. It could be one or many, exogenous or endogenous. Suctorians are prone to budding. Noctiluca, Tokophrya, and other species are examples of asexual reproduction in protozoa budding. 

Sexual Reproduction in Protozoa

Sexual reproduction in protozoa refers to the process of two gametes joining together to generate a new individual. By fusing their cytoplasm and nuclei, the two units (male and female gametes) from two different individuals come together. Most protists (protozoa) can multiply asexually for lengthy periods of time and only engage in sexual reproduction in protozoa happens at irregular intervals.

Sexual reproduction in protozoa on a regular basis. Meiotic division, which reduces the number of chromosomes to haploid, is required for Sexual reproduction in protozoa. The bulk of the time, reduced division happens right before syngamy. Gametes become haploid during this process, which is known as gametic meiosis.

However, reduction division happens in one of the successive divisions after zygote formation in some protozoans. In zygotic meiosis, only the zygote is diploid, whereas the rest of the life cycle is haploid. Syngamy, conjugation, and automyxis are key methods of sexual reproduction in protozoa.

I. Syngamy

Syngamy is the complete and permanent union or fusion of two specialised protozoan individuals or gametes resulting in the for­mation of a fertilized cell or zygote or oospore. The nuclei of the gametes fuse to form the zygote nucleus or synkaryon. The zygotes develop into adult, either directly or through encystment and fission of various types. Depending upon the degree of differen­tiation of the fusing gametes syngamy may be of the following types:

a. Autogamy

The gametes derived from the same parent cell fuse. Examples: Actinophrys, Actinosphaerium, Paramoecium aurelia, etc.

b. Paedogamy

The fusion occurs between two nuclei coming from two different cells of a parent. The fusing individuals are young. Example: Actinophrys. 

Reproduction in Protozoa with Diagram

Reproduction in Protozoa with Diagram: Sexual reproduction in protozoa – Paedogamy

c. Hologamy

The two mature individu­als behave as gametes and fuse. Example: Copromonas. 

Reproduction in Protozoa with Diagram

Reproduction in Protozoa with Diagram: Sexual reproduction in protozoa – Hologamy

d. Merogamy

The uniting individuals are smaller than the ordinary vegetative indi­viduals, called merogametes.

e. Isogamy

Union of the gametes of simi­lar size and shape. The isogametes are pro­duced by multiple or repeated binary fission. Isogamy has been reported in Foraminifera (Elphidium), Phytomonadina (Chlamydomonas, Copromonas) and Gregarinida (Monocystis).

f. Anisogamy

The two fusing gametes differ in size, shape and behaviour. The ga­metes are termed as heterogametes or anisogametes and their fusion is known as anisogamy or heterogamy. The formation of morphologically different gametes, is the first indication of sex differentiation in Protozoa.

The smaller gametes, the microgametes, or male gametes, are active, motile, generally flagellated and more numerous. They are produced by multiple or repeated fissions.

The fusion of two microgametes is called Micro-gamy. Example: Foraminifera, Arcella, etc. The larger gametes, macrogametes, are immotile, voluminous, and referred to as female gametes. The fusion of two macrogametes is called Macro-gamy. Examples: Plas­modium, Eimeria, Volvox, etc.

The syngamy brings about a combination of two different lines of hereditary characters. It increases the external differences in offspring’s. It also renews the vigour which is lost due to repeated binary fissions. The fu­sion of two nuclei initiates the development of eggs.

II. Conjugation

The conjugation is the temporary union of two mating types of individuals of the same species to facilitate exchange of nuclear ma­terials. They retain their distinct individual­ity and separate out after nuclear exchange. The pairing gametes are known as conjugants. The conjugants may be either isogamous (Paramecium) or anisogamous (Vorti­cella).

Conjugation is considered to be an epi­sode in reproduction and not a mode of multiplication. In conjugation (i) reorganiza­tion of a fresh meganucleus occurs to accel­erate the metabolic activities, (ii) rejuvenation and revival of lost vigour, (iii) new nuclear combinations and new hereditary combina­tions arise.

III. Automixis

Automixis is the fusion of two gametic nuclei originating by the division of the single nucleus of an individual.

a. Autogamy

The fusing nuclei come from the same cell as in Paramecium. All the steps in nuclear changes are similar to conjugation but the union occurs between the pronuclei of the same individual.

b. Paedogamy

The fusion occurs between two nuclei coming from two different cells of a parent. A single organism encysts and then divides into two or more gametocytes. The nuclei of these gametocytes undergo meiosis and the gametes thus produced unite in pairs forming the zygotes. Examples: Actinosphaerium, Actinophrys, myxosporidians, etc.

c. Cytogamy

In a number of species of Paramoecium the two individuals fuse with their oral surfaces. The nuclear changes occur as in conjugation but no nuclear exchange occurs. The two gametic nuclei in each indi­vidual fuse to form synkaryon. Cytogamy is said to be intermediate between conjugation and autogamy.

d. Hemixis

Plasmogamy: Two or more individuals may fuse by their cytoplasm to form a plasmodium and separate out unchanged with their distinct nuclei. This sexual phenomenon is known as Plasmogamy and occurs in certain Rhizopoda and Mycetozoa.

Regeneration: The regeneration and replacement of lost parts among free-living and few parasitic protists is widespread. A proper proportion of cytoplasm and nucleus can regenerate into an entire individual.

Parthenogenesis: The gametes which fail to fertilize start their development parthenogenetically. Examples: Actinophrys, Chlamydomonas, etc.

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