REPRODUCTION IN PROTOZOA: CHARACTERISTICS AND TYPES - BIOLOGY - 2024

The reproduction in protozoa can give sexually or asexually. Sexual reproduction can happen by the formation of gametes through different mechanisms, and asexual reproduction happens by bipartition.

In general, protozoa are microscopic, single-celled organisms that have a nucleus but lack a true cell wall. These characteristics are involved in its way of reproduction.

Photograph of an Amoeba, one of the best known protozoa

In addition to being unicellular, protozoa have different organelles that facilitate their mobility in fresh and salty water environments, which are favorable environments for their reproduction.

Among the best known and most studied protozoa in their reproductive functions are Amoeba and Paramecium.

Sexual reproduction in protozoa

Protozoa can perform meiotic divisions to become haploid gametes, that is, with a single set of chromosomes.

The subsequent union of two gametes forms a new diploid individual (or with two sets of chromosomes), which is constituted as a type of sexual reproduction.

Sexual conjugation does not occur in all protozoa and is characteristic of ciliated protozoa. Depending on the way the gametes are attached, sexual reproduction can occur by syngamy or autogamy.

Types of gamete binding

Protozoan, Balantidium coli in wet mount. Photography by: Euthman. Taken and edited from commons.wikimedia.org

A first way of joining gametes is syngamy. This happens when two different protozoan cells turn into gametes and later unite.

If the joining gametes have similar morphology they are known as isogametes. If the morphology differs, they are known as anisogametes.

The second form of gamete union is known as autogamy, which consists of the union of two gametes formed within a single cell.

On the other hand, when the union of gametes involves the exchange of genetic material (as in syngamy), the process of sexual reproduction is known as conjugation.

Asexual reproduction

Asexual reproduction happens in all types of protozoa. It is usually known by the name of fission or bipartition. This partition occurs in a similar way to mitosis in other organisms.

Asexual reproduction can generate two new individuals that are the same size or different in size. Individuals of equal size result from a symmetric partition, while budding processes generate individuals of different sizes.

In some cases a single cell can divide into more than two parts. This multiple cleavage occurs when several nuclei are formed within the same protozoan.

Factors affecting reproduction in protozoa

The presence of layers of water significantly affects the reproduction of protozoa present in soils.

Water provides an important medium for the mobility of these organisms and for the union of gametes by syngamy. In addition, if the water is insufficient, many protozoa form resistance structures that do not allow reproduction.

The number of individuals has also been found to significantly affect reproduction. A cell density common protozoa surface, surrounding water at 10 ⁵ organisms per gram, helps happens successfully sexual reproduction.

References

1. Bell G. (1988). Sex and death in Protozoa. The history of an Obsession. Cambridge University Press. Melbourne, Australia
2. Madigan M. Martinko J. Parker J. Brock Biology of Microorganisms. Prentice hall. 10ed
3. Nill K. (2002) Glosary of Biotechnology Terms. CRC Press. Florida, USA. 3ed
4. Okafor N. (2007). Modern Industrial Microbiology and Biotechnology. Science Publishers. New Hampshire, USA.
5. Sibly R. Calow P. Asexual reproduction in protozoa and invertebrates. Journal of Theoretical Biology. 1982; 3 (7): 401-424.