In this explainer, we will learn how to describe the characteristics of organisms belonging to the kingdom Monera, recall the divisions of kingdom Monera as Eubacteria and Archaebacteria, and apply knowledge of these kingdoms to classify given organisms correctly.
There is a great variety of organisms living on Earth. As of 2018, around 1.8 million species have been formally identified, but scientists believe there are many, many more species that remain undiscovered. Some estimates for the number of species currently inhabiting Earth even reach 1 trillion!
Definition: Species
A species is a group of organisms with similar characteristics that can breed together to produce fertile offspring.
To try and organize these species and better understand them, scientists classify them into groups. An example of one of these groups is a kingdom. In 1969, a scientist called Robert Whittaker proposed the 5-kingdom classification system; this is outlined in Figure 1.
Kingdom Monera is a large taxonomic group that contains many different species. The organisms that belong to kingdom Monera will all have some characteristics in common.
Organisms that belong to kingdom Monera are unicellular, so they are only made up of one cell. E. coli is an example of an organism belonging to kingdom Monera, and below is a picture (micrograph) of E. coli as viewed through an electron microscope.
These unicellular organisms will be surrounded by a cell wall for structure and support. The cells of other organisms, like plants and fungi, do also possess cell walls. Unlike plants, however, the cell walls of organisms in kingdom Monera will not contain cellulose, and unlike fungi, they will not contain chitin.
In a stark difference from eukaryotic organisms, like animals, plants, and fungi, organisms belonging to kingdom Monera will not contain a membrane-bound nucleus. Instead, their genetic material will be found in the form of chromosomal loops or plasmids that are contained in the cytoplasm of the cell. Organisms in kingdom Monera are prokaryotes, where karyote refers to the nucleus and pro- means “before.” In contrast, eu in eukaryotes means “true.” They can also all reproduce by binary fission, which is an asexual process of producing multiple daughter cells from the division of a single parent cell.
Example 1: Recalling Characteristics of Kingdom Monera
Which of the following is a characteristic of an organism belonging to kingdom Monera?
- Most of these organisms are large and multicellular.
- The cells of these organisms contain a cellulose cell wall.
- These organisms only reproduce sexually.
- The cells of these organisms do not contain a membrane-bound nucleus.
Answer
Classification relies on sorting organisms with similar characteristics, or that are evolutionarily closely related, into distinct groups. Organisms that belong to the kingdom Monera will all have some characteristics in common. Kingdom Monera contains organisms that are commonly referred to as prokaryotes. These organisms are unicellular, and the cell they are made up of will not contain a membrane-bound nucleus. The cells will possess a cell wall that differs from cell walls found in eukaryotes as it will not contain cellulose or chitin. Organisms belonging to kingdom Monera will reproduce by binary fission, which is an asexual process as it does not require the exchange of genetic material with another organism.
Therefore, the only correct answer from the choices is that the cells of these organisms do not contain a membrane-bound nucleus.
All living organisms require some form of nutrition to stay alive, whether they are large multicellular organisms like humans or small and relatively simple organisms like those belonging to kingdom Monera. There are two primary methods of nutrition throughout the kingdoms of life, heterotrophic and autotrophic.
Definition: Autotroph
An autotroph is an organism that is able to synthesize its own food from inorganic materials.
Definition: Heterotroph
A heterotroph is an organism that obtains food from consuming other organisms or organic matter.
Organisms belonging to kingdom Monera can be autotrophic and make their own food by chemosynthesis or photosynthesis or be heterotrophic and consume organic matter as a food source.
Since its initial formation, kingdom Monera can be reclassified into two subdivisions. These are Archaebacteria and Eubacteria. Let’s have a look at the similarities and differences between these two groups, as outlined in Figure 3.
As we can see from the Venn diagram, both subkingdoms share some characteristics. They are both made up of unicellular organisms, and these organisms do not contain membrane-bound nuclei and will reproduce by binary fission. However, there are also some notable differences.
One of these differences is where you are likely to find these organisms. Eubacteria are found in almost every environment on Earth, from marine ecosystems to forests to inside the human body! Archaebacteria are also found in many environments, but importantly, they can survive and thrive in very extreme environments. These environments include volcanic hot springs that can reach temperatures of above or bodies of water that have very high salt levels.
Archaebacteria and Eubacteria also differ in their cellular components. Organisms belonging to subkingdom Eubacteria will have peptidoglycan as a major component of their cell wall, whereas organisms belonging to Archaebacteria will not. Although organisms belonging to both kingdoms will have their genetic material contained in chromosomal loops or plasmids, the composition of their genes will differ. Protein-coding genes in prokaryotes predominately do not contain intron (noncoding sections of genes). However, some archaebacteria protein-coding genes possess introns.
Example 2: Classifying Organisms as Archaea or Bacteria
A unicellular organism has been discovered. The organism is adapted to survive in hot springs that have very high temperatures and low pH levels. Which taxonomic group, Archaebacteria or Eubacteria, is this organism most likely to belong to?
Answer
Although Eubacteria and Archaebacteria are groups belonging to the larger taxonomic group of kingdom Monera, there are some differences between the characteristics of organisms belonging to the two groups. If we take a look at the environments they usually inhabit, we will find that organisms belonging to the Eubacteria subkingdom live almost everywhere, in most environments, and also within the bodies of other organisms or on their surface. As humans, we have hundreds of species of eubacteria living within our digestive system, without which we could not survive. However, Archaebacteria are often found in very extreme environments. Thermophiles are types of Archaebacteria that can survive above temperatures of , often found in places like volcanic hot springs.
Therefore, we can conclude that the organism detailed in this question would most likely belong to subkingdom Archaebacteria.
Example 3: Describing the Difference in the Cellular Components of Archaebacteria and Eubacteria
Which of the following correctly describes the difference between the cell walls of Archaebacteria and Eubacteria?
- Eubacteria have cell walls that are composed of peptidoglycan, which is not present in Archaebacteria cell walls.
- Archaebacteria have cell walls that are composed of peptidoglycan, which is not present in Eubacteria cell walls.
Answer
Both Archaebacteria and Eubacteria are subdivisions of kingdom Monera. Organisms belonging to kingdom Monera are characterized by being prokaryotic (which means they do not have a membrane-bound nucleus), being single-celled organisms, and having their cells surrounded by a cell wall.
However, there are some key differences between Archaebacteria and Eubacteria that can help us distinguish between the two. Some protein-coding genes in Archaebacteria contain introns or noncoding sections. Eubacteria will not usually have these introns. Eubacteria—also known as true bacteria—have cell walls that are largely composed of the polymer peptidoglycan. Archaebacteria, on the other hand, have cell walls that do not contain peptidoglycan but are formed from the linking of other polymers.
Therefore, the statement that correctly describes the difference between the cell walls of these two groups is A: Eubacteria have cell walls that are composed of peptidoglycan, which is not present in Archaebacteria cell walls.
Let’s summarize what we have learned about organisms belonging to kingdom Monera.
Key Points
- Organisms belonging to the kingdom Monera share some common characteristics, including being unicellular, having a cell wall, and not possessing a membrane-bound nucleus.
- Kingdom Monera can be divided into Eubacteria and Archaebacteria.
- Organisms belonging to the Eubacteria and Archaebacteria subkingdoms show differences in their characteristics and the environments they inhabit.
