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What Are the Six Kingdoms of Life?
While animals, plants, and fungi are some of the more commonly recognized kingdoms in biological taxonomy, there are also other less well-known kingdoms of organisms that exist and play an essential role in the biosphere.
It’s true that there is some debate among biologists regarding the classification of kingdoms and how many truly exist. However, the following six kingdoms have mainly been agreed upon by a number of prominent biologists, and the six-kingdom system is generally taught in schools across the United States.
In this post, we will offer a quick overview of each kingdom and the role it plays in the world. Take a look and discover the differences between these fascinating life forms.
Of course, animals are the most widely recognized kingdom, with human beings belonging within this classification. It is also the largest sector, with more than 1 million identified species. Animals include organisms that dwell on land and in the sea, such as mammals, amphibians, and reptiles. Invertebrates also fit within this kingdom and make up 97% of all animal species.
Plants are the second-largest kingdom of the six and are critically important to the wellbeing of the earth. Species within this kingdom create their own food via the process of photosynthesis, while also providing oxygen that many animals need to breathe. Plants also serve as food for many land and sea animals.
In previous schools of thought, fungi were categorized within the plant kingdom. However, you will find a few notable differences between the two kingdoms. For instance, fungi are not able to feed themselves through photosynthesis and must rely on the organic matter around them for sustenance. Common examples of fungi include mushrooms, yeast, and molds.
The organisms within the Protista kingdom fit within a wide-ranging spectrum. Most consist of a single cell (unicellular), but all protists are eukaryotes, just like fungi, animals, and plants. This means that their cells have a complex composition, including a nucleus and organelles. Examples of protists include algae and amoebas.
Unlike each of the four kingdoms listed above, eubacteria are single-celled prokaryotes (as are archaebacteria). This means that the nucleus within the cell is not bound by a membrane. These bacteria are found almost everywhere and include things like Escherichia coli (better known as E. coli) and Streptococcus pneumoniae (which causes strep throat).
Archaebacteria were discovered in the 1980s and joined the six kingdoms shortly after that. Like eubacteria, they are single-celled prokaryotes. However, they are in a realm of their own, because biologists discovered that they are the oldest living organisms on the planet. Scientists believe that archaebacteria derive from ancient bacteria that used to live in hydrothermal vents in the deep sea. Interestingly, they are not closely related to eubacteria.
Within each of these six kingdoms, organisms can be further classified into phyla, classes, orders, families, genera, and species. Biological taxonomy is complex and sophisticated, as scientists continue to study life forms all around the globe.
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