Life on Earth is really incredibly diverse, according to Domain Eukarya. As a result, early scientists divided living creatures into two groups: Animalia (animals) and Plantae (plants) to easily distinguish them.
Several pieces of evidence, however, during the nineteenth century, challenged this categorization, despite being insufficient to explain such variety. To overcome this, scientists suggested new systems with four or more kingdoms.
In the system that divides organisms into five kingdoms, one of the most commonly used is:
Monera (Bacteria)
Fungi
Protista
Animalia
Plantae
This system divides life into two categories: prokarya (bacteria) and eukarya (fungi, animals, plants, chromalveolates, rhizarians, and excavates).
However, more recent research has shown and backed up the existence of a new domain: Archaea.
Bacteria and Archaea have been separated into two distinct sub-domains in the previous Prokarya domain, which is entirely dominated by bacteria. Archaea are tiny creatures that flourish in high-pressure and temperature environments.
Three Domains of Life
In summary, the three domains of life are:
Prokarya (Bacteria)
Archaea
Eukaryote
Prokarya (Bacteria), Archaea, and Eukarya are represented and distinguished in the figure below. Each of these domains has its own distinct and separable features, as well as common characteristics, and none of them is ancestral to the other. The term Eukarya will be highlighted on this page.
What is Domain Eukarya? (aka Eukaryota)
The domain Eukarya is made up of organisms having a “genuine nucleus,” according to the Greek terms “eu” and “karyon,” which mean “genuine.”
In terms of both external and internal structures, as well as physiological and reproductive processes, eukaryotic cells are perhaps the most complex. Members of the Eukarya kingdom have the greatest bodily size and mass among all kingdoms in the biological realm.
Where Did Eukaryotes Come From?
Eukaryotic cells first appeared more than 0.6 billion years ago, according to archeological findings. Many people have thought of their development as one of the most unusual occurrences in biological history up until now.
The so-called “Endosymbiotic Theory” was proposed by scientist Lynn Margulis to explain such a strange occurrence.
- According to this hypothesis, “proto-eukaryotic” cells absorbed single-celled organisms, including the mitochondria (cell powerhouse) and chloroplasts (structure for photosynthesis).
- In comparison to the cell itself, eukaryotic mitochondria and chloroplasts contain a distinct set of genetic materials. As a result, it is evident that they were once bacterial cells.
- Both cells needed to replicate at the same pace and not digest each other in order for their symbiosis to be continuous and sustained.
- As a consequence, using light, the resultant cells might now create energy and repair carbon.
Characteristics of Eukaryotes
1. Presence of membrane bound organelles
The organelles are the internal membrane-bound structures found in eukaryotic cells.
- Organelles perform important physiological and metabolic activities in cells, and their role is to execute them.
- Support and motility are performed by other organelles. Cilia, flagella, and intracellular filaments were all found.
2. Presence of a double membrane nucleus
The DNA of eukaryotic species is housed in the nucleus, unlike that of other species from different domains (which has it embedded in the cytoplasm).
The nuclear membrane, a double membrane with openings for the movement of DNA in and out of it, surrounds the nucleus of eukaryotes.
3. Cell division is different
The way eukaryotes replicate themselves is another distinguishing feature. Cell division in eukaryotes involves two processes: mitosis and cytokinesis, rather than just splitting themselves and copying their genetic material (as other domains do).
- The genetic material, which is distributed as chromosomes to each cell’s opposite during mitosis, divides into two while the nucleus of the cell divides similarly.
- The cytokinesis is the process by which the cell’s cytoplasm divides evenly, resulting in genetic material being evenly divided.
4. Mode of reproduction may vary
Asexual (through mitosis) and sexual reproduction (through meiosis) are two methods that eukaryotic cells may reproduce themselves.
- The cell divides mitosis and cytokinesis during asexual reproduction.
- They may also reproduce sexually by combining their sex cells, known as gametes, which they do through sexual intercourse. The offspring receives a chromosome from each of its parents in this form of reproduction.
Kingdoms Under Domain Eukarya
1. Fungi
The Kingdom Fungi consists of heterotrophic organisms or organisms that cannot make their food. Instead, they acquire all the essential nutrients by absorption.
- The members of the kingdom’s cell wall is composed of chitin, a form of carbohydrate. Their glycogen (energy) is stored, on the other hand, as carbohydrates.
- Yeast, mushrooms, and mold are all examples of Kingdom fungi.
- Fungi aid in the recycling of nutrients in ecosystems by breaking down organic materials from dead creatures.
2. Animalia
The Kingdom Animalia is made up of heterotrophic organisms and is derived from the Latin term “animalis,” which means “have breath.” These creatures get their nutrition from ingesting other creatures, as previously stated.
- This kingdom has two characteristics: multi-cellularity and the absence of cell walls.
- This kingdom’s majority of citizens are mobile (can walk) and reproduce.
- This kingdom includes almost all animals (fishes, amphibians, reptiles, birds, mammals, and insects).
3. Plantae
Also called the Kingdom Metaphyta, the Kingdom Plantae consists of all multicellular, eukaryotic, and photosynthetic organisms on the planet.
- Being photosynthetic, these organisms are autotrophs and can make their food using the energy from the sun.
- Yet, since some members synthesize and metabolize food from different sources, they might also be producers and consumers. Here you’ll find out what a carnivorous plant is.
- The survival of a large number of species has been made possible by members of this kingdom. Heterotrophic species would not have survived if it hadn’t been for them.
4. Chromoalveolata
This kingdom, formerly known as Kingdom Chromista, was one of the “newly considered” kingdoms proposed by Thomas Cavalier in 1981.
- Dinoflagellates, diatoms, and ciliates make up this kingdom.
- It is thought that a bikont (a cell with two flagella) and a red alga (the progenitor of all plants with chlorophyll C) became the progenitors of this kingdom’s members.
- Some evidence, however, suggests that this kingdom is not monophyletic (coming from a single ancestor), as it was originally thought. This remains a topic of debate.
5. Rhizaria
Unicellular eukaryotes make up the majority of the domain Rhizaria. The members of this kingdom come in different shapes, according to Thomas Cavalier-Smith (2002). Nevertheless, amoeboids (false feet) account for the majority of them.
- The foraminiferans and radiolarians make up this kingdom.
- The rhizarians were formerly classified as part of the Kingdom Protista, along with chromalveolates and excavates.
- There are, however, signs that rhizarians are a monophyletic group, unlike the Kingdom Chromoalveolata.
6. Excavata
Excavata kingdom also includes a diverse collection of photosynthetic, heterotrophic, and parasitic creatures (in addition to the last).
- The two Latin words “ex cavatum,” which mean “cavity,” gave this kingdom its name.
- Euglenozoa, kinetoplastids, and parabasalids are all members of this kingdom.