Domain Eukarya Kingdoms | Three Domains Of Life | BioExplorer.Net

Characteristics of Eukaryotes

1. Presence of membrane-bound organelles

The eukaryotic cell contains various internal membrane-bound structures referred to as the “organelles.”

• In cells, the job of organelles is to carry out physiological and metabolic processes that are important for the cell’s survival.
• Other organelles function for support and motility. Such were the intracellular filaments, cilia, and flagella.

2. Presence of a double membrane nucleus

Unlike other organisms of other domains (which have their genetic material suspended in the cytoplasm), the DNA of eukaryotic organisms is stored in the nucleus.

The nucleus of eukaryotes is surrounded by the nuclear envelope, a double membrane with pores to allow the movement of the DNA in and out.

3. Cell division is different

Another distinguishing feature of eukaryotes is their different replicating modes. Instead of merely dividing themselves and copying their genetic materials (like what other domains do), cell division in eukaryotes involves two processes: mitosis and cytokinesis.

• During mitosis, the cell’s nucleus divides into two while the genetic material, present as chromosomes, are equally distributed to each opposite of the cell.
• Following that step is cytokinesis, when the cell’s cytoplasm divides, developing the equal division of the genetic material.

4. Mode of reproduction may vary

Eukaryotic cells can reproduce themselves in two ways: asexual (through mitosis) or sexual reproduction (through meiosis).

• During asexual reproduction, the cell divides through mitosis followed by cytokinesis.
• Conversely, they may also reproduce sexually by involving their sex cells called the gametes. In this type of reproduction, the offspring inherits a chromosome from each of its parents.

Suggested Reading: Explore the differences between Mitosis and Meiosis

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 cell wall of the members of the kingdom is made of chitin, a type of carbohydrate. In contrast, their carbohydrates (energy) is stored in the form of glycogen.
• The Kingdom fungi consist of organisms such as yeast, mushroom, and mold.
• Fungi break down the organic materials of dead organisms, and as a result, they help continue nutrient cycling in ecosystems.

2. Animalia

Coming from the Latin word “animalis“, meaning “have breath“, the Kingdom Animalia is comprised of heterotrophic organisms. As alluded to earlier, these organisms obtain their nutrient requirements by ingesting organisms.

• A distinguishing characteristic of this kingdom includes multi-cellularity and the lack of cell walls.
• Most members of this kingdom are capable of movement (locomotion) and reproduction.
• Members of this kingdom consist of almost all animals known (e.g., 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.
• However, some members can be producers and consumers as they can synthesize food and metabolize it from other sources. See carnivorous plants here.
• Members of this kingdom have made the perpetuation of many organisms possible. Basically, without them, heterotrophic organisms would have never survived.

4. Chromoalveolata

Formerly called Kingdom Chromista, this kingdom is one of the “newly-considered” kingdoms in the biological world (as proposed by Thomas Cavalier in 1981).

• This kingdom is consist of dinoflagellates, diatoms, and ciliates.
• It is believed that the members of this kingdom originated from a bikont (a cell with two flagella) and a red alga that became the ancestor of all organisms with plastids having Chlorophyll C.
• However, it is still being debated as some evidence shows that this kingdom is not monophyletic (coming from a common ancestor) as it was initially observed.

5. Rhizaria

The domain Rhizaria is widely composed of unicellular eukaryotes. Also proposed by Thomas Cavalier-Smith (2002), the members of this kingdom differ in form. Still, most of them are amoeboids with pseudopods (false feet).

• This kingdom is composed of the foraminiferans and radiolarians.
• Together with chromalveolates and excavates, the rhizarians were previously under the Kingdom Protista.
• However, unlike the Kingdom Chromoalveolata, there are pieces of evidence showing that rhizarians are a monophyletic group.

6. Excavata

Last, but not the least, Excavata kingdom consists of a wide variety of organisms (photosynthetic, heterotrophic, and parasitic).

• The name of this kingdom came from the two Latin words, “ex cavatum“, meaning “cavity.”
• The members of this kingdom include the euglenozoa, kinetoplastids, and parabasalids.

Key References

• Classification: The Three Domain System. – Accessed December 08, 2016. Link.
• Extremophiles and Extreme Environments. – Life : Open Access Journal. 2013. Accessed December 08, 2016. Link.
• Domain Eukaryota. Accessed December 08, 2016. Link.
• The Evolution of the Cell – Accessed December 08, 2016. Link.
• Introduction to the Fungi – Accessed December 09, 2016. Link.
• Chromalveolata – Biocyclopedia. Accessed December 09, 2016. http://www.eplantscience.com/index/lua/chromalveolata.php.
• EXCAVATA – Accessed December 09, 2016. Link.