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Domain Eukarya: Life on Earth is genuinely very diverse. Hence, to easily distinguish living organisms, early scientists classified them into two kingdoms: Animalia (animals) and Plantae (plants). However, during the 19th century, this classification was challenged by numerous pieces of evidence that were just too insufficient to explain such diversity. To address this, scientists began to propose other systems having four or more kingdoms. Table of Contents
One of the most widely used in the system which classifies organisms into five kingdoms, namely: Monera (Bacteria)FungiProtistaAnimaliaPlantaeThis system connectedly classifies life into two, namely Prokarya (includes bacteria) and Eukarya (includes fungi, animals, plants, chromalveolates, rhizarians, and excavates). However, recent studies revealed and provided support for the emergence of another domain: Archaea. The former domain Prokarya, which consists only of bacteria, has been divided into two separate sub-domains: Bacteria and Archaea. Archaea are minute organisms that thrive at extreme environmental conditions like high pressure and temperature. In summary, the three domains of life are: Prokarya (Bacteria)ArchaeaEukaryoteIn the diagram below, the domains Prokarya (Bacteria), Archaea, and Eukarya are illustrated and differentiated. None of these domains is ancestral to each other, and each has unique and distinguishable features and shared characteristics. In this page, the domain Eukarya will be on focus. 3 Domains of Life Tree (Source: Wikimedia)What is Domain Eukarya? (aka Eukaryota)Coming from the Greek words “eu“, which means “true“, and “karyon” which means, “nut“, the domain Eukarya is composed of organisms having “true nucleus“. Eukaryotic cells, as their cells are called, are perhaps the most complex in terms of both external and internal structures, and physiological and reproductive processes. Among all domains in the biological world, Eukarya members have the most significant body size and body mass. Where Did Eukaryotes Come From?According to various archeological evidences, eukaryotic cells have started to exist more than 0.6 billion years ago. Up until now, their evolution is viewed by many as one of the most unusual events in biological history. To explain such a bizarre event, scientist Lynn Margulis proposed the so-called “Endosymbiotic Theory“.
Characteristics of EukaryotesDiagram of a typical animal cell (Organelles are labelled inside the diagram)1. Presence of membrane bound organelles
The eukaryotic cell contains various internal membrane-bound structures referred to as the “organelles“. 2. Presence of a double membrane nucleusUnlike 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, which has pores to allow the movement of the DNA in and out of it. 3. Cell division is differentAnother distinguishing feature of eukaryotes is that they have a different mode of replicating themselves. 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. 4. Mode of reproduction may varyEukaryotic cells can reproduce themselves in two ways: asexual (through mitosis) or sexual reproduction (through meiosis). Kingdoms Under Domain Eukarya1. FungiThe Kingdom Fungi consists of heterotrophic organisms or organisms that cannot make their food. Instead, they acquire all the essential nutrients by absorption. 2. AnimaliaComing 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. 3. PlantaeAlso called the Kingdom Metaphyta, the Kingdom Plantae consists of all multicellular, eukaryotic, and photosynthetic organisms on the planet. 4. ChromoalveolataFormerly called Kingdom Chromista, this kingdom is one of the “newly-considered” kingdoms in the biological world (as proposed by Thomas Cavalier in 1981). 5. RhizariaThe 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). 6. ExcavataLast, but not the least, Excavata kingdom consists of a wide variety of organisms (photosynthetic, heterotrophic, and parasitic). Key References What domain is fungi in?Eukaryote
Are fungi domain Archaea?All life can be classified into three domains: Bacteria, Archaea, and Eukarya. Organisms in the domain Eukarya keep their genetic material in a nucleus and include the plants, animals, fungi, and protists.
What classification group is fungi in?Fungi are eukaryotic organisms that include microorganisms such as yeasts, moulds and mushrooms. These organisms are classified under kingdom fungi. The organisms found in Kingdom fungi contain a cell wall and are omnipresent. They are classified as heterotrophs among the living organisms.
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