 - Plantae
- Protozoa
- Animalia
- Chromista
- Fungi

Kingdoms in Eukarya Domain

Protists represent an informal grouping of eukaryotic organisms that do not strictly fit into the categories of plants, animals, or fungi. This diverse group includes all protozoa as well as some forms of algae.

Protists

The domain Eukarya comprises all eukaryotes, which include both unicellular and multicellular organisms such as protists, fungi, plants, and animals. The primary defining characteristic of these organisms is that their cells contain a true nucleus.

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In modern genetics-based taxonomy, life is categorized into three domains above the kingdom level: Archaea, Bacteria, and Eukarya. Based on the analysis of small subunit ribosomal RNA (rRNA) gene sequences, this phylogenetic model suggests all three evolved from a common ancestral cell type, but is skewed to show that Archaea and Eukarya share a closer evolutionary relationship with each other than either does to Bacteria.

Three Domains of Life

Eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane and membrane-bound organelles in the cytoplasm, which are supported and held in place by an internal cytoskeleton. These cells, which can exist as independent, single-celled microorganisms or as part of multicellular organisms (comprising protozoans, algae, fungi, plants, and animals), feature plasma membranes structured as a bilayer consisting of ester-linked, straight-chain fatty acids and sterols, and they contain multiple, linear chromosomes associated with histones.

Eukaryotic cell

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https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Bacteria is a very diverse domain, characterized by their prokaryotic cells and lack of ether linkages, with membranes made of phospholipid bilayers.

Bacteria (domain)

Microorganisms are found across all three domains of life: Archaea, Bacteria, and Eukarya. Microbes within the domains Archaea and Bacteria are exclusively prokaryotes, which means their cells lack a nucleus. Conversely, microbes within the Eukarya domain are eukaryotes, characterized by cells that have a true nucleus. Certain microbes, like viruses, are acellular and therefore do not fit into any of the three domains.

Microbial Classification by Domain

Eukarya

Eukaryotes have membrane-bound organelles, each with their own structure and function. Organelles commonly found in eukaryotes include:
- Nucleus
- Endoplasmic Reticulum
- Golgi Apparatus
- Lysosome
- Vacuole
- Mitochondria
- Chloroplast
- Peroxisomes

Organelles Commonly Found in Eukaryotes

Eukaryotic cells contain multiple, linear chromosomes that are haploid or diploid and are wrapped around histone proteins. In contrast, prokaryotes typically possess a single, circular chromosome that is haploid, with bacteria lacking histones and archaea containing histones.

Comparison of Eukaryotic and Prokaryotic Chromosomes

In eukaryotic cells, the cytoskeleton is an internal network of fibers and tubes consisting of microfilaments, intermediate filaments, and microtubules. It provides structural support, anchors organelles, and serves as a transport network to move materials within the cell.

Eukaryotic Cytoskeleton

Eukaryotic cells exhibit a diverse range of shapes, including spheroid, ovoid, cuboidal, cylindrical, flat, lenticular, fusiform, discoidal, crescent, ring, stellate, and polygonal, and some can even be irregular or change their shape. These cellular morphologies are influenced by the cell's primary function, cytoskeleton organization, cytoplasm viscosity, membrane or cell wall rigidity, and external physical pressure from the environment or adjacent cells.

Eukaryotic Cell Shapes

Mitosis is a eukaryotic cell division process of asexual reproduction wherein a single parent cell divides to generate two genetically identical daughter cells.

Mitosis

The eukaryotic cell cycle is a regulated, sequential series of events involving cell growth, DNA replication, and cell division that results in the production of two clonal daughter cells.

Eukaryotic Cell Cycle

Meiosis is a eukaryotic cell division process involving two separate nuclear divisions that yields four genetically distinct gametes, each containing half the parent cell's chromosomes. This reduction in chromosome number is vital for sexual reproduction, ensuring that the resulting zygote after fertilization possesses a complete set of chromosomes.

Meiosis

The endomembrane system, unique to eukaryotic cells, is a network of membranous tubules, sacs, and flattened disks that function to synthesize cellular components and transport materials within the cell.

Endomembrane System

Eukaryotic cells that lack a cell wall, such as animal cells and certain protozoans, secrete a sticky mixture of carbohydrates and proteins into the intercellular spaces to form an extracellular matrix. This matrix provides shape maintenance and structural stability, consisting of a protein-based basement membrane, a bulky mass of proteoglycans, and strength-providing collagen fibers, all of which are linked via fibronectins to membrane-spanning integrin proteins.

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