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Appendage

An appendage is a part or organ joined to the axis or trunk of an organism's body, such as limbs, fins, antennae, or wings in animals. The term also applies to projecting structures in prokaryotes, such as flagella and pili, and in plants, such as leaves and thorns.^[1]^[2] In biology, appendages are external outgrowths that protrude from the main body structure, often developing orthogonally to the primary body axes and featuring a proximodistal patterning axis essential for their formation.^[3] Animal appendages exhibit diverse forms and functions across phyla, enabling critical adaptations for survival. In arthropods, such as insects and crustaceans, appendages include jointed limbs used for locomotion, feeding, sensing, mating, respiration, and defense, with specialized types like antennae for chemoreception or chelicerae for capturing prey.^[4] Vertebrate appendages, including tetrapod limbs like arms and legs, evolved from ancestral fins and support weight-bearing, manipulation, and propulsion in aquatic or terrestrial environments.^[5] These structures often arise from genetic mechanisms involving genes like Distal-less (Dll) and Dlx, which are conserved across protostomes and deuterostomes, indicating a shared evolutionary toolkit.^[3] In addition to locomotor and sensory roles, appendages encompass skin-derived structures in mammals, known as adnexa, which include hair, nails, sebaceous glands, and sweat glands. These originate from epidermal downgrowth during fetal development in the third month and perform functions such as thermoregulation, protection, lubrication, and excretion.^[6] Hair follicles, for instance, consist of a shaft and root sheath, providing insulation and sensory input, while eccrine sweat glands distribute across the body to aid in cooling via perspiration.^[6] The evolutionary origin of appendages traces back to a common pre-Cambrian ancestor of bilaterian animals, where outgrowths like parapodia in annelids or tube feet in echinoderms repurposed ancient genetic circuits for diverse morphological innovations.^[3]

General Concepts

Definition

In biology, an appendage is defined as a projection or outgrowth from the main body or trunk of an organism, which may be external or internal, often serving specialized functions such as locomotion, sensing, or reproduction, distinct from core structural elements.^[1] These structures are typically subordinate to the primary body axis and can be found across diverse taxa, including limbs in animals, flagella or pili in microorganisms, and leaves or flowers in plants.^[1] Unlike internal organs, which are deeply integrated into the body's systems for vital processes like circulation or digestion (e.g., the heart), appendages are generally modular and externally oriented, enabling adaptability without compromising the organism's central architecture.^[7] The term "appendage" originates from the Latin appendere, meaning "to hang upon" or "to attach," reflecting its connotation as a dependent extension.^[8] It entered the English language in the mid-17th century, initially in general usage before becoming established in anatomical and biological literature to describe such outgrowths.^[7]

Functions and Evolutionary Role

Biological appendages serve multiple essential functions that enhance organismal survival and adaptation. Primarily, they facilitate locomotion, enabling propulsion through fluids or across substrates, which is critical for foraging, migration, and predator avoidance. Appendages also support manipulation tasks, such as grasping objects or processing food, thereby improving resource acquisition efficiency. Additionally, they contribute to sensory perception by detecting environmental stimuli like chemical gradients, vibrations, or light, allowing organisms to respond to their surroundings. In reproductive contexts, appendages aid in mating behaviors, gamete transfer, or dispersal mechanisms, promoting genetic diversity and species propagation. These roles underscore the versatility of appendages as multifunctional structures across diverse taxa. The evolutionary origins of appendages trace back to simple cellular extensions in early life forms, emerging around 3.5 billion years ago as prokaryotes developed motility structures for navigating microbial environments. In multicellular animals, these structures diversified through gene duplication events, notably involving Hox genes in bilaterians, which act as master regulators of body patterning and appendage formation. Hox genes, conserved across bilaterians, orchestrate the spatial and temporal expression required for appendage outgrowth and identity, with variations in their regulation driving morphological innovations. This genetic framework likely predates the divergence of major animal lineages, providing a foundational mechanism for appendage evolution.^[9] Following the Cambrian explosion approximately 541 million years ago, appendages underwent adaptive radiation, diversifying rapidly to exploit new ecological niches and contributing to the proliferation of complex body plans. This period saw accelerated phenotypic evolution, with appendages enabling specialized interactions with environments, such as enhanced mobility and resource competition. A key concept in this diversification is serial homology, where similar appendage-like structures repeat along the body axis, arising from shared developmental pathways that allow modular evolution. For instance, in vertebrates, paired appendages exhibit serial homology rooted in ancient genetic modules, facilitating adaptations like fin-to-limb transitions. These evolutionary dynamics highlight how appendages promoted biodiversity by balancing functional specialization with structural repetition. Despite their advantages, appendages impose energetic trade-offs, requiring substantial resources for maintenance, growth, and operation relative to the benefits they provide. In prokaryotes, motility appendages like flagella can consume up to 40% of a cell's energy budget, illustrating the high metabolic cost of propulsion.^[10] In larger organisms, maintaining complex appendages demands ongoing investment in tissue repair and structural support, which can limit allocation to other life-history traits like reproduction or growth. Reduced or vestigial-like appendages in modern species, such as the pelvic bones in whales—homologous to ancestral hindlimbs but minimized and adapted for reproductive musculature—exemplify how evolutionary pressures can favor cost reduction when primary functions are lost, yet retain secondary roles under selection.^[11] These trade-offs reflect the selective balance between appendage utility and energetic efficiency throughout evolutionary history.

Appendages in Animals

In Protostomes

Protostomes constitute a major clade of bilaterian animals characterized by the embryonic development of the mouth from the blastopore, encompassing phyla such as Arthropoda, Mollusca, and Annelida.^[12] In these organisms, appendages frequently exhibit serial homology and segmentation, aligning with the metameric organization of their bodies that facilitates diverse locomotor, sensory, and feeding adaptations.^[13] Arthropod appendages represent a hallmark of the phylum, featuring jointed, segmented structures that evolved from unjointed lobopodian precursors during the Cambrian period. Fossils such as Hallucigenia sparsa from the Burgess Shale illustrate transitional forms with fleshy, lobe-like lobopods that prefigure the articulated limbs of modern arthropods, highlighting a close evolutionary link between lobopods and arthropod ancestors.^[14]^[15] These jointed appendages enable functions including walking, as seen in the three pairs of legs (six legs total) of insects for terrestrial locomotion, swimming in crustacean pleopods, and feeding via chelicerae in spiders that grasp and shred prey.^[16]^[17] Specialized forms like antennae in insects and crustaceans primarily facilitate chemosensation, detecting pheromones and environmental cues to guide behavior.^[4] In annelids, appendages take the form of parapodia in polychaetes, which are paired, fleshy lobes projecting from each body segment to support locomotion through undulating waves and anchoring via embedded setae—bristle-like chitinous extensions that provide traction against substrates.^[18] These parapodia also contribute to respiration by increasing surface area for gas exchange in aquatic environments, while setae enhance burrowing and prevent backward slipping during peristaltic movement.^[19] Molluscan appendages diverge from the segmented pattern seen in arthropods and annelids, often modified for specific ecological roles; cephalopods employ muscular tentacles surrounding the mouth for prey manipulation and capture, with suckers aiding in adhesion and handling.^[20] The radula, a ribbon-like structure armed with rows of chitinous teeth, functions as a primary feeding appendage across many mollusks, enabling scraping, rasping, or tearing of food sources like algae or soft tissues.^[21] The diversity of protostome appendages underscores their adaptive radiation, particularly in arthropods, where over one million described species showcase specialized modifications that underpin ecological dominance in terrestrial, freshwater, and marine habitats.^[22]

In Deuterostomes

Deuterostomes are a major clade of bilaterian animals characterized by embryonic development in which the blastopore forms the anus before the mouth, encompassing phyla such as Chordata (including vertebrates) and Echinodermata.^[23] In this group, appendages are generally supported by endoskeletons, such as the ossicles in echinoderms or the bony frameworks in vertebrates, which provide internal structural reinforcement for mobility and manipulation.^[24] In vertebrates, a subgroup of chordates, appendages primarily manifest as limbs that evolved from the paired fins of sarcopterygian fishes during the late Devonian period approximately 375 million years ago.^[25] Tetrapod limbs, including forelimbs and hindlimbs, exhibit a conserved pentadactyl (five-digit) structure in many mammals, facilitating diverse functions like grasping and weight-bearing, while in birds, forelimbs are modified into wings for flight, retaining homologous bone elements such as the humerus, radius, and ulna.^[26] Echinoderms, the sister group to chordates within deuterostomes, possess appendages adapted to their radial symmetry and marine lifestyles, including tube feet and spines. Tube feet, extensions of the water vascular system, enable slow locomotion, prey capture, and feeding in species like starfish (Asterias spp.), where hydraulic pressure from seawater forces the feet to extend and adhere via suction cups.^[27] Spines serve as defensive outgrowths, deterring predators through mechanical barriers or, in some cases, venom delivery, as seen in sea urchins where they project from the endoskeletal test.^[28] The evolutionary transition from aquatic fins to terrestrial limbs in deuterostomes involved genetic mechanisms conserved across vertebrates, notably the Sonic hedgehog (Shh) gene, which patterns the anterior-posterior axis of limb buds by establishing signaling gradients that specify digit identity and number.^[29] This process reflects broader adaptations for terrestrial locomotion, with fin rays transforming into digits through modifications in Hox gene expression and Shh-mediated proliferation.^[30] In humans, as advanced vertebrates, appendages include arms and legs, which are homologous to the limbs of other tetrapods, sharing a common developmental blueprint involving Shh signaling for proximal-distal and anterior-posterior patterning. The vestigial coccyx, or tailbone, represents a remnant of the embryonic tail, underscoring the evolutionary continuity of deuterostome appendage structures from aquatic ancestors.^[31]^[32]

Appendages in Prokaryotes

In Archaea

Archaea are single-celled prokaryotes that predominantly inhabit extreme environments, including hypersaline conditions, high temperatures, and acidic or alkaline settings, where their surface appendages exhibit adaptations for stability and functionality under such stresses. These appendages, such as archaella and pili-like structures, are composed of proteins with enhanced resistance to high salt concentrations and thermal denaturation, enabling archaea to maintain motility and adhesion in environments where bacterial counterparts might fail. With fewer than 1,000 archaeal species formally described as of 2025, research on these appendages remains limited compared to other domains, yet highlights their role in survival within niche habitats like salt flats and hydrothermal vents.^[33]^[34]^[35] The primary motility appendage in many archaea is the archaellum, a rotary motor apparatus structurally and mechanistically distinct from bacterial flagella, featuring a filament assembled from the cell base outward through extension and glycosylation of S-layer-bound proteins. Unlike bacterial flagella powered by proton-motive force, archaella rotate via ATP hydrolysis at the basal motor complex, propelling cells in a swimming motion through liquid media at speeds up to 500 cell lengths per second in some species, such as hyperthermophiles. The filament, composed of multiple archaellin subunits (e.g., FlaB), is glycosylated for stability and flexibility, contributing to the archaellum's adaptation to extreme conditions like high salinity.^[36]^[37]^[38]^[39] Archaea also possess diverse adhesion structures, including hami—unique, hook-like appendages observed in species such as Ignicoccus hospitalis—which feature nano-scale grappling hooks and barb-like spikes for secure attachment to surfaces and facilitation of cell-cell interactions. These hami, extending 1–3 μm from the cell, enable adherence to biotic and abiotic substrates in hyperthermal environments, promoting symbiotic associations. Additionally, pilus-like filaments, structurally akin to type IV pili, mediate surface attachment, twitching motility, and DNA transfer between cells, enhancing genetic exchange in archaeal communities.^[40]^[41]^[42] Evolutionarily, archaella trace their origins to a common ancestor with type IV pilus systems, diverging from a non-rotary pilus-like structure in early archaeal evolution, which allowed archaea to develop specialized motility independent of bacterial mechanisms. This ancient adaptation underscores the archaellum's role as a high-impact innovation in archaeal lineage, with genetic and assembly pathways conserved across diverse phyla despite the domain's understudied species diversity. In methanogenic archaea, such as Methanococcus maripaludis and Methanosarcina mazei, appendages like archaella and pili facilitate biofilm formation in anaerobic sediments, where they promote aggregation and metabolic cooperation for methane production in oxygen-deprived habitats.^[38]^[43]^[44]

In Bacteria

Bacteria are prokaryotic microorganisms distinguished by their peptidoglycan-containing cell walls, which confer rigidity and protect against osmotic stress in varied habitats.^[45] These appendages, including flagella, pili, and others, are essential for bacterial survival, enabling functions such as locomotion, surface attachment, and intercellular genetic exchange across diverse environments like soil, water, and host tissues.^[45]^[46] Bacterial flagella consist of helical filaments composed primarily of flagellin protein, extending from the cell surface to facilitate swimming motility in aqueous environments.^[47] Unlike eukaryotic cilia, bacterial flagella are powered by the proton motive force generated across the inner membrane, driving rotation of the basal body motor at speeds up to 100,000 rpm.^[47] Flagellar arrangements vary, with monotrichous types featuring a single polar flagellum for directed propulsion and peritrichous types displaying multiple flagella that bundle during swimming for enhanced efficiency.^[48] Chemotaxis, the directed movement toward nutrients or away from toxins, operates through alternating "runs" of smooth swimming and "tumbles" that reorient the cell, biased by sensory signaling pathways.^[49] Pili and fimbriae are thinner, protein-based filamentous appendages, typically shorter than flagella, that mediate adhesion to host cells or environmental surfaces.^[50] Type IV pili, exemplified in Pseudomonas aeruginosa, enable twitching motility—a jerky, surface-associated gliding—via ATP-dependent extension, pilus tip attachment to substrates, and retraction that pulls the cell forward.^[51] Sex pili, such as the F-pilus in Escherichia coli, are specialized for conjugation, extending to bridge donor and recipient cells and forming a conduit for single-stranded DNA transfer during horizontal gene exchange.^[52] Additional appendages include holdfasts in stalked bacteria like Caulobacter crescentus, which are polar adhesive structures, often polysaccharide-based, that anchor cells irreversibly to surfaces, promoting biofilm formation and nutrient access in static environments.^[53] Bacteria exhibit vast diversity, with over 20,000 formally described species as of 2025, though estimates suggest millions more undiscovered.^[54] The evolution of appendages, particularly pili involved in conjugation, is closely linked to horizontal gene transfer mechanisms, facilitating rapid adaptation and genetic diversification in prokaryotes.^[55]

Appendages in Eukaryotes

Cellular Appendages

Eukaryotic cells, characterized by membrane-bound organelles such as the nucleus and mitochondria, feature cellular appendages that project from the plasma membrane to facilitate interactions with the extracellular environment, including motility and sensing.^[56] These appendages, primarily cilia and flagella, are microtubule-based structures that extend from the cell surface and are essential for various physiological processes across eukaryotic organisms.^[57] Cilia are typically short, numerous projections, often hundreds per cell, that beat in coordinated waves to generate fluid flow.^[57] Their core structure, the axoneme, consists of a 9+2 arrangement of microtubules: nine outer doublet microtubules surrounding two central singlet microtubules, with dynein arms attached to the doublets enabling sliding motions for beating.^[56] In the respiratory tract, motile cilia drive mucociliary clearance, propelling mucus and trapped pathogens out of the airways to protect against infections.^[57] In contrast, primary cilia are non-motile, solitary sensory organelles lacking the central microtubule pair and dynein arms, functioning as antennae to detect mechanical and chemical signals for cellular decision-making.^[57] Flagella, longer and usually fewer in number (often one or two per cell), undulate in a whip-like manner to propel the cell through fluid environments, such as in sperm cells or free-swimming protists.^[56] Like cilia, flagella share the 9+2 axoneme architecture, where dynein motors—ATP-dependent proteins forming cross-bridges between adjacent doublet microtubules—generate force by sliding the doublets relative to each other, resulting in bending waves.^[58] Each dynein head exerts approximately 5 pN of force, collectively enabling the propulsive motion essential for locomotion.^[58] The assembly of both cilia and flagella begins at the basal body, a cylindrical structure composed of nine triplet microtubules that anchors the appendage to the cytoplasm and is derived from or associated with centrioles.^[59] The basal body templates the axoneme's microtubule organization, transitioning from triplets to doublets at the transition zone.^[56] Intraflagellar transport (IFT) is crucial for this assembly, involving bidirectional movement of protein complexes along the axonemal microtubules: anterograde transport by kinesin-2 motors delivers tubulin and other building blocks to the distal tip at speeds of about 2 µm/s, while retrograde transport by cytoplasmic dynein-2 returns turnover products at around 3.5 µm/s.^[60] IFT complexes A and B, along with associated cargos like tubulin-binding modules (e.g., IFT74/IFT81), ensure the dynamic growth and maintenance of these structures.^[60] Beyond motility, these appendages play key roles in fluid movement and cell signaling; for instance, primary cilia concentrate receptors for pathways like Hedgehog signaling, influencing development and homeostasis.^[57] Defects in ciliary structure or function lead to ciliopathies, a group of genetic disorders; mutations affecting primary cilia, such as in polycystin-1/2 or IFT components, disrupt sensory functions and cause cyst formation in polycystic kidney disease (PKD), impairing renal tubule flow sensing.^[57] Similarly, motile cilia dysfunction results in conditions like primary ciliary dyskinesia, highlighting the appendages' critical role in health.^[57]

Organismal Appendages in Unicellular Eukaryotes

Unicellular eukaryotes, collectively known as protists, encompass a diverse array of organisms such as ciliates and flagellates, where cellular appendages serve as the primary means of whole-body locomotion and interaction with the environment.^[61] These appendages enable free-living protists to navigate aquatic habitats, capture prey, and respond to stimuli, fundamentally defining their organismal behavior at the microscopic scale.^[62] In ciliates, thousands of short cilia coordinated across the cell surface facilitate rapid, directional swimming, while in flagellates, one or more longer flagella propel the cell through undulating motions.^[61] Ciliates like Paramecium exemplify the role of cilia in both locomotion and feeding, with approximately 5,000–15,000 cilia covering the body surface that beat in metachronal waves to achieve speeds up to 1 mm/s.^[63] These cilia direct water currents into an oral groove, a specialized ciliated channel that funnels bacteria and small particles toward the cytostome for ingestion, forming food vacuoles essential for heterotrophic nutrition.^[64] This coordinated ciliary action not only supports efficient predation but also allows Paramecium to perform avoidance maneuvers, such as the "avoiding reaction," by reversing ciliary beat direction in response to obstacles.^[63] Flagellates demonstrate versatile motility adapted to specific niches, as seen in Trypanosoma brucei, a parasitic protist that uses its single flagellum to navigate the bloodstream of mammalian hosts at speeds of up to 20 μm/s.^[65] The flagellum's undulating waveform, powered by dynein motors along the axoneme, enables the slender cell to evade immune responses through rapid, irregular swimming patterns.^[66] In contrast, Euglena gracilis combines motility with autotrophy, employing a single anterior flagellum for phototactic swimming toward light sources at frequencies of 20–40 Hz, while its chloroplasts support photosynthesis in nutrient-poor environments.^[67] This dual capability allows Euglena to alternate between heterotrophic feeding and light-dependent energy production.^[68] Amoeboid protists, such as those in the genus Amoeba, rely on pseudopodia—dynamic, lobe-like extensions formed by actin polymerization—for locomotion and phagocytosis.^[69] These temporary appendages arise from the assembly of actin filaments at the cell periphery, driven by Arp2/3 complex nucleation, enabling the cell to engulf prey like bacteria or algae through pseudopodial engulfment.^[70] The process involves rapid polymerization at the leading edge and depolymerization at the rear, allowing directional crawling at rates of 0.5–3 μm/s without fixed organelles.^[71] Ecologically, these appendage-driven protists play pivotal roles as predators in microbial food webs, consuming bacteria and smaller protists to regulate community structure and nutrient cycling.^[72] Many also engage in symbiosis, such as flagellates hosting bacterial partners that aid in digestion or protection, enhancing mutual survival in diverse habitats from freshwater to host tissues.^[73] Their predatory and symbiotic interactions channel energy through trophic levels, influencing ecosystem productivity.^[74] The appendage-based motility of these unicellular eukaryotes represents an evolutionary precursor to multicellularity, with protist-like ancestors aggregating around 1.2–1.5 billion years ago to form early colonial forms that eventually gave rise to complex eukaryotes.^[75] This transition likely involved coordinated appendage functions for collective movement, bridging unicellular autonomy to multicellular specialization.^[76]

Appendages in Plants

Vegetative Appendages

Vegetative appendages in plants are non-reproductive outgrowths that primarily facilitate resource acquisition, structural support, and environmental adaptation, arising from meristematic tissues on stems and roots. These structures develop from apical and lateral meristems, which produce primary and secondary tissues essential for elongation and girth increase, enabling plants to optimize uptake of water, minerals, and light.^[77]^[78] Leaves represent the primary vegetative appendages dedicated to photosynthesis, typically flattened organs with a network of veins for transport and stomata for gas exchange. Veins, composed of xylem and phloem, deliver water and nutrients while removing sugars, while stomata regulate carbon dioxide intake and transpiration. Modifications of leaves enhance survival in specific environments; for instance, in cacti, leaves evolve into spines that reduce water loss and provide defense against herbivores by deterring feeding. In Acacia species, true compound leaves are replaced by phyllodes—flattened, leaf-like petioles that perform photosynthetic functions while minimizing surface area in arid conditions.^[79]^[80]^[81] Tendrils and thorns exemplify specialized vegetative appendages for mechanical support and protection. Tendrils, modified leaves or stems, coil around supports in response to touch (thigmotropism), as seen in pea plants (Pisum sativum), where they enable climbing to access sunlight by wrapping around nearby structures. Thorns, sharp outgrowths from stems, serve a defensive role; in roses (Rosa spp.), they deter herbivores by inflicting physical damage, enhancing plant survival in competitive or predator-rich habitats.^[82]^[83] Root hairs, epidermal extensions on young roots, vastly increase absorptive capacity for water and minerals. These tubular projections emerge in the maturation zone, significantly increasing the root surface area (typically by 5- to 10-fold), which dramatically boosts ion and water uptake efficiency without expanding the overall root volume.^[84]^[85] Vegetative appendages in vascular plants evolved approximately 420 million years ago during the Devonian period, coinciding with the diversification of shoots and early leaf-like structures that improved resource capture. Adaptations such as phototropism, where appendages bend toward light, are mediated by auxin redistribution, promoting uneven cell elongation on the shaded side to optimize photosynthetic exposure.^[86]^[87]

Reproductive Appendages

In plants, reproductive appendages are specialized structures derived from modified shoots or leaves that facilitate sexual reproduction, primarily through the production and dispersal of gametes or spores. These appendages include both sterile and fertile components, with the latter directly involved in gametogenesis. In angiosperms, the flower represents the primary reproductive appendage, consisting of four whorls of modified leaves attached to a receptacle: the calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels).^[88] The sterile appendages—sepals and petals—protect developing buds and attract pollinators, respectively, while enhancing reproductive success indirectly.^[88] The fertile appendages in angiosperms are the stamens and carpels, which produce pollen and ovules, respectively. Stamens consist of a filament supporting an anther containing microsporangia, where pollen grains develop; carpels enclose ovules within an ovary, leading to seed formation post-fertilization.^[88] Phylogenetic reconstructions indicate that the ancestral angiosperm flower was bisexual, featuring more than 10 stamens and more than 5 carpels arranged in whorls, with superior ovaries and introrse anthers for efficient pollen release.^[89] Examples include the radial symmetry in lily flowers (actinomorphic, with distinct whorls) and bilateral symmetry in orchids (zygomorphic, adapted for specific pollinators), illustrating evolutionary diversification of these appendages for enhanced reproductive efficiency.^[88] In gymnosperms, reproductive appendages are organized into cones (strobili), where microsporophylls and megasporophylls serve as leaf-like structures bearing sporangia. Male cones produce microspores in microsporangia on microsporophylls, while female cones feature megasporophylls with megasporangia containing ovules exposed on scales, enabling wind pollination without enclosed seeds.^[90] These appendages evolved from simpler seed plant ancestors, with developmental genetics showing conserved pathways for their formation and modification across seed plants.^[91] Representative examples include the smaller, pollen-releasing male cones at the base of conifer branches and larger, ovule-bearing female cones at the top, optimizing dispersal and protection.^[90] In non-seed vascular plants like ferns, reproductive appendages manifest as sporangia clustered into sori on the undersides of fronds, which are vegetative leaves modified for spore production. These structures release spores for gametophyte development, with water-dependent fertilization occurring on the independent gametophyte.^[92] Bryophytes, such as mosses, feature reproductive appendages like gametangia (antheridia and archegonia) on gametophytes and sporangia on elevated setae of sporophytes, emphasizing spore dispersal over complex floral or cone structures.^[93]

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Sep 15, 2008 · They have been cultivated from environments that mark the upper limits of life in regard to temperature, pH, and salt concentration. Furthermore ...
[36]
The Archaellum: An Update on the Unique Archaeal Motility Structure
Each of the three domains of life exhibits a unique motility structure: while Bacteria use flagella, Eukarya employ cilia, and Archaea swim using archaella.
[37]
The archaellum: how Archaea swim - Frontiers
This review illustrates the key findings that led to the realization that the archaellum was a novel motility structure and presents the current knowledge.
[38]
How Did the Archaellum Get Its Rotation? - Frontiers
Apr 25, 2022 · Figure 1. The archaellum is a rotary motor that evolved from a non-rotary ancestor. The archaellum descends from a clade of the type IV filament ...
[39]
The Iho670 Fibers of Ignicoccus hospitalis: a New Type of Archaeal ...
In the case of hami, their function is obvious: they are 1- to 3-μm-long filamentous structures with regular spikes, ending in a hook to resemble in ...
[40]
S-layers at second glance? Altiarchaeal grappling hooks (hami ...
Our results provide new insights into the structure of the unique hami and their major protein and indicate their divergent evolution with S-layer proteins.
[41]
Versatile cell surface structures of archaea - Wiley Online Library
Dec 1, 2017 · Archaeal surface structures are involved in a range of processes such as motility, species-specific DNA exchange, adhesion, biofilm formation ...
[42]
The evolution of archaeal flagellar filaments - PNAS
We show how the archaeal flagellum likely evolved from simpler archaeal type IV pili, taking advantage of the structural diversity among the archaeal type IV ...Missing: archaella | Show results with:archaella
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Biofilm formation of mucosa-associated methanoarchaeal strains - NIH
This study provides the first evidence that methanoarchaea can develop and form biofilms on different substrates.
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Structure - Medical Microbiology - NCBI Bookshelf - NIH
Two types of surface appendage can be recognized on certain bacterial species: the flagella, which are organs of locomotion, and pili (Latin hairs), which are ...General Concepts · Introduction · The Nucleoid · Surface Appendages
[45]
Architectural dissection of adhesive bacterial cell surface ...
These appendages are usually adhesive, allowing them to directly bind to their targets, which can range from signaling molecules, abiotic surfaces, other ...
[46]
Structure, Function and Assembly of Flagellar Axial Proteins - NCBI
The bacterial flagellum is a biological macromolecular nanomachine for locomotion. A membrane embedded molecular motor rotates a long helical filament that ...
[47]
Structure, Assembly, and Function of Flagella Responsible for ...
The bacterial flagellum is divided into five distinct structural parts: a basal body, a hook, a hook-filament junction, a filament, and a filament cap. The ...
[48]
The physics of flagellar motion of E. coli during chemotaxis - NIH
Helical flagella are rotated in clockwise or counterclockwise direction using reversible flagellar motors situated at the base of each flagellum. The swimming ...
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Bacterial Structures - an overview | ScienceDirect Topics
Fimbriae, Flagella and Pili Flagella are long mobile appendages that facilitate the attachment of the bacterial cell to biomaterial surfaces, and are ...
[50]
Bridging Bacteria and the Gut: Functional Aspects of Type IV Pili
Here, we focus on conserved type IV pili (T4P) produced by bacteria in the intestinal tract, one of the most densely populated human ecosystems. Computational ...
[51]
Role of Pili in Bacterial Conjugation - PMC - NIH
We conclude that F pili play at least three roles in mating: (i) they initiate contacts between mating pairs; (ii) they facilitate the transfer of genetic ...
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Bacterial Capsule - an overview | ScienceDirect Topics
The biosynthesis of bacterial capsules is regulated by tyrosine phosphatase (PTP) and a protein tyrosine kinase [200,201]. Inhibition of these proteins may stop ...
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A Genome-Wide Analysis of Adhesion in Caulobacter crescentus ...
Caulobacter crescentus produces a specialized structure at one of its cell poles called the holdfast that enables attachment to surfaces. Previous studies have ...
[54]
Species Numbers in Bacteria - PMC - PubMed Central - NIH
I estimate there are a million species of bacteria in 30 grams of rich forest topsoil and propose that there will be at least a billion species worldwide.
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Motility and adhesion through type IV pili in Gram-positive bacteria
Despite the ~2 billion years of evolution that separate Gram-negative and Gram-positive bacteria, the structure of the type IV pilus is remarkably well ...
[56]
Structural insights into the architecture and assembly of eukaryotic ...
Cilia and flagella are slender projections found on most eukaryotic cells including unicellular organisms such as Chlamydomonas, Trypanosoma and Tetrahymena.
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Cilia Structure and Function in Human Disease - PubMed Central
Feb 20, 2024 · Throughout the eukaryotic kingdom, cilia and flagella serve as sensory and force generating organelles (Bloodgood, 2010). To carry out these ...
[58]
Structural-Functional Relationships of the Dynein, Spokes, and ...
In the axoneme of eukaryotic flagella the dynein motor proteins form crossbridges between the outer doublet microtubules. These motor proteins generate force ...
[59]
Basal body assembly in ciliates: the power of numbers - PMC
Nine triplet microtubule blades are arranged in a barrel configuration (Figure 2), which extend from the proximal end, or base, containing the nine-fold ...
[60]
Intraflagellar Transport and Ciliary Dynamics - PMC - PubMed Central
Cilia and flagella are microtubule-based organelles whose assembly requires a motile process, known as intraflagellar transport (IFT), to bring tubulin and ...
[61]
Coordination of eukaryotic cilia and flagella - PMC - PubMed Central
Nov 21, 2018 · Here I review the two main mechanisms for motile cilia coordination, namely, intracellular and hydrodynamic, and discuss their relative importance in different ...
[62]
The evolution of animal cell motility
May 18, 2020 · The cell locomotion that underlies these critical behaviors can be divided into two main categories: flagellar motility and actin-dependent cell.
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Integrative Neuroscience of Paramecium, a “Swimming Neuron” - PMC
Food is brought into its oral groove by powerful cilia, which have different properties from locomotor cilia (Jung et al., 2014; Aubusson-Fleury et al., 2015).
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Sample Descriptive Lab Report - LabWrite
The protists' motion was consistent with their locomotion organ: cilia, flagella, or pseudopod. This motion was very clear under the light microscope, but ...Missing: appendages | Show results with:appendages
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The Trypanosoma brucei Flagellum: Moving Parasites
African trypanosomes are highly motile, moving at speeds of up to 20 um s−1 (58). Wild-type cells exhibit alternating periods of translational cell movement and ...
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Motility and more: the flagellum of Trypanosoma brucei - PMC
In this review, we discuss the structure, assembly and function of the trypanosome flagellum, including canonical roles in cell motility as well as novel and ...Missing: locomotion | Show results with:locomotion
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Euglena: a unicellular algae – Inanimate Life - Milne Publishing
Photosynthetic forms contain a chloroplast. They possess two flagellae, one long, one short, that can allow the organisms to move.
[68]
Euglena, a Gravitactic Flagellate of Multiple Usages - PubMed Central
E. gracilis is an excellent candidate for biological life support systems, since it produces oxygen by photosynthesis, takes up carbon dioxide, and is even ...
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Cell motility driven by actin polymerization - ScienceDirect.com
ABSTRACT Certain kinds of cellular movements are apparently driven by actin polymerization. Examples include the lamellipodia of spreading and migrating ...
[70]
Generation of membrane structures during phagocytosis and ...
This review will focus on the mechanisms by which macrophages regulate actin polymerization through initial receptor signaling and subsequent Arp2/3 activation.
[71]
independent F-actin assembly and disassembly during Fc receptor ...
Relationship of pseudopod extension to chemotactic hormone-induced actin polymerization in amoeboid cells. ... phagocytosis mediated by Fc gamma receptor ...
[72]
Protist feeding patterns and growth rate are related to their predatory ...
Predatory protists are major consumers of soil micro-organisms. By selectively feeding on their prey, they can shape soil microbiome composition and functions.
[73]
Protists as determinants of the One Health framework - PMC
Protists also play positive roles under the One Health framework as mutualists, primary producers, nutrient catalyzers, and regulators of microbial communities.
[74]
The planktonic protist interactome: where do we stand after a ... - NIH
Protist predation or grazing is crucial for channeling carbon and energy to higher trophic levels [55, 63] as well as for the release of dissolved nutrients to ...<|control11|><|separator|>
[75]
Biological Diversity 3 - An On-Line Biology Book
Ciliates are complex, heterotrophic protozoans that lack cell walls and use multiple small cilia for locomotion. ... Food is taken into the cell by an oral groove ...<|control11|><|separator|>
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Protists – Introduction to Living Systems
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[77]
[PDF] Vegetative plant morphology — stems, leaves, and roots
Tendrils are modified leaves that assist in supporting the stem by ... Root Hairs. Root Tip. Rootcap. Zone of Maturation. Zone of Elongation. Meristematic Zone.
[78]
[PDF] Chapter 2. Vegetative morphology of plants
Climbing plants coil around other plants or inanimate objects as a means of support, and their stems are often transformed into tendrils, or twining shoots.
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[PDF] Plant Structures: Leaves - Colorado Master Gardener
Tendril – Modified leaf, stipule, or other plant part used for climbing or as an attachment mechanism (Virginia creeper, peas, grapes).
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Teddy Bear Cholla (Cylindropuntia bigelovii) joints
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[81]
[PDF] M - AgEcon Search
deanei, therefore have phyllodes. (flattened petioles or leaf rachis) replacing true leaves, the latter existing only during the early juve- nile stage ...
[82]
Artificial and biological supports are different for pea plants - NIH
Jun 5, 2024 · Tendrils are modified leaves or flower peduncles sensitive to mechanical stimulation and capable of coiling around potential support. Tendrils ...
[83]
Plant Defenses - Learn Genetics Utah
Examples of physical defenses are thorns on roses and spikes on trees like hawthorn. These physical defenses hurt the herbivores and stop them from eating ...
[84]
Root Hairs - PMC - PubMed Central - NIH
Jun 25, 2014 · A major function of root hairs is to increase root surface area and hence facilitate the uptake of nutrients from the soil. Plants with more ...Missing: absorption | Show results with:absorption
[85]
The origin and early evolution of vascular plant shoots and leaves
Dec 18, 2017 · This review discusses fossil, developmental and genetic evidence relating to the evolution of vascular plant shoots and leaves in a phylogenetic framework.
[86]
Phototropism: Growing towards an Understanding of Plant Movement
Intracellular responses to light cues are processed to regulate cell-to-cell movement of auxin to allow establishment of a trans-organ gradient of the hormone.
[87]
[PDF] Chapter 3. Reproductive morphology of plants
The fertile appendages are also typically of two types, the stamens and the carpels. The first are the male reproductive organs, producing pollen, and the ...
[88]
The ancestral flower of angiosperms and its early diversification - Nature Communications
### Summary of Floral Appendages in Angiosperms (Sauquet et al., 2017, Nature Communications)
[89]
11.7: Sexual Reproduction in Gymnosperms - Biology LibreTexts
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[90]
The evolution of reproductive structures in seed plants: a re ...
Mar 13, 2012 · We summarize emerging developmental genetic insights into how angiosperm reproductive structures are formed, modified and recombined.
[91]
Fern Reproduction - USDA Forest Service
Ferns reproduce via spores, sexual gametophytes, bulblets, walking fern tips, and rhizome growth.
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Reproduction & dispersal - bryophyte
Sep 12, 2012 · Bryophytes reproduce sexually using water for sperm, and vegetatively via fragmentation. Spores are wind-dispersed, while propagules are ...