Wrist: structure, function, common conditions and care Wrist Overview of the wrist joint connecting forearm and hand, its anatomy, movements, common injuries and treatments, and clinical and evolutionary importance.
Xenacoelomorpha: simple bilaterians and their place in animal evolution Xenacoelomorpha Xenacoelomorpha is a small group of simple, wormlike bilaterian animals (xenoturbellids and acoelomorphs). Its exact position in the animal tree is debated and informs early bilate…
Xenotransplantation: cross‑species transplantation of cells, tissues and organs Xenotransplantation Xenotransplantation is the transfer of living cells, tissues or organs between species. This article explains its goals, biological challenges, donor sources, history, ethics and c…
Xenoturbella — simple marine deuterostome worms and their biology Xenoturbella Xenoturbella is a small genus of simple marine deuterostomes. This article summarizes their anatomy, classification, ecology, discovery history and significance for animal evolutio…
Xerophile — organisms adapted to very dry conditions Xerophile Xerophiles are organisms that tolerate or prefer environments with very little available water. They occur among fungi, yeasts and some bacteria and are important in ecology, food…
Xylem: structure, function, and role in vascular plants Xylem Xylem is the vascular tissue that conducts water and dissolved minerals from roots to shoots. This article explains its cell types, transport mechanism, development, and ecological…
Y chromosome: function, structure, evolution and significance Y chromosome The Y chromosome is the male-associated sex chromosome in most mammals. This article summarizes its role in sex determination, structure and genes, evolution, clinical importance,…
Yeast: single-celled fungi — biology, uses, and significance Yeast Overview of yeast as single-celled fungi: biology and life cycle, historical and modern uses in baking, brewing and biotechnology, industrial forms, and health and ecological roles…
Yersinia: Overview, species, disease and public health significance Yersinia Yersinia is a genus of Gram-negative bacteria in the Enterobacteriaceae family that includes species responsible for plague and gastrointestinal infections; overview, traits, histo…
Yersinia pestis: the bacterium that causes plague Yersinia pestis Yersinia pestis is a Gram-negative bacterium that causes bubonic, septicemic and pneumonic plague; historically linked to major pandemics and still found in animal reservoirs world…
Zika virus (ZIKV): biology, transmission, clinical features, and history Zika virus Overview of Zika virus: taxonomy, transmission routes, clinical manifestations including congenital risks, historical outbreaks, prevention, diagnosis, and public health responses.
Zinc finger: structure, natural roles and engineered applications Zinc finger Zinc fingers are small protein motifs that bind DNA or RNA using a zinc ion; they occur naturally in many transcription factors and have been engineered into tools such as zinc-fin…
Zooid: modular individual unit in colonial animals Zooid A zooid is an individual animal module within a colonial organism. Zooids are often clonally produced, may be physically connected, and can be specialized for feeding, reproduction…
Zoology: the scientific study of animals Zoology Zoology is the branch of biology that examines animals — their form, function, evolution, behaviour and relationships in ecosystems, and the methods scientists use to study them.
Zoonosis: diseases transmitted from animals to people Zoonosis Zoonosis—infectious diseases transmitted between animals and humans—causes include bacteria, viruses, fungi and parasites. Transmission routes, history, prevention, and public heal…
Zoospore: motile asexual spore of algae, fungi and related organisms Zoospore A zoospore is a flagellated, asexual spore produced by certain algae, fungi and water molds. It swims using one or more flagella, disperses in water, encysts on contact and germina…
Zygnemataceae: a family of filamentous and unicellular green algae Zygnemataceae Zygnemataceae are mostly freshwater green algae, ranging from unicells to uniseriate filaments. Important in ecology and research, they reproduce by conjugation and include genera…
Zygnematales (Conjugales): filamentous green algae known for conjugation Zygnematales An order of mostly freshwater, unbranched filamentous green algae (e.g., Spirogyra, Zygnema) that reproduce by conjugation, form algal scums, and are important in ecology and plant…
Zygomatic bone (cheekbone) Zygomatic bone Paired facial bone forming the cheek prominence and part of the orbital floor and zygomatic arch; important in facial structure, muscle attachment, and maxillofacial surgery.
Zygomycota (zygote fungi): biology, ecology, and taxonomy Zygomycota Zygomycota, historically the ‘zygote fungi’, are a group of mostly soil-dwelling, saprotrophic and parasitic fungi known for zygosporangia; modern studies have revised their classi…
Zygote: the fertilized cell that begins a new multicellular organism Zygote A zygote is the single cell formed when two gametes fuse. This article explains its formation, cellular properties, early development, differences across species, and biological si…
