ZooScholar: Zoology Glossary: 200+ Terms & Definitions

By Dr Ahsan Shafiq, PhD Zoology — reviewed for scientific accuracy.

Quick answer: A zoology glossary is an A–Z reference of zoological terms and definitions covering animal diversity, classification, physiology, and evolution. This expert-reviewed glossary defines 200+ essential zoology terms — from acoelomate to zygote — with simple, exam-focused explanations for MDCAT, FSc, and BS Zoology students in Pakistan.

Mastering zoological terms is the fastest way to raise your score in MDCAT and FSc biology: examiners test definitions directly, and most "difficult" MCQs are simply animal biology vocabulary in disguise. This zoology glossary collects 200+ important zoological terms with precise one-line zoology definitions, organized by branch so you can revise one topic at a time.

Unlike scattered PDF glossaries, every entry here is written in the exam English used in Pakistani board and MDCAT papers, and high-yield terms carry an MDCAT badge. The main branches of zoology covered are morphology, anatomy, physiology, embryology, ecology, ethology, parasitology, taxonomy, ichthyology, ornithology, entomology, and herpetology — jump straight to any branch below.

Animal Diversity & Classification — Zoology Terms and Definitions

Core taxonomy terms, body plan (bauplan) vocabulary, symmetry, germ layers, and coelom types — the foundation of every classification question in MDCAT biology.

Acoelomate MDCAT: An animal with no body cavity between the gut and the body wall; the space is filled with parenchyma (e.g., flatworms, Phylum Platyhelminthes).
Asymmetry: Lack of any plane of symmetry in the body; seen in some sponges and adult gastropods with coiled shells.
Bilateral symmetry MDCAT: Body divisible into mirror-image left and right halves by a single plane; associated with cephalization and active movement (e.g., humans, insects).
Bilateralia: The clade of animals with bilateral symmetry, comprising protostomes and deuterostomes — nearly all animal phyla except sponges, cnidarians, and ctenophores.
Binomial nomenclature MDCAT: The two-name system of naming species (Genus + species, e.g., Homo sapiens), proposed by Carolus Linnaeus; genus capitalized, species in lowercase, both italicized.
Body plan (bauplan): The basic structural organization of an animal — its symmetry, number of germ layers, presence of a coelom, and segmentation pattern.
Cephalization MDCAT: Concentration of nervous tissue and sense organs at the anterior (head) end of a bilaterally symmetrical animal.
Chordata MDCAT: The phylum of animals possessing a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some life stage; includes all vertebrates.
Classification: The arrangement of organisms into hierarchical groups (species, genus, family, order, class, phylum, kingdom) based on shared characteristics.
Coelom MDCAT: A fluid-filled body cavity lined on both sides by mesoderm-derived epithelium (peritoneum), housing the internal organs.
Coelomate (eucoelomate): An animal possessing a true coelom, e.g., annelids, arthropods, molluscs, echinoderms, and chordates.
Deuterostome MDCAT: An animal in which the blastopore becomes the anus and the mouth forms secondarily; includes echinoderms and chordates (humans are deuterostomes).
Dioecious: Having male and female reproductive organs in separate individuals; the animal equivalent of "unisexual" (opposite: monoecious/hermaphrodite).
Diploblastic MDCAT: Having two embryonic germ layers (ectoderm and endoderm); characteristic of cnidarians and ctenophores.
Eumetazoa: Animals with true tissues organized into germ layers — all animal phyla except sponges (Parazoa).
Genus: A taxonomic rank above species and below family, grouping closely related species (plural: genera).
Germ layers MDCAT: The primary cell layers of the early embryo — ectoderm, mesoderm, and endoderm — from which all tissues and organs develop.
Hermaphrodite (monoecious) MDCAT: An individual possessing both male and female reproductive organs (e.g., earthworm, Taenia); opposite of dioecious.
Heterotroph: An organism that obtains nutrition by consuming other organisms, since it cannot photosynthesize; all animals are heterotrophs.
Metamerism: Serial repetition of body segments along the anterior–posterior axis, each containing similar sets of organs (e.g., earthworm segments).
Monophyletic: A group containing a common ancestor and all of its descendants; the only scientifically valid basis for a taxon.
Non-chordata: Animals lacking a notochord at any life stage — all invertebrate phyla from Porifera to Echinodermata.
Nomenclature (zoological nomenclature): The formal system of rules (ICZN) governing the scientific naming of animals, ensuring each species has one unique valid name.
Parazoa: Animals lacking true tissues and organs, i.e., sponges (Phylum Porifera) — the "beside-animals" grade.
Phylum MDCAT: A major taxonomic rank below kingdom and above class; animals are divided into about 35 phyla (plural: phyla).
Protostome MDCAT: An animal in which the blastopore becomes the mouth; includes arthropods, molluscs, and annelids — the largest animal group.
Pseudocoelomate MDCAT: An animal with a "false" body cavity not fully lined by mesoderm (e.g., roundworms, Phylum Nematoda).
Radial symmetry MDCAT: Body divisible into similar halves by multiple planes through a central axis; typical of sessile or drifting animals (cnidarians, adult echinoderms).
Segmentation: Division of the body into repeated segments (metameres); true in annelids and arthropods, also seen in chordate somites.
Species MDCAT: The basic unit of classification: a group of actually or potentially interbreeding organisms reproductively isolated from other groups.
Symmetry: The balanced arrangement of body parts around a point or axis — asymmetrical, radial, or bilateral.
Taxon: Any named taxonomic group, such as a species, genus, or phylum (plural: taxa).
Taxonomy MDCAT: The science of naming, describing, and classifying organisms into hierarchical groups.
Triploblastic MDCAT: Having three embryonic germ layers (ectoderm, mesoderm, endoderm); characteristic of all bilaterian animals from flatworms to humans.

Exam-favorite differences: classification pairs

Feature	Protostomes	Deuterostomes
Blastopore fate	Becomes the mouth	Becomes the anus
Cleavage	Spiral, determinate	Radial, indeterminate
Coelom formation	Schizocoely (splitting of mesoderm)	Enterocoely (outpocketing of gut)
Examples	Arthropods, molluscs, annelids	Echinoderms, chordates

Feature	Acoelomate	Pseudocoelomate	Coelomate
Body cavity	Absent	False cavity, partly mesoderm-lined	True cavity, fully mesoderm-lined
Example phylum	Platyhelminthes	Nematoda	Annelida, Chordata

Feature	Chordata	Non-chordata
Notochord	Present at some stage	Absent throughout life
Nerve cord	Dorsal, hollow, single	Ventral, solid, often double
Pharyngeal slits	Present at some stage	Absent (except hemichordates)
Heart position	Ventral	Dorsal (when present)

Feature	Diploblastic	Triploblastic
Germ layers	Two (ectoderm, endoderm)	Three (ectoderm, mesoderm, endoderm)
Body cavity	Acoelomate	Acoelomate to coelomate
Examples	Cnidaria, Ctenophora	Platyhelminthes to Chordata

Feature	Vertebrates	Invertebrates
Vertebral column	Present	Absent
Proportion of animals	About 5% of described species	About 95% of described species
Endoskeleton	Bony or cartilaginous	Absent, or exoskeleton present

Invertebrate Zoology — Terms & Definitions

Sponges, cnidarians, worms, molluscs, arthropods, and echinoderms — the invertebrate vs vertebrate divide examined through body plans, larval stages, and skeletons.

Amoeboid movement: Locomotion by temporary cytoplasmic projections (pseudopodia), as in Amoeba and white blood cells.
Bipinnaria larva: The free-swimming ciliated larva of starfish (echinoderms), strikingly similar to the tornaria larva — evidence of hemichordate–echinoderm affinity.
Budding: Asexual reproduction in which a new individual grows as an outgrowth of the parent (e.g., Hydra, sponges, corals).
Choanocyte (collar cell) MDCAT: The flagellated, collar-bearing cell lining sponge chambers; it drives the water current and captures food — the defining cell of Porifera.
Cnidoblast (cnidocyte) MDCAT: The stinging cell of cnidarians containing the nematocyst; used for prey capture and defense.
Ecdysis MDCAT: Shedding of the old exoskeleton (cuticle) to allow growth; characteristic of ecdysozoans (arthropods, nematodes).
Ephyra: The free-swimming juvenile medusa stage released by strobilation of a scyphozoan polyp.
Exoskeleton MDCAT: A rigid external skeleton of chitin (arthropods) or calcium carbonate (molluscs) that supports and protects but must be molted for growth.
Flame cell MDCAT: The ciliated excretory cell of flatworms (protonephridia); flickering cilia drive waste-laden fluid into excretory tubules.
Gemmule: A resistant, internally budded resting body of freshwater sponges that survives drought and cold, germinating into a new sponge.
Hydrostatic skeleton: Support by pressurized fluid in a body cavity; used by earthworms and other soft-bodied invertebrates for burrowing and movement.
Medusa MDCAT: The free-swimming, bell-shaped sexual stage of cnidarians (e.g., jellyfish Aurelia); alternates with the polyp in many life cycles.
Mesoglea: The gelatinous, non-cellular layer between ectoderm and endoderm in cnidarians and ctenophores.
Metamorphosis MDCAT: Abrupt developmental transformation from larva to adult; complete metamorphosis (egg → larva → pupa → adult, e.g., butterfly) vs incomplete metamorphosis (egg → nymph → adult, e.g., grasshopper).
Molting: Periodic shedding of the cuticle/exoskeleton during ecdysis in arthropods and nematodes, controlled by ecdysone hormone.
Nauplius larva: The first free-swimming larval stage of crustaceans, with three pairs of appendages and a single median eye.
Nematocyst MDCAT: The coiled, harpoon-like stinging thread inside a cnidoblast that everts on contact to inject venom.
Nephridium: The tubular excretory organ of annelids and molluscs (metanephridia), filtering coelomic fluid into urine.
Osculum: The large opening of a sponge through which filtered water exits the body (plural: oscula).
Parapodium: Paired, fleshy lateral appendages of polychaete worms used in swimming and crawling (plural: parapodia).
Planula larva: The ciliated, free-swimming larva of cnidarians that settles to form a polyp.
Polyp MDCAT: The sessile, tubular, asexual stage of cnidarians (e.g., Hydra, corals), with mouth and tentacles facing upward.
Radula: The chitinous, rasping tongue-like organ of molluscs used for scraping food.
Regeneration: Regrowth of lost body parts; extreme in Hydra and planarians, which can reform whole bodies from fragments.
Sessile: Permanently attached to a substrate and non-motile as an adult (e.g., sponges, corals, barnacles).
Spicule: Microscopic calcareous or siliceous skeletal element of sponges, used in their classification.
Spongin: The flexible protein fiber forming the skeleton of bath sponges (replaces or supplements spicules).
Tornaria larva: The free-swimming larva of Balanoglossus (hemichordates), resembling the echinoderm bipinnaria — key evidence for the Ambulacraria clade.
Trochophore larva MDCAT: The ciliated, top-shaped larva shared by annelids and molluscs — strong evidence these phyla are closely related (Trochozoa).
Water vascular system MDCAT: The hydraulic network of canals and tube feet unique to echinoderms, used in locomotion, feeding, and gas exchange.

Chordate Biology — Terms & Definitions

Protochordates, fishes, amphibians, reptiles, birds, and mammals — built around the four chordate hallmarks: notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail.

Amnion MDCAT: The innermost extraembryonic membrane enclosing the amniotic fluid that cushions the developing embryo of reptiles, birds, and mammals.
Amniote MDCAT: A vertebrate whose embryo develops within protective extraembryonic membranes (amnion, chorion, allantois) — reptiles, birds, and mammals.
Anamniote: A vertebrate lacking an amnion, laying eggs in water — fishes and amphibians.
Cartilage: Flexible skeletal tissue of chondrin; the entire skeleton of sharks and rays, and the embryonic precursor of bone in other vertebrates.
Cloaca: A single posterior chamber receiving the digestive, urinary, and reproductive tracts in amphibians, reptiles, birds, and monotremes.
Diaphragm MDCAT: The muscular sheet separating thorax and abdomen in mammals; its contraction drives breathing movements.
Dorsal hollow nerve cord MDCAT: One of the four chordate characters: a single hollow nerve cord running dorsally, developing into the brain and spinal cord.
Ectotherm MDCAT: An animal whose body temperature follows the environment ("cold-blooded") — fishes, amphibians, reptiles; heats behaviorally.
Endoskeleton: An internal skeleton of bone or cartilage supporting vertebrates from within and growing with the animal.
Endotherm MDCAT: An animal that maintains a constant high body temperature metabolically ("warm-blooded") — birds and mammals.
Feather: The keratinous epidermal outgrowth unique to birds, serving flight, insulation, and display.
Fin: The flattened appendage of fishes (and secondarily of whales/penguins) used in swimming and balance.
Gill MDCAT: The feathery respiratory organ of fishes and aquatic larvae where dissolved oxygen diffuses into blood.
Hair (fur): The keratinous filament unique to mammals, providing insulation and sensory function.
Homeotherm: An animal with a stable internal body temperature regardless of the environment — birds and mammals (endothermic homeotherms).
Lateral line system: The row of mechanoreceptor neuromasts along a fish's flank detecting water movement, vibration, and pressure changes.
Mammary gland MDCAT: The milk-producing skin gland unique to mammals, nourishing the young after birth.
Monotreme: An egg-laying mammal (duck-billed platypus, echidna) — the most primitive living mammals, found in Australia.
Notochord MDCAT: The flexible, rod-like skeletal axis of chordate embryos; replaced by the vertebral column in most vertebrates, retained for life in lancelets.
Oviparous MDCAT: Egg-laying: the embryo develops outside the mother's body, nourished by yolk (e.g., birds, most reptiles, monotremes).
Ovoviviparous MDCAT: Eggs hatch inside the mother's body and young are born alive, but with no placental nourishment (e.g., some sharks, vipers).
Pharyngeal (gill) slits MDCAT: Openings in the embryonic pharynx of chordates; become gills in fishes, and ear/Eustachian structures in terrestrial vertebrates.
Placenta: The organ joining mother and fetus in eutherian mammals, exchanging nutrients, gases, and wastes across (not mixing) bloodstreams.
Poikilotherm: An animal whose internal temperature varies with the environment; essentially synonymous with ectotherm.
Scale: Protective epidermal/dermal plates of fishes and reptiles; modified into feathers in birds and hair in mammals.
Swim (air) bladder: The gas-filled sac of bony fishes regulating buoyancy, allowing them to hover at a chosen depth.
Tetrapod: A vertebrate with four limbs (or descended from four-limbed ancestors) — amphibians, reptiles, birds, mammals.
Vertebra: One of the segmental bones of the vertebral column, protecting the spinal cord (plural: vertebrae).
Vertebral column: The jointed series of vertebrae forming the backbone — the defining character of vertebrates (subphylum Vertebrata).
Viviparous MDCAT: Giving birth to live young nourished through a placenta or equivalent structure (e.g., most mammals, some sharks).

Exam-favorite differences: chordate pairs

Feature	Oviparous	Viviparous	Ovoviviparous
Development site	Outside, in a laid egg	Inside the mother	Inside the mother (in egg)
Nutrition	Yolk only	Placental/maternal	Yolk only
Examples	Birds, platypus	Humans, whales	Some sharks, vipers

Feature	Exoskeleton	Endoskeleton
Position	Outside the body	Inside the body
Material	Chitin or calcium carbonate	Bone or cartilage
Growth	Shed periodically (ecdysis)	Grows with the animal
Found in	Arthropods, molluscs	Vertebrates

Feature	Ectotherms (cold-blooded)	Endotherms (warm-blooded)
Heat source	Environment (basking)	Metabolism (food energy)
Body temperature	Variable	Nearly constant, high
Energy need	Low — long fasting possible	High — must eat frequently
Examples	Fishes, frogs, lizards	Birds, mammals

Animal Physiology — Terms & Definitions

Circulation, respiration, excretion, nerves, and hormones compared across animal groups — the body-systems vocabulary behind every physiology MCQ.

Alveolus MDCAT: The microscopic air sac of mammalian lungs where oxygen and carbon dioxide diffuse between air and blood (plural: alveoli).
Antibody: A Y-shaped protein (immunoglobulin) produced by B-lymphocytes that binds a specific antigen to neutralize it.
Antigen: Any foreign molecule that triggers an immune response and binds specifically to an antibody.
Aorta: The largest artery of the body, carrying oxygenated blood from the left ventricle to the systemic circulation.
Atrium: An upper receiving chamber of the heart; mammals and birds have two atria feeding the two ventricles.
Bile: The alkaline, greenish liver secretion stored in the gall bladder; it emulsifies fats but contains no enzymes.
Capillary MDCAT: The thinnest blood vessel (one cell thick) where exchange of gases, nutrients, and wastes occurs between blood and tissues.
Cardiac muscle: The striated, involuntary, branched muscle of the heart wall, contracting rhythmically without fatigue.
Digestion: Mechanical and chemical breakdown of food into absorbable molecules, completed in the small intestine of vertebrates.
Enzyme MDCAT: A protein catalyst speeding a specific biochemical reaction; named with the suffix -ase (e.g., amylase, pepsin).
Erythrocyte (red blood cell): The hemoglobin-filled, anucleate (in mammals) cell transporting oxygen from lungs to tissues.
Excretion MDCAT: Removal of metabolic nitrogenous wastes (ammonia, urea, uric acid) and excess salts from the body.
Expiration: Breathing out: the diaphragm relaxes and the rib cage recoils, expelling CO₂-rich air.
Glomerulus: The tuft of capillaries inside Bowman's capsule where blood plasma is filtered into the nephron.
Hemoglobin MDCAT: The iron-containing respiratory pigment of red blood cells binding oxygen cooperatively (four O₂ per molecule).
Homeostasis MDCAT: Maintenance of a stable internal environment (temperature, pH, water, glucose) despite external change, largely via negative feedback.
Hormone MDCAT: A chemical messenger secreted by an endocrine gland into blood, acting on distant target organs (e.g., insulin, thyroxine).
Inspiration: Breathing in: the diaphragm contracts and flattens while intercostal muscles raise the ribs, drawing air into the lungs.
Kidney MDCAT: The bean-shaped vertebrate organ filtering blood, forming urine, and regulating water–salt balance via about a million nephrons each.
Leukocyte (white blood cell): The nucleated immune cell of blood (neutrophils, lymphocytes, monocytes) defending against pathogens.
Nephron MDCAT: The microscopic structural and functional unit of the kidney — glomerulus, Bowman's capsule, tubules, and loop of Henle.
Neuron MDCAT: The nerve cell: dendrites receive signals, the axon conducts the impulse, and the synapse passes it to the next cell.
Osmoregulation MDCAT: Control of water and solute balance; freshwater animals excrete dilute urine, marine animals conserve water.
Peristalsis: Rhythmic waves of smooth-muscle contraction pushing food through the alimentary canal.
Plasma: The straw-colored fluid matrix of blood (about 55%) carrying cells, proteins, hormones, and dissolved nutrients.
Reflex arc: The neural pathway of a reflex: receptor → sensory neuron → interneuron → motor neuron → effector, bypassing conscious control.
Respiration MDCAT: Cellular oxidation of glucose releasing ATP (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy); breathing is only its first step.
Synapse: The junction between two neurons (or neuron and muscle) where the impulse crosses via neurotransmitters such as acetylcholine.
Thermoregulation: Physiological and behavioral control of body temperature — sweating and vasodilation in heat, shivering and vasoconstriction in cold.
Urea: The main nitrogenous waste of mammals and amphibians (ureotelic animals), formed in the liver by the ornithine cycle and excreted by kidneys.
Ventricle: A lower pumping chamber of the heart; the thick-walled left ventricle drives the systemic circulation.
Villus MDCAT: A finger-like fold of the small-intestinal wall vastly increasing the absorptive surface for digested food (plural: villi).

Evolution & Behavior — Terms & Definitions

Natural selection, speciation, and the ethology vocabulary — mimicry, camouflage, hibernation, and aestivation — that examiners love to test.

Adaptation MDCAT: A heritable trait increasing an organism's fitness in its environment, shaped by natural selection (e.g., streamlined fish body).
Aestivation: Summer dormancy in hot, dry conditions to conserve water and energy (e.g., lungfish, desert snails); the warm-climate counterpart of hibernation.
Altruism: Behavior reducing the actor's fitness while benefiting another, explained by kin selection (e.g., worker bees defending the hive).
Camouflage MDCAT: Coloration or patterning blending an animal with its background to evade predators or ambush prey (e.g., stick insect).
Convergent evolution: Independent evolution of similar traits in unrelated lineages facing similar pressures (e.g., wings of insects, birds, bats).
Courtship behavior: Ritualized displays and signals by which animals attract mates and assess partner quality (e.g., peacock dance).
Divergent evolution: Accumulation of differences between related populations, producing homologous structures adapted to different functions (e.g., vertebrate forelimbs).
Ethology: The scientific study of animal behavior in natural conditions, founded by Lorenz, Tinbergen, and von Frisch.
Fossil MDCAT: Preserved remains or traces of ancient organisms (bones, imprints, amber inclusions) — the direct evidence of evolution.
Hibernation MDCAT: Winter dormancy with lowered metabolism, heart rate, and body temperature to survive cold and food scarcity (e.g., bears, hedgehogs).
Imprinting: Rapid, irreversible learning during a critical early period, e.g., goslings following the first moving object they see (Lorenz).
Innate behavior: Instinctive behavior performed correctly without prior experience (e.g., spider web-building, suckling reflex).
Learned behavior: Behavior modified by experience — habituation, conditioning, and insight learning.
Migration: Regular seasonal movement between breeding and feeding grounds (e.g., Arctic tern, wildebeest, salmon).
Mimicry MDCAT: Resemblance of one species to another (or to an object) for protection or predation — Batesian (harmless mimics harmful) vs Müllerian (both harmful).
Natural selection MDCAT: Differential survival and reproduction of the best-adapted individuals, driving adaptive evolution — Darwin's mechanism, summarized as "survival of the fittest".
Reflex: An automatic, involuntary response to a stimulus (e.g., knee-jerk), mediated by a reflex arc.
Speciation MDCAT: Formation of new species, typically via reproductive isolation of populations (allopatric speciation by geographic barriers is most common).
Survival of the fittest: Spencer's phrase for natural selection: individuals best adapted to the environment leave the most offspring.
Taxis: Directed movement toward or away from a stimulus (phototaxis, chemotaxis); plural: taxes.
Territoriality: Defense of an area against rivals of the same species, securing food, mates, or nesting sites.
Vestigial structure: A reduced, functionless remnant of an ancestral organ (e.g., human appendix, whale pelvic bones) — evidence of evolution.

Parasitology — Terms & Definitions

Parasitism, symbiosis, commensalism, and mutualism plus host and life-cycle vocabulary — essential for Plasmodium, Taenia, and Ascaris questions.

Commensalism MDCAT: A symbiosis in which one partner benefits and the other is neither helped nor harmed (e.g., barnacles on whales, Entamoeba coli in the human gut).
Cyst: The resistant, thick-walled dormant stage of many parasites (e.g., Entamoeba histolytica cysts) surviving harsh conditions and spreading infection.
Definitive (primary) host MDCAT: The host in which a parasite reaches sexual maturity (e.g., humans for Taenia solium, female Anopheles for Plasmodium).
Ectoparasite MDCAT: A parasite living on the body surface of the host (lice, ticks, mites, leeches).
Endoparasite MDCAT: A parasite living inside the host's body — in the gut, blood, or tissues (tapeworms, Plasmodium, Ascaris).
Hyperparasite: A parasite that parasitizes another parasite (e.g., wasps laying eggs in parasitic fly larvae).
Intermediate (secondary) host MDCAT: The host harboring the parasite's larval/asexual stages (e.g., pig for Taenia solium bladder worms, humans for Plasmodium).
Mutualism MDCAT: A symbiosis benefiting both partners (e.g., cellulose-digesting flagellates in termite guts, cleaner fish and clients).
Obligate parasite: A parasite unable to complete its life cycle without a host (e.g., Plasmodium); opposite: facultative parasite.
Parasite MDCAT: An organism living in or on a host, obtaining nourishment at the host's expense.
Parasitism MDCAT: The symbiotic association in which the parasite benefits and the host is harmed.
Parasitoid: An insect whose larva develops inside a single host arthropod, ultimately killing it — intermediate between parasite and predator (e.g., ichneumon wasps).
Pathogen: Any disease-causing agent — virus, bacterium, fungus, protozoan, or helminth.
Reservoir host: A host species maintaining a parasite in nature and serving as a source of infection for others (e.g., rats for plague bacteria).
Schizogony: Multiple asexual fission in which the nucleus divides repeatedly before the cytoplasm splits — the blood-stage multiplication of Plasmodium.
Symbiosis MDCAT: Any persistent living-together of two different species — encompassing mutualism, commensalism, and parasitism.
Trophozoite: The active, feeding, growing stage of a protozoan parasite (e.g., the amoeboid trophozoite of Entamoeba histolytica).
Vector MDCAT: An arthropod (or other agent) transmitting a parasite between hosts — biological (e.g., Anopheles for malaria) or mechanical (housefly).
Virulence: The degree of harm a pathogen causes its host; often trades off against transmission success.
Zoonosis: A disease transmissible between animals and humans (rabies, bird flu, tapeworm infections); plural: zoonoses.

Ecology & Wildlife — Terms & Definitions

Ecosystems, food chains, and conservation vocabulary — including Pakistan's wildlife context (markhor, Indus dolphin, national parks).

Biodiversity MDCAT: The variety of life at genetic, species, and ecosystem levels; Pakistan's ranges from Indus delta mangroves to Himalayan alpine zones.
Biome: A large regional ecosystem defined by climate and dominant vegetation (desert, tundra, tropical rainforest).
Biosphere: The global zone of life — all ecosystems of Earth interacting as one system.
Carnivore: A flesh-eating animal; a secondary or tertiary consumer in food chains (e.g., snow leopard, shark).
Community: All populations of different species living and interacting in one area.
Conservation MDCAT: Protection and sustainable management of wildlife and habitats — e.g., Pakistan's national parks safeguarding the markhor and Indus dolphin.
Consumer: An organism feeding on other organisms; primary (herbivores), secondary, and tertiary consumers occupy successive trophic levels.
Decomposer MDCAT: An organism breaking down dead matter and recycling nutrients — bacteria, fungi, and detritivores like earthworms.
Ecosystem MDCAT: A community of organisms plus their physical environment, interacting through energy flow and nutrient cycles.
Endangered species: A species at high risk of extinction in the wild (IUCN Red List category), e.g., the Indus river dolphin.
Food chain MDCAT: The linear sequence of who-eats-whom transferring energy: producer → primary consumer → secondary consumer → decomposer.
Food web: The network of interconnected food chains in a community, showing the true complexity of feeding relationships.
Habitat MDCAT: The natural environment where an organism lives — its "address" (e.g., freshwater river for the Indus dolphin).
Herbivore: A plant-eating animal; the primary consumer of terrestrial food chains (e.g., markhor, rabbit).
Niche MDCAT: An organism's functional role in its ecosystem — its "profession", including food, habitat use, and activity timing.
Omnivore: An animal eating both plants and animals (e.g., bears, crows, humans).
Population: All individuals of one species living in an area at one time — the unit of evolution and ecology.
Predator: An animal that kills and eats other animals (e.g., wolf, eagle).
Prey: An animal hunted and eaten by a predator.
Trophic level: Each feeding step in a food chain — producers (level 1), herbivores (level 2), carnivores (levels 3+); only ~10% of energy transfers upward.

Cell & Genetics Basics — Terms & Definitions

Mitosis, meiosis, and inheritance vocabulary that underpins every genetics and reproduction question in FSc and MDCAT biology.

Allele MDCAT: An alternative form of a gene at the same locus (e.g., T for tall, t for dwarf in pea plants).
Cell: The structural and functional unit of life; animals are multicellular eukaryotes with membrane-bound organelles.
Chromatid: One of the two identical halves of a duplicated chromosome, joined at the centromere.
Chromosome MDCAT: The thread-like DNA–protein (chromatin) body carrying genes; humans have 46 (23 pairs) in somatic cells.
Crossing over: Exchange of segments between homologous chromosomes in prophase I of meiosis — the main source of genetic variation.
Cytokinesis: Division of the cytoplasm after nuclear division, producing two daughter cells.
Diploid MDCAT: Having two chromosome sets (2n) — the condition of somatic cells and the zygote.
DNA MDCAT: Deoxyribonucleic acid: the double-helical molecule storing hereditary instructions in the sequence of its bases (A, T, C, G).
Dominant (allele): An allele expressed in the phenotype even when present in a single copy (heterozygous condition).
Gamete MDCAT: A haploid reproductive cell — sperm or egg — fusing at fertilization to restore diploidy.
Gene MDCAT: The hereditary unit: a DNA segment coding for a polypeptide or functional RNA.
Genotype: An organism's genetic constitution (e.g., Tt); contrasted with phenotype, its observable expression.
Haploid MDCAT: Having a single chromosome set (n) — the condition of gametes.
Heterozygous: Carrying two different alleles of a gene (e.g., Tt).
Homozygous: Carrying two identical alleles of a gene (e.g., TT or tt).
Karyotype: The photographed, ordered display of an individual's chromosomes used to detect abnormalities like Down syndrome (trisomy 21).
Meiosis MDCAT: Two-stage reduction division producing four haploid gametes from one diploid cell — the basis of sexual reproduction and variation.
Mitosis MDCAT: Single nuclear division producing two genetically identical diploid daughter cells — for growth and repair (stages: prophase, metaphase, anaphase, telophase).
Phenotype: The observable traits of an organism resulting from genotype plus environment.
Recessive (allele): An allele expressed only in the homozygous condition (e.g., tt dwarf pea plants).
Somatic cell: Any body cell other than gametes; diploid in most animals.
Zygote MDCAT: The diploid cell formed by fusion of sperm and egg — the first cell of the new individual.

Exam-favorite difference: cell division

Feature	Mitosis	Meiosis
Divisions	One	Two (meiosis I and II)
Daughter cells	2, diploid, identical	4, haploid, genetically different
Crossing over	Absent	Occurs in prophase I
Purpose	Growth and repair	Gamete formation
Where	Somatic cells	Reproductive cells

General / Exam Terms — Zoology Vocabulary

Must-know branches of zoology and general MDCAT biology vocabulary / FSc biology important definitions that appear across papers.

Anatomy: The branch of zoology studying the internal structure of animals (gross and microscopic).
Biology: The science of life; zoology is the branch of biology devoted to animals, botany to plants.
Carcinology: The branch of zoology studying crustaceans (crabs, shrimps, lobsters).
Embryology: The study of embryonic development from zygote to birth/hatching.
Entomology MDCAT: The branch of zoology studying insects — the largest animal group on Earth.
Helminthology: The study of parasitic worms (helminths): flukes, tapeworms, and roundworms.
Herpetology: The branch of zoology studying amphibians and reptiles.
Histology: The microscopic study of tissues — epithelial, connective, muscular, and nervous.
Ichthyology MDCAT: The branch of zoology studying fishes.
Malacology: The study of molluscs — snails, clams, squids, and octopuses.
Mammalogy: The branch of zoology studying mammals.
Morphology: The study of the form and external structure of organisms.
Ornithology MDCAT: The branch of zoology studying birds.
Paleontology: The study of fossils and ancient life, linking zoology with geology.
Parasitology: The branch of zoology studying parasites and their relationships with hosts.
Physiology: The study of the functions and processes of living organisms and their parts.
Protozoology: The study of protozoans — unicellular eukaryotes such as Amoeba and Plasmodium.
Sociobiology: The study of the biological basis of social behavior in animals.
Zoogeography: The study of the geographic distribution of animals across the Earth.
Zoology MDCAT: The scientific study of animals — their structure, function, development, classification, behavior, and distribution.

Frequently Asked Questions — Zoology Glossary

What is the definition of zoology?

Zoology is the branch of biology that studies animals — their structure, physiology, development, classification, behavior, evolution, and distribution. The word comes from Greek zoon (animal) and logos (study).

What are the main branches of zoology?

The main branches of zoology include morphology, anatomy, physiology, embryology, ecology, ethology (behavior), parasitology, taxonomy, and group-specific fields: ichthyology (fishes), herpetology (amphibians and reptiles), ornithology (birds), entomology (insects), and mammalogy (mammals).

What is the difference between zoology and biology?

Biology is the study of all living things; zoology is the branch of biology restricted to animals. Botany (plants) and microbiology (microbes) are zoology's sister branches within biology.

What is binomial nomenclature in zoology?

Binomial nomenclature, introduced by Linnaeus, gives every species a two-part Latinized name: the genus (capitalized) followed by the species epithet (lowercase), both italicized — e.g., Homo sapiens for humans.

What does acoelomate mean? How is it different from coelomate and pseudocoelomate?

Acoelomate means having no body cavity (e.g., flatworms). Pseudocoelomates have a false cavity not fully lined by mesoderm (e.g., roundworms). Coelomates (eucoelomates) have a true mesoderm-lined coelom (e.g., annelids, chordates). It is one of the most repeated MDCAT classification concepts.

What is the difference between protostomes and deuterostomes?

In protostomes (arthropods, molluscs, annelids) the blastopore becomes the mouth and cleavage is spiral and determinate. In deuterostomes (echinoderms, chordates) the blastopore becomes the anus, cleavage is radial and indeterminate, and the coelom forms by enterocoely.

What is metamorphosis? What is the difference between complete and incomplete metamorphosis?

Metamorphosis is the abrupt transformation from larva to adult. Complete metamorphosis has four stages — egg, larva, pupa, adult (butterfly, housefly). Incomplete metamorphosis has three — egg, nymph, adult — with the nymph resembling a small adult (grasshopper, cockroach).

What do oviparous, viviparous and ovoviviparous mean?

Oviparous animals lay eggs that develop outside the body (birds). Viviparous animals give birth to live young nourished via a placenta (most mammals). Ovoviviparous animals retain eggs inside the body until hatching, with no placental nourishment (some sharks, vipers).

What is the difference between ectotherms and endotherms (cold-blooded vs warm-blooded)?

Ectotherms ("cold-blooded": fishes, amphibians, reptiles) rely on the environment for body heat and eat less. Endotherms ("warm-blooded": birds, mammals) generate heat metabolically, keeping a constant high body temperature at the cost of much more food.

What is cephalization in animals?

Cephalization is the evolutionary concentration of nervous tissue and sense organs at the anterior (head) end of bilaterally symmetrical animals — the basis of the brain, and a hallmark of active, mobile animals.

What is a hermaphrodite in zoology?

A hermaphrodite (monoecious animal) is an individual with both male and female reproductive organs, e.g., earthworms and tapeworms. It is the opposite of dioecious, where sexes are in separate individuals.

How can I memorize zoology terms quickly for MDCAT?

Group terms by branch (as in this glossary), learn 15–20 daily with one example organism each, use the Greek/Latin roots (e.g., coel- = cavity, derm = skin), and revise with the MDCAT-badged hotspot terms first — they carry the highest exam weightage.

References: Hickman, Roberts & Larson, Integrated Principles of Zoology; Miller & Harley, Zoology; Campbell, Biology; FSc Biology (Punjab Textbook Board) and MDCAT syllabi.