Share interesting photos to engage biology enthusiasts.

Biology Terms - Glossary of Biology Terms and Definitions

Biology Terms - Glossary of Biology Terms and Definitions

Biology refers to the science of living organisms. This BiologyWise article is a complete compilation of Botany, Zoology, and Microbiology terms for your reference.
Priya Johnson
Last Updated: Mar 10, 2018
Biology is the branch of science concerned with the study of life: structure, growth, functioning, and evolution of living things. This discipline of science comprises three sub-disciplines which are botany (study of plants), Zoology (study of animals), and Microbiology (study of microorganisms).
This vast subject of science involves the usage of myriad of biology terms, which essentially need to be comprehended correctly. People involved in the science field encounter innumerable jargons during their study, research, or work. Moreover, since science is a part of everyone's life, it is something that is important to all individuals.
A-Z List of Biology Terms and Definitions.
Glossary of Zoology Terms and Definitions
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Abdomen: Abdomen in mammals is the portion of the body which is located below the rib cage, and in arthropods below the thorax. It is the cavity that contains stomach, intestines, etc.
Abscission: Abscission is a process of shedding or separating part of an organism from the rest of it. Common examples are that of, plant parts like leaves, fruits, flowers, and bark being separated from the plant.
Accidental: Accidental refers to the occurrences or existence of all those species that would not be found in a particular region under normal circumstances.
Acclimation: Acclimation refers to the morphological and/or physiological changes experienced by various organisms to adapt or accustom themselves to a new climate or environment.
Active Transport: The movement of cellular substances like ions or molecules by traveling across the membrane, towards a level of higher concentration, while consuming energy.
Activity Space: The entire range of climatic and environmental conditions suitable to normal functions, process, and activities of a living organism.
Adaptation: Adaptation refers to the genetic mechanism of an organism to survive, thrive, and reproduce by constantly enhancing itself, by altering its structure or function, in order to become better suited to the changing environment. Read more on adaptations in desert animals.
Adaptive Radiation: The evolutionary diversification from an ancestral group of organisms, into a number of newer and more specialized forms, each suited to live in new habitats. Read more on animal adaptations.
Aerial Behavior: Aerial behavior is a type of behavior that deals with communicative or playful behavior. It is most seen in whales and dolphins when they surface above water to either jump, leap, or just flit across.
After-Shaft: A small supplementary feather, growing from the underside of the base of the shafts of a body feather. It is found in many birds and essential to keep them warm.
Aigrette: A tuft of long and loose feathers used by breeding herons and egrets, during courtship displays.
Air Sac: A thin-walled, air filled structure which is a part of the respiratory system of birds. The air passing through the air sac aids in their breathing and temperature regulation.
Airfoil: A structure designed to lift and control the airflow by making use of different levels of air waves. A bird in flight uses the concept of airfoil to control its speed.
Alligator: A broad snouted crocodilians of the genus Alligator found in subtropical regions. This reptile is known for its sharp teeth and powerful jaws.
Allopatric: Organisms that occur, originate, or occupy in separate geographical areas.
Alpha Diversity: A measurement of species richness in a natural unit (specified area) consisting of all plants, animals, and micro-organisms in a habitat functioning together.
Altruism: Instinctive behavior performed towards the welfare of others, sometimes at personal cost.
Alula: A set of quill-like feathers located close to the base of the primary feathers that play a part in increasing or decreasing the bird's lift by affecting the airflow of the wings.
Alveolus: A small angular cavity, sac, or pit in the body.
Ambulacra: This term refers to echinoderm's five part radial areas (undersurfaced side) from where the tube feet protrude as well as withdraw.
Amnion: The innermost delicate embryonic or fetal membranes of higher vertebrates like mammals, birds, and reptiles.
Amniotic Egg: Eggs found in a water-impermeable, amniotic membrane, filled with fluid in the amniotic cavity, that can develop on land without dehydrating themselves.
Amphibians: Animals that can survive and live on land as well as in water. Amphibians are vertebrates and cold-blooded.
Amphisbaenian: A long reptile (worm-like) with a short tail and ring-shaped scales that has well adapted itself to burrowing.
Amplexus: Mating position of the frogs and toads, in which the female sheds the eggs into the water and the male fertilizes it. Fertilization takes place outside the female's body.
Anapsid: An extinct subclass of reptiles except for the turtles, that have no opening in the temporal region of the skull.
Anastomosis: A network of intersecting or connecting blood vessels, nerves, or leaf veins that form a plexus.
Animalia: The taxonomic kingdom of animals that includes organisms that are multicellular, eukaryotic, (having cells with membrane-bound nuclei) and heterotropic (require organic compounds for nourishment).
Annelida: The taxonomic group of animals that includes coelomate, and elongated and segmented invertebrates such as leeches, earthworms, marine worms, etc.
Antenna: A sensory apparatus found on the heads of insects and most arthropods. It usually occurs in pairs.
Antler: One pair of bony, deciduous, and branched hornlike structure found on the head of a deer, moose, elk, etc.
Anus: An opening at the lower end of the digestive tract through which all solid waste is eliminated from the body.
Apomorph: A new specialized trait in an evolving organism which is completely different from its ancestral line.
Aposematic: Color construct characteristics in animals (changing color), either as a warning to other animals or as a self defense mechanism.
Arboreal: Arboreal refers to animals that have adapted themselves to live and move in the trees.
Arthropod: A group of invertebrate animals such as the insects, crustaceans, arachnids, centipedes, etc that are characterized by a exoskeleton and a segmented body with jointed appendages.
Artificial Selection: A selection process where the breeder chooses the animals for mating and producing offspring of desired inheritable qualities.
Aspect Diversity: It is the measure of the different physical appearances that are found in a group of species living in a common habitat and are hunted by other animals that use visual hunting skills to identify and kill their prey.
Auriculars: Auriculars is a set of feathers that are found near a bird's ear openings.
Autonomic Nervous System: The part of the vertebrate nervous system that regulates involuntary action of an animal's internal organs like the intestines, heart, and glands.
Autotroph: An organism capable of acquiring nourishment from its surrounding environment using photosynthesis or chemosynthesis as opposed to ingesting another organism.
Aves: A class of vertebrates comprising the entire bird family.
Balanced Polymorphism: A situation where more than one allele is maintained in a population, which is the outcome of the heterozygote being superior to both homozygotes.
Baleen: Baleen whales are those whales that filter plankton for ingestion, out of large quantities of water. Baleen is the fibrous structure in their mouths, usually referred to as baleen plates, that enable them to feed in this way. They do not have teeth.
Banding: The manner in which a metal or plastic band is attached to the legs of birds and other animals. This is done with the purpose of identifying the individual/creature at the time of recapture.
Barbel: Often found on fish, a barbel is a slim, whisker-like tactile organ located near the mouth. In some fish, they contain the taste buds, and assist the fish to locate food in murky water.
Barbicels: Barbicels are tiny curved structures on barbules, that connect contiguous barbules to form the firm, mesh-like structure of the feather vane.
Barbs: The barbs are attached to the main shaft of a feather, and make up its vanes.
Barbules: Barbules are tiny structures that emerge from the barbs of a bird's feather. They interlock, overlap, and knit together, making the feather solid and stiff.
Basic Plumage: Among the bird species that molt only once a year, the basic plumage are those feathers they have on them throughout the year. Whereas, among species that molt twice annually, the basic plumage (in most cases) are the feathers that grow after the first complete molt, and is present at the time of the bird's non-breeding season.
Batesian Mimicry: In a situation where a harmless species has evolved to replicate the warning signal given by a harmful species (directed at a common predator), Batesian mimicry occurs.
Beak: The protruding part of the mouth of several groups of vertebrates, including some cetaceans. Birds use them not only to eat, but also to groom, kill prey, manipulate objects, in courtship, and to feed the young.
Benthic: A Benthic zone is the ecological region that encompasses the bottom most level of any body of water, be it a river, lake, or ocean. When used in conjunction with a living organism, it refers to bottom-dwelling.
Beta Diversity: A term of measurement, that gauges the variety of organisms in a region. It is impacted by the turnover of species among habitats.
Bilateral Symmetry: This type of symmetry is exhibited by most animals, and simply implies that, if a line were drawn down the middle of the body, both sides would be equal and symmetrical.
Bill: The projecting mouth of a bird. It is the same as a Beak.
Binocular Vision: An animal with this kind of vision has eyes that are projected forward, due to which the field of view overlap, enabling the creature to judge depth.
Biodiversity: A term of measurement, that gauges the diversity of organisms in a habitat or ecosystem. This measurement can be made based on the number of species or genetic variation that exist within an ecosystem or region.
Biogeography: It is a term used to define the study of the geographic distribution of organisms throughout a region over a given period of time. It is carried out with the aim of examining where organisms dwell, and at what populations.
Biome: A region that is defined based on its climate and geography, which has ecologically similar communities of plants, animals, and soil organisms. The similarity is based on plant structures (such as trees, grasses and shrubs), plant spacing (forest, savanna, woodland), leaf types (such as needle-leaf and broad-leaf), and climate.
Biota: They constitute the living components (flora and fauna) of an ecosystem, biome, or habitat.
Blowhole: A blowhole is an opening on the top of a cetacean's head, from which air is inhaled and exhaled.
Bipedal: Bipedalism is a manner of moving on land, where the organism progresses using only its two rear limbs, or legs.
Birth Rate: The term is the average number of young produced within a specific period of time. It is calculated per individual, and is usually communicated as a function of age.
Book Lung: It is an organ used for respiration, and is part of the body system of arachnids, such as spiders and scorpions. The book lung is located inside the ventral abdominal cavity.
Bow Riding: It is an activity carried out by cetaceans (most commonly dolphins), in which they swim or drift along the crests of waves in the ocean.
Breeding System: A breeding system includes all the different breeding behavior (polygyny, outcrossing, or selective mating) of a population, and the methods in which the members of the population adapt to them.
Brilles: The German word for 'glasses', it is a transparent, immovable layer of scale/skin that covers the eyes of some creatures, such as snakes and lizards, and provides a protective layer.
Bristles: Bristles are long, stiff strands of hair or feathers. In birds, they are situated near the mouth or eyes. Their function may be to assist the bird in eating and give protection to the eyes.
Brood Parasite: A brood parasite is an organism (usually a bird) which manipulates another individual of the same or different species to raise its offspring. A method usually adopted to do this is to lay eggs in another birds nest.
Brood Parasitism: The method adopted by one organism to make another individual of the same or different species to raise its offspring. In case of birds, this is done by laying ones eggs in another birds nest.
Brood Patch: Located on the lower abdomen of birds, this patch develops by the shedding of feathers in this area, and the consequent thickening of the skin, after which it becomes densely populated with blood vessels. The brood patch is used to incubate the eggs and keep the young warm.
Brood Reduction: When a clutch of eggs hatch sequentially, if there is inadequate food, brood reduction takes place. This happens when the weakest chick or chicks, being deprived of food either fail to survive out of starvation, or are devoured by their stronger siblings.
Brooding: The practice of birds, where the parent birds continue to provide warmth to their young, during the time when they are unable to maintain their own body temperatures.
Caching: Storing of food for later use, when food is not available or is short in supply.
Caiman: A tropical American crocodilian amphibian, found in Central and South America.
Calamus: It is the hollow base of a feather shaft, which attaches the feather to the skin.
Calcereous: Calcium contained parts such as shells, bones, and exoskeletons, which protects an animal.
Call Matching: This is a behavioral trait, often displayed by members of the finch family. This refers to the male and female of a pair duplicating each others flight call, vocally.
Camouflage: A feature common to invertebrates, which helps them blend with their surroundings using its skin colors or patterns.
Canine Tooth: A single point tooth that is shaped and used for piercing and holding on to food. It is located near the front of the jaw, and is prominently seen in carnivores.
Carapace: A hard shell which shields the dorsal side of an animal's body. It is used more specifically to refer to the upper side of a tortoise or turtle's shell.
Carnasial Tooth: A premolar tooth, which is used to efficiently tear and slice meat of prey. This tooth is seen only in the carnivores.
Carnivore: A mammal belonging to the order Carnivora, that sustains by eating the flesh of other animals.
Carrying Capacity: It is the maximum population of a particular species, which can be supported for an indefinite period of time in a particular environment.
Caruncle: A fleshy outgrowth, without feathers, seen on the neck and face of a bird. It is also referred to as fowl's comb and usually seen in the turkey family.
Casque: A formation on the head resembling a helmet, that is located on the head of a lizard.
Caste: A group of species, which shares similar features, form, or behavior and belong to the same social group.
Central Nervous System: A part of the nervous system, made up of inter-neurons, which exercises control over the nervous system.
Centrifugal Tail Molt: The process of shedding and replacing of feathers of a birds tail, that starts with the replacement of the innermost pair of feathers first and then moves from the center outward.
Cephalization: It is a tendency within animals, with localization of neural control and sensory organs located at an end of the body, usually near the head.
Cere: A raised and membranous covering, that is located at the base of the upper mandible in a bird.
Cetaceans: Mainly marine mammals belonging to the Cetacea species. Toothed whales and toothless filter feeding whales are among those that belong to this catergory.
Character Displacement: Adaptations of different sets of characteristics in two similar species, brought about by overlapping territories, resulting in competition.
Cladistics: It is the study of evolutionary history of a group of organisms, especially as shown in a family tree.
Clappeing: Slapping of the upper and lower parts of bills together, as a non vocal form of communication, seen especially in birds like storks.
Climax: The steady, end stage in the ecological evolution of a plant or animal species.
Climograph: Annual cycle of temperature and rainfall for a particular geographical area depicted in a graphical format.
Cloacal Spur: A claw in boas and pythons, which is an extremity of the pelvic girdle. It is used by the male snake, while courting.
Clutch: Eggs or young offspring of a species produced in single breeding attempt by a female.
Cnidaria: A name given to the invertebrate phylum Coelenterata, the emphasis is given to the stinging characteristic of the phylum, which makes up its basic structure comprising nettles, which are generally toxic in nature.
Coelenterates: An invertebrate belonging to Coelenterata phylum characterized by a single interval cavity used for digestion, excretion, and for other survival activities and which has tentacles on the oral end. Hydras, jellyfish, corals, and sea anemones belong to this group.
Colt: Male horse less than four years of age. For interesting facts about horses, click here.
Competition: When two or more individuals compete for the same set of available and limited resources, affecting both the parties negatively.
Conditioning: A learning method either using a stimulus - response, or a reward - punishment method, in which associations are made.
Constriction: This is a method used by non-venomous snakes to tightly grip and suffocate their prey, by coiling around the prey.
Contour Feathers: The feathers which form the topmost layer of a bird's feathers, including the wings and tail, which gives the bird its characteristic look.
Convergent Evolution: The similar structural appearance in organisms, which have different lines of descent.
Corallum: The skeleton of a zoophyte, which can be calcareous or in the formation of horns. For example, the set of parallel vertical grooves which are present on the sides of salamanders and newts.
Countershading: The development of dark colors on the areas exposed to the sun and light colors on the undercarriage.
Creche: Flock of birds, not necessarily belonging to the same species that flock together for protection.
Critical Habitat: A habitat which is critical for the survival and conservation of a species, designated by a rule published in the Federal Register.
Crocodile: Reptile belonging to the order crocodylia, which inhabits tropical regions. Note: Crocodiles differ from alligators.
Crop: Expandable pouch found in the esophagus of some birds.
Cryptic: These refer to the characteristics that help in concealing an animal.
Consumer: An organism, often an animal, which feeds on plants or other animals.
Dabble: Bird behavior pertaining to foraging for food with their beaks or bills from shallow water.
Death Rate: The average number of newborns or young ones dying within a specified period of time. This value is in comparison to the population of the desired species.
Definitive Plumage: The plumage of a bird attained after the shedding of all previous feathers that do not change significantly in color or pattern, as long as the bird lives.
Delayed Plumage Maturation: A common phenomenon seen in male birds where the definitive plumage is delayed due to a number of factors.
Delist: The act of removing an animal species from the list of endangered, threatened, and vulnerable wildlife list.
Delphinidae: A group of marine mammals that belong to the family Delphinidae and the Order Cetacea, like dolphins and their relatives.
Deme: A local breeding that interbreeds organisms of the same species or individuals.
Detritivore: Organisms that feed on dead, decomposed, or organic waste.
Detritus: Organic matter that is either freshly dead or partially decomposed.
Developmental Response: The development of morphological and physiological qualities of an organism in response to prolonged or changing environmental conditions.
Diapause: A period of inactive hormonal development as a response to unfavorable environmental conditions. This is a temporary phase.
Diffuse Coevolution: Evolution of a species depending upon the evolution of some other species, which itself may be evolving depending on some other factors. Coevolution is basically, the evolution of groups depending on each other together, in order to survive.
Diffuse Competition: The weak interactions between species that are ecologically and distantly related.
Dimorphism: The occurrence or existence of two forms within the same species bearing distinct structure, features, coloration, etc.
Diving Reflex: A developed reflexive response to diving, found in most aquatic mammals and birds, that are characterized by complex physiological changes and adaptations.
Evolution: At the most basic level, evolution is change that takes place over time. In reference to lifeforms, evolution refers to the genetic changes observed amongst the population of organisms from generation to generation. Read more on theory of evolution.
Ecological Isolation: It refers to the situation where closely related (sometimes virtually indistinguishable) species live in the same territory, but slight differences in their niche causes them to reproduce in isolation to the others.
Ecological Release: It refers to the progression in which a species expands its living habitat as well as the resources it utilizes into areas that have a lower density of species in terms of diversity.
Ecomorphology: It is the study of the relation between an individual's ecological role, its form, and structural adaptations.
Ecosystem Approach: This is a method of resource management that acknowledges that the different components of an ecosystem (structure, function, and species composition) are interlinked, and this factor must be taken into consideration, while restoring and protecting the ecosystem's natural balance.
Ectoparasite: An organism, such as a tick, that latches itself to the surface of its host, in order to survive.
Ectothermy: Refers to an organism's ability to maintain its body temperature by availing heat from the environment, either by absorbing radiation or through conduction.
Effective Population Size: The average size of a population expressed in terms of individuals assumed to contribute genes equally to the next generation; generally smaller than the actual size of the population, depending on the variation in the reproductive success among individuals.
Egestion: Process of removal of undigested food material.
Egg Dumping: Refers to a bird laying its eggs in the nest of another, with the purpose of making the host bird to hatch and raise its young.
Elliptical: The shape of an egg which is widest in the middle and rounded at both ends.
Embryo: An animal or plant that is in its nascent stages of development and is usually still contained within the seed, egg, or uterus.
Endangered Species: The entire population of organisms (plant or animal) that face extinction due to a steady reduction of their numbers. This may be the outcome of environmental changes, loss of habitat, or predation.
Endoparasite: This type of organism or parasite (such as tapeworm) exists and feeds inside the bloodstream or tissue of its host.
Endothermic: The ability of an organism to constantly maintain its body temperature, usually keeping itself warm, irrespective of the external or surrounding conditions.
Endothermy: The ability of an organism to maintain its body temperature, by generating heat metabolically.
Estivation: Similar to hibernation, it is a period of inactivity that the animal goes into, during a dry hot season.
Eyeshine: The phenomenon when light is shone into the eye of certain animals and birds, the pupil seems to glow. This effect is created by the layer of tissue called tapetum lucidum that lies immediately behind the retina.
Facial Shield: Some birds, such as the Eurasian coot, have a hard plate on their forehead called a facial shield, which serves as a display ornament.
Fallout: Refers to those birds that need to land while migrating, in areas they would not normally inhabit, due to harsh weather.
Family: It is a term of classification of living things, in which this group falls below an order. It is further divided into one or more genera. The ranks start with life, followed by domain, kingdom, phylum, class, order, family, genus, and species.
Fang: Fangs are long, pointed teeth located in the front of the mouth. In mammals, these fangs are called canine teeth and are used for tearing flesh. In snakes, they are used to inject venom into the victim.
Fauna: All the animal life that exists in a particular area during a specific period of time.
Feces: Indigestible waste products expelled from an organisms digestive tract. Usually referred to as stool.
Fecundity: In a general sense, it refers to an organisms ability to reproduce. In biology, it refers to a females potential capacity to reproduce, based on the number of gametes (eggs), seed set, or asexual propagules.
Femur: In vertebrates having four limbs the femur is the upper bone of the hind limb. In insects, it is the third segment in the leg.
Feral: It is a term used to refer to an animal that has been domesticated, but has escaped and returned to being wild, while still living in its current environment. Cats, Goats, and pigs are examples of such animals.
Fetus: A fetus is a developing organism, which has moved beyond the embryonic stage, but is yet to be born.
Filly: A female horse that is four years or younger in age.
Filter Feeder: Organisms that feed by sieving water for food particles, with the help of special filtering structures in their mouths. Clams, sponges, krill, and baleen whales use this method.
Fitness: The measure of an individual's genetic contribution to the next generation's gene pool.
Fledge: It is that stage in a young bird's life, when the feathers and wing muscles are developed and the bird is capable of flight. Alternately, it is also used to describe the act of raising chicks to a fully grown state by the parents.
Fledgling: Is a young bird that has recently fledged, but is still being fed and cared for by the parents.
Flight Feathers: Describes the stiff, large feathers of the tail and wings of a bird that are essential for flight.
Foal: A male or female horse that is up to six months old.
Food Chain: The food chain is the transfer of life-giving energy from one organism to another, which is compatible to receive the same form of energy that was passed on, when the organism perished. Read more on the desert food chain.
Food Web: A food web comprises a set of interconnected food chains which exist within an ecosystem.
Founder Effect: In terms of describing the genetic outcome of a new population being established by a very small number of individuals, from a larger population. The founder effect refers to the loss of genetic variation.
Frugivorous: Fruit-eating living being. A frugivore is any organism whose preferred food type is fruits.
Functional Response: The relationship between prey and predator, or deviation in the rate of exploitation of prey by an individual predator due to change in the prey density.[Back]
Gamma Diversity: This term refers to the measure of biodiversity, which means the total species richness within an area.
Gaping: The open width of space, created by forcefully opening the jaws or mandibles of a vertebrate.
Gelding: A male horse that has been spayed.
Generalist: Any organism that can survive in a wide-ranging habitat.
Gharial: An Asian crocodile with a very narrow jaw.
Gill: The respiratory organ of any aquatic animal. Its basic function is to help the animal breathe the oxygen dissolved in water.
Gill Arches: Cartilaginous arches located on each side of the pharynx to provide support to the gills of aquatic as well amphibian animals.
Gill Slits: A narrow external opening connected with the pharynx, to allow passage of water, which helps in cleaning the gills.
Gizzard: A chamber found in the lower stomach of animals that facilitates food grinding.
Gonads: The testes or ovaries (sex glands) found in the animal reproductive organ.
Gorget: A small patch on the throat of an organism which is distinguished by its color, texture, and thickness quality.
Guano: Large deposits of substances composed chiefly of the feces of birds or bats.
Gular Fluttering: A cooling mechanism adopted by birds, in which they flap their flap membranes rapidly in the throat to increase evaporation.
Gular Pouch: A bare sac or pouch that can be expanded to accommodate a large prey, or for the show off during courtship display.
Habitat Compression: When local population is forced or restricted within a set boundary, to accommodate more species.
Habitat Expansion: Increase in the habitat (overall area) distribution of the species.
Habitat Patch: A location that encompasses a distinct habitat type.
Habitat Selection: Habitats chosen over other habitats to suit climatic and environmental conditions.
Hacking: Part of the wildlife conservation rehabilitation program, where the animals or birds released in the wild for the first time, are periodically provided with food until they become independent.
Hatchling: A young one that has just been hatched from an egg.
Heat Sensitive Pit: An organ located on each side of the head, below a line from the eye to the nostril of some snakes, especially the vipers. It helps the snake detect its prey.
Herbaceous: Stems and branches that are soft, and not hard and woody.
Herbivore: Grass or plant eating organisms are called herbivores.
Hermaphroditic: Organism that have, as well as are capable of reproducing using both male and female reproductive organs.
Hibernation: To withdraw in a state of seclusion in a dormant condition. Most animals like the bear, prefer the winters to go into hibernation.
Histology: The study of tissues of organisms. It includes its structure, arrangement, functions, make up, etc.
Holotype: A single specimen used as standard type to name, describe, and illustrate, and represent a set of species and subspecies.
Home Range: The habitat that an animal normally lives and uses for daily activities.
Homeostasis: The process of maintaining internal stability of the physiological system of animals, in course of varying external conditions.
Homeothermy: The capacity to maintain the condition of being warm-blooded under all climatic situations.
Humus: Fine organic substance, composed of partial or fully-decomposed animal or plant matter, and found in soil.
Hyoid Apparatus: A veterinary anatomy term for the upper throat bones of the tongue and connective tissues.
Hypostracum: The shell located below all other shell layers in some mollusks.
Ichthyology: A branch of zoology dedicated to the systematic study of fish.
Imago: Sexually mature adult stage in the life of certain insects.
Immature: A young animal or bird, capable of feeding itself, but has yet not reached the stage of sexual maturity.
Imprinting: It is a process of phase sensitive learning, where the young animals follow the first moving thing they see.
Incubation Patch: The featherless patch developed on the abdomen of certain brooding birds, that becomes thick due to high levels of vascularity. This patch comes under direct contact with the eggs during the incubation period.
Insectivore: An organism that feeds chiefly on insects.
Interstitial Skin: The skin found between the scales of a snake.
Introduced Species: Organism that would not normally occur but have been introduced in the habitat.
Invertebrate: Pertaining to organisms without a backbone.
Isolating Mechanism: Prevention of breeding between species due to behavior, morphology, genetics, or a geographical barrier.
Juvenal: Refers to the first covering of feathers on a bird, after it loses its down (undersurface) feathers.
Juvenile: This term refers to a young bird in the stage when it has fledged, or young ones of the animals that have not yet reached its adult form, size, and sexual maturity.
Keratin: A hard insoluble protein substance found in hair, nails of mammals, scales of reptiles and bird feathers. This substance is responsible for the structure of hair, nails, scales, etc.
Kleptoparasitism: A parasitic characteristic of opportunistically stealing food and/or nests from other organisms.
Labial: Labial refers to the lips.
Lanceolate: An elongated shape that is slender and tapers towards the apex or base.
Larva: A premature form of animal or insect awaiting transformation to reach adulthood.
Last Common Ancestor: This term refers to the most recent known and shared common ancestor between two species, as well as individuals.
Lateral: Refers to the side location or view.
Lek: The courtship display for mating of certain animals, where males gather around the females for being selected for copulation.
Life Cycle: Phases of life that animals go through starting from birth, to sexual maturity, till death.
Lift: The airfoil (see airfoil) that controls the movement of the birds when in flight, as well as the force with which the birds fly is termed as lift.
Live Bearing: Animals that bear live young ones, rather than laying eggs are called live bearing.
Loafing Platform: A nest like structure built by few birds that can float on water. These birds keep their young ones in this platform to keep them out of water and afloat.
Lores: The space between the eye and the bill of a bird, or the eyes and tip of the mouth of any animal.
Lung: An internal sac-like chamber that forms the respiratory organ in animals.
Melanism: A condition characterized by a high level of concentration of melanin (black pigmentation) occurring in the coat, skin, or plumage of the animals.
Mendelian Trait: Transmission of hereditary traits from parent organisms to their offspring, the trait mainly emphasizes on a single locus.
Mammalia: Mammalia is a group of animals known as the vertebrates (have backbones) and belong to the class Mammalia.
Mandible: The lower jaw of a vertebrate animal, or the upper or lower part of the beak (bill) in birds.
Mantle: Single or paired set of feathers located on the mid-back of a bird, or an outgrowth that lines the inner surface of the valves of the shell.
Mare: Mare is a female horse that has attained the age of more than four years.
Maxilla: A paired appendage usually located behind the mandibles of arthropods.
Medusa: The sexual stage in the life cycle of a coelenterate, such as a jellyfish or a hydra, in which it is free-swimming.
Meiosis: It is the process of nuclear division in a cell, in which the total number of chromosomes is reduced to half. Meiosis results in the formation of gametes in animals and spores in other organisms. Before the process begins, the DNA in the original cell are replicated during a phase called S-phase and this is similar to that in mitosis. Once the replication is completed, two cell divisions separate the replicated chromosomes into four haploid gametes or spores.
Metamorphosis: It is the process of marked change in the appearance and habits of some animals, as a part of their normal development. Metamorphosis of a caterpillar into a butterfly is one such example.
Migration: The annual movement pattern of animals and birds between their breeding grounds and hibernating sites.
Migratory Overshooting: The phenomenon of traveling beyond the normal distance in migratory birds as well as animals, while being on correct migration travel route.
Mirror-Image Orientation: During migration, birds tend to reverse the orientation of their migratory route in opposite (mirror like image) directions.
Mobbing: An aggressive stand taken by some birds to ward off an intruder or predator from the area.
Molt Migration: Molt migration involves movement of birds from their breeding ground to a temporary location where they shed their feathers, plumage, skin, etc.
Molt: Molt is a process where birds and animals shed their hair, plumage, feathers, skin, horns, etc. to facilitate the growth of new ones.
Morphology: The study of form and structure of organisms.
Mouthparts: An appendage found close to the mouth of some animals, birds, and insects, which they use for all eating functions.
Muscle: Tissues that facilitate movement in animals.
Mysticetes: Whales of the suborder Mysticeti, like Right whales, finback, gray whale, humpback whales, rorquals, etc.
Naricorns: The raised, tough, horny nostrils found atop the bird bill.
Nectivorous: Animals, birds, or insects that rely on nectar as a source of food.
Nematocyst: This refers to tiny hairlike structures in coelenterates which is used by them to eject stingers.
Neonate: The phenomenon of producing live young ones instead of laying eggs.
Nephridium: A tube like excretory organ of many invertebrates such as mollusks and earthworms.
Nest Parasitism: The process of laying eggs in the nest of other or own species (not making one).
Nidicolous: The time spent in the nest after its hatched.
Nidifugous: The phenomenon of leaving the nest within a few days of hatching.
Obligate: Is an adjective that means "necessary" when used in biology. Also, exhibited by all members of a species without exception.
Odontocetes: Used while referring to any whale of the suborder Odontoceti, such as killer whales, dolphins, and sperm whales. They are characterized by a single blowhole, an asymmetrical skull and rows of teeth. They feed primarily on squid, fish, and crustaceans.
Oscines: Members of the suborder Oscines, of the order Passeriformes. They comprise songbirds that have highly developed vocal organs.
Osteichthyes: Are a taxonomic group of fish that includes the lobe-finned fish (Sarcopterygii) and ray-finned fish (Actinopterygii). They are also referred to as bony fish.
Ostracum: The calcified portion of an invertebrate's shell. While the organism is living, the ostracum is covered by layers of protein forming a periostracum.
Partial Molt: Partial molt is a process where some of the bird's feathers get replaced.
Passerine: Pertaining to the order Passeriformes (type of a bird).
Patagium: A thin membrane that extends between the body and the limb to form wings. It is basically the extensible fold of skin found in certain insects, reptiles, and birds.
Peep: A generic name for several sandpiper species.
Pelagic: Organism that live and thrive in open oceans or seas rather than waters adjacent to the land.
Pellet: A mass of regurgitate indigestible matter like fur, feathers, and bones of certain predatory birds like the hawk, owl, etc.
Pentaradial Symmetry: The balanced distribution of duplicate body parts or shapes (sensory and feeding structures) in a five fold circular pattern, i.e body parts arranged in fives or multiples of 5, in a symmetry in organisms.
Periostracum: The external, outermost covering of the shell of some mollusks. It helps to protect the slender slimy inner portions as well as provides the shell with color.
Pineal Eye: A developed third eye in certain cold-blooded vertebrates which helps to regulate body temperature and register light intensity.
Plankton: Microscopic organisms like algae and protozoa that drift on the oceans' currents.
Plastron: The ventral surface of the shell of a tortoise or turtle.
Predator: Organism that feeds off or preys on other organisms for survival.
Preen Gland: It refers to the gland found on the back, at the base of the tail in most birds. This gland secretes oil that the birds use for preening which is part of its feather care activities.
Proboscis: An elongated mouth organ which is an important feeding appendage in organisms.
Pulmonate: Land snails and other air breathers belonging to Pulmonata Subclass and Sorbeconcha Clade.
Radiation: Evolution of multiple species from a single ancestry, but these species have morphological differences, however, they coexist in the same habitat or spread to different habitats or they have a change of ecological role.
Radula: A rough and raspy tongue normally seen in mollusks, used to grate food.
Range: A particular geographical area in which particular species of organisms are found.
Rare: A species of an organism found in very small numbers and hence, visible with a lot of effort only for a short duration.
Rattle: Shed skin, which is often seen on tail of a rattlesnake, used to make a rattling sound in order to deter predators.
Rectrices: The stiff and main feather of a bird that is used to navigate, when the bird is in flight.
Remiges: Flight feather of a bird used to control direction during flying. Their function is similar to that of the rectrices to a certain extent.
Reptilia: Reptiles or vertebrates, who possess a dry scaly skin and reproduce amniotic eggs. Snakes, lizards, and alligators belong to this category.
Resident: A non-migratory species of birds, which stays in a given geographical area throughout its life.
Reticulated: Species whose veins or nerves are like threads of a net, arranged in a network.
Reverse Migration: Phenomenon wherein the migrating organism migrates in the opposite direction, normal to other migrating species.
Rictal Bristles: A stiff bristle like feather, which grows at the base of a bird's bill.
River Dolphins: A species of dolphins, which dwell in major rivers like the Amazon in Brazil, Yangste in China, and the Ganges in India.
Rostral Scale: Is a scale present on the tip of the upper jaw of a snout, usually seen in snakes.
Rostrum: An anatomical structure, present in a species in the form of a snout, which projects out from the head of the animal.
Rounded: Smallest size elliptical, spherical egg.
Salamander: Any tailed amphibian, that has soft and scaleless skin with a long body, tail, and short limbs.
Saw-Scaling: Action of a snake curving its body in concentric curves and rasping its keeled scales together to make a sawing sound as a warning.
Scale: A thin plate that forms the covering of certain animals. This covering can either be hard or soft depending upon the morphology of the organism.
Scape: A tiny stem like first segment in an insect's antennae, as the shaft of a feather.
Scrape Nest: Unlike normal nest, a shallow depression is made by some ground birds as a nest. This nest has no soft lining.
Scute: A large well-defined dermal bony or horny plate found on many reptiles.
Secondary: It refers to the set of flight feathers on the second segment of a bird's wing.
Sedentary: Organism that are nonmigratory in nature, which means they move about little or not at all from their habitats.
Semi-Precocial: This term refers to hatchlings that are capable of leaving the nest but are dependent on their parents for their feed.
Semiplumes: Semiplumes are a type of feathers that are found under the contour feather on a bird's body. They are responsible for providing insulation as well as some flexibility to the bird.
Shaft: The main stiff stem or midrib of a bird's feather.
Shell: A hard outer covering of an organism made up of carapace and plastron.
Shorebirds: Birds that prefer the coastal area as their habitat.
Songbird: A generic name given to the members of the order Passeriformes.
Spy Hopping: A vertical rise out of the water or tall grasses performed by certain cetaceans or land mammals respectively.
Stallion: A male horse which is more than four years old.
Stoop: To swoop down while in flight for catching a prey.
Strandings: Aquatic mammals that get stranded on the beaches or shores.
Stary: An individual animal that has been left alone or has parted ways with others of its flock during movement or migration.
Subelliptical: An egg that is elongated and tapered towards its rounded ends.
Supplemental Plumage: A third set of feathers found in birds that have three different plumages in their annual cycle of molts. See molts.
Tentacle: The slender, elongated, flexible, appendages found in animals, located near their mouth.
Taiga: Coniferous evergreen forests found in the south of the tundra and north temperate region, characterized by harsh winters.
Tail Slapping: The forceful slapping of tails on the surface of water by dolphins.
Tarsus: The bone, which contributes in making the ankle joint, located between the tibia, fibula and metatarsus in mammals.
Taxon: A word used to group or name species of living organisms.
Taxonomic Classification: The hierarchical system used for grouping and naming species of living organisms.
Taxonomy: A practice used to classify animals with evolutionary relationships, as basis of this classification.
Territory: The area of belonging, which is guarded by animals against intruders, especially belonging to the same species.
Thorax: The part of the body in mammals situated between the neck and the abdomen, just above the diaphragm. In case of insects the part situated between the head and the abdomen, excluding legs and wings.
Threatened Species: A species which has the possibility of becoming endangered in the near future.
Torsion: The asymmetrical positioning of the body achieved, due to twisting and repositioning, during development.
Trachea: The pipe serving as the principal passage for movement of air to and from the lungs, in humans and other vertebrates. It extends from the larynx to the bronchus.
Triangulation: The method used by animals to find out the distance between themselves and their prey using two or more fixed points. This technique is used especially by owls and harriers.
Tribe: A category in the classification of organisms between a genus, which contains one or more genera.
Tubenoses: Vernacular name for members belonging to Procellariiformes species.
Tuberculate: An organism or part of an organism which is covered in fleshy and raised protuberances, also called tubercules.
Turtle: A reptile belonging to the Testudines species, which include both terrestrial and aquatic animals. The trunk of these species is enclosed in a shell.
Tympanic Membrane: It is the membrane which picks up vibrations through a medium and transports them to the inner part of the ear. It is also called the eardrum.
Type Specimen: An organism which is used to represent a particular taxon. It becomes the standard for the original name and to describe the species.
Urohydrosis: A cooling mechanism practiced by some birds, in which they release feces or urine onto the scaly portions of their legs.
Uropygial Gland: This is the same as the Preen Gland. It is located at the tip of the tail of birds. It is known to secret oil.
Vagrant: An individual organism found outside the region that is known for that particular species.
Vane: This term refers to that portion of the feather which is made of flat parallel rows of barbs and is attached to the center stiff part of the feather.
Ventral Scale: Scales found on the underside of the snake's body.
Ventral: Refers to the stomach or belly.
Vestigal: The part of an animal that does not develop during evolution. It is underdeveloped and serves no important function.
Viscers: The organs located in the cavities of the organism body.
Vocal Sac: The flexible membrane of the skin found in male frogs and toads that inflates and acts as amplifier for their mating calls.
Warning Coloration: Distinctive bold color patterns found on certain organisms, that work as a warning to predators.
WatchList: A cooperative project of the National Audubon Society and Partners in Flight that keeps track of declining species, that are not yet threatened or endangered.
Water Vascular System: A system of fluid filled tubes and ducts, that connect with the tube feet of most marine invertebrates. They help in functions such as respiration, feeding, etc.
Wattle: A soft fleshy brightly colored appendage that hangs down from the throat or chin of certain birds.
Weaning: The period where the mother ceases to feed the young ones. This only refers to mammals.
Weanling: A male or female horse that is between the age of six months to one year.
Wing-Bar: A line of color, usually contrasting across the middle, tip, or base of a bird's wing, which has been made by the wing coverts.
Wing-Flicking: Rapid movement made by the bird's wings when it is not in flight and is at rest.
Xenophobic Alliance: A union of individual chimpanzees in a group, which challenges intruders who threaten their territory and boundaries.
Xeric: A habitat which has an extremely dry environment. It also refers to animals who have adapted themselves to such an environment.
Xerophyte: A plant which has adapted itself to a dry environment and is able to conserve water.
Xylophagous: Organisms that feed entirely or primarily on wood.


Yearling: This term is used to describe both a male and female horse between the age of one and two years.
Yolk: Food that is stored in an egg.


Zooid: An organism which is capable of existing separately. A number of zooid together function like a single animal, example coral.
Zooplankton: A collection of various species of plankton.
Zooxanthellae: Unicellular, yellow-brown in color algae, which live in the gastrodermis of corals.
Zygodactyly: This is the arrangement of toes formed in birds, in which the outer front toe faces the back, resulting in two toes facing forward and two backward.
Glossary of Microbiology Terms and Definitions
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
Abiotic Factors: Non-living factors that can affect life, like soil, nutrients, climate, wind etc.
Absorption Field: An organized system of meticulously constructed narrow trenches, which are partially filled with washed gravel or crushed stone, into which a pipe is placed. Discharges from septic tanks are passed through these trenches.
Acetogenic Bacterium: An aerobic, gram negative bacteria, that is rod-shaped, which is made of non-sporogenous organisms that produce acetic acid as a waste product.
Acetylene Block Assay: Determines the release of nitrous oxide gas from acetylene treated soil, which is used to estimate denitrification.
Acetylene Reduction Assay: This is used to estimate nitrogenase activity by measuring the rate of reduction of ethylene to acetylene.
Acid Soil: Soil which has a pH value lesser than 6.6.
Acidophile: An organism that grows well in an acidic medium (up to a pH of 1).
Actinomycete: These are gram positive, nonmotile, nonsporing, noncapsulated filaments that break into bacillary and coccoid elements. They resemble fungi, and most are free living, particularly in soil.
Actinorhizae: The association present between actinomycetes and roots of plants.
Activated Sludge: Sludge particles which are produced in raw or settled wastewater, by the growth of organisms in aeration tanks. This is all done in the presence of dissolved oxygen. This sludge contains living organisms that can feed on incoming wastewater.
Activation Energy: The amount of energy required to bring all molecules in one mole of a substance, to their reactive state, at a given temperature.
Active Carrier: An infected person who has visible clinical symptoms of a disease, and is capable of transmitting the disease to other individuals.
Active Site: The location on the surface of the enzyme where the substrate binds.
Adjuvant: The material added to an antigen to increase its immunogenicity, for example, alum.
Aerobic: This includes organisms that require molecular oxygen to survive (aerobic organisms), an environment that has molecular oxygen, and processes that happen only in the presence of oxygen (aerobic respiration).
Aerobic Anoxygenic Photosynthesis: Photosynthetic process which takes place under aerobic conditions. However, this process does not result in the formation of oxygen.
Aerotolerant Anaerobes: Microbes that can survive in both, aerobic and anaerobic conditions, because they obtain their energy by fermentation.
Aflatoxin: A toxin produced by Aspergillus flavus and Aspergillus parasiticus, which contaminate groundnut seedlings. This is said to be a cause of hepatic carcinoma.
Agar: A dried hydrophilic, colloidal substance extracted from red algae species, used as a solid culture media for bacteria and other micro-organisms. Also used as a bulk laxative, in making emulsions and as a supporting medium for immunodiffusion and immunoelectrophoresis.
Agarose: Agarose is obtained from seaweed and is used as a resolving medium in electrophoresis. It consists of non-sulfated linear polymer, which contains D-galactose and 3:6-anhydro-L-galactose alternately.
Agglutinates: The visible clumps that are formed as a result of an agglutination reaction.
Agglutination Reaction: The process of clumping together, in suspension of antigen bearing cells, micro-organisms, or particles in the presence of specific antibodies called agglutinins. This leads to the formation of an insoluble immune complex.
Airborne Transmission: A type of transmission, wherein the organism is suspended in or spreads its infection by air.
Akinete: A resting non-motile, dormant, thick-walled spore state of cyanobacteria and algae.
Alcoholic Fermentation: A fermentation process that produces alcohol (ethanol) and carbon dioxide from sugars.
Alga: Phototrophic eukaryotic micro-organisms, that may be unicellular or multicellular. These include phaeophyta: brown algae, spirogyra, and red algae.
Aliphatic: Pertaining to any member of one of the two major groups of organic compounds, with the main carbon structure as a straight chain.
Alkaline Soil: Soil having pH greater than 7.3.
Alkalophile: Organisms that have an affinity for alkaline media, thus, growing best in such conditions.
Allochthonous Flora: Organisms that are not originally found in soil, but reach there via precipitation, sewage, diseased tissue, and other such means. They do not contribute much ecologically.
Allosteric Site: A non-active site on the enzyme body, where a non-substrate compound binds. This may result in conformational changes at the active site.
Allotype: Any of various allelic variants of a protein, characterized by antigenic differences.
Alpha Hemolysis: A partial clearing zone, greenish in color, around a bacterial colony that grows on blood agar.
Alpha-proteobacteria: One of the five sub-groups of proteobacteria, each with distinctive 16S rRNA sequences. Mostly contains oligotrophic proteobacteria, many of which have distinctive morphological features.
Alternative Complement Pathway: A pathway of complement activation, including the C3-C9 components of the classical pathway. It is independent of the antibody activity.
Alveolar Macrophage: A highly active and aggressive phagocytic macrophage, located on the epithelial lining of the lung alveoli, which ingests and destroys any inhaled particles and micro-organisms.
Amensalism (Antagonism): A type of symbiosis, wherein one population is adversely affected, while the other is unaffected.
Ames Test: A test that uses a special strain of salmonella to test chemicals for mutagenicity and carcinogenicity.
Amino Acid Activation: The first stage of synthesis of proteins, where the amino acid is attached to transfer RNA.
Amino Group: The monovalent radical NH2, attached to a carbon skeleton, as seen in amines and amino acids.
Aminoacyl or Acceptor Site (A site): The site on the ribosome that contains an aminoacyl-tRNA at the beginning of the elongation cycle during protein synthesis.
Ammonia Oxidation: A test which is conducted during manufacturing process, to evaluate ammonia oxidation rate for nitrifiers.
Ammonification: Liberation of ammonia by micro-organisms acting on organic nitrogenous compounds.
Amoeba: A minute protozoan, occurring as a single cell with a nucleus, that changes shape by extruding its cytoplasm, leading to the formation of pseudopodia, by means of which it absorbs food and moves.
Amoeboid Movement: Movement by means of extrusions of the cytoplasm, leading to formation of foot-like processes called pseudopodia.
Amphibolic Pathways: Metabolic pathways that function both anabolically, as well as catabolically.
Amphitrichous: A cell which has a single flagellum at each end.
Amphotericin B: An antibiotic derived from streptomyces nodosus which is effective against many species of fungi and certain species of leishmania.
Anaerobic: Refers to organisms that survive in the absence of oxygen (anearobic organisms), the absence of molecular oxygen, processes occurring in the absence of oxygen like anearobic respiration.
Anamorph: A stage of fungal reproduction, where cells are asexually formed by the process of mitosis.
Anaplerotic Reactions: Reactions that help replenish intermediates in the tricarboxylic acid cycle when their reserves are depleted.
Anergy: Decreased responsiveness to antigens, to the extent that there is an inability to react to substances that are expected to be antigenic.
Anion Exchange Capacity: Total exchangeable anions that a soil can adsorb. The unit used to express the amount is in centimoles of negative charge per kilogram of soil.
Annotation: The process of determining the exact location of specific genes in a genome map.
Anoxic: A condition or state which is devoid of oxygen.
Anoxygenic Photosynthesis: A type of photosynthesis where oxygen is not produced. This phenomenon is seen in green and purple bacteria.
Antagonist: A drug that binds to a hormone, neurotransmitter, or another drug, thus, blocking the action of the other substance.
Antheridium: The male gametangium found in phylum Oomycota (kingdom Stramenopila) and phylum Ascomyta (kingdom Fungi).
Anthrax: An often fatal and infectious disease, caused by ingestion or inhalation of spores of Bacillus anthracis, which are normally found in soil. It is acquired by humans through contaminated wool or animal products or by inhalation of airborne spores.
Anthropogenic: Something that is derived from human activities.
Antibiosis: Lysis of an organism brought about by metabolic products of the antagonist. This can be caused by enzymes, lytic agents, or other toxic compounds.
Antibiotic: A chemical substance produced by a microorganism, which has the capacity to inhibit the growth of, or kill other micro-organisms.
Antibody: An immunoglobulin molecule that reacts with a specific antigen that induced its synthesis and with molecules that have a similar structure.
Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC): A type of reaction wherein, cells with Fc receptors that recognize the Fc region of the bound antibody and kill the antibody-coated target cells.
Anticodon Triplet: A triplet of nucleotides in transfer RNA that is complementary to the codon in messenger RNA.
Antigen: Any substance capable of instigating the immune system into action, inciting a specific immune response and reacting with the products of that response.
Antimetabolite: A substance that interferes with a specific metabolic pathway, by inhibiting a key enzyme, due to its resemblance with the normal enzyme substrate.
Antimicrobial Agent: An agent that has the capacity to kill or inhibit the growth of micro-organisms.
Antisense RNA: One of the strands of a double-stranded molecule, which does not directly encode the product, but is complementary to it, thus, inhibiting its activity.
Antiseptic: A substance that inhibits the growth and development of micro-organisms, but does not necessarily kill them.
Aplanospore: A spore that is formed during asexual reproduction, which is non-flagellated and non-motile.
Apoenzyme: A protein part of an enzyme that is separable from the prosthetic group (the coenzyme).
Apoptosis: A pattern of cell death which is often called 'programmed death' or 'suicide of cells', wherein the cell breaks up into fragments, which are membrane bound. These fragments are then eliminated by phagocytosis. This is a protective mechanism, by which the cell sacrifices itself to prevent spread of infection to other cells.
Aporepressor: A product of regulator genes, that combines with the corepressor to form the complete repressor.
Arbuscule: Special structure formed in the root cortical cells by arbuscular mycorrhizal fungi. The structure formed resembles a tree.
Artificially Acquired Passive Immunity: A type of temporary immunity that results from the introduction of antibodies produced by another organism or by in vitro methods, into the body.
Aseptic Technique: Procedures that are performed under strict sterile conditions. These procedures maybe laboratory procedures such as microbiological cultures.
Assimilatory Nitrate Reduction: Reduction of nitrate to compounds like ammonium, for the synthesis of amino acids and proteins.
Associative Dinitrogen Fixation: An enhanced rate of dinitrogen fixation, brought about by a close relationship between free-living diazotrophic organisms and a higher plant.
Associative Symbiosis: Interaction between two dissimilar organisms or biological systems, which is normally mutually beneficial.
Autogenous Infection: An infection which occurs due to the microbiota of the patient himself.
Autoimmune Disease: A disease where the target is the body's own tissues, that is, there is attacking of self-antigens.
Autoimmunity: A condition where a specific humoral or cell mediated immune response is initiated against the constituents of the body's own tissues. It normally leads to hypersensitivity reactions, and if it persists, can even escalate to an autoimmune disease.
Autolysins: A lysin that originates in an organism, which is capable of destroying its own cells and tissues.
Autoradiography: Making a radiograph of an object or tissue by recording the radiation emitted by it on a photographic plate. The radiation is emitted by radioactive material within the object or tissue.
Autotrophic Nitrification: The combined nitrification action of two autotrophic organisms, one converting ammonium to nitrite and the other oxidizing nitrite to nitrate.
Auxotroph: A mutated type of organism that requires specific organic growth factors, in addition to the carbon source present in a minimal medium.
Axenic: Pure cultures of micro-organisms, that is, which are not contaminated by any foreign organisms.
Axial Filament: Found in spirochetes, it is the organ of motility.
B-cell (B lymphocyte): Bursa-dependent lymphocytes which are precursors of antibody-producing cells (plasma cells) and the cells primarily responsible for humoral immunity.
B-cell Antigen Receptor (BCR): The membrane which is formed of membrane immunoglobulin or surface immunoglobulin, which allows a B-cell to detect, when a specific antigen is present in the body, and triggers B-cell activation.
Bacteria: A domain that contains prokaryotic cells that are not multicellular.
Bacteremia: Presence of bacteria in the blood.
Bacterial Artificial Chromosome: A cloning vector that is derived from E. coli, which is used to clone foreign DNA fragments in E. coli.
Bacterial Photosynthesis: A mode of metabolism, which is light-dependent and where carbon dioxide is reduced to glucose, which is used for energy production and biosynthesis. It is an anaerobic reaction.
Bactericide: A substance that kills bacteria.
Bacteriochlorophyll: A light absorbing pigment found in phototrophic bacteria, like green sulfur and purple sulfur bacteria.
Bacteriocin: Substances that are produced by bacteria which kill other strains of bacteria by inducing a metabolic block.
Bacteriorhodopsin: A protein involved in light mediated ATP synthesis, which contains retinal. It is one of the main characteristics of archaebacteria.
Bacteriostatic: An agent that inhibits the growth or multiplication of bacteria, but does not kill them.
Bacteroid: A genus of bacteroides, these are gram negative, rod-shaped, anaerobic bacteria which are normal inhabitants of the oral, respiratory, urogenital, and intestinal cavities of animals and humans.
Baeocytes: Reproductive cells formed by cyanobacteria through multiple fission. They are small and spherical in shape.
Balanced Growth: Microbial growth where all cellular constituents are synthesized at constant rates, in relation to each other.
Barophile: An organism that thrives in conditions of high hydrostatic pressure.
Barotolerant: An organism that can tolerate high hydrostatic pressure, although it will grow better under normal pressure.
Basal Body: A cylindrical structure that attaches the flagella to the cell body at the base of prokaryotic or eukaryotic organisms.
Basal Medium: A basal medium allows the growth of many types of micro-organisms which do not require special nutrient supplements.
Base Composition: The proportion of total bases consisting of 'guanine plus cytosine' or 'thymine plus adenine' base pairs.
Basidioma: Fruiting body that produces the basidia.
Basidiospore: The sexual spore of the Basidiomycotina, which is formed on the basidium.
Batch Culture: A culture of micro-organisms which is obtained by inoculating a dish containing a single batch of medium.
Batch Process: A treatment procedure wherein, a tank or reactor is filled, the solution is treated, and the tank is emptied. Batch processes are mostly used to cleanse, stabilize, or condition chemical solutions for use in industries.
Benthic Zone: The ecological region at the lowest level of a water body, including the sediment surface and some sub-surface layers.
Beta Hemolysis: A clear zone seen around a bacterial colony growing on blood agar.
Bio-Tower: A tower filled with a media similar to a rachet or plastic rings, where air and water are forced up the tower by a counterflow movement. It is an attached culture system.
Bioaccumulation: Intracellular accumulation of chemical substances in living tissue.
Bioaugmentation: Addition to the micro-organism's environment that can metabolize and grow on specific organic compounds.
Bioavailability: The extent to which a drug or other substance becomes available to the target tissue after administration.
Biochemical Oxygen Demand: The amount of dissolved oxygen consumed in five days by biological processes breaking down organic matter. It is a test that measures the oxygen consumed (in mg/L) over five days at 20 ºC.
Biodegradable: The property by which a substance is capable of being degraded by biological processes, like bacterial or enzymatic action.
Biodegradation: The process of breakdown of substances by chemical reactions, thus rendering these substances less harmful to the environment.
Bioinsecticide: A pathogen (either bacteria, virus or fungi) used to kill or inhibit the activity of unwanted insect pests.
Bioluminescence: The production of light in living organisms by the enzyme luciferase.
Biomagnification: Increase in the concentration of a chemical substance, as its position progresses in the food chain.
Biostimulation: A process which helps catalyze the activity of micro-organisms involved in biodegradation.
Biosynthesis: Production of cellular constituents from simpler compounds.
Biotransformation: The chemical alterations of a drug, occurring in the body, due to enzymatic activity.
Biotrophic: Close associations seen between two different organisms, that work mutually to benefit each other.
Bioventing: A procedure where the subsurface is aerated to enhance biological activity of naturally occurring micro-organisms in the soil.
Blastomycosis: An infection caused due to Blastomyces dermatitidis, it predominantly affects skin, lungs, and bones.
Burst size: The number of phages ejected by a host cell over the course of its lytic life cycle.
Butanediol Fermentation: A kind of fermentation found in Enterobacteriaceae family, where 2,3-Butanediol is a major product.
Capsid: The outer proteinaceous coat of a virus.
Capsomere: A protein sub-unit of the capsid of a virus.
Carbon Cycle: The cycle where carbon-dioxide is taken in and converted to organic compounds by photosynthesis or chemosynthesis, after which it is partially incorporated into sediments, and then returned to the atmosphere by respiration or combustion. Read more on carbon cycle steps.
Carbon Fixation: Conversion of carbon-dioxide and other single carbon compounds to organic compounds such as carbohydrates.
Carbon-Nitrogen (C/N) ratio: Ratio of carbon mass to nitrogen mass in soil or other organic material.
Carboxyl Group: The -COOH group found attached to the main carbon skeleton in certain compounds, like carboxylic acids and fatty acids.
Carboxysomes: Polyhedral cell inclusions which form the key enzyme of the Calvin cycle.
Carcinogen: An often mutated substance which is implicated as one of the causing agents of cancer.
Catabolism: A process by which complex substances are broken down into simpler compounds, often accompanied by the release of energy.
Catabolite Repression: Transcription-level inhibition of inducible enzymes by glucose, or other easily available carbon sources.
Cell-mediated Immunity: Immunity resulting from destruction of foreign organisms and infected cells by the active action of T-lymphocytes on them. It can be acquired by individuals by the transfer of cells.
Cellular Slime Molds: Slime molds with a vegetative phase containing amoeboid cells that come together to form a pseudoplasmodium.
Cellulitis: A diffused inflammation of the soft or connective tissue, in which a thin and watery exudate spreads through tissue spaces, often leading to ulceration and abscess formation.
Cephalosporin: A group of broad-spectrum, penicillinase-resistant antibiotics, derived from Cephalosporium.
Chaperonin: Heat shock proteins that oversee correct folding and assembly of polypeptides in bacteria, plasmids, eukaryotic cytosol, and mitochondria.
Chelate: A chemical compound in which a metallic ion is firmly bound into a ring within the chelating molecule. Chelates are used in metal poisoning.
Chemoautotroph: Organisms that obtain their energy from the oxidation of inorganic chemicals and other carbon compounds.
Chemoheterotroph: Organisms that obtain energy and carbon from the oxidation of organic compounds.
Chemolithotroph: Living organisms that obtain their energy from oxidation of inorganic compounds, which act as electron donors.
Chemoorganotroph: Organisms that obtain energy and electrons from the oxidation of organic compounds.
Chemostat: A continuously used culture device, controlled by limited amounts of nutrients and dilution rates.
Chemotaxis: Movement of a motile organism under the influence of a chemical. It maybe attracted towards the chemical or maybe repulsed by it.
Chemotrophs: Organisms that obtain their energy by the oxidation of chemical compounds are chemotrophs.
Chlamydospore: A thick walled intercalary or terminal asexual spore which is not shed. It is formed by rounding up of a cell.
Chronic Carrier: An individual carrying a pathogen over an extended period of time.
Chytrid: A fungus belonging to the genus Chytridomycota. It is spherical in shape and has rhizoids, which are short, thin filamentous branches, that resemble fine roots.
Cilia: Minute hairlike extensions present on a cell surface, which move in a rhythmic manner.
Ciliate: A protozoan that moves with the help of cilia.
Clarification: The process of purification of water, where suspended material in the water is removed. It can be done by using sedimentation, filtration, or by the use of adsorbing chemicals like alum.
Clone: Cells which have descended from a single parent cell. Organisms having identical copies of DNA structure, which is obtained by replication.
Colonization: Establishment of an entire community of micro-organisms at a designated site.
Colorless Sulfur Bacteria: A group of non-photosynthetic bacteria that oxidize sulfur compounds, thus deriving their energy by this process.
Combinatorial Biology: The process of transfer of genetic material from one microorganism to another. Mostly used to synthesize products such as antibiotics. It is also used in genetic engineering.
Cometabolism: Transformation of a substrate by a microorganism without deriving energy or nutrients from the substrate.
Competent: The ability to take up DNA.
Complementary DNA: A DNA copy of any RNA molecule, like mRNA or tRNA. To find out the exact difference between DNA and RNA, click here.
Complex Viruses: Viruses with capsids that are neither icosahedral nor helical. They have a complicated symmetry.
Conditional Mutations: Mutations occurring only under certain specific conditions.
Conidiospore: A thin-walled, asexual spore seen on hyphae which is not contained in sporangium.
Conjugants: Mating partners that participate in conjugation, which is a type of sexual reproduction, seen in protozoans.
Conjugative Plasmid: A self transmissible plasmid, or a plasmid that can encode all functions required to bring about its conjugation.
Consortium: Two or more members working together, where each organism benefits from the other, thus often performing functions that may not be possible to carry out individually.
Constitutive Enzyme: Enzymes synthesized in the cell, irrespective of the environmental conditions surrounding the cell.
Cosmid: A plasmid vector which can be packed in a phage capsid. It is useful for cloning large fragments of DNA.
Cyanobacterium: A photosynthetic, nitrogen fixing bacteria which includes the blue-green bacteria.
Cyst: Resting stage of certain bacteria and protozoans, wherein the entire cell is surrounded by a protective layer.
Cytokine: Non-antibody proteins released by a cell when it comes in contact with specific antigens.
Cytoplasm: The protoplasm of a cell, exclusive of the nucleus. Read more on the structure and functions of cytoplasm.
Cytoplasmic Membrane: A selectively permeable membrane which is present around the cytoplasm of the cell.
Decomposition: Chemical breakdown of a compound into smaller and simpler compounds by micro-organisms.
Defined Medium: A medium whose quantitative and chemical composition is exactly known.
Degradation: Process by which a compound is transformed into simpler compounds.
Denaturation: Process by which double stranded DNA unwinds into two single strands.
Denitrification: Reduction of nitrate or nitrite into simpler nitrogenous compounds like molecular nitrogen or nitrogen oxides.
Derepressible Enzyme: Enzyme produced in the absence of a specific inhibitory compound.
Dew point: The temperature to which air must be cooled to bring about the condensation of water vapor.
Diazotroph: Organism capable of using dinitrogen as its sole nitrogen source.
Differential Medium: A medium with certain indicators, which helps distinguish between different chemical reactions during growth of organisms on it.
Diffused Air Aeration: A diffused air activated sludge plant takes air, compresses it, and discharges it with force, below the surface of water.
Dikaryon: When two nuclei are present in the same hyphal compartment (they may be homokaryon or heterokaryon), it is known as dikaryon.
Dilution Plate Count Method: A method of estimating the number of viable micro-organisms in a sample.
Dinitrogen Fixation: Conversion of molecular dinitrogen into ammonia and other organic combinations useful in other biological processes.
Direct Count: Using direct microscopic examination to determine the number of micro-organisms present in a given mass of soil.
Disinfectant: An agent that kills micro-organisms.
DNA Fingerprinting: Techniques by which possible differences between different DNA samples can be assessed.
Dolipore Septum: Specialized cross-wall that separates hypha of fungi belonging to the genus Basidiomycota.
Domain: The highest level of biological classification which goes beyond kingdoms. The three domains of biological organisms are Bacteria, Eukarya, and Archaea.
Doubling Time: The time needed for a certain population to double in number.
Endoenzyme: Enzyme that acts along the internal portion of a polymer.
Endonuclease: The endoenzyme responsible for breaking the phosphodiester bonds in a nucleic acid molecule.
Endophyte: An organism, which may be parasitic or symbiotic, with a plant that is grown within.
Endospore: A cell which is formed by certain gram-positive bacteria in unfavorable conditions. An endospore is extremely resistant to heat and other harmful agents.
Enhanced Rhizosphere Degradation: Enhanced activity of micro-organisms involved with biodegradation of contaminants near plant roots which is brought about by compounds exuded by the plant roots.
Enrichment Culture: Technique wherein environmental conditions are altered to aid the growth of a specific organism or group of organisms.
Enteric Bacteria: These are bacteria present in the intestinal tract of humans and other animals. They may be physiologic or pathologic.
Episome: An extrachromosomal replicating genetic element found in certain bacteria.
Epitope: An antigenic determinant of known structure. It is the region of the antigen to which the variable region of the antibody binds.
Ericoid Mycorrhizae: The type of mycorrhizae found in Ericales plants. These hyphae are capable of penetrating cortical cells.
Estuaries: Water bodies located at river ends. They are subjected to tidal fluctuations.
Eubacteria: A genus of bacteria belonging to the family Propionibacteriaceae, found as saprophytes in soil and water.
Exoenzyme: An enzyme which acts outside the cell that secretes it.
Exons: The region of a split DNA that codes for RNA.
Extracellular: Outside the cell.
Exudate: A fluid high in protein and cellular debris which has escaped from blood vessels, usually as a result of inflammation.
Facultative Organism: An organism which is able to adjust to a particular circumstance or has the ability to take up different roles in a process.
Feedback Initiation: Inhibition by an end product of the biosynthetic pathway involved in its synthesis.
Fertilizer: Any organic or inorganic material added to the soil to enhance the growth of plants.
Field Capacity: Content of water remaining in the soil after being saturated with water.
Filamentous: In the form of very long rods, mostly seen in bacteria. Seen as branching strands in fungi.
Fimbria: Short filamentous structure present on a bacterial cell, involved with adhesion of the bacteria to other surfaces it comes in contact with.
Frustule: Siliceous wall and protoplasm seen in diatoms.
Fulvic Acid: The yellow organic material that remains behind after removal of humic acid by the process of acidification.
Fungistasis: Suppression of growth of new fungal cells, due to excessive competition for nutrients, or due to the presence of excessive inhibitory compounds in the soil.
Fungus: Eukaryotic heterotrophic organisms that live as saprophytes or parasites. This group includes mushrooms, yeast and molds. They have a rigid cell wall.
Fluorescent Antibody: This is a laboratory test that is done, wherein antibodies are tagged with fluorescent dye to detect the presence of micro-organisms.
Gas Vacuole: A sub-cellular organelle, found only in prokaryotes, which are gas-filled vesicles.
Gene Cloning: Isolation of a desired gene from an organism and its replication in large amounts. It is used extensively in DNA research.
Gene Probe: A strand of nucleic acid which can be labeled and hybridized to a complementary molecule from a mixture of other nucleic acids. It is helpful in DNA sequencing.
Generation Time: The time required for a population to double in number.
Genetic Code: The information on the DNA, which is required for the synthesis of proteins.
Glycosidase: The enzyme responsible for hydrolizing a glucosidic linkage between two sugar molecules.
Gram Stain: A differential stain that divides bacteria into two groups, as Gram positive and Gram negative, depending on the ability of the organism to retain crystal violet when decolorized with an organic solvent like ethanol.
Growth: An increase in the number of cells, the size, and constituents present in the cells.
Growth Factor: Organic compound essential for growth which is required in trace amounts, and which cannot be synthesized by the organism itself.
Growth Rate: The rate at which growth occurs.
Growth Rate Constant: Slope of log10 of the number of cells per unit volume plotted against time.
Growth Yield Coefficient: Quantity of carbon formed per unit of substrate carbon consumed.
Halophile: An organism that thrives, or at least which can survive in a saline environment.
Halotolerant: An organism that can survive in a saline environment, but does not require a saline environment for growth.
Hapten: A substance not inducing antibody formation, but which is able to combine with a specific antibody.
Heterokaryon: Hypha that contains at least two genetically dissimilar nuclei.
Heterolactic Fermentation: A kind of lactic acid fermentation, wherein various sugars are fermented into different products.
Heterothallic: Hyphae that are incompatible with each other, thus requiring another compatible hypha to mate with, to form a dikaryon or a diploid.
Heterotrophic Nitrification: The oxidation of ammonium to nitrite and nitrate by heterotrophic organisms.
Hexose Monophosphate Pathway: A metabolic pathway involving the oxidative decarboxylation of glucose:6:phosphate.
Holomictic: These are those lakes, wherein the water in them at some point of time will have a uniform temperature and density from top to bottom, thus allowing the lake waters to mix completely.
Holomorph: A fungus which consists of all sexual and asexual stages in its life cycle.
Homofermentation: A type of fermentation where there is only one type of end product generated.
Homokaryon: A fungal hypha containing nuclei which are genetically identical.
Homolactic Fermentation: A type of lactic acid fermentation, in which all sugars involved are converted into lactic acid.
Homothallic: Hyphae that are self-compatible, that is, sexual reproduction occurs in the same organism by meiosis and genetic recombination. Fusion of these hyphae lead to the formation of dikaryon or diploid.
Host: An organism that can harbor or nourish another organism.
Heterofermentation: Any fermentation where there is more than one main end product.
Humic Acid: Dark-colored organic material extracted from the soil by the use of reagents and which is precipitated by acid.
Humic Substances: High molecular weight substances formed by secondary synthesis reactions, for example, humic acid and fulvic acid.
Humification: The process of conversion of organic residues into humic substances by biochemical processes.
Hybridization: Natural or artificial construction of a duplex nucleic acid molecule by complementary base pairing between two nucleic acid strands derived from different sources.
Hydrocarbon: An organic compound containing carbon and hydrogen only.
Hydrogen Oxidizing Bacterium: These are bacteria that oxidize hydrogen for energy and synthesize carbohydrates, using carbon dioxide as their source of carbon in the absence of other organic compounds.
Hyperparasite: Parasite that feeds on another parasite.
Hyperthermophile: An organism that thrives in temperatures ranging around 80 ºCelsius or more.
Hypolimnion: This is the dense, bottom layer of water, that lies below the thermocline, in a thermally stratified lake.
Illuviation: Repositioning of soil removed from one horizon to another.
Immobilization: Conversion of an element from inorganic to organic form.
Immunity: The protection mechanism against infections caused by micro-organisms or toxins, that is inherent in the body.
Immunoblot: The technique for analyzing or identifying proteins via antigen-antibody specific reactions.
Immunofluoresence: The technique to determine the location of an antigen or antibody in a tissue section or smear by fluorescence.
Immunogen: A substance that has the capacity to bring about an immune response.
Immunoglobulin: A protein which has antibody activity.
In vivo: Inside the body.
Inducible Enzyme: An enzyme generated in response to an external factor.
Infection: Invasion and multiplication of micro-organisms in body tissues, leading to various diseases and disorders.
Infection Thread: The tube in root hair, through which rhizobia reach and infect roots.
Infrared (IR): The portion of the electromagnetic spectrum whose wavelength ranges from 0.75 microns to 1 millimeter.
Inoculate: To treat a medium with micro-organisms for the purpose of creating a favorable response.
Inoculum: The material used to introduce an organism into a certain medium for growth.
Insertion: A type of genetic mutation, wherein single or multiple nucleotides are added to DNA.
Insertion Sequence: The simplest possible type of transposable elements.
Integration: The process by which a DNA molecule becomes incorporated into another genome.
Interspecies Hydrogen Transfer: The process of hydrogen production and consumption reactions, occurring by the interaction of various micro-organisms.
Intracellular: Inside the cell.
Isoenzyme: When two different enzymes, which may be different in their composition, act as catalysts for the same reaction, or set of reactions.
Isolation: A procedure wherein a pure culture of an organism is obtained from a sample or an environment.
Isomorphous Substitution: The substitution of an atom by a similarly sized atom of lower valence, in a crystalline clay sheet.
Jaccard's Coefficient: An association coefficient of numerical taxonomy, which is the proportion of characters that match, excluding those that both organisms lack.
K- Strategy: Ecological strategy where organisms depend on adapting physiologically to the resources available in their immediate environment.
Koch's Postulates: Laws given by Robert Koch which prove that an organism is the causative agent of a disease.
Lag Phase: The time period when there is no increase in the number of micro-organisms, seen after inoculation of fresh growth medium.
Lamella: Seen in plants as the layers of protoplasmic membranes in chloroplast that contain photosynthetic pigments.
Leaching: Removal of metals from ores by the help of micro-organisms.
Lectins: Plant proteins with a high affinity for specific sugar residues.
Leghemoglobin: Red colored pigments rich in iron, which are produced in root nodules during symbiotic association between rhizobia and leguminous plants.
Ligand: A molecule, ion or group of molecules or ions, bound to the central atom by means of a chelate or coordination compound.
Light Compensation Point: The point where the rate of respiration is higher than the rate of photosynthesis, which usually occurs at about 1% of sunlight intensity.
Lime (agricultural): Soil amendment containing high levels of calcium compounds, like calcium carbonate and other such mineral which are used to neutralize soil acidity, and provide calcium for plant growth.
Lipopolysaccharide (LPS): Complex lipid structure containing sugars and fatty acids, which is commonly found in most Gram negative bacteria.
Lithotroph: An organism that uses inorganic substrate such as ammonia or hydrogen to act as electron donors in energy metabolism. They may be chemolithotrophs or photolithotrophs.
Litter: The surface layer of forests which is laden with leaves, twigs, fruits etc.
Lophotrichous: An organism that has a tuft of flagella that is polar in nature.
Luxury Uptake: Uptake of nutrients in excess of what is required by an organism for its normal growth.
Lysis: The rupture and destruction of a cell, resulting in loss of cellular contents.
Lysogeny: An association where a prokaryote contains a prophage and the virus genome is replicated in sync with the chromosome of the host.
Lysosome: A cell organelle which contains lytic enzymes.
Macronutrient: A substance required in large amounts for normal growth of an individual.
Macropore: Larger soil pores from which water drains readily by gravity.
Magnetosome: Small particles of magnetite, which is a compound containing magnesium, present in cells that exhibit magnetotaxis.
Magnetotactic Bacteria: Bacteria that orient themselves according to the earth's magnetic field due to the presence of the magnetosomes.
Manure: Animal excreta, with or without a bedding of litter at various stages of decomposition. It's normally considered to be a good fertilizer.
Mass Flow (nutrient): The movement of solutes in relation to the movement of water.
Medium: A source where micro-organisms are grown.
Mesofauna: Animals residing in the soil which are 200 to 1000 microns in length. This group includes nematodes, oligochaete worms, smaller insect larvae, and certain anthropods.
Mesophile: An organism that thrives in temperatures ranging from 15 - 40 ºCelsius.
Methanogenesis: The production of methane by biological reactions.
Methanogenic Bacterium: Bacteria that produce methane as a by-product of their chemical reactions.
Methanotroph: An organism capable of oxidizing methane.
Microaerophile: Micro-organisms that grow well in relatively low oxygen concentration environment.
Microaggregate: Clusters of clay stabilized by organic matter and precipitated inorganic matter.
Microbial Biomass: Total mass of micro-organisms living in a given mass or volume of soil.
Microbial Population: Total number of micro-organisms living in a given mass or volume of soil.
Microbiology: The study of micro-organisms, often with the aid of a microscope.
Microcosm: A community or any other unit that is representative of a larger community.
Microenvironment: The immediate physical and chemical surroundings of a microorganism.
Microfauna: Protozoa, nematodes, and anthropods that are smaller than 200 microns.
Microflora: This includes bacteria, virus, fungi, and algae.
Micrometer: One millionth of a meter (10-6 meters).
Micronutrient: Elements that are required for growth in trace amounts. These include copper, iron, zinc etc.
Micro-organism: An organism that is too small to be seen by the naked eye. Also called microbes, these include bacteria, fungi, protozoans, algae, and viruses.
Micropore: A small-sized soil pore (approximately less than 30 microns in diameter) which is normally found within structural aggregates.
Microsite: A small part of the soil where the biological or chemical processes are different from the rest of the soil.
Mixotroph: Organisms that are capable of assimilating organic compounds as carbon sources, while using inorganic compounds as electron donors.
Mold: A group of saprobic or parasitic fungi causing a cottony growth on organic substances.
Monoclonal Antibody: Antibody produced from a single clone of cells, which has a uniform structure and specificity.
Monokaryon: Fungal hyphae where the compartments contain only nucleus.
Morphometric Characters: These are characteristics regarding the depth, dimension, sediment distribution, water currents etc.
Motility: The ability of a cell to move from one place to another.
Mucigel: Gelatinous material found on the surface of roots growing in normal soil.
Mucilage: Gelatinous secretions and exudates produced by plant roots and most micro-organisms.
Mulch: Materials which are laid down on soil to protect it from rain, crusting, freezing etc. These materials could be sawdust, plastic, leaves etc.
Municipal Solid Waste: The total consumer and commercial waste generated in a certain confined and restricted geographic area.
Mycophagous: Organisms that eat fungi.
Mycovirus: Viruses that infect fungi.
Nanopore: Soil pore having dimensions in nanometers.
NAPL: A non:aqueous phase liquid which may be lighter or denser than water.
Necrotrophic: A mechanism by which an organism produces lytic enzymes that kill and then breakdown host cells for its nutrition.
Nematode: Eukaryotes that are unsegmented, usually microscopic roundworm.
Neutralism: Lack of interaction between two organisms in the same habitat.
Niche: Functional role of an organism in a certain habitat.
Nictotinamide Adenine Dinucleotide (NAD+): An important oxidized coenzyme that is a hydrogen and electron carrier in redox reactions.
Nicotinamide Adenine Dinucleotide Phosphate (NADP+): An important oxidized coenzyme that acts as a hydrogen and electron carrier in various redox reactions.
Nitrate Reduction (biological): The process of reduction of nitrate to simpler forms like ammonium by plant and micro-organisms.
Nitrification: Biological oxidation of ammonium to nitrite and nitrate.
Nitrifying Bacteria: Chemolithotrophs that can carry out the transformation from ammonia to nitrite or nitrate.
Nitrogen Cycle: The cycle where nitrogen is used by a living organism, then after the organism dies is restored to soil, followed by its final conversion to its original state of oxidation. Read more on interesting facts about nitrogen cycle.
Nitrogenase: The enzyme required for biological nitrogen fixation.
Nodulin: Proteins produced in root hair or nodules in response to rhizobial infection.
Nonpolar: A substance that is hydrophobic and does not easily dissolve in water.
Northern Blot: Hybridization of single stranded DNA or RNA to RNA fragments.
Nucleic Acid: A high molecular weight nucleotide polymer.
Nucleoid: The nuclear region of certain organisms like bacteria, which contains chromosomes, but which is not limited by a nuclear membrane.
Nucleophilic Compound: An electron donor in chemical reactions involving covalent catalysis in which the donated electrons bond with other chemical groups.
Oligonucleotide: A short nucleic acid chain, which is obtained from an organism or is synthesized chemically.
Oligotroph: A microorganism that has adapted itself to grow in environments that are low in nutrients.
Oospore: Thick-walled spore formed in an oogonium by fungus like organisms like the phylum Oomycota.
Operon: Genes whose expression is controlled by a single operator.
Parasitism: Feeding by one organism on the cells of a second, normally larger organism, thus, harming the host.
Parasexual Cycle: A nuclear cycle wherein genes of haploid nuclei recombine without meiosis.
Particle Density: Density of particles present in soil.
Particle Size: Effective diameter of a particle measured by sedimentation or micrometric methods.
Pasteurization: Process of using heat to kill or reduce the activity of micro-organisms in heat-sensitive materials.
Pathogen: An organism that is capable of causing an infection, or harming a host cell.
Pathogen Suppressive soil: Soil where a pathogen does not persist, either in its own survival or in its pathogenicity.
Pathogenicity: The ability of a parasite to infect or inflict damage on a host.
Peat: Unconsolidated soil material consisting mostly of undecomposed organic matter with excessive moisture content.
Pellicle: A rigid protein layer just below the cell membrane.
Peptidoglycan: Rigid cell wall layer seen in bacteria. It's also called murein.
Peribacteroid Membrane: A plant derived membrane which surrounds rhizobia in host cells of legume nodules.
Periplasmic space: The area between the cell membrane and cell wall in Gram negative bacteria.
Perithecium: Flask shaped ascocarp open at the tip.
Peritrichous Flagellation: Multiple flagella present all over the cell surface.
Permanent Wilting Point: The highest concentration of soil at which plants present in it, will irreversibly wilt when placed in a humid chamber.
Phosphobacterium: Bacteria that are good at dissolving insoluble inorganic phosphate that is present in the soil.
Photoautotroph: Self-sufficient organisms that can generate energy from light and carbon dioxide.
Photoheterotroph: Organisms able to use light as a source of energy and organic materials as carbon source.
Photophosphorylation: Synthesis of high energy phosphate bonds by the use of light as a source of energy.
Phototaxis: Movement of an organism, or a part of it, towards light.
Phytoextraction: The use of plants or algae for removing contaminants from soil, sediments, or water, and turning them into harvestable plant biomass.
Phycobilin: Water-soluble pigment that is seen in cyanobacteria and is the light harvesting pigment for Photosystem II.
Pilus: Fimbria like substance present on fertile cells that deals with transfer of DNA during the process of conjugation.
Plaque: A localized area of lysis or cell inhibition which is caused due to virus infection.
Plasmogamy: Fusion of two cell contents, inclusive of the cytoplasm and nuclei.
Plate Count: Number of colonies formed on a solid culture medium, when uniformly inoculated with a known amount of soil.
Polar Flagellation: The presence of flagella at one or both ends.
Protoplast: A cell devoid of cell wall.
Pour Plate: The method of performing a plate count of micro-organisms.
Psychrotroph: An organism that is able to grow at zero degrees and above twenty degrees Celsius.
Pure Culture: A microorganism population of a single strain.
Radioimmunoassay: An immunological assay that makes use of radioactive antibodies or antigens to detect certain substances.
Reaction Center: A photosynthetic complex containing chlorophyll and other compounds.
Reannealing: The process seen on cooling, where two complementary strands of DNA hybridize back into a single strand.
Recalcitrant: Resistance of an organism to a microbial attack.
Recombination: Process by which genetic elements in two separate genomes are brought together in one unit. This is an important step in gene therapy.
Replication: Conversion of one double stranded DNA molecule into two identical double stranded DNA molecules.
Repression: Process by which an enzyme synthesis is suppressed due to the presence of certain external substances.
Reverse Transcription: Process of copying information from RNA to DNA.
Rhizobacteria: Bacteria that are found in roots, where they aggressively colonize.
Rhizobia: Bacteria capable of living symbiotically in leguminous plant roots, from where they receive energy and commonly fix molecular dinitrogen.
Rhizomorph: Mass of fungal hyphae that are organized in long, thick strands with a darkly pigmented outer rind that contains specialized tissues for absorption and water transport.
Rhizoplane: Plant root surface and strongly adhering soil particles.
Rhizosphere: The zone of soil immediately adjacent to plant roots in which the activity and type of micro-organisms present differ from that in the rest of the soil.
Rhizosphere Competence: Ability of an organism to colonize the rhizosphere.
Sanitization: Elimination of pathogenic or harmful organisms, including insect larvae, intestinal parasites, and weed seeds.
Sclerotium: Modified fungal hyphae that form a compact and hard vegetative resting structure with a thick pigmented outer rind.
Secondary Metabolite: Product of intermediary metabolism released from a cell, for example, antibiotic.
Selective Medium: A medium that is biased in allowing only certain types of micro-organisms to grow.
Serial Dilution: Series of stepwise dilutions, normally done in sterile water, which is done to reduce microorganism populations to manageable numbers.
Serology: Study of reactions that take place between antigens and antibodies in vitro.
Sheath: Tubular structure that is found either around a chain of cells or around a bundle of filaments.
Siderochromes: The compounds that are synthesized by the micro-organisms themselves, which are responsible for iron uptake.
Siderophore: A metabolite that is formed by some micro-organisms, that forms a strong coordination compound with iron.
Slime Layer: A diffuse layer found immediately outside the cell wall in certain bacteria.
Slime Mold: Micro-organisms that are eukaryotic and which lack cell walls.
Solarization: A technique to control the growth of pathogens, wherein a plastic sheet is used to cover moistened soil in hot climates, thereby trapping the incoming radiation.
Specific Activity: Expressed as micromoles formed per unit time per milligram of protein, this is the amount of enzyme activity units per mass of protein.
Spermosphere: The area seen around a germinating seed, where there is increased microbiological activity.
Spread Plate: A technique for performing a plate count of micro-organisms.
Sterilization: The process whereby an object or surface is rendered free of any living micro-organisms.
Storage Polysaccharide: The energy reserves which are stored in a cell when there is excess of carbon available.
Strain: Population of cells, all of which arise from a single pure isolate.
Substrate: A base on which an organism is grown. They can also be the substances on which compounds and enzymes act.
Sulfur Cycle: The cycle wherein sulfur, the element is taken up by living organisms, then released upon the death of the organism, and then converted to its final state of oxidation.
Symbiosis: Two dissimilar organisms, living together. Their association maybe commensal or mutualistic.
Synergism: Association between two organisms that is mutually beneficial.
Syntrophy: Interaction between two or more populations that supply each other's nutritional needs.
Systemic: Something that involves the entire body and is not localized in the body.
Teichoic Acids: All wall, membrane, or capsular polymers containing glycerophosphate or ribitol phosphate residues.
Telemorph: One of the stages of sexual reproduction, wherein cells are formed by meiosis and genetic recombination.
Temperate Virus: A virus that does not cause destruction and lysis of the cells of its host, but instead, its genome may replicate in sync with that of the host.
Terminal Electron Acceptor: The last acceptor of the electron, as it exits the electron transport chain.
Thermocline: That point in a lake, where there is a drastic drop in temperature with increase in depth.
Thermophile: An organism that grows best at temperatures around 45 and 80 ºCelsius.
Ti plasmid: A conjugative tumor inducing plasmid that can transfer genes into plants. Seen in the bacterium Agrobacterium tunefaciens.
Toxin: A foreign substance present in the body, which is mostly generated by micro-organisms, that is capable of inflicting damage on the host cell.
Transduction: The process where host genetic information is transferred through an agent like a virus or a bacteriophage.
Transgenic: Genetically modified plants or organisms, which contain foreign genes, which have been inserted by means of recombinant DNA techniques.
Transposable Element: A genetic element that can be transposed from one site on a chromosome to another.
Transposon: Transposable element which, in addition to transposable genes, carries other genes.
Transposon Mutagenesis: A mutant phenotype is formed by inactivation of the host gene, which occurs due to the insertion of a transposon.
Tricarboxylic Acid Cycle: A series of metabolic reactions, by which pyruvate is oxidized to carbon dioxide.
Trophic Level: Describes the residence of nutrients in various organisms along a food chain ranging from the primary nutrient assimilating autotrophs to carnivorous animals.
Uronic Acid: A class of acidic compounds that contain both carboxylic and aldehydic groups and are oxidation products of sugars. They occur mainly in polysaccharides.
Vadose Zone: Unsaturated zone of soil which is above the groundwater, extending from the bottom of the capillary fringe to the soil surface.
Vector: An agent that can carry pathogens from one host to another. It can also denote a plasmid or virus used in genetic engineering to insert genes into a cell.
Vegetative Cell: A growing or actively feeding form of a cell, as against a spore.
Vesicles: Spherical structures formed intra-cellularly, by certain arbuscular mycorrhizal fungi.
Viable but Nonculturable: Living organisms that cannot be cultured on artificial media.
Viable Count: Measurement of the concentration of live cells in a microbial population.
Vibrio: Curved, rod-shaped bacteria that cause cholera, belonging to the genus Vibrio.
Virion: The virus particle and the virus nucleic acid surrounded by a protein coat.
Virulence: The degree of pathogenicity of a parasite.
Water Content: The amount of water contained in a material, which is expressed as the mass of water per unit mass of oven:dry material.
Water Retention Curve: A graph showing soil water content as a function of increasingly negative soil water potential.
White Rot Fungus: Fungus that attacks lignin, along with cellulose and hemicellulose, leading to marked lightening of the infected wood.
Wild Type: Strain of a microorganism that is isolated from nature. The native and original form of a gene or organism.
Winogradsky Column: A glass column that allows growth of micro-organisms under conditions similar to those found in nutrient-rich water and sediments. This column contains an anaerobic lower zone and an aerobic upper zone.
Woronin Body: A spherical structure found in fungi belonging to the phylum Ascomycota, which are associated with the simple pore in the septa separating the hyphal compartments.
Xenobiotic: A compound that is foreign to the biological systems.
Xerophile: An organism that is capable of growing at low water potentials, that is, in very dry habitats.
Zymogenous Flora: Refers to micro-organisms that respond rapidly by enzyme production and growth when simple organic substrates become available. [Back]
With inputs from Bhakti Satalkar, Dr. Sumaiya Khan, Loveleena Rajeev, and Marian K.
For information on scientific terms and definitions, one can refer to Science - Glossary of Science Terms and Scientific Definitions.
Green Algae Cluster
Blood Cells
Ants Tending Aphids Herd