Life Science Dictionary596 terms
The Life Science Dictionary
A free biology dictionary: plain definitions of the words life science and medical students meet, with how to say them, the word parts they are built from, and quizzes to practice them.
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A
- AcetylcholineNeuroscienceAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
- Action potentialNeuroscienceAn action potential is a brief, all-or-none reversal of the voltage across a nerve or muscle cell membrane that travels along the cell as a signal.
- Active siteBiochemistryThe active site is the pocket or groove on an enzyme where the substrate binds and the chemical reaction is catalyzed.
- Active transportCell BiologyActive transport is the movement of a substance across a cell membrane against its concentration gradient, powered by energy, usually from ATP.
- AdaptationEvolutionAn adaptation is an inherited trait, shaped by natural selection, that helps an organism survive and reproduce in its current environment.
- Adaptive immunityImmunologyAdaptive immunity is the branch of the immune system that learns to recognize specific antigens and remembers them, so it responds faster next time.
- Adaptive radiationEvolutionAdaptive radiation is the rapid evolution of many new species from one ancestral species, each adapted to a different way of life or ecological niche.
- Adrenal glandHuman AnatomyAn adrenal gland is one of two small endocrine glands atop the kidneys, with a cortex that makes steroid hormones and a medulla that makes epinephrine.
- AgarMicrobiologyAgar is a jelly-forming polysaccharide extracted from red seaweeds, used above all to solidify culture media for growing microorganisms.
- AgonistPharmacologyAn agonist is a drug or natural substance that binds to a receptor and activates it, producing a biological response.
- AldosteronePhysiologyAldosterone is a steroid hormone from the adrenal cortex that makes the kidneys keep sodium and water and excrete potassium, raising blood volume.
- Algor mortisForensic MedicineAlgor mortis is the gradual cooling of a body after death until it matches the temperature of its surroundings, used to estimate time since death.
- AlleleGeneticsAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- AllergyImmunologyAn allergy is an immune overreaction to a normally harmless substance, such as pollen or peanuts, driven mainly by IgE antibodies and mast cells.
- Allosteric regulationBiochemistryAllosteric regulation is control of an enzyme's activity by a molecule that binds somewhere other than the active site and changes the enzyme's shape.
- Alternation of generationsBotanyAlternation of generations is a life cycle in which a multicellular haploid gametophyte and a multicellular diploid sporophyte produce each other in turn.
- AlveolusPhysiologyAn alveolus is one of the tiny air sacs at the end of the lung's airways, where oxygen passes into the blood and carbon dioxide passes out.
- Alzheimer's diseaseNeuroscienceAlzheimer's disease is a progressive brain disease that destroys neurons and their connections and is the leading cause of dementia in older adults.
- Amino acidBiochemistryAn amino acid is a small organic molecule with an amino group, a carboxyl group and a side chain; amino acids link together to form proteins.
- AmygdalaNeuroscienceThe amygdala is an almond-shaped cluster of nuclei deep in each temporal lobe that processes emotion, especially fear, and colors memories with feeling.
- AmyloidosisPathologyAmyloidosis is a group of diseases in which misfolded proteins clump into insoluble amyloid fibrils that build up in organs and disrupt how they work.
- Analogous structuresEvolutionAnalogous structures are body parts in different species that look alike or do the same job but evolved separately rather than from a shared ancestor.
- AnemiaPathologyAnemia is a condition in which the blood has fewer healthy red blood cells or less hemoglobin than normal, so less oxygen reaches the tissues.
- AnesthesiaSurgeryAnesthesia is a medically induced loss of sensation or awareness, produced by drugs called anesthetics, that prevents pain during surgery and other procedures.
- AngiogenesisOncologyAngiogenesis is the growth of new blood vessels from existing ones, needed for growth and healing and exploited by tumors to feed themselves.
- AngiospermBotanyAn angiosperm is a flowering plant, a seed plant whose ovules develop inside an ovary that ripens into a fruit enclosing the seeds.
- AntagonistPharmacologyAn antagonist is a drug that binds to a receptor without activating it, blocking the natural signal or an agonist from producing an effect.
- AntibioticMicrobiologyAn antibiotic is a drug that kills bacteria or stops them from growing, used to treat or prevent bacterial infections; it has no effect on viruses.
- Antibiotic resistanceMicrobiologyAntibiotic resistance is the ability of bacteria to survive and multiply despite an antibiotic that once killed them or stopped their growth.
- AntibodyImmunologyAn antibody is a Y-shaped protein made by B cells and plasma cells that binds tightly to one specific antigen and helps the body destroy it.
- AnticoagulantPharmacologyAn anticoagulant is a substance that slows blood clotting by interfering with clotting factors, used to prevent and treat harmful blood clots.
- Antidiuretic hormonePhysiologyAntidiuretic hormone is a peptide hormone made in the hypothalamus and released by the posterior pituitary that makes the kidneys keep water.
- AntigenImmunologyAn antigen is any molecule the immune system can recognize as a target, especially one that prompts antibodies or T cells to respond against it.
- AntioxidantFood NutritionAn antioxidant is a substance that prevents or slows oxidation, especially damage to cells from free radicals and other reactive oxygen species.
- Antiviral drugPharmacologyAn antiviral drug is a medicine that treats or prevents a viral infection by blocking a step in the virus's life cycle inside the host's cells.
- AortaHuman AnatomyThe aorta is the body's largest artery, carrying oxygenated blood out of the heart's left ventricle to the arteries that supply every organ.
- ApoptosisCell BiologyApoptosis is programmed cell death, a controlled process in which a cell dismantles itself in an orderly way without harming its neighbors.
- AppendicitisSurgeryAppendicitis is inflammation of the appendix, the small pouch off the large intestine, and the most common reason for emergency abdominal surgery.
- ArchaeaMicrobiologyArchaea are single-celled prokaryotes that form their own domain of life, distinct from bacteria in their membranes, cell walls and genes.
- ArthropodEntomologyAn arthropod is an invertebrate animal with a segmented body, a hard exoskeleton containing chitin and jointed legs, such as an insect, spider or crab.
- Artificial selectionEvolutionArtificial selection is the process in which people choose which plants or animals breed, so that the traits they want become more common over generations.
- Aseptic techniqueMicrobiologyAseptic technique is the set of practices that keeps microbes from contaminating sterile materials, cultures or a patient's tissues during a procedure.
- AsphyxiaForensic MedicineAsphyxia is a life-threatening state in which the body is starved of oxygen, usually as carbon dioxide builds up, because breathing or oxygen use fails.
- AsthmaMedicineAsthma is a long-term lung disease in which the airways become inflamed and narrowed, causing wheezing, coughing, chest tightness and breathlessness.
- AtherosclerosisPathologyAtherosclerosis is a disease in which fatty plaque builds up inside artery walls, stiffening and narrowing the arteries and reducing blood flow.
- ATPBiochemistryATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- AtrophyPathologyAtrophy is the shrinking of a cell, tissue or organ that had reached normal size, usually as cells lose substance in response to reduced demand or support.
- AutoimmunityImmunologyAutoimmunity is an immune response wrongly directed at the body's own healthy cells and tissues, and it is the cause of autoimmune diseases.
- Autonomic nervous systemNeuroscienceThe autonomic nervous system is the division of the nervous system that runs involuntary functions such as heart rate, digestion and gland secretion.
- AutopsyForensic MedicineAn autopsy is a medical examination of a body after death, inside and out, to find the cause of death and study the effects of disease or injury.
- AuxinBotanyAuxin is a plant hormone, chiefly indole-3-acetic acid, that controls cell elongation, bending toward light and the overall shape of a plant.
- AxonNeuroscienceAn axon is the single long projection of a neuron that carries electrical impulses away from the cell body toward other neurons, muscles or glands.
B
- B cellImmunologyA B cell is a lymphocyte, a kind of white blood cell, that produces antibodies and forms a key part of the adaptive immune system.
- Bacterial conjugationMicrobiologyBacterial conjugation is the direct transfer of DNA, usually a plasmid, from one bacterial cell to another through a pilus and close cell contact.
- Bacterial growth curveMicrobiologyA bacterial growth curve is a graph of living cell numbers over time in a closed culture, showing lag, exponential, stationary and death phases.
- Bacterial transformationMicrobiologyBacterial transformation is the uptake of free DNA from the surroundings by a bacterial cell, which can then gain the genes that DNA carries.
- BacteriophageVirologyA bacteriophage, or phage, is a virus that infects bacteria, injecting its genome and using the host cell's machinery to make new phages.
- BacteriumMicrobiologyA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
- Basal metabolic rateFood NutritionBasal metabolic rate is the energy the body uses per unit of time just to stay alive when awake, lying at rest, fasting and in a comfortable temperature.
- Basic reproduction numberEpidemiologyThe basic reproduction number, R0, is the average number of people one infectious person would infect in a population with no immunity.
- Benign tumorOncologyA benign tumor is an abnormal growth of cells that stays in one place and does not invade nearby tissue or seed new growths elsewhere.
- Beta blockerPharmacologyA beta blocker is a drug that stops epinephrine and norepinephrine from acting on beta receptors, which slows the heart and lowers blood pressure.
- Beta oxidationBiochemistryBeta oxidation is the pathway, mainly in mitochondria, that breaks fatty acids down two carbons at a time into acetyl CoA, yielding NADH and FADH2.
- Binary fissionMicrobiologyBinary fission is how bacteria and archaea reproduce: a cell copies its DNA, grows, and splits in the middle into two identical daughter cells.
- Binomial nomenclatureZoologyBinomial nomenclature is the system of naming each species with two Latin-form words, a genus name followed by a specific epithet, as in Homo sapiens.
- BioavailabilityPharmacologyBioavailability is the fraction of a drug dose that reaches the general circulation unchanged, along with how quickly it gets there.
- BioBrickSynthetic BiologyA BioBrick is a standardized piece of DNA, such as a promoter or gene, flanked by fixed sequences so it can be joined to other parts in a repeatable way.
- BiodiversityEcologyBiodiversity is the variety of life in a place or on Earth as a whole, from genetic differences within species to the range of species and ecosystems.
- BiofilmMicrobiologyA biofilm is a community of microbes stuck to a surface and to each other inside a slimy matrix they produce, such as the plaque on teeth.
- BioinformaticsBioinformaticsBioinformatics is the science of using computers to gather, store, analyze and share biological data, especially DNA, RNA and protein sequences.
- BioluminescenceMarine BiologyBioluminescence is the production of light by a living organism through a chemical reaction, as seen in fireflies and in many deep-sea animals.
- BiomeEcologyA biome is a large region of Earth defined by its climate and its typical plants and animals, such as tundra, desert or tropical rainforest.
- BioreactorBiotechnologyA bioreactor is a vessel that keeps living cells or enzymes under controlled conditions so they can grow and make a product, such as a drug or vaccine.
- BioremediationBiotechnologyBioremediation is the use of living organisms, mostly microbes and sometimes plants, to break down or remove pollutants from soil, water or air.
- BiotechnologyBiotechnologyBiotechnology is the use of living organisms, cells or their molecules to make products or carry out processes that are useful to people.
- BLASTBioinformaticsBLAST is a widely used program that searches databases for DNA or protein sequences similar to a query and ranks the matches by statistical significance.
- BlastocystDevelopmental BiologyA blastocyst is the hollow ball of cells that a mammalian embryo forms about five days after fertilization, shortly before it implants in the uterus.
- Blood pressurePhysiologyBlood pressure is the force that circulating blood exerts on the walls of the arteries, recorded as systolic over diastolic pressure in mm Hg.
- Blood–brain barrierNeuroscienceThe blood–brain barrier is the tightly sealed lining of the brain's capillaries that controls which substances can pass from the blood into brain tissue.
- Body mass indexFood NutritionBody mass index is a screening measure that relates body weight to height, found by dividing weight in kilograms by height in meters squared.
- BoneHuman AnatomyBone is the hard, mineralized connective tissue that makes up most of the adult skeleton, and the name for each skeletal organ built from it.
- Bottleneck effectEvolutionThe bottleneck effect is the loss of genetic variation that follows a sudden, steep fall in population size, leaving only a few survivors to breed.
- Brachial plexusHuman AnatomyThe brachial plexus is the network of nerves formed from spinal nerves C5 to T1 that supplies movement and feeling to the shoulder, arm and hand.
C
- CalorieFood NutritionA calorie is a unit of energy, the heat needed to warm one gram of water by one degree Celsius; food energy is given in kilocalories, often written Calories.
- Cambrian explosionPaleontologyThe Cambrian explosion is the relatively rapid appearance of most major animal groups in the fossil record, beginning about 540 million years ago.
- CancerOncologyCancer is a group of diseases in which abnormal cells divide without control, invade nearby tissue and can spread to distant parts of the body.
- CapsidVirologyA capsid is the protein shell of a virus that surrounds and protects its genome, built from many repeating protein subunits called capsomeres.
- CarbohydrateBiochemistryA carbohydrate is a sugar or a chain of sugars, such as starch or cellulose, built from carbon, hydrogen and oxygen and used for energy and structure.
- Carbon cycleEcologyThe carbon cycle is the movement of carbon among the air, oceans, living things, soils and rocks through processes like photosynthesis and respiration.
- CarcinogenOncologyA carcinogen is any substance, radiation, microbe or other exposure that can cause cancer or raise the chance of it developing.
- CarcinomaOncologyA carcinoma is a cancer that starts in epithelial cells, the cells that cover the skin and line the inner and outer surfaces of organs.
- Cardiac cyclePhysiologyThe cardiac cycle is the sequence of contraction and relaxation of the heart's chambers that makes up one complete heartbeat.
- Cardiac outputPhysiologyCardiac output is the volume of blood each ventricle of the heart pumps in one minute, equal to heart rate multiplied by stroke volume.
- Carrying capacityEcologyCarrying capacity is the largest population of a species that an environment can sustain over time with the food, water and space available.
- CartilageHuman AnatomyCartilage is a tough, flexible connective tissue without blood vessels that cushions joints and shapes the nose, ears and airways.
- Case fatality rateEpidemiologyThe case fatality rate is the share of people diagnosed with a particular disease who die of it, a basic measure of how severe that disease is.
- Case–control studyEpidemiologyA case–control study is an observational study that compares people with a disease and people without it to find past exposures linked to it.
- CellCell BiologyA cell is the smallest unit that can carry out all the processes of life, enclosed by a membrane and holding its own genetic material.
- Cell cycleCell BiologyThe cell cycle is the ordered series of growth, DNA copying and division stages that a cell passes through to produce two daughter cells.
- Cell differentiationStem Cell BiologyCell differentiation is the process by which an unspecialized cell becomes a specialized type, such as a neuron or muscle cell, by switching on a set of genes.
- Cell membraneCell BiologyThe cell membrane is the thin, flexible boundary of lipids and proteins that encloses every cell and controls what enters and leaves it.
- Cell wallCell BiologyA cell wall is a rigid layer outside the plasma membrane of plant, fungal, algal and most bacterial cells that gives shape and stops them bursting.
- Cellular respirationCell BiologyCellular respiration is the set of pathways by which cells break down fuel molecules such as glucose and capture the released energy as ATP.
- CelluloseBotanyCellulose is a strong, unbranched polysaccharide of glucose units joined by beta 1-4 bonds and the main structural material of plant cell walls.
- Central dogmaMolecular BiologyThe central dogma is the principle that genetic information flows from DNA into RNA and then into protein, and never back from protein into nucleic acid.
- Central nervous systemNeuroscienceThe central nervous system is the brain and spinal cord, the part of the nervous system that takes in sensory input, integrates it and sends out commands.
- CentromereCell BiologyA centromere is the constricted region of a chromosome where its two sister chromatids are held together and where spindle fibers attach in cell division.
- CerebellumNeuroscienceThe cerebellum is the folded hindbrain structure below the cerebrum that coordinates movement, balance and posture and helps us learn motor skills.
- Cerebral cortexNeuroscienceThe cerebral cortex is the thin, folded layer of gray matter covering the cerebrum, where perception, movement, language and thought are processed.
- ChemotherapyOncologyChemotherapy is the treatment of cancer with drugs that kill rapidly dividing cells or stop them from multiplying, usually given in repeated cycles.
- ChitinEntomologyChitin is a tough, nitrogen-containing polysaccharide built from N-acetylglucosamine units that forms arthropod exoskeletons and fungal cell walls.
- ChlorophyllBotanyChlorophyll is the green pigment in plants, algae and cyanobacteria that absorbs light energy to drive photosynthesis.
- ChloroplastCell BiologyA chloroplast is the green organelle in plant and algal cells that captures light energy and uses it to make sugars by photosynthesis.
- CholecystectomySurgeryA cholecystectomy is an operation to remove the gallbladder, most often because gallstones are causing pain, inflammation or blocked bile flow.
- CholesterolBiochemistryCholesterol is a waxy steroid lipid found in animal cell membranes and used to make steroid hormones, vitamin D and the bile salts that digest fat.
- ChordateZoologyA chordate is an animal of the phylum Chordata, which at some stage has a notochord, pharyngeal slits, a hollow dorsal nerve cord and a tail.
- ChromatinCell BiologyChromatin is the complex of DNA and proteins, mainly histones, that packs a eukaryotic cell's genome into its nucleus and makes up its chromosomes.
- ChromosomeGeneticsA chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.
- Chronic kidney diseaseMedicineChronic kidney disease is a gradual, lasting loss of kidney function in which the kidneys filter blood less well, so wastes and fluid build up in the body.
- Circadian rhythmNeuroscienceA circadian rhythm is a roughly 24-hour cycle in an organism's body and behavior, driven by an internal clock and reset each day mainly by light.
- Citric acid cycleBiochemistryThe citric acid cycle is a loop of reactions in mitochondria that breaks down acetyl groups to carbon dioxide, capturing energy as NADH and FADH2.
- CodominanceGeneticsCodominance is a pattern of inheritance in which both alleles in a heterozygote are fully expressed, so the traits of both appear together.
- CodonMolecular BiologyA codon is a sequence of three nucleotides in DNA or messenger RNA that stands for one amino acid or tells the ribosome to stop.
- CoenzymeBiochemistryA coenzyme is a small organic molecule, often made from a vitamin, that an enzyme needs to catalyze its reaction, usually by carrying electrons or atoms.
- CoevolutionEvolutionCoevolution is the process in which two or more species that interact closely each drive evolutionary change in the other over many generations.
- Cohort studyEpidemiologyA cohort study is an observational study that follows groups differing in an exposure over time to compare how often they develop an outcome.
- Common ancestorEvolutionA common ancestor is an ancestral species or population from which two or more later species or groups of organisms have all descended.
- Communicable diseasePublic HealthA communicable disease is an infection that can pass from one person or animal to another, directly or through air, water, food, objects or vectors.
- CompetitionEcologyIn ecology, competition is an interaction in which organisms needing the same scarce resource, such as food, light or space, reduce each other's success.
- Competitive inhibitionBiochemistryCompetitive inhibition is enzyme inhibition in which a molecule resembling the substrate occupies the active site and keeps the substrate out.
- Complement systemImmunologyThe complement system is a set of blood proteins that switch each other on in a cascade to tag microbes, drive inflammation and punch holes in them.
- Complementary DNAMolecular BiologyComplementary DNA is DNA built from an RNA template, usually messenger RNA, by the enzyme reverse transcriptase, giving a DNA copy of an expressed gene.
- ConfoundingEpidemiologyConfounding is a distortion in a study where a third factor, linked to both the exposure and the outcome, creates, hides or exaggerates an apparent effect.
- Convergent evolutionEvolutionConvergent evolution is the independent evolution of similar traits in unrelated lineages that face similar environmental pressures.
- COPDMedicineCOPD is a long-term lung disease, usually caused by smoke or polluted air, in which damaged airways and air sacs limit the flow of air out of the lungs.
- Copy number variationGenomicsCopy number variation is a difference between people in how many copies of a given stretch of DNA their genomes carry, due to deletions or duplications.
- Coral bleachingMarine BiologyCoral bleaching is the paling of stressed corals as they lose the tiny symbiotic algae inside their tissue, most often because the water is too warm.
- Coral reefMarine BiologyA coral reef is an underwater ridge built over centuries from the limestone skeletons of colonial coral animals, home to some of Earth's richest sea life.
- CoronavirusVirologyA coronavirus is an enveloped RNA virus with club-shaped surface spikes; members cause illnesses ranging from colds to SARS, MERS and COVID-19.
- CortisolPhysiologyCortisol is a steroid hormone made by the adrenal cortex that helps the body cope with stress, raises blood glucose and dampens inflammation.
- CRISPRBiotechnologyCRISPR is a genome-editing technology, adapted from a bacterial defense system, that uses a guide RNA to direct an enzyme such as Cas9 to cut DNA.
- Crossing overGeneticsCrossing over is the exchange of matching DNA segments between paired homologous chromosomes during meiosis, creating new combinations of alleles.
- Cytochrome P450PharmacologyCytochrome P450 is a large family of heme-containing enzymes that oxidize drugs, toxins and the body's own molecules, working mainly in the liver.
- CytokineImmunologyA cytokine is a small signaling protein released by cells, especially immune cells, that changes how other cells behave, grow or respond to infection.
- CytokinesisCell BiologyCytokinesis is the last stage of cell division, in which the cytoplasm of one cell is split to form two separate daughter cells.
- CytoplasmCell BiologyThe cytoplasm is everything inside a cell's plasma membrane apart from the nucleus: the jelly-like cytosol and the structures suspended in it.
- CytoskeletonCell BiologyThe cytoskeleton is a network of protein filaments inside a cell that gives it shape, holds organelles in place and powers movement and division.
- Cytotoxic T cellImmunologyA cytotoxic T cell is a white blood cell of adaptive immunity that finds and kills body cells infected by viruses or turned cancerous.
D
- DebridementSurgeryDebridement is the removal of dead, damaged or infected tissue and foreign material from a wound so that the healthy tissue beneath can heal.
- DecomposerEcologyA decomposer is an organism, mainly a bacterium or fungus, that breaks down dead organisms and wastes and returns their nutrients to the environment.
- DenaturationBiochemistryIn biochemistry, denaturation is the unfolding of a protein or nucleic acid by heat, acid or chemicals, which ruins its shape but not its sequence.
- DendriteNeuroscienceA dendrite is one of the short, branching extensions of a neuron that receive signals from other cells and carry them toward the cell body.
- Dendritic cellImmunologyA dendritic cell is an antigen-presenting immune cell that captures microbes in tissues and carries their fragments to lymph nodes to activate T cells.
- Diabetes mellitusMedicineDiabetes mellitus is a chronic disease in which blood glucose stays too high because the body makes too little insulin or cannot use it well.
- DiaphragmHuman AnatomyIn anatomy, the diaphragm is the dome-shaped sheet of muscle and tendon dividing the chest from the abdomen, and the main muscle of breathing.
- Dietary fiberFood NutritionDietary fiber is the part of plant foods, mostly carbohydrate, that human digestive enzymes cannot break down, so it reaches the large intestine intact.
- DiffusionCell BiologyDiffusion is the net movement of molecules from a region of higher concentration to one of lower concentration, driven by their random motion.
- DigestionPhysiologyDigestion is the process by which the body breaks food down, by chewing, churning and enzymes, into molecules small enough to absorb into the blood.
- DinosaurPaleontologyA dinosaur is a member of the reptile group Dinosauria, which dominated life on land for most of the Mesozoic Era and survives today as the birds.
- DiploidGeneticsDiploid describes a cell or organism with two complete sets of chromosomes, one inherited from each parent, as in most human body cells.
- Disability-adjusted life yearPublic HealthA disability-adjusted life year (DALY) equals one year of healthy life lost, counting both early death and time spent living with illness or disability.
- DNAMolecular BiologyDNA is the double-stranded molecule that carries the genetic instructions of nearly all living things, written in a code of four bases: A, T, C and G.
- DNA ligaseMolecular BiologyDNA ligase is an enzyme that links two pieces of DNA end to end, making a phosphodiester bond that seals a break in the sugar-phosphate backbone.
- DNA methylationMolecular BiologyDNA methylation is the addition of a small methyl group to DNA, usually on cytosine, which can switch a gene off without changing its sequence.
- DNA polymeraseMolecular BiologyDNA polymerase is an enzyme that builds new DNA by adding nucleotides one at a time to a growing strand, using an existing strand as a template.
- DNA profilingForensic MedicineDNA profiling is a laboratory method that identifies a person from highly variable regions of their DNA, used in forensics and kinship testing.
- DNA repairMolecular BiologyDNA repair is the set of processes by which cells detect and correct damage and copying errors in their DNA, protecting the genome from mutation.
- DNA replicationMolecular BiologyDNA replication is how a cell copies all of its DNA before it divides, so that each daughter cell receives a complete genome.
- Dominant alleleGeneticsA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
- DopamineNeuroscienceDopamine is a catecholamine neurotransmitter made from tyrosine that helps control movement, motivation and learning from reward.
- Dose–response curvePharmacologyA dose–response curve is a graph showing how the size of a drug's effect changes as its dose or concentration increases.
- DysplasiaPathologyDysplasia is the presence of abnormal-looking, disordered cells within a tissue, a precancerous change that may regress or progress to cancer.
E
- Ecological nicheEcologyAn ecological niche is a species' role in its community: the conditions it tolerates, the resources it uses and how it interacts with other species.
- Ecological successionEcologyEcological succession is the gradual, fairly predictable change in the species that make up a community over time, as on bare rock or after a fire.
- EcosystemEcologyAn ecosystem is a community of living organisms together with the nonliving environment they interact with, linked by energy flow and nutrient cycling.
- EctothermZoologyAn ectotherm is an animal whose body temperature depends mainly on heat from its surroundings rather than on heat made by its own metabolism.
- EdemaPathologyEdema is swelling caused by excess fluid collecting in the spaces between the cells of a tissue, most often seen in the feet, ankles and legs.
- ElectrolyteFood NutritionAn electrolyte is a substance that forms ions in water so the solution conducts electricity; in the body, it means charged minerals such as sodium.
- Electron transport chainBiochemistryThe electron transport chain is a series of membrane proteins that pass electrons to oxygen and use the energy released to pump protons.
- ELISAImmunologyELISA is a lab test that uses enzyme-linked antibodies to detect and measure a specific antigen or antibody in a sample through a color change.
- EmbolismPathologyAn embolism is a blocked blood vessel caused by an embolus, a clot or other mass carried in the bloodstream from elsewhere in the body.
- EmbryoDevelopmental BiologyAn embryo is an organism in its earliest stage of development; in humans, from about the second week after fertilization to the end of the eighth week.
- Embryonic stem cellStem Cell BiologyAn embryonic stem cell is a pluripotent stem cell taken from the inner cell mass of an early embryo, the blastocyst, and able to form every type of body cell.
- EndemicEpidemiologyIn epidemiology, endemic describes a disease that is always found in a population or region at a fairly steady, expected level.
- Endocrine systemPhysiologyThe endocrine system is the set of glands and cells that release hormones into the blood to regulate growth, metabolism, reproduction and more.
- EndocytosisCell BiologyEndocytosis is how a cell brings material in from outside: its membrane folds inward around the material and pinches off to form a vesicle.
- Endoplasmic reticulumCell BiologyThe endoplasmic reticulum is a network of membrane sacs and tubes in eukaryotic cells that makes and processes proteins and lipids.
- EndosporeMicrobiologyAn endospore is a tough, dormant structure formed inside some bacteria, such as Bacillus and Clostridium, that survives heat, drying and chemicals.
- EndothermZoologyAn endotherm is an animal that keeps its body warm mainly with heat produced by its own metabolism, as mammals and birds do.
- EnzymeBiochemistryAn enzyme is a biological catalyst, usually a protein, that speeds up a specific chemical reaction without being used up in the process.
- EpidemicEpidemiologyAn epidemic is a rise in cases of a disease, often sudden, above the level normally expected in a given population, area and time.
- EpidemiologyEpidemiologyEpidemiology is the study of how often diseases and other health events occur in populations, what causes them and how they can be controlled.
- EpigeneticsMolecular BiologyEpigenetics is the study of chemical marks on DNA and its packaging proteins that switch genes on or off without changing the DNA sequence.
- EpilepsyMedicineEpilepsy is a long-term brain disorder in which a person has repeated unprovoked seizures caused by bursts of abnormal electrical activity in neurons.
- EpistasisGeneticsEpistasis is an interaction between genes in which the effect of one gene masks or alters the effect of another gene on the same trait.
- Escherichia coliMicrobiologyEscherichia coli is a rod-shaped, gram-negative gut bacterium that is mostly harmless but includes strains that cause diarrhea and urinary infections.
- EsophagusHuman AnatomyThe esophagus is the muscular tube, about 25 centimeters long, that carries swallowed food and liquid from the pharynx down to the stomach.
- EstuaryMarine BiologyAn estuary is a partly enclosed coastal body of water where river water meets and mixes with seawater, so that the water there is brackish.
- EukaryoteCell BiologyA eukaryote is an organism whose cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles.
- EusocialityEntomologyEusociality is the most complex form of animal social life, in which colony members share brood care and only a few reproduce while the rest work.
- EutrophicationEcologyEutrophication is the over-enrichment of a lake, river or coastal sea with nutrients, fueling algal blooms that later decay and use up the water's oxygen.
- EvolutionEvolutionEvolution is change in the inherited traits of populations over generations, the process that has produced all life's diversity from common ancestors.
- ExocytosisCell BiologyExocytosis is the release of substances from a cell when a membrane-bound vesicle fuses with the plasma membrane and empties its contents outside.
- ExomeGenomicsThe exome is the complete set of exons in a genome, its protein-coding part, which makes up only about 1 to 2 percent of human DNA.
- ExonMolecular BiologyAn exon is a section of a gene that stays in the final RNA after splicing removes the introns, and most exons carry code for protein.
- ExoskeletonEntomologyAn exoskeleton is a hard external skeleton that supports and protects an animal's body, as in insects, spiders and crustaceans.
- ExtinctionPaleontologyExtinction is the permanent loss of a species, which happens when the last living individual of that species dies.
F
- FASTA formatBioinformaticsFASTA format is a plain-text format for DNA, RNA or protein sequences in which each record starts with a header line beginning with > followed by the sequence.
- Fatty acidBiochemistryA fatty acid is a long chain of carbon and hydrogen atoms with a carboxyl group at one end, and is the building block of fats, oils and phospholipids.
- FemurHuman AnatomyThe femur is the thigh bone, the longest and strongest bone in the human body, running from the hip joint down to the knee.
- FermentationBiochemistryFermentation is a way cells get energy from sugar without oxygen, passing electrons to an organic molecule so that glycolysis can keep going.
- FertilizationDevelopmental BiologyFertilization is the fusion of a sperm and an egg, the male and female gametes, into a single diploid cell, the zygote, that can develop into a new organism.
- FibrosisPathologyFibrosis is the buildup of excess fibrous connective tissue, chiefly collagen, in an organ as a result of repeated injury or chronic inflammation.
- First-pass metabolismPharmacologyFirst-pass metabolism is the breakdown of an oral drug in the gut wall and liver before it reaches the general circulation, reducing how much survives.
- FitnessEvolutionIn evolution, fitness is an organism's success at surviving and reproducing, measured by its genetic contribution to the next generation.
- FlagellumMicrobiologyA flagellum is a long, whip-like projection that some cells, including many bacteria and sperm, use to swim through liquid.
- Flow cytometryImmunologyFlow cytometry is a laboratory technique for measuring the size, inner complexity and fluorescent labels of single cells as thousands stream past a laser.
- Food chainEcologyA food chain is a single line of feeding links in an ecosystem, tracing one path that energy and nutrients take from a producer up to a top predator.
- Food webEcologyA food web is the network of interconnected food chains in an ecosystem, showing the many feeding links through which energy and nutrients pass.
- Forensic entomologyForensic MedicineForensic entomology is the use of insects found on bodies or at scenes to answer legal questions, especially how long a person has been dead.
- FossilPaleontologyA fossil is any preserved evidence of past life in rock or sediment, from bones, shells and leaves to footprints and burrows.
- Founder effectEvolutionThe founder effect is the loss of genetic variation and shift in allele frequencies that occurs when a few individuals start a new population.
- Frameshift mutationGeneticsA frameshift mutation is an insertion or deletion of DNA bases, in a number not divisible by three, that shifts how the rest of a gene's codons are read.
- Frontal lobeNeuroscienceThe frontal lobe is the front part of each cerebral hemisphere, in charge of voluntary movement, speech production, planning, judgment and personality.
- FungusMycologyA fungus is a eukaryote, such as a yeast, mold or mushroom, that has chitin in its cell walls and feeds by absorbing nutrients from its surroundings.
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- GameteDevelopmental BiologyA gamete is a haploid reproductive cell, such as a sperm or an egg, that fuses with a gamete of the opposite type at fertilization to form a zygote.
- Gas exchangePhysiologyGas exchange is the movement of oxygen into the blood and carbon dioxide out of it by diffusion across thin membranes, mainly in the lungs and tissues.
- GastrulationDevelopmental BiologyGastrulation is the stage of early embryonic development in which cells move and fold to turn a simple ball or disc of cells into three germ layers.
- Gel electrophoresisMolecular BiologyGel electrophoresis is a lab technique that uses an electric field to pull DNA, RNA or proteins through a gel, separating them by size.
- GenBankBioinformaticsGenBank is the public database of DNA and RNA sequences run by the US National Center for Biotechnology Information, with annotated records free to use.
- GeneGeneticsA gene is a stretch of DNA that carries the instructions for making a protein or a working RNA molecule, and is the basic unit of heredity.
- Gene expressionMolecular BiologyGene expression is the use of a gene's information to make a working product, usually a protein or a functional RNA molecule.
- Gene flowEvolutionGene flow is the movement of alleles from one population into another when individuals or their gametes migrate and then breed.
- Gene therapyBiotechnologyGene therapy is a treatment that changes the genes inside a patient's cells, by adding, replacing, silencing or editing DNA, to treat or prevent disease.
- Genetic circuitSynthetic BiologyA genetic circuit is a designed set of genes and regulatory DNA that lets a cell sense inputs and respond in a programmed way, like an electronic circuit.
- Genetic driftEvolutionGenetic drift is a random change in allele frequencies from one generation to the next, caused by chance rather than by natural selection.
- Genetic engineeringBiotechnologyGenetic engineering is the direct change of an organism's DNA using laboratory techniques, to add, remove or alter genes and give it new traits.
- Genetic linkageGeneticsGenetic linkage is the tendency of genes that lie close together on the same chromosome to be inherited together rather than sorted independently.
- Genetically modified organismBiotechnologyA genetically modified organism is a plant, animal or microbe whose DNA has been changed by genetic engineering in a way mating could not achieve.
- GenomeGenomicsA genome is the complete set of DNA in an organism or cell, including all of its genes and the stretches of DNA between them.
- Genome annotationGenomicsGenome annotation is the process of identifying where genes and other features lie in a genome sequence and describing what each of them does.
- Genome-wide association studyGenomicsA genome-wide association study (GWAS) scans the genomes of many people to find genetic variants that are more common in those with a trait or disease.
- GenotypeGeneticsA genotype is the genetic makeup of an organism, either at one locus, such as Aa, or across its whole genome, including alleles it does not express.
- Geologic time scalePaleontologyThe geologic time scale divides Earth's 4.6-billion-year history into eons, eras, periods and epochs, marked by events in the rock record.
- Germ layerDevelopmental BiologyA germ layer is one of the primary cell layers of an early animal embryo (ectoderm, mesoderm or endoderm) from which all its tissues and organs develop.
- GerminationBotanyIn botany, germination is the restart of growth by a seed's embryo, from the first uptake of water until the young root breaks out of the seed coat.
- GiardiaParasitologyGiardia is a genus of flagellated protozoan parasites; Giardia duodenalis infects the small intestine and causes giardiasis, a common diarrheal illness.
- Glial cellNeuroscienceA glial cell is a non-neuronal cell of the nervous system that supports, insulates, feeds and protects neurons and helps regulate their signaling.
- Glomerular filtration ratePhysiologyGlomerular filtration rate is the volume of fluid both kidneys filter out of the blood each minute, the standard measure of kidney function.
- GlucagonPhysiologyGlucagon is a peptide hormone made by alpha cells of the pancreas that raises blood glucose, mainly by making the liver release glucose.
- GluconeogenesisBiochemistryGluconeogenesis is the metabolic pathway that makes new glucose from non-carbohydrate sources such as lactate, glycerol and certain amino acids.
- GlucoseBiochemistryGlucose is a six-carbon simple sugar, C6H12O6, that serves as the main fuel for most cells and is the sugar carried in human blood.
- Glycemic indexFood NutritionThe glycemic index is a scale up to 100 ranking carbohydrate foods by how much they raise blood glucose after eating, compared with the same amount of glucose.
- GlycogenBiochemistryGlycogen is a large, highly branched polymer of glucose that animals and fungi use to store carbohydrate, mainly in the liver and skeletal muscle.
- GlycolysisBiochemistryGlycolysis is the ten-step metabolic pathway that splits one glucose molecule into two pyruvate molecules, giving a net gain of two ATP.
- Golgi apparatusCell BiologyThe Golgi apparatus is a stack of flattened membrane sacs that modifies, sorts and packages proteins and lipids sent from the endoplasmic reticulum.
- Gram stainMicrobiologyThe Gram stain is a lab staining method that sorts bacteria into Gram-positive (purple) and Gram-negative (pink) groups based on their cell walls.
- Gram-negative bacteriaMicrobiologyGram-negative bacteria have a thin peptidoglycan wall wrapped in an outer membrane, so they lose the purple dye in a Gram stain and look pink.
- Gram-positive bacteriaMicrobiologyGram-positive bacteria have a thick peptidoglycan cell wall and no outer membrane, so they keep the purple crystal violet dye in a Gram stain.
- GranulomaPathologyA granuloma is a small, organized cluster of activated macrophages and other immune cells that walls off something the body cannot easily clear.
- GymnospermBotanyA gymnosperm is a seed plant whose seeds develop exposed on cone scales or similar structures rather than enclosed in an ovary, as in pines and cycads.
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- HabitatEcologyIn ecology, a habitat is the natural place where an organism or population lives, which supplies the food, water, shelter and space it needs to survive.
- Half-lifePharmacologyHalf-life is the time it takes for the concentration of a drug in the blood, or its amount in the body, to fall by half.
- HaploidGeneticsHaploid describes a cell or organism that has a single set of chromosomes, such as a human egg or sperm cell with 23 chromosomes.
- Hardy–Weinberg equilibriumGeneticsHardy–Weinberg equilibrium is the state in which allele and genotype frequencies in a population stay constant from one generation to the next.
- Health equityPublic HealthHealth equity means every person has a fair chance to be as healthy as possible, with no avoidable, unjust differences in health between social groups.
- HeartHuman AnatomyThe heart is the hollow, muscular organ in the chest whose four chambers pump blood through the lungs and then around the rest of the body.
- Heart failureMedicineHeart failure is a long-term condition in which the heart fails to pump as much blood as the body needs, even though it has not stopped beating.
- HelicaseMolecular BiologyA helicase is an enzyme that uses energy from ATP to unwind a nucleic acid double helix, separating the two strands so they can be copied or repaired.
- HelminthParasitologyA helminth is a parasitic worm, such as a roundworm, tapeworm or fluke, that lives in a host and is usually visible to the eye as an adult.
- Helper T cellImmunologyA helper T cell is a CD4 T lymphocyte that coordinates immune responses, releasing cytokines that activate B cells, killer T cells and macrophages.
- Hematopoietic stem cellStem Cell BiologyA hematopoietic stem cell is a multipotent stem cell, found mainly in the bone marrow, that renews itself and gives rise to every type of blood cell.
- HemoglobinPhysiologyHemoglobin is the iron-containing protein in red blood cells that picks up oxygen in the lungs and releases it to the body's tissues.
- HemorrhagePathologyA hemorrhage is an escape of blood from a ruptured or damaged blood vessel, either out of the body or into its tissues and cavities.
- HemostasisPhysiologyHemostasis is the body's process for stopping bleeding from a damaged blood vessel, through vessel constriction, a platelet plug and a fibrin clot.
- HepatitisMedicineHepatitis is liver inflammation, most often caused by a hepatitis virus but also by alcohol, toxins, some medicines or autoimmune disease.
- Herd immunityEpidemiologyHerd immunity is the indirect protection a population gains when so many people are immune that an infection can no longer spread easily.
- HerniaSurgeryA hernia is a bulge of an organ or tissue, often fat or a loop of bowel, through a weak spot in the wall that normally holds it in place.
- HeterozygousGeneticsHeterozygous describes an organism that carries two different alleles of a gene at a given locus, such as one dominant and one recessive allele.
- HippocampusNeuroscienceThe hippocampus is a curved structure deep in each temporal lobe of the brain that is essential for forming new memories and finding our way around.
- HistamineImmunologyHistamine is a small signaling molecule, released mainly by mast cells and basophils, that drives many allergy symptoms and also controls stomach acid.
- HistoneMolecular BiologyA histone is a small, positively charged protein that DNA winds around to form nucleosomes, packing DNA in the nucleus and helping control gene activity.
- HIVVirologyHIV is a retrovirus that infects and destroys CD4 helper T cells, weakening the immune system and, without treatment, leading to AIDS.
- HomeostasisPhysiologyHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- HomininPaleontologyA hominin is any member of the human lineage, the group of species, including modern humans, that are more closely related to us than to chimpanzees.
- Homologous structuresEvolutionHomologous structures are body parts in different species that share an underlying plan because they were inherited from a common ancestor.
- HomozygousGeneticsHomozygous describes an organism that carries two identical alleles of a gene at a given locus, one inherited from each parent.
- HormonePhysiologyA hormone is a chemical messenger released into the blood by a gland or cell that changes the activity of distant target cells with matching receptors.
- Hox genesDevelopmental BiologyHox genes are a family of genes coding for transcription factors that give each region along an animal's head-to-tail axis its identity during development.
- Hydrogen bondBiochemistryA hydrogen bond is a weak attraction between a slightly positive hydrogen atom, bonded to oxygen or nitrogen, and a nearby electronegative atom.
- HyperplasiaPathologyHyperplasia is the enlargement of a tissue or organ through a rise in its number of cells, which still look normal under the microscope.
- HypersensitivityImmunologyHypersensitivity is an immune response that is excessive or misdirected, so that it damages the body's own tissues instead of only removing a threat.
- HypertensionMedicineHypertension is a long-term condition in which the pressure of blood against artery walls stays higher than normal, straining the heart and vessels.
- HyperthyroidismMedicineHyperthyroidism is a condition in which the thyroid gland releases more hormone than the body needs, speeding up metabolism and many body functions.
- HypertrophyPathologyHypertrophy is the enlargement of a tissue or organ because its individual cells grow larger, rather than because the number of cells increases.
- HyphaMycologyA hypha is one of the long, branching threads that make up the body of most fungi; a tangled mass of hyphae forms a mycelium.
- HypothyroidismMedicineHypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone, so metabolism and many body functions slow down.
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- ImmunotherapyOncologyImmunotherapy is treatment that works by boosting, steering or suppressing the immune system, best known as a way to help it attack cancer.
- IncidenceEpidemiologyIncidence is the number of new cases of a disease that arise in a population at risk during a specified period of time.
- Incomplete dominanceGeneticsIncomplete dominance is a pattern of inheritance in which a heterozygote has a phenotype intermediate between those of the two homozygotes.
- Incubation periodEpidemiologyThe incubation period is the time between infection with a pathogen and the first appearance of signs or symptoms of the disease it causes.
- Index fossilPaleontologyAn index fossil is the fossil of a widespread, short-lived species used to identify and match rock layers of the same age in different places.
- Induced pluripotent stem cellStem Cell BiologyAn induced pluripotent stem cell is an adult body cell, such as a skin cell, reprogrammed in the lab to be pluripotent, much like an embryonic stem cell.
- InfarctionPathologyInfarction is the death of an area of tissue, called an infarct, caused by a sudden loss of its blood supply, as in a heart attack or a stroke.
- InflammationImmunologyInflammation is the body's protective response to infection or injury, in which leaky, widened blood vessels bring immune cells and fluid to the site.
- InfluenzaVirologyInfluenza, or flu, is a contagious infection of the nose, throat and lungs caused by influenza viruses that brings sudden fever, cough and aches.
- Innate immunityImmunologyInnate immunity is the inborn, fast-acting set of body defenses that reacts to any invader in the same general way, with no prior exposure needed.
- InsectEntomologyAn insect is an arthropod with a body divided into head, thorax and abdomen, three pairs of jointed legs, one pair of antennae and usually wings.
- InsulinPhysiologyInsulin is a peptide hormone made by beta cells in the pancreas that lowers blood glucose by helping body cells take up and store sugar.
- InterferonImmunologyAn interferon is a cytokine that cells release when infected by a virus, putting nearby cells into an antiviral state and activating immune cells.
- IntronMolecular BiologyAn intron is a stretch of a gene that is copied into RNA but cut out by splicing before the RNA is used, so it does not code for protein.
- Invasive speciesEcologyAn invasive species is a non-native organism that spreads after people bring it to a new region and harms the environment, the economy or human health.
- InvertebrateZoologyAn invertebrate is any animal without a backbone, a broad grouping that includes insects, worms, mollusks, jellyfish and most animal species.
- IschemiaPathologyIschemia is a shortage of blood supply to an organ or tissue, usually from a narrowed or blocked artery, that starves its cells of oxygen and nutrients.
- Isoelectric focusingProteomicsIsoelectric focusing is a technique that separates proteins by their isoelectric point, the pH at which a protein carries no net electric charge.
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- JaundiceMedicineJaundice is yellowing of the skin and the whites of the eyes that occurs when the pigment bilirubin builds up in the blood.
- JejunumHuman AnatomyThe jejunum is the middle stretch of the small intestine, lying between the duodenum and ileum, and a main site where digested nutrients are absorbed.
- Jugular veinHuman AnatomyA jugular vein is one of the large paired veins in the neck that return blood from the brain, face and scalp toward the heart.
- Juxtaglomerular apparatusPhysiologyThe juxtaglomerular apparatus is a cluster of specialized kidney cells beside each glomerulus that senses salt and blood pressure and releases renin.
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- KaryotypeGeneticsA karyotype is the full set of chromosomes in a cell, or a picture of them sorted into pairs, used to check chromosome number and structure.
- Ketone bodyBiochemistryA ketone body is a water-soluble fuel made by the liver from fatty acids when glucose is scarce and used for energy by the brain, heart and muscle.
- Keystone speciesEcologyA keystone species is one whose effect on its ecosystem is far larger than its numbers suggest, so that removing it reshapes the whole community.
- KidneyHuman AnatomyThe kidneys are two bean-shaped organs that filter the blood to make urine, balancing the body's water, salts and acid and helping set blood pressure.
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- LaparoscopySurgeryLaparoscopy is a minimally invasive procedure that passes a thin camera, the laparoscope, through a small cut to view and operate inside the abdomen or pelvis.
- LarvaEntomologyA larva is the young, free-living stage of an animal that hatches in a form unlike the adult and must change shape, by metamorphosis, to mature.
- LarynxHuman AnatomyThe larynx, or voice box, is the cartilage-framed passage in the neck between the pharynx and trachea that guards the airway and produces the voice.
- LeukemiaOncologyLeukemia is a cancer of the blood-forming tissue, usually the bone marrow, that fills the marrow and blood with abnormal white blood cells.
- LichenMycologyA lichen is a composite organism formed by a fungus living in close partnership with a photosynthetic alga or cyanobacterium, or sometimes both.
- Life expectancyPublic HealthLife expectancy is the average number of further years people of a given age would live if current death rates at each age stayed the same.
- LigamentHuman AnatomyA ligament is a band of tough, fibrous connective tissue that joins one bone to another and keeps a joint stable while letting it move.
- Lineweaver–Burk plotBiochemistryA Lineweaver–Burk plot is a straight-line graph of an enzyme's 1/rate against 1/substrate concentration, used to find Km and Vmax.
- LipidBiochemistryA lipid is one of a varied group of biological molecules, including fats, oils, phospholipids, waxes and steroids, that do not dissolve in water.
- LiverHuman AnatomyThe liver is the largest gland and internal organ, lying in the upper right abdomen, where it makes bile, processes nutrients and clears toxins.
- Livor mortisForensic MedicineLivor mortis is the purplish-red discoloration that appears in the lowest parts of a body after death as blood settles under the pull of gravity.
- Lymph nodeImmunologyA lymph node is a small, bean-shaped organ of the lymphatic system that filters lymph and is where lymphocytes meet antigens to start immune responses.
- LymphomaOncologyLymphoma is a cancer of lymphocytes, the immune cells of the lymphatic system, that usually forms solid tumors in lymph nodes and lymphoid tissue.
- Lysogenic cycleVirologyThe lysogenic cycle is a phage life cycle in which viral DNA joins the host bacterium's chromosome and is copied with it instead of killing the cell.
- LysosomeCell BiologyA lysosome is a membrane-bound organelle filled with acidic digestive enzymes that break down worn-out cell parts, food particles and microbes.
- Lytic cycleVirologyThe lytic cycle is a viral life cycle in which a phage takes over a bacterial cell, makes many copies of itself, then bursts the cell to release them.
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- MacronutrientFood NutritionA macronutrient is a nutrient needed in large amounts, namely carbohydrate, protein or fat, which together supply energy and the raw materials for growth.
- MacrophageImmunologyA macrophage is a large white blood cell that engulfs and digests microbes, dead cells and debris, and signals other immune cells to act.
- Major histocompatibility complexImmunologyThe major histocompatibility complex is a set of genes whose proteins display protein fragments on cell surfaces so that T cells can inspect them.
- MalariaParasitologyMalaria is a life-threatening infection caused by Plasmodium parasites, which infected female Anopheles mosquitoes pass to people when they bite.
- Malignant tumorOncologyA malignant tumor is a cancerous mass whose cells grow without control, invade surrounding tissue and can spread to distant organs.
- MalnutritionFood NutritionMalnutrition is a state in which someone's intake of energy or nutrients is too low, too high or unbalanced, harming growth, health or body function.
- MammalZoologyA mammal is a vertebrate animal that has hair and feeds its young on milk made by the mother's mammary glands.
- Mass extinctionPaleontologyA mass extinction is an event in which a large share of Earth's species, often three-quarters or more, dies out in a geologically short time.
- Mass spectrometryProteomicsMass spectrometry is an analytical technique that turns molecules into charged ions and sorts them by mass-to-charge ratio to identify and measure them.
- Mast cellImmunologyA mast cell is a tissue-dwelling immune cell packed with granules of histamine and other mediators, which it releases in allergy and inflammation.
- MediastinumHuman AnatomyThe mediastinum is the middle region of the chest, between the two lungs, that holds the heart, great vessels, trachea, esophagus and thymus.
- MeiosisCell BiologyMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- Mendelian inheritanceGeneticsMendelian inheritance is the pattern by which single genes pass from parents to offspring, following the laws of segregation and independent assortment.
- Menstrual cyclePhysiologyThe menstrual cycle is the roughly monthly series of hormone-driven changes in the ovaries and uterus that prepares the body for a possible pregnancy.
- MeristemBotanyA meristem is a region of unspecialized, dividing plant cells, as at shoot and root tips, that supplies new cells for growth throughout a plant's life.
- Mesenchymal stem cellStem Cell BiologyA mesenchymal stem cell is a multipotent adult cell, found in bone marrow, fat and other tissues, that can turn into bone, cartilage or fat cells.
- Messenger RNAMolecular BiologyMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- Metabolic engineeringSynthetic BiologyMetabolic engineering is the redesign of a cell's metabolic pathways with genetic tools so that it makes more of a useful product, or makes a new one.
- Metabolic syndromeMedicineMetabolic syndrome is a cluster of linked risk factors, including a large waist, high blood pressure, high blood sugar and abnormal blood fats.
- MetabolismBiochemistryMetabolism is the full set of chemical reactions in a cell or organism, both those that break molecules down for energy and those that build them up.
- MetagenomicsGenomicsMetagenomics is the study of all the DNA recovered directly from a sample, such as soil, seawater or stool, to reveal its whole community of microbes.
- MetamorphosisEntomologyMetamorphosis is a marked change in body form during an animal's development, as when a caterpillar becomes a butterfly or a tadpole a frog.
- MetaplasiaPathologyMetaplasia is the replacement of one mature cell type by another in a tissue, usually as an adaptation to long-term irritation or injury.
- MetastasisOncologyMetastasis is the spread of a cancer from its first site to distant organs, where escaped cells settle and grow into secondary tumors.
- Michaelis constantBiochemistryThe Michaelis constant (Km) is the substrate concentration at which an enzyme-catalyzed reaction runs at half its maximum rate.
- MicrobiomeMicrobiologyA microbiome is the community of bacteria, fungi, viruses and other microbes, with their genes, that lives in a particular place, such as the human gut.
- MicronutrientFood NutritionA micronutrient is a vitamin or mineral that the body needs only in tiny amounts but cannot do without, such as iron, iodine, vitamin A or folate.
- MicroRNAMolecular BiologyA microRNA is a short RNA, about 22 nucleotides long, that does not code for protein but silences genes by pairing with their messenger RNAs.
- MicrotubuleCell BiologyA microtubule is a hollow tube built from the protein tubulin, one of the main cytoskeleton fibers, used for cell shape, transport and cell division.
- Minimal genomeSynthetic BiologyA minimal genome is the smallest set of genes that allows a cell to grow and divide on its own under defined laboratory conditions.
- MitochondrionCell BiologyA mitochondrion is a double-membraned organelle that makes most of a eukaryotic cell's ATP by breaking down fuel molecules with oxygen.
- MitosisCell BiologyMitosis is the division of a cell's nucleus that gives each of two daughter cells an identical, complete set of chromosomes.
- MoldMycologyA mold is a fungus that grows as a fuzzy network of branching threads called hyphae, often seen on damp walls and spoiling food.
- Molecular cloningBiotechnologyMolecular cloning is a set of laboratory methods for inserting a specific DNA fragment into a vector and copying it many times inside host cells.
- Monoclonal antibodyBiotechnologyA monoclonal antibody is one of a set of identical antibodies made by clones of a single B cell, so that all of them bind the same site on one antigen.
- MorbidityPublic HealthMorbidity is the state of having a disease, injury or disability, and also the amount of illness in a population, measured by incidence and prevalence.
- MorphogenDevelopmental BiologyA morphogen is a signaling molecule that spreads through developing tissue as a gradient, so cells adopt different fates depending on how much they receive.
- Mortality rateEpidemiologyA mortality rate is how often death occurs in a defined population over a set period, usually given as deaths per 1,000 or 100,000 people.
- mRNA vaccineVirologyAn mRNA vaccine delivers messenger RNA coding for a pathogen's protein, so the body's own cells make that antigen and train the immune system.
- MRSAMicrobiologyMRSA is any strain of the bacterium Staphylococcus aureus that resists methicillin and nearly all other beta-lactam antibiotics, including penicillins.
- Multiple sequence alignmentBioinformaticsA multiple sequence alignment lines up three or more DNA, RNA or protein sequences so that positions sharing an evolutionary origin fall in one column.
- MultipotencyStem Cell BiologyMultipotency is the ability of a stem cell to develop into several kinds of specialized cell, but only those of one tissue or a closely related family.
- MushroomMycologyA mushroom is the visible spore-producing fruiting body of certain fungi, usually a stalk and cap that grows from a mycelium hidden in soil or wood.
- MutationGeneticsA mutation is a lasting change in an organism's DNA sequence, ranging from a single altered base to large rearrangements of chromosomes.
- MutualismEcologyMutualism is a relationship between two species in which both partners benefit, such as flowering plants and the insects that pollinate them.
- MyceliumMycologyA mycelium is the branching network of thread-like hyphae that forms the main feeding body of a fungus, usually hidden in soil, wood or food.
- MycorrhizaMycologyA mycorrhiza is a mutually beneficial partnership between a fungus and plant roots, trading water and soil minerals for sugars made by the plant.
- MycosisMycologyA mycosis is a disease caused by fungi infecting the body, from mild skin infections like athlete's foot to life-threatening lung or blood infections.
- MyelinNeuroscienceMyelin is the fatty, layered sheath that glial cells wrap around many axons, insulating them so nerve impulses travel faster and more efficiently.
- Myocardial infarctionMedicineA myocardial infarction, or heart attack, is the death of part of the heart muscle after its blood supply through a coronary artery is suddenly cut off.
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- Natural killer cellImmunologyA natural killer cell is an innate lymphocyte that recognizes and kills virus-infected and cancerous cells without needing earlier exposure to them.
- Natural selectionEvolutionNatural selection is the process by which inherited traits that improve survival and reproduction become more common in a population over generations.
- NecrosisPathologyNecrosis is the unplanned death of cells or tissue caused by injury, infection, toxins or loss of blood supply, and it usually triggers inflammation.
- Needleman–Wunsch algorithmBioinformaticsThe Needleman–Wunsch algorithm is a dynamic programming method that finds the best-scoring global alignment of two sequences along their entire length.
- Negative feedbackPhysiologyNegative feedback is a control process in which a change in a body variable sets off responses that reverse the change, keeping it near a set point.
- NematodeParasitologyA nematode, or roundworm, is an unsegmented worm with a round body and a tough cuticle, from a vast phylum of free-living and parasitic species.
- NephronPhysiologyA nephron is the microscopic functional unit of the kidney, which filters blood and then adjusts the filtered fluid to form urine.
- NeuronNeuroscienceA neuron is a nerve cell, the basic signaling unit of the nervous system, which receives information and passes it on as electrical and chemical signals.
- NeuroplasticityNeuroscienceNeuroplasticity is the nervous system's ability to change its structure and connections in response to experience, learning, development or injury.
- NeurotransmitterNeuroscienceA neurotransmitter is a chemical messenger that a neuron releases at a synapse to excite or inhibit a target neuron, muscle cell or gland cell.
- NeurulationDevelopmental BiologyNeurulation is the embryonic process in which a strip of ectoderm folds up into the neural tube, the forerunner of the brain and spinal cord.
- NeutrophilImmunologyA neutrophil is the most common white blood cell in human blood, a short-lived phagocyte that rushes to infections and destroys bacteria and fungi.
- Next-generation sequencingGenomicsNext-generation sequencing (NGS) is a set of high-throughput methods that read the sequences of millions of short DNA fragments in parallel.
- Nitrogen cycleEcologyThe nitrogen cycle is the set of mainly microbial processes that move nitrogen between atmospheric gas, ammonium, nitrate and living organisms.
- Noncommunicable diseasePublic HealthA noncommunicable disease is a long-lasting illness, such as heart disease, cancer or diabetes, that does not pass from one person to another.
- NondisjunctionGeneticsNondisjunction is the failure of paired chromosomes or sister chromatids to separate in cell division, leaving cells with the wrong chromosome number.
- NSAIDPharmacologyAn NSAID is a non-steroid medicine, such as ibuprofen or aspirin, that relieves pain, fever and inflammation by blocking cyclooxygenase enzymes.
- NucleolusCell BiologyThe nucleolus is a dense region inside the nucleus, with no membrane of its own, where ribosomal RNA is made and built into ribosome subunits.
- NucleotideBiochemistryA nucleotide is a single unit of DNA or RNA, made of a nitrogen-containing base, a five-carbon sugar and one or more phosphate groups.
- NucleusCell BiologyThe nucleus is the membrane-bound organelle that holds a eukaryotic cell's chromosomes and controls which of its genes are used and when.
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- ObesityMedicineObesity is a chronic disease in which excess body fat builds up enough to harm health, defined in adults as a body mass index of 30 or more.
- Ocean acidificationMarine BiologyOcean acidification is the ongoing fall in the pH of seawater, driven mainly by the uptake of carbon dioxide that human activities release into the air.
- Odds ratioEpidemiologyAn odds ratio is a measure of association that compares the odds of an outcome or exposure in one group with the odds in another group.
- Okazaki fragmentMolecular BiologyAn Okazaki fragment is one of the short pieces of DNA made on the lagging strand during DNA replication and later joined into one continuous strand.
- Omega-3 fatty acidFood NutritionAn omega-3 fatty acid is a polyunsaturated fatty acid whose first double bond is three carbons from the methyl end of its chain, as in ALA, EPA and DHA.
- OncogeneOncologyAn oncogene is a mutated or overactive form of a normal growth-promoting gene that pushes cells to divide uncontrollably and can cause cancer.
- OogenesisDevelopmental BiologyOogenesis is the process by which egg cells form in the ovary, beginning before birth and yielding one mature egg and small polar bodies from each oocyte.
- OperonMolecular BiologyAn operon is a cluster of genes in bacteria that share one promoter, are switched on and off together and are copied into a single messenger RNA.
- OpioidPharmacologyAn opioid is a natural or synthetic substance that acts on the body's opioid receptors, giving strong pain relief along with a risk of addiction.
- OrganelleCell BiologyAn organelle is a specialized structure inside a cell, usually wrapped in its own membrane, that carries out a particular job for the cell.
- OrganogenesisDevelopmental BiologyOrganogenesis is the stage of embryonic development in which the three germ layers form the rudiments of the body's organs and organ systems.
- OrganoidStem Cell BiologyAn organoid is a tiny, self-organizing, three-dimensional tissue grown from stem cells in the lab that mimics the structure and some functions of an organ.
- OsmosisCell BiologyOsmosis is the diffusion of water across a selectively permeable membrane, from the side with fewer dissolved solutes to the side with more.
- Oxidative phosphorylationBiochemistryOxidative phosphorylation is how cells make most of their ATP, using a proton gradient built by the electron transport chain to drive ATP synthase.
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- PancreasHuman AnatomyThe pancreas is a gland behind the stomach that sends digestive enzymes to the small intestine and releases insulin and glucagon into the blood.
- PandemicEpidemiologyA pandemic is an epidemic that crosses international borders and spreads over several continents, typically infecting very many people.
- ParasiteParasitologyA parasite is a living thing that makes its home on or inside a host organism and feeds from it, usually causing the host harm.
- Parasympathetic nervous systemNeuroscienceThe parasympathetic nervous system is the autonomic division that conserves energy and controls rest-and-digest activities such as digestion.
- Parkinson's diseaseNeuroscienceParkinson's disease is a progressive brain disorder in which dopamine-producing neurons die, causing tremor, stiffness, slow movement and poor balance.
- PathogenMicrobiologyA pathogen is a microbe or other agent, such as a virus, bacterium, fungus, parasite or prion, that can cause disease in a host.
- PedigreeGeneticsA pedigree is a family tree chart that shows how a trait or genetic condition is passed down through the generations of a family.
- PenicillinPharmacologyPenicillin is a group of beta-lactam antibiotics, first found in a mold, that kill bacteria by blocking the building of their cell walls.
- Peptide bondBiochemistryA peptide bond is the covalent link that joins the carboxyl group of one amino acid to the amino group of the next, releasing a water molecule.
- PeptidoglycanMicrobiologyPeptidoglycan is the mesh-like polymer of sugars and short peptides that forms the bacterial cell wall and gives bacteria their shape and strength.
- pHBiochemistrypH is a number, usually on a scale of 0 to 14, that shows how acidic or basic a water-based solution is from its concentration of hydrogen ions.
- PhagocytosisCell BiologyPhagocytosis is the way a cell engulfs a large particle, such as a bacterium or a dead cell, in a pocket of membrane and then digests it.
- PharmacodynamicsPharmacologyPharmacodynamics is the study of what a drug does to the body: how it acts on its molecular target and how its effects vary with dose.
- PharmacokineticsPharmacologyPharmacokinetics is the study of how the body absorbs, distributes, metabolizes and excretes a drug, and how drug levels change over time.
- PharynxHuman AnatomyThe pharynx, or throat, is the muscular tube behind the nose and mouth that carries air to the larynx and food to the esophagus.
- PhenotypeGeneticsA phenotype is the set of observable traits of an organism, such as its height or blood group, produced by its genotype acting with its environment.
- PheromoneEntomologyA pheromone is a chemical signal released by an animal that triggers a specific behavior or physiological response in other members of its species.
- PhloemBotanyPhloem is the living vascular tissue of plants that carries sugars and other organic nutrients from leaves to the parts that use or store them.
- PhospholipidBiochemistryA phospholipid is a lipid with two fatty acid tails and a head containing phosphate, and it is the main building block of all cell membranes.
- PhosphorylationBiochemistryPhosphorylation is the attachment of a phosphate group to a protein, sugar or other molecule, a key way cells make ATP and switch proteins on or off.
- PhotosynthesisBotanyPhotosynthesis is the process in which plants, algae and cyanobacteria capture light energy and store it in sugar built from carbon dioxide and water.
- PhototropismBotanyPhototropism is the growth of a plant or other organism toward or away from light, as when a seedling bends toward a sunny window.
- Phylogenetic treeEvolutionA phylogenetic tree is a branching diagram that shows the evolutionary relationships among organisms or genes as a hypothesis of shared descent.
- PhylumZoologyA phylum is a major rank in biological classification, below kingdom and above class, grouping organisms that share a basic body plan.
- PhytoplanktonMarine BiologyPhytoplankton are microscopic photosynthetic organisms that drift near the surface of oceans and lakes and form the base of most aquatic food webs.
- Pituitary glandHuman AnatomyThe pituitary gland is a pea-sized endocrine gland below the brain that, under hypothalamic control, releases hormones governing growth and other glands.
- PlaceboPharmacologyA placebo is an inactive treatment, such as a sugar pill or a sham procedure, made to look like a real one and used for comparison in clinical trials.
- PlanktonMarine BiologyPlankton are organisms that drift in oceans, lakes and rivers because they cannot swim against currents, from microscopic algae to large jellyfish.
- PlasmidMolecular BiologyA plasmid is a small, usually circular DNA molecule that copies itself independently of the main chromosome, found mostly in bacteria.
- PlasmodiumParasitologyPlasmodium is a genus of single-celled parasites, spread by Anopheles mosquitoes, that infect liver and red blood cells and cause malaria.
- PlateletPhysiologyA platelet is a small cell fragment in the blood that helps stop bleeding by plugging damaged vessels and helping a blood clot form.
- PluripotencyStem Cell BiologyPluripotency is the ability of a cell to give rise to every cell type of the body, from all three germ layers, though not to a whole organism on its own.
- PneumoniaMedicinePneumonia is an infection of one or both lungs in which the tiny air sacs fill with fluid and pus, making it harder to take in oxygen.
- PollinationBotanyPollination is the delivery of pollen to the female reproductive parts of a seed plant, the step that makes fertilization and seed formation possible.
- Polygenic inheritanceGeneticsPolygenic inheritance is the inheritance of a trait controlled by many genes, each with a small effect, giving continuous variation such as height.
- Polymerase chain reactionMolecular BiologyThe polymerase chain reaction (PCR) is a lab technique that copies one chosen stretch of DNA over and over until there are billions of copies.
- PopulationEcologyIn ecology, a population is all the individuals of one species that live in the same area at the same time and can breed with one another.
- Positive feedbackPhysiologyPositive feedback is a control process in which a change triggers responses that amplify that same change, driving a process quickly to an end point.
- Post-translational modificationMolecular BiologyA post-translational modification is a chemical change made to a protein after it is built on the ribosome, often altering its activity or location.
- Postmortem intervalForensic MedicineThe postmortem interval is the time since a person died, estimated by forensic experts from body changes, temperature, insects and other evidence.
- PredationEcologyPredation is an interaction between species in which one organism, the predator, catches, kills and eats another living organism, its prey.
- PrevalenceEpidemiologyPrevalence is the share of a population living with a particular disease or condition, either at one point in time or across a set period.
- Primary producerEcologyA primary producer is an organism that makes its own food from inorganic substances, using light or chemical energy, and so forms the base of a food chain.
- ProbioticMicrobiologyA probiotic is a live microbe, usually a bacterium or yeast, taken in large enough numbers to give a health benefit shown in studies.
- ProkaryoteCell BiologyA prokaryote is a usually single-celled organism, a bacterium or an archaeon, whose cell has no nucleus or other membrane-bound organelles.
- PromoterMolecular BiologyIn molecular biology, a promoter is a stretch of DNA, usually just upstream of a gene, where RNA polymerase binds so that transcription can begin.
- ProteinBiochemistryA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
- Protein foldingBiochemistryProtein folding is the process by which a newly made chain of amino acids coils and folds into the specific three-dimensional shape it needs to work.
- ProteomeProteomicsA proteome is the complete collection of proteins made by a cell, tissue or organism at a given time, including all their modified forms.
- ProteomicsProteomicsProteomics is the large-scale study of the proteome, the full set of proteins in a cell, tissue or organism, including their amounts, changes and interactions.
- ProtozoaParasitologyProtozoa are single-celled eukaryotes that do not photosynthesize, usually move on their own and feed on other organisms or organic matter.
- Public healthPublic HealthPublic health is the science and practice of preventing disease and injury and promoting health across whole communities rather than individual patients.
- Punnett squareGeneticsA Punnett square is a grid used in genetics to predict the possible genotypes of offspring, and how likely each is, from the alleles of two parents.
- PupaEntomologyA pupa is the non-feeding stage between larva and adult in insects with complete metamorphosis, during which the body is rebuilt into its adult form.
- PutrefactionForensic MedicinePutrefaction is the breakdown of a dead body's soft tissues by bacteria, which produces gas, discoloration and the foul smell of decay.
Q
- Quantitative PCRMolecular BiologyQuantitative PCR (qPCR) is a form of PCR that tracks DNA copying by fluorescence after every cycle to measure how much of a target sequence is present.
- QuarantinePublic HealthQuarantine is the separation and restricted movement of people or animals exposed to a contagious disease who are not yet sick, in case they become ill.
- Quaternary structureBiochemistryQuaternary structure is the way two or more folded polypeptide chains, called subunits, fit together to form a single working protein.
- Quorum sensingMicrobiologyQuorum sensing is a system of chemical signals that lets bacteria sense how crowded their population is and switch genes on or off together.
R
- Radiometric datingPaleontologyRadiometric dating is a method of finding the age of rocks, fossils or artifacts by measuring how much of a radioactive isotope in them has decayed.
- Randomized controlled trialEpidemiologyA randomized controlled trial is an experiment that assigns people by chance to a treatment or a comparison group to test whether the treatment works.
- ReceptorPharmacologyA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- Recessive alleleGeneticsA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- Recombinant DNABiotechnologyRecombinant DNA is DNA made in the laboratory by joining pieces of DNA from different sources, often different species, into one molecule.
- Red blood cellPhysiologyA red blood cell, or erythrocyte, is a disc-shaped blood cell without a nucleus that is packed with hemoglobin and carries oxygen around the body.
- Regenerative medicineStem Cell BiologyRegenerative medicine is the field that aims to repair or replace damaged cells, tissues and organs using cells, biomaterials and genes.
- Relative riskEpidemiologyRelative risk is the risk of an outcome in an exposed group divided by the risk in an unexposed group, showing how strongly the two are linked.
- Renin–angiotensin–aldosterone systemPhysiologyThe renin–angiotensin–aldosterone system is a hormone cascade, begun by renin from the kidneys, that raises blood pressure and blood volume when they fall.
- Reporter geneMolecular BiologyA reporter gene is a gene whose product is easy to see or measure, joined to DNA of interest so that its activity or location can be tracked.
- Resting membrane potentialPhysiologyThe resting membrane potential is the steady voltage across a cell's membrane when it is not signaling, about -70 mV in a typical neuron, inside negative.
- Restriction enzymeMolecular BiologyA restriction enzyme is a bacterial protein that cuts DNA at a specific short sequence, making it a basic tool for cutting and joining DNA.
- RetrovirusVirologyA retrovirus is an RNA virus that copies its genome into DNA with reverse transcriptase and inserts that DNA into the host cell's chromosomes.
- Reverse transcriptaseVirologyReverse transcriptase is an enzyme that builds DNA from an RNA template, letting retroviruses such as HIV turn their RNA genome into DNA.
- Rheumatoid arthritisMedicineRheumatoid arthritis is a long-lasting autoimmune disease in which immune cells attack the lining of the joints, leaving them painful, swollen and stiff.
- RibosomeCell BiologyA ribosome is a molecular machine of RNA and protein that reads messenger RNA and joins amino acids in the order it specifies to build a protein.
- Ribosome binding siteMolecular BiologyA ribosome binding site is a short stretch of messenger RNA just before the start codon where a ribosome attaches to begin translating a bacterial gene.
- Rigor mortisForensic MedicineRigor mortis is the temporary stiffening of muscles after death, caused by loss of ATP, which leaves myosin locked onto actin until muscle proteins break down.
- Risk factorEpidemiologyA risk factor is a trait, exposure or behavior linked to a higher chance of developing a particular disease, injury or other health problem.
- RNAMolecular BiologyRNA is a usually single-stranded nucleic acid, built with the sugar ribose and the base uracil, that carries and uses genetic information to make proteins.
- RNA interferenceMolecular BiologyRNA interference is a natural process in which small RNA molecules guide the destruction or blocking of matching messenger RNAs, silencing specific genes.
- RNA sequencingGenomicsRNA sequencing (RNA-seq) is a method that uses high-throughput sequencing to identify and count the RNA molecules in a sample.
- RNA splicingMolecular BiologyRNA splicing is the step in which introns are cut out of a newly made RNA and its exons are joined, producing a mature RNA ready for use.
S
- Sanger sequencingGenomicsSanger sequencing is a method for reading the order of bases in DNA that uses chain-terminating nucleotides, developed by Frederick Sanger in the 1970s.
- SarcomaOncologyA sarcoma is a malignant tumor that arises in connective tissue, such as bone, cartilage, fat, muscle, blood vessels or fibrous tissue.
- SarcomerePhysiologyA sarcomere is the repeating contractile unit of striated muscle, the section of a myofibril between two Z-discs where actin and myosin interact.
- SchistosomiasisParasitologySchistosomiasis is an infection with Schistosoma blood flukes, whose larvae burrow through skin in fresh water and whose eggs damage organs.
- SDS-PAGEProteomicsSDS-PAGE is a lab technique that separates proteins by size, coating them in a charged detergent and pulling them through a gel with an electric field.
- Selection biasEpidemiologySelection bias is an error that arises when the people recruited into, or remaining in, a study differ in systematic ways from the target population.
- SensitivityEpidemiologySensitivity is the proportion of people who truly have a condition whom a diagnostic or screening test correctly identifies as positive.
- SepsisPathologySepsis is a life-threatening emergency in which the body's reaction to infection runs out of control and damages its own tissues and organs.
- Sequence alignmentBioinformaticsSequence alignment is a way of lining up two or more DNA, RNA or protein sequences so that matching positions share a column, showing how similar they are.
- SerotoninNeuroscienceSerotonin is a chemical messenger made from tryptophan that acts as a neurotransmitter in the brain and as a signal in the gut and blood.
- Sexual selectionEvolutionSexual selection is a form of natural selection in which traits spread because they help individuals win mates, even when they make survival harder.
- ShockPathologyShock is a life-threatening state in which the circulation fails to bring tissues the oxygen and nutrients their cells need.
- Sickle cell diseaseMedicineSickle cell disease is an inherited blood disorder in which abnormal hemoglobin bends red blood cells into stiff crescents that block small blood vessels.
- Signal transductionCell BiologySignal transduction is the chain of molecular events by which a cell turns a signal received at a receptor into a specific response inside the cell.
- Single nucleotide polymorphismGenomicsA single nucleotide polymorphism (SNP) is a position in the genome where people differ by a single DNA base, the most common kind of genetic variation.
- Skeletal muscleHuman AnatomySkeletal muscle is the striated, voluntary muscle tissue attached to bones by tendons that moves the body, holds posture and produces heat.
- Sliding filament theoryPhysiologyThe sliding filament theory is the model of muscle contraction in which thin actin filaments slide past thick myosin filaments, shortening each sarcomere.
- Small intestineHuman AnatomyThe small intestine is the long, coiled tube between the stomach and the large intestine where most digestion and nearly all nutrient absorption happen.
- Smith–Waterman algorithmBioinformaticsThe Smith–Waterman algorithm is a dynamic programming method that finds the highest-scoring local alignment, the best-matching region, of two sequences.
- Social determinants of healthPublic HealthSocial determinants of health are the nonmedical factors, such as income, education, housing and work, that shape a person's health throughout life.
- Sodium–potassium pumpPhysiologyThe sodium–potassium pump is a membrane enzyme that uses ATP to move three sodium ions out of a cell and two potassium ions in on each cycle.
- Southern blotMolecular BiologyA Southern blot is a laboratory method that finds a specific DNA sequence by separating DNA fragments on a gel, moving them to a membrane and probing them.
- SpeciationEvolutionSpeciation is the evolutionary process in which one ancestral species splits into two or more species whose members can no longer interbreed.
- SpeciesEvolutionIn biology, a species is a set of populations whose members can interbreed in nature and produce fertile offspring, isolated from other such sets.
- SpecificityEpidemiologySpecificity is the proportion of people who do not have a condition whom a diagnostic or screening test correctly identifies as negative.
- SpermatogenesisDevelopmental BiologySpermatogenesis is the process by which diploid stem cells in the testes divide and develop into haploid sperm, continuing from puberty through adult life.
- Spinal cordHuman AnatomyThe spinal cord is the column of nerve tissue in the vertebral canal that relays signals between the brain and the body and runs many reflexes.
- SporeMycologyA spore is a small, hardy reproductive cell made by fungi, plants and some microbes that can spread widely and grow into a new organism on its own.
- Staphylococcus aureusMicrobiologyStaphylococcus aureus is a gram-positive bacterium, carried in the nose by about a third of people, that causes skin and invasive infections.
- StatinPharmacologyA statin is a cholesterol-lowering drug that blocks HMG-CoA reductase, the liver enzyme that controls how fast the body makes its own cholesterol.
- Stem cellStem Cell BiologyA stem cell is an unspecialized cell that can both copy itself by dividing and give rise to specialized cell types such as blood, muscle or nerve cells.
- SterilizationMicrobiologyIn microbiology, sterilization is any process that kills or removes all microbial life, including bacterial endospores and viruses, from an object.
- StomachHuman AnatomyThe stomach is a J-shaped, muscular sac of the digestive tract that stores food, churns it with acid and enzymes, and starts the digestion of protein.
- StomataBotanyStomata are tiny pores in the epidermis of leaves and stems, each opened and closed by two guard cells to control gas exchange and water loss.
- StrokeMedicineA stroke is a sudden loss of brain function that happens when an artery supplying the brain is blocked or bursts and bleeds.
- Stroke volumePhysiologyStroke volume is the volume of blood that one ventricle of the heart pumps out with each beat, about 70 mL in a resting adult.
- SutureSurgeryIn surgery, a suture is a stitch, or the thread used to make it, that holds the edges of a wound or incision together while the tissue heals.
- SymbiosisEcologySymbiosis is a close, long-lasting relationship between two different species that may benefit both, benefit one, or benefit one at the other's expense.
- Sympathetic nervous systemNeuroscienceThe sympathetic nervous system is the division of the autonomic nervous system that readies the body for action, producing the fight-or-flight response.
- SynapseNeuroscienceA synapse is the junction where a neuron passes a signal to another cell, usually by releasing a neurotransmitter across a narrow gap.
- Synthetic biologySynthetic BiologySynthetic biology applies engineering design to living systems, building new genetic parts, circuits and genomes so that organisms can do useful jobs.
- Systems biologyBioinformaticsSystems biology studies how genes, proteins, metabolites and cells work together as networks, using big datasets and computer models to explain the whole.
T
- T cellImmunologyA T cell is a white blood cell that matures in the thymus and drives cell-based immunity, directing other immune cells or killing infected cells.
- TapewormParasitologyA tapeworm is a parasitic flatworm of the class Cestoda that lives in the intestines of vertebrates and absorbs food through its body surface.
- TaxonomyZoologyIn biology, taxonomy is the science of describing, naming and classifying organisms into a nested hierarchy of groups such as genus, family and order.
- TendonHuman AnatomyA tendon is a tough cord of dense connective tissue linking a muscle to a bone, which passes on the muscle's pull to move it.
- Therapeutic indexPharmacologyThe therapeutic index is a ratio comparing the dose of a drug that causes toxicity with the dose that produces the desired effect.
- ThermoregulationPhysiologyThermoregulation is the set of processes an organism uses to keep its body temperature within a set range by balancing heat gain and heat loss.
- ThrombosisPathologyThrombosis is the formation of a blood clot, called a thrombus, inside a blood vessel or the heart, where it can narrow or block the flow of blood.
- Thyroid glandHuman AnatomyThe thyroid gland is a butterfly-shaped endocrine gland in the front of the neck whose iodine-containing hormones set the body's metabolic rate.
- Tidal volumePhysiologyTidal volume is the amount of air that moves into or out of the lungs in one normal, relaxed breath, about 500 mL in a healthy adult.
- TotipotencyStem Cell BiologyTotipotency is the ability of a single cell to produce a whole organism, including the placenta and other tissues that lie outside the embryo.
- ToxicologyPharmacologyToxicology is the science of poisons: how chemicals and other agents harm living things, at what doses, and how poisoning is detected and treated.
- ToxoplasmosisParasitologyToxoplasmosis is an infection with the protozoan Toxoplasma gondii, usually mild but dangerous in pregnancy and for people with weakened immunity.
- Trace fossilPaleontologyA trace fossil is preserved evidence of an ancient organism's activity, such as a footprint, burrow or dropping, rather than a part of its body.
- TranscriptionMolecular BiologyTranscription is the process in which a cell copies the DNA sequence of a gene into a matching strand of RNA.
- Transcription factorMolecular BiologyA transcription factor is a protein that binds specific DNA sequences and controls whether, when and how strongly a nearby gene is transcribed into RNA.
- TranscriptomeGenomicsThe transcriptome is the full set of RNA molecules made in a cell, tissue or organism at a given time, showing which genes are active.
- TransductionMicrobiologyIn microbiology, transduction is the transfer of bacterial DNA from one cell to another by a bacteriophage, a virus that infects bacteria.
- Transfer RNAMolecular BiologyTransfer RNA is a short adaptor RNA that brings a specific amino acid to the ribosome and pairs with the matching mRNA codon through its anticodon.
- Transgenic organismBiotechnologyA transgenic organism is a living thing, such as a crop, mouse or bacterium, whose genome carries DNA from another species added by genetic engineering.
- TranslationMolecular BiologyTranslation is the process in which a ribosome reads the codons of a messenger RNA and links amino acids in that order to build a protein.
- TranspirationBotanyTranspiration is the escape of water vapor from a plant, mostly through open stomata in its leaves, which pulls more water up through the xylem.
- TransposonGeneticsA transposon is a DNA sequence that can move from one place in a genome to another, in some cases leaving a copy behind as it goes.
- TriglycerideBiochemistryA triglyceride is a fat molecule made of one glycerol joined to three fatty acids, and it is the main form in which the body stores energy.
- Trophic levelEcologyA trophic level is a feeding position in a food chain, such as producer, herbivore or carnivore, defined by how an organism obtains its energy.
- TuberculosisMedicineTuberculosis is a contagious disease caused by the bacterium Mycobacterium tuberculosis that most often attacks the lungs and spreads through the air.
- TumorOncologyA tumor is an abnormal mass of tissue made by cells that multiply too much or fail to die on time; it can be benign or malignant.
- Tumor suppressor geneOncologyA tumor suppressor gene makes a protein that restrains cell division or repairs damage, so losing both working copies can help a cell turn cancerous.
U
- UbiquitinCell BiologyUbiquitin is a small, highly conserved protein that cells attach to other proteins as a tag, most often to mark them for destruction.
- UnicellularCell BiologyUnicellular describes an organism whose whole body is a single cell, which carries out every life process, from feeding to reproducing, on its own.
- UracilMolecular BiologyUracil is one of the four nitrogen-containing bases in RNA, where it pairs with adenine and stands in for the thymine found in DNA.
- Urea cycleBiochemistryThe urea cycle is a loop of reactions, mainly in liver cells, that turns toxic ammonia from protein breakdown into urea for excretion in urine.
V
- VaccineImmunologyA vaccine is a preparation that trains the immune system to recognize a pathogen, so the body can fight it off quickly if it meets the real thing later.
- VacuoleCell BiologyA vacuole is a membrane-bound sac in a cell that stores water, nutrients or waste; most plant cells have one large central vacuole.
- VectorParasitologyIn disease biology, a vector is a living organism, often a bloodsucking insect or tick, that carries a pathogen from one host to another.
- VertebrateZoologyA vertebrate is an animal with a backbone of vertebrae and a skull around the brain, such as a fish, amphibian, reptile, bird or mammal.
- VesicleCell BiologyIn cell biology, a vesicle is a small sac bounded by a membrane that carries, stores or releases materials inside a cell or across its surface.
- Vestigial structureEvolutionA vestigial structure is a body part inherited from an ancestor that has become reduced and lost most or all of the function it had in that ancestor.
- Viral envelopeVirologyA viral envelope is the outer lipid membrane, taken from a host cell and studded with viral proteins, that surrounds the capsid of some viruses.
- VirusVirologyA virus is a tiny infectious particle of DNA or RNA inside a protein coat that can multiply only by taking over the machinery of a living host cell.
- VitaminFood NutritionA vitamin is an organic compound that the body needs in small amounts for normal metabolism, growth and health, and must mostly obtain from food.
W
- Western blotProteomicsA Western blot is a laboratory method that detects a specific protein in a sample by separating proteins by size on a gel and probing them with antibodies.
- White blood cellPhysiologyA white blood cell, or leukocyte, is any of the nucleated immune cells in blood that defend the body against infection and clear away debris.
- Whole-genome sequencingGenomicsWhole-genome sequencing is a laboratory method that reads nearly all of an organism's DNA, its genes and the noncoding DNA between them, in one test.
X
- X-linked inheritanceGeneticsX-linked inheritance is the way traits governed by X-chromosome genes pass down through families, often affecting males more than females.
- XylemBotanyXylem is the vascular tissue of plants that carries water and dissolved minerals upward from the roots to the stems and leaves.
Y
Z
- ZoonosisVirologyA zoonosis is an infectious disease that passes between animals and people, caused by a virus, bacterium, parasite or fungus carried by animals.
- ZooplanktonMarine BiologyZooplankton are animals and animal-like protists that drift in open water, ranging in size from microscopic single cells to krill and jellyfish.
- ZygoteDevelopmental BiologyA zygote is the single diploid cell formed when a sperm fertilizes an egg, carrying one set of chromosomes from each parent.
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