Introduction: Understanding Biological Terminology
Biological terminology forms the specialized language that allows scientists to communicate precisely about living organisms and their processes. Mastering these terms is essential for anyone studying or working in any biological discipline. This comprehensive cheatsheet provides clear, concise definitions for key terms across all major fields of biology, serving as both a learning tool and quick reference guide.
Cell Biology & Molecular Biology
Cell Structure
| Term | Definition |
|---|---|
| Cell | Basic structural and functional unit of all living organisms |
| Cell membrane | Phospholipid bilayer that encloses cellular contents and regulates passage of materials |
| Cytoplasm | Gel-like substance between cell membrane and nucleus containing organelles |
| Nucleus | Membrane-bound organelle containing genetic material in eukaryotes |
| Mitochondria | Organelles that generate energy (ATP) through cellular respiration |
| Chloroplast | Plant organelle containing chlorophyll for photosynthesis |
| Ribosome | Cellular structures where protein synthesis occurs |
| Endoplasmic reticulum (ER) | Network of membranes involved in protein synthesis (rough ER) and lipid synthesis (smooth ER) |
| Golgi apparatus | Organelle that packages and modifies proteins for secretion or use within the cell |
| Lysosome | Membrane-bound organelle containing digestive enzymes |
| Vacuole | Membrane-bound sac storing water, nutrients, waste, or specialized materials |
| Cytoskeleton | Network of protein filaments providing structural support and intracellular transport |
| Centriole | Cylindrical organelle involved in cell division and forming cilia/flagella |
| Flagellum | Long, whip-like structure that propels cells |
| Cilium | Short, hair-like structure that moves substances across cell surface |
Cell Processes
| Term | Definition |
|---|---|
| Metabolism | Sum of all chemical reactions in an organism |
| Anabolism | Metabolic processes that build complex molecules from simpler ones |
| Catabolism | Metabolic processes that break down complex molecules into simpler ones |
| Cellular respiration | Process converting glucose and oxygen into energy (ATP), CO₂, and water |
| Glycolysis | First stage of cellular respiration; glucose broken down in cytoplasm |
| Krebs cycle | Second stage of cellular respiration; occurs in mitochondrial matrix |
| Electron transport chain | Final stage of cellular respiration; generates most ATP |
| Photosynthesis | Process converting light energy, CO₂, and water into glucose and oxygen |
| Light reactions | Stage of photosynthesis that captures light energy to form ATP and NADPH |
| Calvin cycle | Carbon fixation stage of photosynthesis that produces glucose |
| Diffusion | Random movement of molecules from high to low concentration |
| Osmosis | Diffusion of water across a selectively permeable membrane |
| Active transport | Movement of substances against concentration gradient (requires energy) |
| Endocytosis | Cell engulfing external materials by forming membrane vesicles |
| Exocytosis | Cell releasing materials by vesicle fusion with cell membrane |
| Homeostasis | Maintenance of stable internal conditions despite external changes |
Genetics & Molecular Genetics
DNA Structure & Replication
| Term | Definition |
|---|---|
| DNA | Deoxyribonucleic acid; double-helix molecule containing genetic information |
| Nucleotide | Building block of DNA/RNA; composed of sugar, phosphate group, and nitrogenous base |
| Base pair | Complementary nucleotides (A-T, G-C in DNA; A-U, G-C in RNA) |
| Double helix | Twisted ladder structure of DNA molecule |
| Replication | Process of copying DNA before cell division |
| DNA polymerase | Enzyme that synthesizes new DNA strands |
| Helicase | Enzyme that unwinds and separates DNA strands during replication |
| Origin of replication | Specific DNA sequence where replication begins |
| Replication fork | Y-shaped region where DNA strands separate for replication |
| Leading strand | DNA strand synthesized continuously during replication |
| Lagging strand | DNA strand synthesized discontinuously as Okazaki fragments |
| Okazaki fragment | Short DNA segments synthesized during lagging strand replication |
| Telomere | Protective DNA sequence at chromosome ends |
| Semiconservative replication | Each new DNA molecule contains one original and one new strand |
Gene Expression
| Term | Definition |
|---|---|
| Gene | DNA segment that codes for a specific protein or RNA molecule |
| Genome | Complete set of genetic material in an organism |
| Transcription | Process of creating RNA copy from DNA template |
| RNA polymerase | Enzyme that synthesizes RNA during transcription |
| mRNA | Messenger RNA; carries genetic information from DNA to ribosomes |
| tRNA | Transfer RNA; delivers amino acids to ribosomes during translation |
| rRNA | Ribosomal RNA; major component of ribosomes |
| Translation | Process of synthesizing proteins using mRNA code |
| Codon | Three-nucleotide sequence in mRNA coding for specific amino acid |
| Anticodon | Three-nucleotide sequence in tRNA that pairs with mRNA codon |
| Ribosome | Cellular structure where protein synthesis occurs |
| Promoter | DNA region where transcription begins |
| Terminator | DNA sequence signaling end of transcription |
| Intron | Non-coding region within gene that is removed during RNA processing |
| Exon | Coding region of gene that remains in mature mRNA |
| RNA splicing | Removal of introns and joining of exons in pre-mRNA |
| Central dogma | Information flow from DNA to RNA to protein |
Inheritance & Variation
| Term | Definition |
|---|---|
| Chromosome | DNA structure carrying genetic information |
| Chromatin | Complex of DNA and proteins forming chromosomes |
| Histone | Protein around which DNA wraps to form nucleosomes |
| Allele | Alternative form of a gene |
| Locus | Specific location of a gene on a chromosome |
| Genotype | Genetic makeup of an organism |
| Phenotype | Observable characteristics resulting from genotype and environment |
| Homozygous | Having identical alleles for a specific gene |
| Heterozygous | Having different alleles for a specific gene |
| Dominant | Allele expressed in phenotype when present in heterozygous genotype |
| Recessive | Allele expressed in phenotype only when in homozygous genotype |
| Codominance | Both alleles in heterozygous genotype fully expressed in phenotype |
| Incomplete dominance | Heterozygous phenotype intermediate between homozygous phenotypes |
| Multiple alleles | Three or more allele forms for a single gene in a population |
| Pleiotropy | Single gene affecting multiple traits |
| Polygenic inheritance | Multiple genes influencing a single trait |
| Epistasis | Gene interaction where one gene affects expression of another |
| Mutation | Change in DNA sequence |
| Point mutation | Change in single nucleotide |
| Frameshift mutation | Insertion or deletion causing shift in reading frame |
| Chromosomal mutation | Change in chromosome structure or number |
Cell Division & Reproduction
| Term | Definition |
|---|---|
| Cell cycle | Sequence of growth and division of a cell |
| Interphase | Period between cell divisions (G₁, S, G₂) |
| Mitosis | Division of nucleus resulting in two genetically identical nuclei |
| Cytokinesis | Division of cytoplasm following nuclear division |
| Prophase | First stage of mitosis; chromosomes condense |
| Metaphase | Second stage of mitosis; chromosomes align at equator |
| Anaphase | Third stage of mitosis; chromatids separate to opposite poles |
| Telophase | Final stage of mitosis; nuclear membranes reform |
| Meiosis | Cell division producing four haploid cells from one diploid cell |
| Crossing over | Exchange of genetic material between homologous chromosomes |
| Independent assortment | Random distribution of homologous chromosomes during meiosis |
| Haploid | Cell containing one set of chromosomes (n) |
| Diploid | Cell containing two sets of chromosomes (2n) |
| Gamete | Sex cell (egg or sperm) with haploid number of chromosomes |
| Zygote | Fertilized egg; diploid cell resulting from fusion of gametes |
| Asexual reproduction | Reproduction without fusion of gametes |
| Sexual reproduction | Reproduction involving fusion of gametes |
Evolution & Biodiversity
Evolutionary Processes
| Term | Definition |
|---|---|
| Evolution | Change in heritable traits of biological populations over generations |
| Natural selection | Process where organisms better adapted to environment survive and reproduce more |
| Adaptation | Heritable trait increasing organism’s fitness in specific environment |
| Fitness | Measure of reproductive success |
| Genetic drift | Random change in allele frequency in a population |
| Gene flow | Transfer of alleles between populations due to migration |
| Mutation | Source of new genetic variation |
| Sexual selection | Selection based on traits that increase mating success |
| Speciation | Formation of new species through evolution |
| Allopatric speciation | Speciation due to geographic isolation |
| Sympatric speciation | Speciation without geographic isolation |
| Reproductive isolation | Mechanisms preventing interbreeding between species |
| Convergent evolution | Independent evolution of similar traits in unrelated species |
| Divergent evolution | Development of different traits in related species |
| Coevolution | Mutual evolutionary influence between two species |
| Phylogeny | Evolutionary history of a species or group |
| Homologous structures | Structures with common evolutionary origin but different functions |
| Analogous structures | Structures with similar functions but different evolutionary origins |
| Vestigial structures | Reduced structures with no or minimal function, derived from functional ancestors |
Taxonomy & Classification
| Term | Definition |
|---|---|
| Taxonomy | Science of classifying and naming organisms |
| Binomial nomenclature | Two-part scientific name (genus + species) |
| Clade | Group of organisms that includes a common ancestor and all descendants |
| Taxon | Any named group of organisms |
| Species | Group of similar organisms that can interbreed and produce fertile offspring |
| Genus | Group of closely related species |
| Family | Group of related genera |
| Order | Group of related families |
| Class | Group of related orders |
| Phylum/Division | Group of related classes |
| Kingdom | Group of related phyla/divisions |
| Domain | Highest taxonomic rank; Bacteria, Archaea, Eukarya |
| Biodiversity | Variety of life forms in an ecosystem or on Earth |
| Phylogenetic tree | Branching diagram showing evolutionary relationships |
Ecology & Environmental Biology
Ecological Concepts
| Term | Definition |
|---|---|
| Ecology | Study of interactions among organisms and their environment |
| Ecosystem | Community of living organisms and their physical environment |
| Habitat | Natural environment where an organism lives |
| Niche | Role and position of a species in its environment |
| Population | Group of organisms of the same species in a particular area |
| Community | All populations of different species in a particular area |
| Biosphere | Sum of all ecosystems on Earth |
| Biome | Large naturally occurring community of flora and fauna |
| Tundra | Cold, treeless Arctic biome with permafrost |
| Taiga/Boreal forest | Northern coniferous forest biome |
| Temperate forest | Forest biome with moderate climate and deciduous trees |
| Tropical rainforest | Warm, wet forest biome with high biodiversity |
| Grassland | Biome dominated by grasses with few trees |
| Desert | Arid biome with sparse vegetation |
| Aquatic biome | Freshwater or marine ecosystem |
Ecological Interactions
| Term | Definition |
|---|---|
| Predation | Interaction where one organism (predator) kills and eats another (prey) |
| Herbivory | Consumption of plant material by animals |
| Parasitism | Relationship where one organism benefits at expense of another |
| Mutualism | Relationship where both organisms benefit |
| Commensalism | Relationship where one organism benefits while other is unaffected |
| Competition | Interaction where organisms vie for limited resources |
| Symbiosis | Close, long-term interaction between different species |
| Keystone species | Species with disproportionately large effect on environment |
| Indicator species | Species that defines environmental characteristics |
Environmental Processes
| Term | Definition |
|---|---|
| Food chain | Linear sequence of organisms where each is food for the next |
| Food web | Interconnected food chains in an ecosystem |
| Trophic level | Position in food chain |
| Producer | Organism that makes its own food (autotroph) |
| Consumer | Organism that eats other organisms (heterotroph) |
| Primary consumer | Herbivore that eats producers |
| Secondary consumer | Carnivore that eats primary consumers |
| Tertiary consumer | Carnivore that eats secondary consumers |
| Decomposer | Organism that breaks down dead organic matter |
| Biomass | Total mass of organisms in a given area or trophic level |
| Energy pyramid | Model showing decreased energy at higher trophic levels |
| Ecological succession | Predictable change in community composition over time |
| Primary succession | Succession beginning in lifeless area (e.g., bare rock) |
| Secondary succession | Succession following disruption of existing community |
| Climax community | Stable end stage of succession |
| Carrying capacity | Maximum population size environment can sustain |
| Limiting factor | Environmental factor restricting population growth |
| Biogeochemical cycle | Pathway of elements through biotic and abiotic components |
| Carbon cycle | Circulation of carbon through ecosystems |
| Nitrogen cycle | Circulation of nitrogen through ecosystems |
| Water cycle | Circulation of water through ecosystems |
| Phosphorus cycle | Circulation of phosphorus through ecosystems |
Physiology & Anatomy
Human Body Systems
| System | Major Components | Primary Functions |
|---|---|---|
| Integumentary | Skin, hair, nails, sweat glands | Protection, temperature regulation, sensation |
| Skeletal | Bones, cartilage, ligaments | Support, protection, movement, blood cell production |
| Muscular | Skeletal, smooth, cardiac muscles | Movement, posture, heat production |
| Nervous | Brain, spinal cord, nerves | Control, coordination, sensation |
| Endocrine | Pituitary, thyroid, adrenal glands | Hormone production, regulation |
| Cardiovascular | Heart, blood vessels, blood | Nutrient transport, waste removal |
| Lymphatic | Lymph nodes, vessels, spleen | Immunity, fluid balance |
| Respiratory | Lungs, trachea, bronchi | Gas exchange |
| Digestive | Mouth, esophagus, stomach, intestines | Food processing, nutrient absorption |
| Urinary | Kidneys, ureters, bladder | Waste elimination, water balance |
| Reproductive | Testes/ovaries, associated structures | Reproduction |
Physiological Terms
| Term | Definition |
|---|---|
| Homeostasis | Maintenance of stable internal conditions |
| Negative feedback | Mechanism that reverses change from set point |
| Positive feedback | Mechanism that amplifies change from set point |
| Hormone | Chemical messenger produced by endocrine glands |
| Neuron | Nerve cell that transmits electrical signals |
| Neurotransmitter | Chemical messenger between neurons |
| Action potential | Electrical signal propagated along neuron |
| Synapse | Junction between neurons where signals are transmitted |
| Enzyme | Protein catalyst that accelerates biochemical reactions |
| Substrate | Molecule upon which enzyme acts |
| Antibody | Protein produced by immune system to neutralize pathogens |
| Antigen | Substance that triggers immune response |
| Metabolism | Sum of chemical reactions in an organism |
| Hemoglobin | Oxygen-carrying protein in red blood cells |
| Peristalsis | Wave-like muscle contractions moving food through digestive tract |
| Excretion | Removal of metabolic waste from organism |
Microbiology & Immunology
Microorganisms
| Type | Characteristics | Examples |
|---|---|---|
| Bacteria | Prokaryotic, single-celled, no nucleus | E. coli, Streptococcus |
| Archaea | Prokaryotic, often in extreme environments | Methanogens, halophiles |
| Fungi | Eukaryotic, cell walls of chitin | Yeasts, molds, mushrooms |
| Protozoa | Eukaryotic, single-celled, heterotrophic | Amoeba, Paramecium |
| Algae | Eukaryotic, photosynthetic | Diatoms, seaweeds |
| Virus | Non-cellular, parasitic | Influenza, HIV, coronavirus |
| Prion | Infectious protein | Cause of CJD, BSE |
Immune Response
| Term | Definition |
|---|---|
| Immunity | Resistance to pathogens and foreign substances |
| Innate immunity | Non-specific defense mechanisms present at birth |
| Adaptive immunity | Specific defense mechanisms developing after exposure |
| Inflammation | Protective response to injury or infection |
| Phagocytosis | Process where cells engulf and destroy particles/microorganisms |
| Lymphocyte | White blood cell (B cell or T cell) involved in adaptive immunity |
| B cell | Lymphocyte that produces antibodies |
| T cell | Lymphocyte that coordinates immune response or kills infected cells |
| Antibody | Protein that binds to specific antigen |
| Antigen | Substance triggering antibody production |
| Pathogen | Disease-causing microorganism |
| Vaccination | Introduction of antigen to stimulate immunity |
| Immunoglobulin | Protein with antibody activity |
| Autoimmunity | Immune response against self-tissues |
Plant Biology
Plant Structure
| Structure | Function |
|---|---|
| Root | Anchoring, water/nutrient absorption |
| Stem | Support, transport of water/nutrients |
| Leaf | Photosynthesis, gas exchange |
| Flower | Reproduction |
| Fruit | Seed protection and dispersal |
| Seed | Plant embryo with stored food |
| Xylem | Tissue transporting water/minerals upward |
| Phloem | Tissue transporting sugars throughout plant |
| Stomata | Pores allowing gas exchange |
| Chloroplast | Organelle where photosynthesis occurs |
| Meristem | Tissue of actively dividing cells |
| Cambium | Lateral meristem producing secondary growth |
Plant Processes
| Process | Description |
|---|---|
| Photosynthesis | Conversion of light energy to chemical energy (glucose) |
| Transpiration | Evaporation of water from plant surfaces |
| Respiration | Breakdown of glucose for energy |
| Translocation | Movement of sugars through phloem |
| Tropism | Growth response to external stimulus |
| Photoperiodism | Response to day/night length |
| Germination | Beginning of growth from seed |
| Pollination | Transfer of pollen to female reproductive structures |
| Fertilization | Fusion of male and female gametes |
| Senescence | Aging process in plants |
Additional Key Concepts
Biochemistry
| Term | Definition |
|---|---|
| Carbohydrate | Organic compound composed of carbon, hydrogen, and oxygen (sugars, starches) |
| Lipid | Fat-soluble organic compound (fats, oils, waxes) |
| Protein | Organic compound made of amino acids |
| Nucleic acid | Organic compound storing and transmitting genetic information (DNA, RNA) |
| Enzyme | Protein catalyst accelerating biochemical reactions |
| ATP | Adenosine triphosphate; energy currency of cells |
| pH | Measure of hydrogen ion concentration; acidity/alkalinity |
| Buffer | Substance maintaining stable pH |
Scientific Method
| Term | Definition |
|---|---|
| Hypothesis | Testable explanation for observation |
| Experiment | Procedure testing hypothesis |
| Variable | Factor that can change in experiment |
| Control | Standard for comparison in experiment |
| Data | Information collected during experiment |
| Theory | Well-supported explanation for natural phenomenon |
| Law | Statement describing consistent phenomenon |
Resources for Further Learning
Online Databases
- NCBI (National Center for Biotechnology Information): Genetic and biochemical data
- UniProt: Protein sequence and function information
- PDB (Protein Data Bank): 3D structures of proteins and nucleic acids
- KEGG (Kyoto Encyclopedia of Genes and Genomes): Metabolic pathways
Educational Websites
- Khan Academy: Free biology lessons and practice
- Biology Online: Dictionary of biological terms
- Cell Biology by the Numbers: Database of cellular measurements and calculations
- HHMI BioInteractive: Interactive biology resources
Scientific Journals
- Nature: Publishes research across all scientific disciplines
- Science: General scientific research and reviews
- Cell: Research in cell biology
- PLOS Biology: Open-access biology research
Professional Organizations
- American Society for Cell Biology (ASCB)
- American Society for Microbiology (ASM)
- Society for Conservation Biology (SCB)
- American Physiological Society (APS)