Biology

The ABO blood group system classifies human blood into A, B, AB and O by red-cell carbohydrate antigens and naturally occurring antibodies, and underlies transfusion compatibility.

An action potential is a brief, regenerative change in membrane voltage that transmits signals in electrically excitable cells.

Adaptation is evolutionary adjustment to an environment, or a trait shaped by selection; more broadly, it denotes adjustment to changing conditions.

Adaptive immunity is antigen-specific defense mediated by B and T lymphocytes, characterized by diverse receptors, selective expansion, and immunological memory.

Adenosine triphosphate (ATP) is a nucleotide that transfers chemical energy to power cellular processes and also serves as a precursor for RNA synthesis.

Affinity maturation improves antibody binding during an immune response through mutation of antibody genes and selection of B cells with higher-affinity receptors.

Alfred Russel Wallace was a British naturalist who independently developed natural selection and helped establish evolutionary biogeography.

An allele is an alternative DNA sequence at a particular genomic location, contributing to inherited variation within and between populations.

An allergen is a substance that can provoke a specific immune-mediated allergic reaction in a susceptible individual.

The alpha helix is a common protein secondary structure consisting of a coiled polypeptide backbone stabilized by regularly spaced hydrogen bonds.

Alternative splicing produces different RNA transcripts from one gene by varying which segments of a precursor RNA are retained and joined.

An amino acid is an organic compound containing amino and carboxyl groups; particular amino acids form proteins and participate in metabolism.

An antibody is an immunoglobulin protein produced by B cells that recognizes specific antigens and supports immune defense.

A substance specifically recognized by antibodies or lymphocyte receptors, whether or not it independently induces an immune response.

A cell that displays antigen-derived material to T cells, helping initiate, direct, or regulate adaptive immune responses.

Antonie van Leeuwenhoek was a Dutch microscopist whose observations of bacteria and other microscopic organisms helped establish microbiology.

Apoptosis is a regulated form of cell death that removes unwanted or damaged cells through coordinated molecular pathways and cellular dismantling.

Archaea are microorganisms distinguished from bacteria by their evolutionary history, membrane chemistry, and cellular machinery, with major roles in global nutrient cycles.

ATP synthase is a membrane-associated rotary enzyme that couples ion flow to the production of ATP, the principal energy currency of cells.

An autoantibody is an antibody that recognizes the body’s own components and may contribute to disease or serve as a marker of autoimmunity.

Autoimmune regulator (AIRE) is a transcriptional regulator that promotes immune tolerance by enabling thymic cells to express diverse self-antigens.

An axon is a specialized neuronal projection that conducts electrical signals and delivers them to other neurons, muscles, or glands.

A B cell is an adaptive immune lymphocyte that recognizes antigens and can develop into an antibody-secreting plasma cell or a memory B cell.

Bacteria are prokaryotic organisms forming a major domain of life, with diverse cellular structures, metabolisms, ecological roles, and relationships with other organisms.

A bacteriophage is a virus that infects bacteria, influencing microbial populations, genetic exchange, and biological research.

Barbara McClintock was an American cytogeneticist who discovered mobile genetic elements in maize and received the 1983 Nobel Prize in Physiology or Medicine.

Base excision repair is a DNA maintenance pathway that removes damaged or inappropriate bases and restores the affected strand through local DNA synthesis and ligation.

A beta sheet is a protein secondary structure formed by extended polypeptide strands joined through backbone hydrogen bonds.

Binary fission is a form of asexual reproduction in which one cell divides into two daughter cells, commonly occurring in bacteria, archaea, and some unicellular eukaryotes.

Biochemistry studies the molecules, chemical reactions, and regulatory processes that underpin the structure and functioning of living organisms.

Biology is the natural science of life. It studies the structure, function, growth, origin, evolution and distribution of living organisms.

C-reactive protein is an acute-phase protein involved in innate immunity and widely measured as a marker of inflammation.

C3 photosynthesis fixes carbon dioxide directly through the Calvin–Benson cycle, producing a three-carbon compound as its first stable product.

C4 photosynthesis concentrates carbon dioxide around Rubisco using four-carbon intermediates, reducing photorespiration under favorable environmental conditions.

The Calvin cycle is a biochemical pathway that uses ATP and NADPH to convert carbon dioxide into organic compounds while regenerating its carbon acceptor.

A class of organic compounds comprising sugars, their polymers, and related derivatives, with roles in energy metabolism, biological structure, and molecular recognition.

Carbon fixation converts inorganic carbon into organic compounds, supplying the material basis of biomass and linking biological metabolism to the global carbon cycle.

Swedish naturalist and physician who standardized binomial species names and developed influential systems of biological classification.

Cas9 is an RNA-guided DNA nuclease from bacterial CRISPR systems, widely used for genome editing and programmable control of gene expression.

The cell is the smallest membrane-bound unit of life. It can metabolize, grow and reproduce, and all living organisms are made of cells.

The cell cycle is the regulated sequence of growth, genome duplication, and division through which a cell produces daughter cells.

Cell division produces daughter cells through coordinated partitioning of genetic material and cellular contents, supporting reproduction, growth, and tissue renewal.

The cell membrane is a dynamic, selectively permeable boundary that regulates exchange, communication, and interactions between a cell and its surroundings.

The cell nucleus is a membrane-enclosed compartment that houses most eukaryotic DNA and organizes genetic activity.

A cell wall is a mechanically supportive layer outside the cell membrane, found in plants, fungi, most bacteria, many archaea, and numerous algae.

Cellular respiration converts energy from chemical fuels into ATP through oxidation and membrane-associated electron transport.

Central immune tolerance limits self-reactivity by eliminating, modifying, or redirecting developing lymphocytes in the thymus and bone marrow.

A specialized chromosome region that organizes kinetochore assembly and enables accurate chromosome segregation during cell division.

Charles Darwin was an English naturalist whose theory of evolution by natural selection transformed the scientific understanding of life’s diversity and shared ancestry.

Chemiosmosis couples the movement of ions down a membrane-spanning electrochemical gradient to ATP synthesis and other energy-requiring cellular processes.

Chlorophyll is a family of magnesium-containing pigments that capture light energy for photosynthesis in plants, algae, and cyanobacteria.

A chloroplast is a photosynthetic organelle in plants and algae that converts light energy into chemical energy and supports carbon assimilation.

Cholesterol is a sterol that stabilizes animal cell membranes and serves as the precursor of steroid hormones, bile acids and vitamin D; its blood levels are central to cardiovascular risk.

Chromatin is the DNA–protein complex that packages eukaryotic chromosomes and regulates access to genetic information.

Chromosomal crossover is the reciprocal exchange of DNA between homologous chromosomes, generating new allele combinations and supporting accurate chromosome segregation during meiosis.

A chromosome is an organized DNA-containing structure that carries genetic information and enables its transmission during cell division and reproduction.

The citric acid cycle is a central metabolic pathway that oxidizes acetyl groups, supplies electrons for ATP production, and provides intermediates for biosynthesis.

Class-switch recombination changes an antibody’s heavy-chain constant region, altering its effector functions while retaining its rearranged antigen-binding region.

Clonal anergy is an acquired state of lymphocyte hyporesponsiveness that limits immune responses to recognized antigens while leaving the affected cells alive.

Clonal deletion eliminates antigen-reactive lymphocytes through programmed cell death, helping establish and maintain immune tolerance.