NCERT Class 11 Biology: Key Terms & Comprehensive Glossary

Rapid, all-or-nothing electrical depolarization along a neuronal axon membrane driven by voltage-gated Na+ channels.

Specific pocket on an enzyme where substrate molecules bind and undergo catalytic chemical reaction.

Mode of arrangement of sepals or petals in floral bud with respect to other members of the same whorl.

Thin-walled, vascularized microscopic air sacs in the lungs providing the primary surface for gas diffusion.

Biochemical pathway involving both catabolic breakdown and anabolic synthesis (e.g., Respiratory TCA cycle).

Inhibition of the growth of lateral axillary buds by auxin synthesized at the growing shoot apical meristem.

Specialized primitive bacteria with unique branched-lipid cell walls enabling survival in extreme habitats (halophiles, thermoacidophiles, methanogens).

Rotary transmembrane complex (F0-F1) synthesizing ATP from ADP and inorganic phosphate driven by proton motive force.

Universal naming system formalized by Carolus Linnaeus assigning two Latinized names: Genus and species.

Principle stating that when a process is conditioned by several factors, its rate is governed by the slowest limiting factor.

Rightward shift of oxygen-hemoglobin dissociation curve in tissues due to elevated pCO2 and acidity, facilitating O2 unloading.

Specialized photosynthetic cells tightly encircling vascular bundles in C4 plants featuring agranal chloroplasts (Kranz anatomy).

Complete sequence of electrical and mechanical events during one heartbeat comprising atrial systole, ventricular systole, and joint diastole.

Biological doctrine formulated by Schleiden, Schwann, and Virchow stating that all organisms are composed of cells arising from pre-existing cells.

Coupling of proton movement down an electrochemical gradient across a biological membrane to drive ATP synthesis.

X-shaped cytological points of attachment between non-sister chromatids where crossing over occurs during meiotic diplotene.

Fluid-filled internal body cavity situated between the alimentary canal and body wall, completely lined by mesoderm.

Reversible enzyme inhibition wherein an inhibitor closely mimics the substrate structure, competing for the active site and increasing Km without altering Vmax.

Fluid flow arrangement in Henle's loop and vasa recta running in opposite directions, maintaining a hyperosmolar medullary gradient for urine concentration.

Enzyme-mediated (recombinase) exchange of genetic material between non-sister chromatids of homologous chromosomes during pachytene.

Phenomenon whereby mature living cells regain the capacity to divide mitotically (e.g., interfascicular cambium formation).

Final stage of meiotic prophase I characterized by complete terminalization of chiasmata and breakdown of nuclear envelope.

Angiosperm class characterized by embryos with two cotyledons, reticulate leaf venation, open vascular bundles in a ring, and tap root systems.

Graphical recording of electrical voltage variations generated by heart muscle during the cardiac cycle (P-QRS-T waves).

Chronic respiratory disease caused by cigarette smoking wherein alveolar walls are damaged, drastically reducing gas exchange surface area.

Functionally coordinated intracellular membranous organelles comprising the ER, Golgi apparatus, lysosomes, and vacuoles.

Biological macromolecular catalyst, almost always a globular protein, accelerating biochemical reaction rates by lowering activation energy.

Severe hemolytic disease of newborn caused by maternal Rh- antibodies destroying fetal Rh+ red blood cells in second pregnancy.

Membrane structural model proposed by Singer and Nicolson (1972) depicting a quasi-fluid phospholipid bilayer with embedded mobile proteins.

Volume of filtrate formed per minute by all renal corpuscles of both kidneys (~125 mL/min = 180 liters/day).

Universal 10-step anaerobic cytosolic pathway converting one 6-carbon glucose into two 3-carbon pyruvate molecules with net gain of 2 ATP and 2 NADH.

Painful inflammatory joint disorder caused by the abnormal accumulation and deposition of uric acid crystals in synovial joints.

C4 photosynthetic carbon-fixing adaptation utilizing PEP carboxylase in mesophyll cells to prevent photorespiration in tropical grasses.

Hairpin-shaped loop of nephron penetrating renal medulla, critical for establishing hyperosmotic osmotic gradients.

Taxonomical repository of preserved, pressed, and mounted plant specimens on paper sheets arranged systematically.

Maintenance of a dynamic, steady internal physical and chemical equilibrium within an organism despite environmental fluctuations.

Specialized transverse cellular junctions in cardiac muscle tissue containing desmosomes and gap junctions for electrical syncytium.

Structural points of contact between two bones or between bone and cartilage facilitating bodily articulation and locomotion.

Disc-shaped protein complex on the centromere of chromosomes serving as the attachment site for mitotic spindle fibers.

Specialized floral arrangement of bundle sheath cells forming a wreath around vascular bundles in C4 plants like maize and sugarcane.

Environmental factor present at lowest or sub-optimal levels that limits the maximum rate of a physiological process.

Water-insoluble organic biomolecules composed of fatty acids and glycerol, soluble in organic non-polar solvents.

U-shaped tubular segment of mammalian nephron responsible for medullary salt gradient maintenance.

Indoleamine hormone secreted by the pineal gland regulating diurnal 24-hour sleep-wake circadian rhythms.

Localized region of plant tissue containing actively dividing, undifferentiated cells responsible for organ formation and elongation.

Neural reflex process of expelling urine from the urinary bladder through the urethra.

Insulating lipid-rich layer wrapped around nerve axons by Schwann cells, enabling fast saltatory impulse conduction.

Microscopic structural and functional filtration unit of the vertebrate kidney, numbering ~1 million per human kidney.

Synaptic motor end-plate contact between the terminal axon of a motor neuron and the sarcolemma of a muscle fiber.

Fundamental subunit of eukaryotic chromatin consisting of 200 base pairs of DNA wound around an octamer of basic histone proteins.

Synthesis of ATP coupled to the transfer of electrons from NADH/FADH2 to molecular oxygen through the mitochondrial ETS.

Placentation mode wherein ovules develop on the inner ovary wall or peripheral part, often with a false septum replum (Mustard).

Protective secondary tissue replacing the epidermis in woody stems, consisting of phellem (cork), phellogen (cork cambium), and phelloderm.

Physiological response of plants to the relative lengths of light and dark periods regulating seasonal flowering.

Shrinkage of plant protoplast away from its rigid cell wall when immersed in a hypertonic external solution.

Neural center in the pons varolii that regulates respiratory rhythm by signaling the shut-off point of inspiration.

Inactive G0 phase of the cell cycle where cells remain metabolically active but do not proliferate unless stimulated.

Hardwired neural pathway controlling a rapid, involuntary reflex action consisting of receptor, sensory neuron, CNS center, motor neuron, and effector.

Ratio of volume of carbon dioxide evolved to volume of oxygen consumed during cellular respiration (RQ = CO2 / O2).

Fundamental contractile unit of a striated myofibril bounded between two adjacent Z-lines.

Intimate side-by-side pairing of homologous maternal and paternal chromosomes during zygotene of meiotic prophase I.

Concrete biological taxonomic group or unit of any rank (e.g., Mammalia, Angiospermae, Homo sapiens).

Iodinated tyrosine hormone (T4) secreted by thyroid follicular cells governing basal metabolic rate and tissue differentiation.

Animals that excrete metabolic nitrogen waste primarily in the form of water-soluble, less-toxic urea (e.g., mammals, amphibians).

Papilionaceous petal arrangement in legumes featuring a large posterior standard, two lateral wings, and two anterior fused keels.

Complex vascular tissue in plants conducting water and dissolved mineral nutrients upward from roots to stems and leaves.

Non-cyclic electron transport flow pathway from water through PSII and PSI to NADP+ shaped like the letter Z.