NCERT Class 12 Biology: Key Terms & Comprehensive Glossary

Evolutionary process wherein an ancestral species diversifies into multiple diverse forms occupying different ecological niches (e.g., Darwin's Finches).

Prenatal diagnostic procedure analyzing fetal amniotic fluid cells for chromosomal abnormalities, strictly banned for sex determination.

Y-shaped immunoglobulin protein (H2L2) produced by plasma B-cells that specifically recognizes and binds to foreign antigens.

Special form of asexual reproduction mimicking sexual reproduction wherein seeds are formed without fertilization (e.g., Asteraceae, grasses).

Clinical laboratory techniques (IVF, ET, ZIFT, GIFT, ICSI) assisting infertile couples to achieve conception.

Biological control pathogen (genus Nucleopolyhedrovirus) targeting insect pests with species-specific narrow-spectrum activity and zero harm to non-target wildlife.

Amount of oxygen required by aerobic microorganisms to break down and oxidize organic matter in one liter of wastewater.

Biogeographical region featuring exceptionally high levels of species richness and endemism under severe human threat (e.g., Western Ghats-Sri Lanka).

Exploitation and commercial patenting of indigenous bioresources and traditional knowledge without authorized consent or fair compensation.

Mammalian embryonic stage comprising an outer trophoblast layer and an inner cell mass surrounding a fluid-filled blastocoel cavity.

Parasitic interaction wherein the cuckoo lays its eggs in the crow's nest, letting the host foster and raise the parasite chicks.

Maximum population size (K) that an environment's finite resources can sustainably support over an indefinite period.

Molecular biology framework proposed by Francis Crick: unidirectional genetic information flow from DNA -> RNA -> Protein.

Obligate extinction of a dependent species when its mutualistic host or partner species goes extinct (e.g., specialized fig-wasp pairs).

Non-Mendelian genetic inheritance wherein both alleles of a heterozygote are fully and simultaneously expressed (e.g., IAIB AB blood group).

Nutrient-rich yellowish milk secreted by mothers during early days of lactation, packed with protective secretory IgA antibodies.

Temporary endocrine structure formed from ruptured Graafian follicle after ovulation, secreting high progesterone to sustain pregnancy.

Ex-situ preservation of viable gametes, embryos, and tissue cultures at ultra-low temperatures (-196°C) in liquid nitrogen.

Angiosperm hallmark event wherein one sperm fertilizes the egg (syngamy -> 2n zygote) and the second sperm fertilizes polar nuclei (triple fusion -> 3n PEN).

Human chromosomal trisomy disorder (47, +21) caused by non-disjunction of chromosome 21, resulting in mental retardation and characteristic palmar crease.

Functional ecological unit formed by the interaction of living biological communities with their physical abiotic environment.

Ecological condition of a biological species being strictly confined to a specific geographic area and nowhere else on Earth.

Loosely packed, transcriptionally active region of eukaryotic chromatin that stains light under microscopy.

Biolistic physical gene transfer method firing gold or tungsten micro-particles coated with foreign DNA directly into plant cells.

Medical technique correcting hereditary disease by replacing or repairing defective mutant genes with functional copies (e.g., ADA deficiency).

Universal triplet dictionary translating 64 mRNA nucleotide codons into 20 standard amino acids during protein translation.

Random fluctuations in allele frequencies from generation to generation occurring strictly in small, isolated populations.

Law stating that allele and genotype frequencies in a large random-mating population remain constant across generations in absence of evolutionary forces.

Densely packed, transcriptionally inactive chromatin that stains dark and replicates late in S phase.

Anatomical structures sharing identical embryonic origin and fundamental layout, adapted to different functions via divergent evolution.

Mega-science international effort (1990-2003) determining the complete 3-billion base-pair sequence of the human genome.

Conservation of endangered biological diversity in its natural wild habitats (National Parks, Wildlife Sanctuaries, Biosphere Reserves).

Genetic condition wherein the heterozygous phenotype is an intermediate blend between both homozygous parents (Snapdragon flower color).

Cytokine glycoproteins secreted by virus-infected cells that protect neighboring uninfected cells from viral replication.

Contraceptive device inserted into the uterus by medical specialists (Copper-T, LNG-20) suppressing sperm motility and preventing implantation.

Chromosomal genetic disorder in males (47, XXY) characterized by sterile hypogonadism, tall stature, and gynecomastia.

Prokaryotic polycistronic transcriptional unit in E. coli regulated by lactose inducer and repressor protein for lactose metabolism.

Ecological thermodynamic rule stating only approximately 10 percent of energy is transferred from one trophic level to the next higher level.

Physical co-localization of genes on the same chromosome preventing them from assorting independently according to Mendel's law.

Landmark 1958 experiment using 15N and 14N heavy nitrogen isotope equilibrium density gradient centrifugation proving semiconservative DNA replication.

Pathological hallmark of malignant cancer wherein neoplastic cells detach from primary tumors and colonize distant organs via circulation.

Classic 1953 experiment simulating primitive reducing Earth conditions with electric sparks, generating amino acids from methane, ammonia, and water.

Obligate symbiotic ecological interaction wherein both interacting partner species derive mutual biological benefits (+/+).

Symbiotic mutualistic association between fungal hyphae and roots of higher plants aiding in phosphorus absorption and drought tolerance.

Baculovirus genus employed as species-specific biological control agents against agricultural insect pests without environmental toxicity.

Short discontinuous single-stranded DNA segments synthesized on the lagging template strand during replication, joined by DNA ligase.

Floral mechanisms preventing self-pollination and promoting cross-pollination (dichogamy, self-incompatibility, unisexual flowers).

Polymerase Chain Reaction: in vitro enzymatic technique amplifying billions of copies of a specific target DNA sequence using Taq polymerase.

Chart recording the transmission of phenotypic genetic traits across several human generations using standard genealogical symbols.

Autonomous, extrachromosomal circular double-stranded DNA molecules in bacteria serving as universal gene cloning vectors.

Genetic alteration caused by substitution of a single base pair in a DNA sequence (e.g., Sickle-cell anemia).

Rate of biological solar energy capture and organic biomass synthesis by autotrophic photosynthetic organisms per unit area and time.

Bacterial defensive molecular scissors recognizing specific palindromic sequences and cleaving both DNA backbones at precise sites.

Paul Ehrlich's ecological analogy comparing ecosystem integrity to airplane wing rivets: losing critical hub species destabilizes the entire biosphere.

Cellular defense mechanism wherein double-stranded RNA triggers sequence-specific silencing and enzymatic degradation of target mRNA.

Elongated somatic nurse cells in seminiferous tubules providing nutritional support and regulation to developing spermatogenic germ cells.

Autosomal recessive point mutation substituting glutamic acid with valine at position 6 of beta-globin, causing RBC sickling under hypoxia.

Vertical spatial layering of different species in an ecosystem community occupying distinct vertical heights (e.g., trees, shrubs, herbs).

Human chromosomal monosomy disorder in females (45, XO) resulting in sterile streak ovaries, short stature, and webbed neck.

Variable Number of Tandem Repeats: hypervariable satellite DNA mini-satellite regions utilized in forensic DNA fingerprinting.