Assam HS Class 11-12 Biology key terms

The branch of biology that identifies, names, and classifies living organisms into hierarchical groups such as kingdom, phylum, class, order, family, genus, and species, based on shared characteristics and evolutionary relationships.

The two-part scientific naming system introduced by Carolus Linnaeus, in which each species receives a Latinised genus name followed by a specific epithet, both italicised when printed, for example Homo sapiens.

The ranked sequence of categories used to classify organisms, from the broadest kingdom down to species, where each lower level contains fewer organisms sharing more specific features.

The basic unit of classification: a group of organisms that can interbreed naturally and produce fertile offspring, and which share a common gene pool distinct from other such groups.

A taxonomic rank above species that groups together closely related species sharing major structural features; its name forms the first part of every scientific binomial.

The idea that species are defined by reproductive isolation, meaning members of one species cannot produce fertile offspring with members of another under natural conditions; it does not apply to asexual organisms.

The study of the external form, structure, and appearance of organisms, including shape, size, colour, and arrangement of parts, widely used as a basis for identifying and classifying plants and animals.

The study of the internal structure and organisation of organisms, such as the arrangement of organs, tissues, and vascular systems, used to compare related groups and establish evolutionary links.

Similarity in structure or origin of organs in different organisms due to shared ancestry, even when the organs perform different functions, as seen in the forelimbs of vertebrates.

Similarity in function or appearance between organs of different organisms that do not share a common evolutionary origin, such as the wings of insects and birds.

The independent development of similar features in organisms that are not closely related, usually because they live in similar environments and face similar selection pressures.

Any inherited feature of structure, physiology, or behaviour that improves an organism's chance of survival and reproduction in its particular habitat, arising through natural selection over generations.

The process by which individuals with inherited traits that improve survival and reproduction leave more offspring, so those traits become more common in later generations of the population.

The gradual change in the heritable characteristics of populations over generations, leading to the diversity of organisms and, over long periods, to the formation of new species.

The process by which one population splits into two or more reproductively isolated groups that diverge genetically until they become distinct species.

The condition in which members of different populations cannot interbreed successfully because of barriers such as differences in timing, habitat, behaviour, or incompatible gametes, keeping their gene pools separate.

The principle stating that all living organisms are made of cells, that the cell is the basic structural and functional unit of life, and that new cells arise from pre-existing cells by division.

A cell lacking a membrane-bound nucleus and other membrane-bound organelles, with genetic material as a single circular DNA molecule in a nucleoid region; bacteria and cyanobacteria are examples.

A cell that contains a true nucleus enclosed by a nuclear membrane and various membrane-bound organelles such as mitochondria, plastids, and the endoplasmic reticulum; found in protists, fungi, plants, and animals.

The selectively permeable boundary of a cell, composed mainly of a phospholipid bilayer with embedded proteins, that controls the movement of substances into and out of the cell.

The movement of solvent molecules, usually water, across a semipermeable membrane from a region of higher water potential to one of lower water potential, without requiring energy input.

The movement of substances across a cell membrane against their concentration gradient, using energy from ATP and carrier proteins, as in the sodium-potassium pump.

A double-membraned organelle whose inner membrane is folded into cristae, where aerobic respiration and ATP synthesis take place; its matrix contains its own DNA and ribosomes.

A green plastid found in plant cells, bounded by a double membrane and containing stacked thylakoids and stroma, where photosynthesis converts light energy into chemical energy.

The process by which green plants and some other organisms use light energy to convert carbon dioxide and water into carbohydrates, releasing oxygen as a by-product.

The stepwise oxidation of food molecules such as glucose within cells, releasing energy stored as ATP; aerobic respiration needs oxygen, while anaerobic respiration does not.

A type of nuclear division producing two daughter cells with the same chromosome number as the parent cell, used for growth, repair, and asexual reproduction.

A reductional nuclear division in which one diploid cell gives rise to four haploid cells through two successive divisions, producing gametes and generating genetic variation by crossing over and independent assortment.

The exchange of segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, which produces new combinations of alleles in the resulting gametes.

The creation of new combinations of alleles in offspring, resulting from crossing over during meiosis and from the independent assortment of chromosomes, and in some cases from random fertilisation.

The principle that the two alleles of a gene separate during gamete formation, so each gamete receives only one allele, and they recombine at fertilisation.

One of two or more alternative forms of a gene occupying the same locus on homologous chromosomes, which may be dominant or recessive and together determine a particular trait.

The genetic constitution of an organism with respect to a particular gene or set of genes, described by the alleles present, for example homozygous dominant, heterozygous, or homozygous recessive.

The observable characteristics of an organism, resulting from the interaction between its genotype and the environment.

The semi-conservative process in which a DNA double helix unwinds and each strand acts as a template for synthesis of a new complementary strand, producing two identical DNA molecules.

The synthesis of a complementary RNA molecule from a DNA template, catalysed by RNA polymerase, forming messenger RNA that carries the genetic message to the ribosome.

The process in which ribosomes read the sequence of codons on messenger RNA and assemble the corresponding amino acids into a polypeptide chain, using transfer RNA molecules.

The set of rules by which the sequence of nucleotide triplets, or codons, in messenger RNA is translated into the sequence of amino acids in a protein; it is triplet-based and degenerate.

A sequence of three consecutive nucleotides in messenger RNA that specifies a particular amino acid or signals a start or stop during protein synthesis.

A sudden, heritable change in the nucleotide sequence of DNA, which may alter a gene, chromosome structure, or chromosome number, and provides raw material for variation and evolution.