CHSE Odisha Elective Biology key terms

The two-part scientific naming system for organisms, giving each a Latinised genus name followed by a specific epithet, both italicised, with the genus capitalised. It provides one universally recognised name per species.

The ranked arrangement of living things from broad to narrow groups: kingdom, phylum or division, class, order, family, genus and species. Each level contains fewer organisms sharing more features than the level above it.

The basic unit of classification: a group of organisms that can interbreed naturally to produce fertile offspring and are reproductively isolated from other such groups. It is the lowest and most inclusive practical rank.

Whittaker's system dividing life into Monera, Protista, Fungi, Plantae and Animalia, based on cell type, body organisation, nutrition and reproduction. It separated prokaryotes and fungi from plants and animals.

The study of the external form, structure and visible features of an organism, such as root, stem, leaf, flower and fruit types in plants. It supplies the descriptive characters used in identification and classification.

The study of the internal structure of organisms, including tissue arrangement in plant organs and organ systems in animals. In plants it covers epidermis, ground tissue and vascular bundles as seen in sections.

A region of undifferentiated, actively dividing plant cells that produces new cells for growth. Apical meristems lengthen roots and shoots, while lateral meristems such as cambium increase girth.

A strand of conducting tissue in plants containing xylem for water transport and phloem for sugar transport, often with cambium between them. Its arrangement differs between monocot and dicot stems.

The arrangement of flowers on a floral axis. It may be racemose, with the main axis growing indefinitely and flowers borne laterally, or cymose, with the axis ending in a flower.

A sheet of closely packed animal cells resting on a basement membrane, covering surfaces and lining cavities. Types include squamous, cuboidal, columnar and ciliated, suited to protection, absorption or secretion.

Animal tissue with widely spaced cells embedded in an abundant matrix that links and supports other tissues. Examples are loose and dense fibrous tissue, cartilage, bone, blood and adipose tissue.

A cell lacking a membrane-bound nucleus and organelles, with circular DNA in a nucleoid and 70S ribosomes. Bacteria and cyanobacteria are prokaryotes; respiration and photosynthesis occur on membranes.

A cell with a true nucleus enclosed by a nuclear envelope and with membrane-bound organelles such as mitochondria, plastids and Golgi bodies. Plants, animals, fungi and protists are eukaryotes.

Double-membraned organelles where aerobic respiration and oxidative phosphorylation occur. The inner membrane is folded into cristae bearing the electron transport chain and ATP synthase, so they are called the cell's powerhouse.

A ribonucleoprotein particle that translates messenger RNA into protein. Prokaryotic 70S ribosomes have 50S and 30S subunits; eukaryotic cytoplasmic 80S ribosomes have 60S and 40S subunits.

A protein, or occasionally RNA, catalyst that speeds a biochemical reaction by lowering its activation energy without being consumed. Most are highly specific for one substrate, determined by the shape of the active site.

Adenosine triphosphate, the universal energy currency of cells. Hydrolysis of its terminal phosphate bond releases usable energy for processes such as muscle contraction, active transport and biosynthesis.

Cell division producing two genetically identical daughter cells with the same chromosome number as the parent. It underlies growth, repair and asexual reproduction, and has prophase, metaphase, anaphase and telophase stages.

Reduction division producing four haploid cells from one diploid cell through two successive divisions. Crossing over in prophase I and independent assortment create genetic variation in gametes.

The ordered sequence of events from one cell division to the next. It comprises interphase, with G1, S and G2 phases for growth and DNA replication, followed by the mitotic phase.

The net movement of water across a selectively permeable membrane from a region of higher water potential to one of lower water potential. It drives water uptake by roots and cell turgidity.

The loss of water vapour from aerial plant parts, mainly through stomata. It pulls water up the xylem by cohesion-tension and cools leaves, but can cause wilting if excessive.

Plant tissue that conducts water and dissolved minerals upward from roots to shoots. It contains tracheids and vessel elements, which are dead at maturity and have lignified walls.

The light-driven synthesis of organic compounds from carbon dioxide and water in chloroplasts, releasing oxygen. Light reactions produce ATP and NADPH, which the Calvin cycle uses to fix carbon.

The green photosynthetic pigment in chloroplast thylakoids that absorbs mainly blue and red light and transfers excitation energy to reaction centres. Chlorophyll a is the primary pigment; chlorophyll b is accessory.

A photosynthetic adaptation in which carbon dioxide is first fixed into a four-carbon acid in mesophyll cells before release to the Calvin cycle in bundle-sheath cells. It reduces photorespiration and suits hot, dry habitats.

The first stage of respiration, in which one glucose molecule is split in the cytoplasm into two pyruvate molecules, with net gain of two ATP and two NADH. It needs no oxygen.

The cyclic mitochondrial pathway in which acetyl coenzyme A is oxidised to carbon dioxide, generating NADH, FADH2 and GTP. It is also called the citric acid or tricarboxylic acid cycle.

The shrinking of a plant cell's protoplast away from its cell wall when water leaves by osmosis in a hypertonic solution. It demonstrates that the wall is freely permeable but the membrane is not.

The maintenance of a stable internal environment within narrow limits despite external change, achieved by negative feedback. Examples include blood glucose regulation, thermoregulation and osmoregulation by the kidneys.

The functional filtering unit of the kidney, comprising a glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule and collecting duct. It forms urine by filtration, reabsorption and secretion.

The iron-containing respiratory pigment in red blood cells that binds oxygen reversibly to form oxyhaemoglobin. Its affinity falls as carbon dioxide rises and pH drops, aiding oxygen release in tissues.

A chemical messenger secreted by an endocrine gland into the blood, acting on distant target cells bearing specific receptors. Examples include insulin, thyroxine, adrenaline and auxin in plants.

A rapid, automatic and involuntary response to a stimulus, mediated by a reflex arc through the spinal cord without waiting for conscious brain processing. It protects the body from harm.

The unique angiosperm process in which one male gamete fuses with the egg to form a zygote and the second fuses with two polar nuclei to form triploid endosperm. It occurs after pollen tube entry.

The transfer of pollen grains from an anther to a stigma, by wind, water, insects or other animals. Self-pollination occurs within one flower; cross-pollination moves pollen between different plants.

The nutritive tissue formed in seeds, triploid in angiosperms after double fertilisation, supplying food to the developing embryo. In some seeds it persists; in others it is consumed by the cotyledons.

Patterns of inheritance described by Mendel's laws of dominance, segregation and independent assortment, based on paired factors transmitted through gametes. They explain monohybrid and dihybrid ratios such as 3:1 and 9:3:3:1.

The genetic constitution of an organism at one or more loci, describing which alleles it carries, for example homozygous dominant, heterozygous or homozygous recessive. It interacts with environment to produce the phenotype.

The exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It recombines alleles and increases genetic variation in gametes.

The synthesis of a messenger RNA copy from one strand of DNA by RNA polymerase, using complementary base pairing. In eukaryotes it occurs in the nucleus and is followed by processing and translation.

The differential survival and reproduction of individuals with heritable traits better suited to their environment, so those traits become more common over generations. It is the main mechanism of adaptive evolution.

A substance produced by or derived from microorganisms that inhibits or kills bacteria, usually acting on cell wall synthesis, protein synthesis or DNA replication. Examples include penicillin and streptomycin.

A preparation of weakened, killed or subunit antigen that stimulates protective immunity without causing serious disease. It generates memory cells so a later natural infection is rapidly neutralised.

A vessel in which living cells or enzymes carry out a desired biochemical reaction under controlled conditions of temperature, pH, oxygen and nutrient supply. It is used for large-scale production of antibiotics, enzymes and vaccines.

An organism whose genome has been deliberately altered by introducing foreign DNA, usually through a vector such as Agrobacterium or a plasmid. Examples are Bt cotton and golden rice.

A self-regulating unit in which a community of organisms interacts with its physical environment, with energy flowing in one direction and nutrients cycling. Examples include ponds, forests and grasslands.

A feeding position in a food chain, such as producer, primary consumer or secondary consumer. Energy transfer between levels is inefficient, so only about ten per cent passes to the next level.

The variety of life at genetic, species and ecosystem levels within a defined area. It underpins ecosystem stability and is threatened by habitat loss, overexploitation, invasive species and pollution.