Tamil Nadu HSE First Year Biology key terms

The two-part naming system for species in which the first word is the genus name, capitalised, and the second is the specific epithet, written in lower case; both are italicised or underlined.

The branch of biology that identifies, describes, classifies and names organisms, arranging them in a hierarchy of categories from species up to kingdom and domain.

The ranked sequence of groups into which organisms are placed, typically species, genus, family, order, class, phylum or division, and kingdom, with each higher rank containing all lower ones.

The basic unit of classification: a group of organisms that resemble one another closely and can interbreed to produce fertile offspring under natural conditions.

A scheme dividing living organisms into Monera, Protista, Fungi, Plantae and Animalia, based mainly on cell type, body organisation, mode of nutrition and reproduction.

A plant body that is not differentiated into true roots, stems and leaves; typical of algae, bryophytes and some fungi.

Chlorophyll-bearing, mainly aquatic thallophytes that photosynthesise and lack a multicellular jacket around their reproductive organs; examples include Spirogyra and Ulva.

A small, non-vascular land plant such as a moss, liverwort or hornwort, in which the dominant plant body is the gametophyte and the sporophyte remains attached to it.

The haploid, gamete-producing phase of a plant life cycle; it arises from a spore and produces gametes by mitosis.

The diploid, spore-producing phase of a plant life cycle; it develops from a zygote and forms haploid spores by meiosis.

The regular alternation of a haploid gametophyte phase and a diploid sporophyte phase in the life cycle of plants and many algae.

A true body cavity lined on all sides by mesoderm-derived tissue, separating the body wall from the gut; present in annelids and most higher animals.

Describing an animal that lacks a body cavity, so that the space between the body wall and gut is filled with solid tissue, as in flatworms.

The condition of having the body divided into a series of similar segments arranged along the long axis, each with its own set of organs, as in earthworms.

A stiff, rod-like supporting structure running along the dorsal side of chordate embryos; retained in adult lancelets and in the larvae of tunicates.

A chordate in which the notochord is replaced during development by a vertebral column of bone or cartilage enclosing the nerve cord.

A cell lacking a membrane-bound nucleus and membrane-bound organelles, with its genetic material present as a nucleoid; found in bacteria and archaea.

A cell in which the genetic material is enclosed within a nuclear membrane and which contains membrane-bound organelles such as mitochondria and plastids.

A double-membrane organelle in eukaryotic cells where aerobic respiration proceeds and most ATP is generated; its inner membrane is folded into cristae.

A small ribonucleoprotein particle, free in the cytoplasm or bound to rough endoplasmic reticulum, on which messenger RNA is translated into protein.

A protein, or occasionally an RNA molecule, that speeds up a specific biochemical reaction by lowering its activation energy without being consumed.

Adenosine triphosphate, the universal energy currency of cells; hydrolysis of its terminal phosphate bond releases energy for cellular work.

Nuclear division producing two genetically identical daughter nuclei with the same chromosome number as the parent cell; it underlies growth and asexual reproduction.

Two successive nuclear divisions that halve the chromosome number and generate genetically varied haploid cells, giving rise to gametes or spores.

The ordered sequence of events through which a cell grows, replicates its DNA and divides, comprising interphase and the mitotic phase.

The loss of water vapour from aerial plant surfaces, chiefly through stomata, which creates the pull that draws water up the xylem.

The water-conducting plant tissue made of dead tracheary elements, which transports water and dissolved minerals upward from the roots.

The plant tissue that conducts sugars and other organic solutes from sources to sinks through living sieve elements assisted by companion cells.

The movement of organic solutes such as sucrose through the phloem from regions of production or storage to regions of use.

A small pore in the leaf epidermis bounded by two guard cells, through which gases and water vapour are exchanged between the leaf and the atmosphere.

The light-driven process in chloroplasts in which carbon dioxide and water are converted into carbohydrate with the release of oxygen.

The first stage of respiration, occurring in the cytoplasm, in which glucose is split into two molecules of pyruvate with a net gain of ATP.

The functional unit of the kidney, comprising a renal corpuscle and a tubule, which filters blood and adjusts the composition of urine.

The maintenance of a relatively stable internal environment, such as constant temperature, pH and solute concentration, despite external change.

A chemical messenger secreted by an endocrine gland into the blood, which acts on specific target cells to regulate their activity.

A circulatory arrangement in which blood passes through the heart twice per circuit, once through the pulmonary and once through the systemic route.

The formation of mature haploid gametes from diploid germ cells by meiosis and subsequent maturation, producing sperm in males and ova in females.

The exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, producing new gene combinations.

The transmission of traits according to Mendel's laws of dominance, segregation and independent assortment, based on paired factors now called genes.

The differential survival and reproduction of individuals that vary in heritable traits, so that advantageous variants become more common over generations.

A DNA molecule formed by joining genetic material from different sources, usually a gene inserted into a vector such as a plasmid.

A graphical representation of the numbers, biomass or energy at successive trophic levels of an ecosystem, usually narrowing towards the top.