Tamil Nadu HSE Second Year Botany key terms

The branch of biology that identifies, describes, names and classifies organisms into hierarchical groups based on shared characteristics and evolutionary relationships, allowing biologists worldwide to communicate about species consistently.

The system introduced by Linnaeus in which every species receives a two-part Latin name: a capitalised genus name followed by a lowercase specific epithet, both italicised or underlined in handwritten work.

A permanently preserved reference specimen, usually deposited in a recognised herbarium, to which the scientific name of a species is permanently attached and against which later collections are compared.

The arrangement of organisms into nested ranks, from kingdom down through phylum, class, order, family, genus and species, so that each level contains the groups below it and reflects degrees of relatedness.

A plant body that is not differentiated into true roots, stems and leaves and lacks vascular tissue; typical of algae, fungi, liverworts and other lower plants, and often flattened or filamentous.

Photosynthetic, mainly aquatic thallophytes containing chlorophyll and lacking true roots, stems, leaves and vascular tissue; they range from unicellular forms to large seaweeds and include green, brown and red groups.

A filamentous algal growth form in which the plant body has a prostrate creeping portion and an upright branched portion, as seen in genera such as Ectocarpus among the brown algae.

A root-like structure at the base of a seaweed that anchors the thallus to a rock or other substrate; it serves only for attachment and does not absorb water or minerals like a true root.

The mass of fine, branching fungal filaments called hyphae that together form the vegetative body of a fungus and absorb nutrients from the substrate or host.

A single tubular filament of a fungus, which may be aseptate and multinucleate or divided into cells by cross walls called septa, and which collectively builds the mycelium.

An organism that obtains its nutrition from dead and decaying organic matter, secreting digestive enzymes into the substrate and then absorbing the soluble products; many fungi and some bacteria live this way.

Symbiotic associations between a fungus, usually an ascomycete, and a photosynthetic partner that is either a green alga or a cyanobacterium; they are sensitive indicators of air pollution, especially sulphur dioxide.

A mutualistic association between a fungus and the roots of a higher plant in which the fungus improves water and mineral uptake, particularly phosphorus, while receiving sugars from the host.

A member of the amphibious group of plants that includes liverworts, hornworts and mosses; the plant body is a gametophyte, vascular tissue is absent and water is required for fertilisation.

The green, branched, filamentous juvenile stage that develops directly from a moss spore and later gives rise to the leafy gametophyte by budding.

The haploid, gamete-producing generation in the life cycle of a plant; it is dominant in bryophytes, reduced in pteridophytes and highly reduced and dependent in gymnosperms and angiosperms.

The diploid, spore-producing generation of a plant life cycle, formed by fusion of gametes; in bryophytes it is dependent on the gametophyte, while in vascular plants it is the dominant phase.

The regular alternation of a haploid gametophyte generation with a diploid sporophyte generation in a plant life cycle, the two phases differing in chromosome number and in the type of reproductive cells produced.

A compact reproductive cone consisting of a central axis bearing closely set sporophylls, as in gymnosperms such as Cycas and Pinus, where microsporophylls and megasporophylls are grouped separately.

The production of two kinds of spores, small microspores and large megaspores, by the same plant species; it occurs in some pteridophytes such as Selaginella and in all seed plants.

A membrane-bound organelle of plant cells that develops from a proplastid and specialises as a chloroplast for photosynthesis, a chromoplast for pigment storage or a leucoplast for storing starch, oil or protein.

The green double-membrane plastid containing stacks of thylakoids, or grana, suspended in stroma; it houses the light reactions on its membranes and the Calvin cycle enzymes in its stroma.

The rigid non-living covering outside the plasma membrane of plant cells, made mainly of cellulose microfibrils in a matrix of hemicellulose and pectin, which gives shape, strength and protection against bursting.

Fine cytoplasmic channels that pass through pits in the walls of adjacent plant cells, connecting their cytoplasm and allowing water, ions and small molecules to move between them.

A reduction division in which one diploid cell gives rise to four haploid cells through two successive divisions, with crossing over in prophase I creating new combinations of alleles.

The exchange of corresponding segments between non-sister chromatids of a homologous pair during pachytene of prophase I of meiosis, which produces recombinant chromosomes and new gene combinations.

A cross of an individual showing the dominant phenotype with a homozygous recessive partner, used to reveal whether the unknown individual is homozygous dominant or heterozygous by examining the offspring ratios.

Mendel's principle that the two alleles of a gene separate from each other during gamete formation, so that each gamete carries only one allele and the pair is restored at fertilisation.

The tendency of genes located close together on the same chromosome to be inherited together rather than assorting independently, with the frequency of recombination falling as the distance between them decreases.

The condition in which a single gene influences several apparently unrelated phenotypic characters, as when one allele affects both flower colour and stem height or seed coat and seed size.

The synthesis of an RNA molecule from a DNA template catalysed by RNA polymerase, proceeding in the 5-prime to 3-prime direction and followed in eukaryotes by processing and splicing before export from the nucleus.

The set of rules by which nucleotide triplets, or codons, in messenger RNA specify particular amino acids during translation; it is degenerate, non-overlapping and reads in a fixed frame from a start codon.

A cluster of functionally related genes in prokaryotes that are transcribed together from one promoter and regulated as a unit, as in the lac operon of Escherichia coli.

A protein-pigment complex embedded in the thylakoid membrane that absorbs light and transfers excitation energy to a reaction centre chlorophyll, driving electron transport in the light reactions.

The light-driven synthesis of ATP from ADP and inorganic phosphate in the chloroplast, coupled to electron transport through the photosystems and the resulting proton gradient across the thylakoid membrane.

Tiny pores in the leaf epidermis, each bounded by two guard cells, that open and close to regulate the diffusion of carbon dioxide inward and water vapour outward during gas exchange.

The loss of water vapour from the aerial parts of a plant, chiefly through the stomata of leaves, which pulls water upward in the xylem and cools the leaf surface.

The continuous network of living cytoplasm of a plant linked from cell to cell by plasmodesmata, forming one of the two main pathways for the radial movement of water and solutes in roots.

The promotion of flowering by exposing seeds or young plants to a period of low temperature, which satisfies a chilling requirement in biennials and winter cereals such as wheat.

The response of a plant to the relative lengths of day and night, which controls flowering in short-day, long-day and day-neutral plants and also influences tuber formation and leaf fall.

A hypothetical flowering hormone, now identified with proteins produced in leaves and transported to the shoot apex, that induces the transition from vegetative growth to flowering.

The unique process in angiosperms in which one male gamete fuses with the egg to form the zygote and a second fuses with the two polar nuclei to form the triploid primary endosperm nucleus.

The nutritive tissue of a seed, normally triploid in angiosperms, formed from the primary endosperm nucleus after double fertilisation and providing food for the developing embryo and seedling.

The transfer of pollen grains from the anther of a flower to the stigma of the same or another flower, brought about by wind, water, insects, birds or other animals.

A species or group whose presence, abundance or condition reveals the quality of its environment, such as lichens for sulphur dioxide pollution or diatoms for water quality.

A biogeographic region with exceptionally high species richness and endemism that has already lost a large proportion of its original habitat; the Western Ghats and Sri Lanka form one such hotspot.

The condition in which a species is naturally restricted to a particular geographical area and is found nowhere else, making it especially vulnerable to habitat loss and extinction.

A collection of dried, pressed and labelled plant specimens arranged systematically for reference and study, together with the facilities for their preservation and the records that accompany them.