Tamil Nadu HSE Second Year Biology key terms

The process in which diploid microspore mother cells inside the anther undergo meiosis to form haploid microspores, each of which later develops into a pollen grain.

A unique event in flowering plants where one male gamete fuses with the egg to form the zygote and the second fuses with two polar nuclei to form the triploid primary endosperm nucleus.

The formation of haploid megaspores from the diploid megaspore mother cell in the ovule through meiosis, typically producing one functional megaspore that develops into the embryo sac.

The nutritive tissue formed in seeds after triple fusion, usually triploid in angiosperms, which nourishes the developing embryo and may be consumed or retained at maturity.

A form of asexual reproduction in which seeds are produced without fertilization, so the offspring are genetically identical to the parent plant; useful in agriculture for preserving hybrid vigour.

The development of fruit without fertilization of the ovule, producing seedless fruits such as banana; it can occur naturally or be induced by growth hormones.

The series of meiotic and maturational events in the seminiferous tubules by which diploid spermatogonia are converted into haploid, motile spermatozoa under hormonal control.

The process in the ovary by which diploid oogonia develop into haploid ova, beginning before birth and completing only after fertilization, producing one large ovum and polar bodies.

The temporary endocrine gland formed from the ruptured follicle after ovulation; it secretes progesterone, which maintains the endometrium and supports early pregnancy.

A prenatal diagnostic procedure in which a sample of amniotic fluid containing foetal cells is withdrawn and analysed for chromosomal abnormalities and genetic disorders.

The characteristic proportion of phenotypes among offspring of a cross, such as 3:1 in a monohybrid F2 generation, arising from segregation of alleles during gamete formation.

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

A cross between an individual of unknown genotype and a homozygous recessive individual, used to reveal whether the unknown is homozygous dominant or heterozygous.

The tendency of genes located close together on the same chromosome to be inherited together, reducing the frequency of recombination between them below independent assortment expectations.

The synthesis of an RNA molecule from a DNA template catalysed by RNA polymerase, transferring genetic information from the nucleus to the cytoplasm in eukaryotes.

The process at the ribosome in which the sequence of codons on mRNA directs the assembly of amino acids into a polypeptide chain with the help of tRNA.

The set of rules by which nucleotide triplets called codons specify particular amino acids or stop signals during protein synthesis; it is degenerate and nearly universal.

The differential survival and reproduction of individuals with heritable variations better suited to their environment, leading to gradual change in the characteristics of a population.

Random change in allele frequencies in a small population due to chance events, which can eliminate or fix alleles independently of their adaptive value.

Similarity of structure or genetic sequence between organisms due to shared ancestry, such as the forelimbs of different vertebrates, which provides evidence for evolution.

A bacterial enzyme that recognises a specific DNA sequence and cuts the double helix at or near that site, producing fragments used in genetic engineering.

A small circular extrachromosomal DNA molecule found in bacteria, commonly used as a vector to carry a foreign gene into a host cell during cloning.

A DNA molecule formed by joining genetic material from two different sources, typically a foreign gene inserted into a vector using restriction enzymes and ligase.

An in vitro technique that repeatedly denatures, anneals primers and extends them with a thermostable DNA polymerase to amplify a specific DNA sequence exponentially.

The unauthorised commercial exploitation of biological resources or traditional knowledge of indigenous communities without fair compensation or benefit sharing.

The overall ability of the body to resist and eliminate pathogenic organisms and foreign molecules, mediated by innate and acquired defence mechanisms including antibodies.

The administration of weakened or inactivated antigens to stimulate the immune system to produce antibodies and memory cells, giving protection against a specific disease.

A class of cytokine proteins secreted by virus-infected cells that inhibit viral replication in neighbouring cells and help activate immune responses.

The breeding or genetic improvement of crop plants to raise their content of essential nutrients such as vitamins, minerals or proteins, improving nutritional value of food.

A period of greatly increased food grain production achieved through improved high-yielding crop varieties, irrigation, fertilizers and modern management practices.

A functional unit in which a community of living organisms interacts with its physical environment, with energy flowing and nutrients cycling between biotic and abiotic components.

A graphical representation of the numbers, biomass or energy at successive trophic levels of a food chain, showing progressive decrease at higher levels.

The variety of living organisms at genetic, species and ecosystem levels within a defined region, valued for ecological stability and human welfare.

Protection of species in their natural habitats through national parks, wildlife sanctuaries and biosphere reserves, allowing natural ecological processes to continue.

Protection of threatened species outside their natural habitat, such as in botanical gardens, zoos, seed banks and cryopreservation facilities.

Nutrient enrichment of water bodies by nitrogen and phosphorus from sewage and fertilizers, causing excessive algal growth, oxygen depletion and death of aquatic life.

A type of cell division producing two genetically identical daughter cells with the same chromosome number as the parent, responsible for growth and repair.

A reduction division producing four haploid cells from one diploid cell through two successive divisions, generating genetic variation and gametes.

The ordered sequence of interphase and mitotic phases through which a cell passes between successive divisions, including DNA replication in S phase.

The movement of water molecules across a semipermeable membrane from a region of higher water potential to one of lower water potential, driven by a concentration gradient.

The shrinkage of the protoplast away from the cell wall when a plant cell loses water in a hypertonic solution, caused by exosmosis.

The system of naming organisms with two Latin words, a genus name and a specific epithet, providing a unique and universally recognised scientific name.

The branch of biology dealing with identification, classification and nomenclature of organisms, arranging them in hierarchical categories based on shared characteristics.