Kerala Plus Two Biology (DHSE) key terms

The process in which diploid microspore mother cells inside the pollen sac of an anther undergo meiosis to produce four haploid microspores, each of which matures into a pollen grain.

The innermost nutritive layer of the anther wall whose cells supply proteins, lipids and sporopollenin precursors to developing pollen grains before degenerating at maturity.

The haploid male gametophyte of a seed plant, enclosed in a sporopollenin-rich exine, that delivers two male gametes to the embryo sac through a pollen tube.

The meiotic division of the megaspore mother cell in the ovule that yields four haploid megaspores, usually only one of which survives to form the embryo sac.

The haploid female gametophyte of a flowering plant, typically with eight nuclei in seven cells, containing the egg, two synergids, three antipodals and a binucleate central cell.

The characteristic event in angiosperms in which one male gamete fuses with the egg to form a zygote while the second fuses with the two polar nuclei to form triploid endosperm.

The nutritive tissue formed from the triploid primary endosperm nucleus after double fertilisation, which feeds the developing embryo and may be consumed or retained in the mature seed.

Asexual seed formation in which the embryo develops without fertilisation, producing offspring genetically identical to the mother plant; useful in agriculture for fixing hybrid vigour.

The development of fruit without fertilisation, giving seedless fruits such as banana; it can occur naturally or be induced by applying growth substances like auxins.

The sequence of mitotic and meiotic divisions plus spermiogenesis by which spermatogonia in the seminiferous tubules become mature haploid spermatozoa capable of motility.

A tall supporting cell of the seminiferous tubule that nourishes developing sperm, secretes inhibin and forms the blood-testis barrier under follicle-stimulating hormone control.

An interstitial cell of the testis that responds to luteinising hormone by secreting testosterone, which drives spermatogenesis and male secondary sexual characters.

The temporary endocrine gland formed from the ruptured ovarian follicle after ovulation; it secretes progesterone and oestrogen to prepare and maintain the uterine endometrium for implantation.

The roughly 28-day cyclic series of hormonal and uterine changes in human females, comprising follicular, ovulatory and luteal phases, ending in menstruation when pregnancy does not occur.

The attachment and embedding of the blastocyst in the endometrium of the uterus about a week after fertilisation, establishing the placental connection for nutrient exchange.

A prenatal diagnostic procedure in which a sample of amniotic fluid containing foetal cells is withdrawn and analysed for chromosomal and metabolic disorders; its misuse for sex determination is prohibited.

The tendency of genes located close together on the same chromosome to be inherited together, producing fewer recombinant offspring than expected from independent assortment.

The production of new allele combinations in offspring, arising from crossing over between homologous chromosomes during meiosis or from independent assortment of unlinked genes.

Mendel's principle that alleles of different genes assort into gametes independently of one another when the genes lie on different chromosome pairs.

A condition in which the heterozygote shows a phenotype intermediate between the two homozygotes, so that the F2 generation shows a 1:2:1 genotypic and phenotypic ratio.

A situation in which both alleles of a heterozygous individual are fully and separately expressed in the phenotype, as in human AB blood group.

The existence of more than two alternative forms of a gene in a population, although any one diploid individual carries only two of them, as with the ABO blood group alleles.

The mode of DNA duplication in which the double helix unwinds and each parental strand serves as a template, so every daughter molecule keeps one original strand.

The synthesis of an RNA molecule by RNA polymerase using a DNA template strand, a process that in eukaryotes occurs in the nucleus and is followed by processing.

The set of rules relating nucleotide triplets called codons in messenger RNA to specific amino acids or stop signals during protein synthesis.

The process on ribosomes in which messenger RNA codons are read and transfer RNA molecules deliver matching amino acids to build a polypeptide chain.

The differential survival and reproduction of individuals that vary in heritable traits, so that favourable variants increase in frequency in later generations.

Random change in allele frequencies in a population from generation to generation, especially strong in small populations, independent of fitness differences.

The rapid evolution of many divergent species from a single ancestral lineage that colonises new habitats or niches, as seen in Darwin's finches on the Galapagos Islands.

The non-specific, present-from-birth defence system that includes physical barriers, phagocytes, natural killer cells, inflammation and fever, without memory of the pathogen.

Pathogen-specific defence mediated by B and T lymphocytes that develops after exposure and retains immunological memory, giving a faster response on re-exposure.

A Y-shaped immunoglobulin protein produced by plasma cells that binds a specific antigen and helps neutralise or eliminate the pathogen bearing it.

A preparation of weakened or killed pathogen, or its antigenic component, given to stimulate protective acquired immunity without causing the disease.

A bacterial enzyme that recognises a specific palindromic DNA sequence and cuts the double strand there, producing fragments with sticky ends for gene cloning.

A small circular extrachromosomal DNA molecule of bacteria, widely engineered as a vector to carry foreign genes into a host cell.

An enzyme that joins two DNA fragments by sealing the phosphodiester bonds between them, used to insert a gene into a cut vector.

An in vitro technique that repeatedly cycles denaturation, primer annealing and extension with a thermostable polymerase to amplify a specific DNA segment into millions of copies.

An organism whose genome has been deliberately altered by recombinant DNA techniques, for example Bt cotton carrying a bacterial insect-resistance gene.

The rate at which autotrophs convert solar energy into organic matter per unit area per unit time, providing the energy base of an ecosystem.

The position an organism occupies in a food chain according to its feeding relationship, such as producer, primary consumer or secondary consumer.

A graphical representation of the numbers, biomass or energy at successive trophic levels; pyramids of energy are always upright while others may be inverted.

The variety of species present in a community, described both by species richness and by the relative abundance of individuals among those species.

A biogeographic region with exceptionally high species richness and endemism that faces serious habitat loss, and is therefore a conservation priority.

The pair of chromosomes, one inherited from each parent, that carry the same gene loci in the same order and pair during meiosis.

The exchange of corresponding segments between non-sister chromatids of homologous chromosomes during pachytene of prophase I, generating new allele combinations.

Any organic molecule characteristic of living systems, such as carbohydrates, proteins, lipids or nucleic acids, built mainly from carbon, hydrogen, oxygen and nitrogen.

A protein catalyst that speeds a specific biochemical reaction by lowering its activation energy, acting through an active site complementary to its substrate.

The loss of water vapour from aerial plant parts, chiefly through stomata, which drives the ascent of sap and cools the leaf.

The explanation of water transport in xylem stating that transpiration creates tension pulling a continuous cohesive water column upward from roots to leaves.

The exudation of liquid water droplets from hydathodes at leaf margins, driven by root pressure when transpiration is low.

A wasteful process in C3 plants in which RuBisCO fixes oxygen instead of carbon dioxide, consuming ATP and releasing carbon dioxide without producing sugar.

The light-independent dark reactions of photosynthesis in which ATP and NADPH fix carbon dioxide into carbohydrate through carboxylation, reduction and regeneration steps.

A photosynthetic route in tropical plants where carbon dioxide is first fixed into a four-carbon acid in mesophyll cells and later released for the Calvin cycle in bundle sheath cells.

The first stage of respiration in the cytoplasm, splitting one glucose molecule into two pyruvate molecules with net gain of ATP and NADH.

The cyclic mitochondrial reactions in which acetyl coenzyme A is oxidised completely to carbon dioxide, generating NADH, FADH2 and ATP.

ATP synthesis in the inner mitochondrial membrane driven by a proton gradient built by electron transport, with oxygen as the final electron acceptor.

The two-part scientific naming system introduced by Linnaeus, giving each species a Latinised genus name followed by a specific epithet, both italicised.

The ordered ranking of taxa from kingdom down through phylum, class, order, family, genus to species, in which each level groups the one below it.

A true body cavity lined entirely by mesoderm that lies between the body wall and the gut, present in annelids, molluscs, arthropods and echinoderms.