Karnataka II PUC Biology (KSEAB) key terms

The process in which a diploid microspore mother cell inside the pollen sac undergoes 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 food and materials such as sporopollenin to developing pollen grains, and which degenerates once the pollen matures.

A tough, resistant polymer forming the outer wall (exine) of pollen grains; it protects the male gametophyte from desiccation, chemicals and microbial attack, and resists decay.

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

The triploid nutritive tissue formed after triple fusion inside the embryo sac; it feeds the developing embryo and may be stored in the seed for the germinating seedling.

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

Development of fruit without fertilisation, so the fruit is seedless; it occurs naturally in some species such as banana and can be induced by growth substances.

The sequence of mitotic and meiotic divisions in the seminiferous tubules by which spermatogonia are converted into mature haploid spermatozoa capable of fertilising an egg.

A tall supporting cell in the seminiferous tubule wall that nourishes developing sperm, secretes inhibin, and forms the blood-testis barrier that isolates germ cells.

A cap-like sac at the tip of the sperm head containing hydrolytic enzymes such as hyaluronidase, which digest the egg coverings during fertilisation.

A thick glycoprotein layer surrounding the mammalian egg; after the first sperm enters, it undergoes changes that block further sperm entry and prevent polyspermy.

The yellowish body formed from the ruptured ovarian follicle after ovulation; it secretes progesterone and oestrogen to prepare and maintain the endometrium for possible pregnancy.

The release of a mature secondary oocyte from a ruptured Graafian follicle, usually around the middle of the menstrual cycle, triggered by a surge of luteinising hormone.

The roughly 28-day repeating cycle of changes in the ovaries and uterine lining, controlled by FSH, LH, oestrogen and progesterone, involving menstruation, follicle growth, ovulation and luteal phases.

A prenatal diagnostic procedure in which a sample of amniotic fluid containing foetal cells is drawn and examined for chromosomal abnormalities; in India its use for sex determination is legally restricted.

Failure to conceive after a year or more of unprotected intercourse; causes may be in the male or female partner and include blocked tubes, low sperm count and hormonal disorders.

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

A cross of an offspring with one of its parents or with an individual of the parental genotype; when the parent is recessive it functions as a test cross.

A condition in which neither allele completely masks the other, so the heterozygote shows an intermediate phenotype, as in pink flowers of Antirrhinum.

A situation in which both alleles in a heterozygote are fully expressed at the same time, so the phenotype shows both traits, as in human AB blood group.

The existence of more than two alternative forms of a gene in a population, as with the three alleles ABO, A, B and O that determine human blood groups.

The tendency of genes located close together on the same chromosome to be inherited together, so their alleles do not assort independently and recombinants appear less often than expected.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during pachytene of meiosis I, producing new combinations of alleles.

Random change in allele frequencies from generation to generation, especially in small populations, caused by chance rather than by natural selection.

A form of genetic drift in which a small group colonises a new area and its restricted gene pool gives the new population allele frequencies different from the original population.

The differential survival and reproduction of individuals whose inherited variations make them better suited to their environment, so those traits become more common over generations.

A bacterial enzyme that cuts DNA at a specific recognition sequence, producing sticky or blunt ends; it is the key tool for inserting genes into vectors.

A short DNA sequence that reads the same on the two strands when both are read in the 5' to 3' direction; it is the recognition site for a restriction enzyme.

Short single-stranded overhangs produced when a restriction enzyme cuts DNA in a staggered way; complementary overhangs allow a gene and a vector to base-pair and be joined by ligase.

A self-replicating DNA molecule, usually a plasmid or bacteriophage, used to carry a foreign gene into a host cell and multiply it there.

An in vitro technique that repeatedly copies a target DNA segment using a thermostable polymerase and short primers, doubling the number of copies in each cycle.

The commercial exploitation of biological resources or traditional knowledge from a country without fair compensation or permission, often through improperly granted patents.

A large vessel in which cells or enzymes are cultured under controlled conditions of temperature, oxygen and nutrients to produce a desired product on an industrial scale.

The rate at which producers in an ecosystem capture and store energy as organic matter; gross primary productivity is total fixation and net primary productivity is what remains after respiration.

A graphical representation of numbers, biomass or energy at successive trophic levels, showing how each level supports a smaller amount than the one below it.

The position an organism occupies in a food chain according to how it obtains energy, such as producer, primary consumer or secondary consumer.

Progressive increase in the concentration of a persistent pollutant in organisms at successive trophic levels, because the substance is stored rather than excreted.

The light reaction in which electrons from photosystem I travel through an electron transport chain and return to photosystem I, generating ATP but not NADPH or oxygen.

The light-independent stage of photosynthesis in the stroma, in which carbon dioxide is fixed by RuBisCO and reduced to sugar using ATP and NADPH.

A wasteful process in which RuBisCO binds oxygen instead of carbon dioxide, consuming ATP and releasing carbon dioxide without producing sugar; it increases in hot, dry conditions.

The pairing of homologous chromosomes along their length during zygotene of prophase I in meiosis, forming bivalents that later allow crossing over.

The visible points where non-sister chromatids of homologous chromosomes remain in contact after crossing over; they hold the homologues together until anaphase I.

The arrangement of the loop of Henle and vasa recta in which filtrate and blood flow in opposite directions, creating a concentration gradient that allows urine to be concentrated.

The pressure-driven movement of water and small solutes from blood in the glomerulus into the Bowman's capsule, while cells and large proteins are retained.

A graph of haemoglobin saturation against oxygen partial pressure; its sigmoid shape shows cooperative binding, and a shift to the right means oxygen is released more readily.

The shift of the oxygen dissociation curve to the right when carbon dioxide and hydrogen ions increase, causing haemoglobin to release oxygen more easily to active tissues.