BSEH SS Biology key terms

The process in the seminiferous tubules of the testis in which diploid spermatogonia divide by mitosis and then meiosis to produce four haploid spermatids that mature into sperm.

The formation of haploid egg cells in the ovary, where one primary oocyte yields a single large ovum plus polar bodies because cytoplasm is partitioned unequally during meiotic divisions.

A roughly 28-day sequence of hormonal changes in human females in which the endometrium thickens, ovulation occurs near mid-cycle, and the lining is shed if pregnancy does not begin.

The temporary gland formed from follicle remnants after ovulation; it secretes progesterone and oestrogen, which maintain the uterine lining and suppress further follicle development.

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

A reduction division in which one diploid cell undergoes two successive divisions to form four haploid cells, with crossing over and independent assortment generating genetic variation.

Exchange of corresponding segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, producing new allele combinations on the resulting chromosomes.

The tendency of genes located close together on the same chromosome to be inherited together, so their alleles appear in offspring in ratios that depart from independent assortment.

The percentage of offspring showing recombination between two genes; values rise with distance between loci and are used to construct genetic maps in centimorgans.

The condition in which allele and genotype frequencies in a population stay constant across generations when there is no mutation, migration, selection, or genetic drift and mating is random.

Random change in allele frequencies between generations due to chance sampling of gametes, most pronounced in small populations where it can fix or eliminate alleles regardless of fitness.

Differential survival and reproduction of individuals whose heritable traits make them better suited to their environment, so those alleles increase in frequency over generations.

A bacterial enzyme that cuts double-stranded DNA at a specific recognition sequence, producing sticky or blunt ends used to insert fragments into vectors during gene cloning.

A small circular extrachromosomal DNA molecule engineered with an origin of replication, a selectable marker, and restriction sites to carry a foreign gene into a host cell.

An enzyme that forms phosphodiester bonds between adjacent nucleotides, sealing nicks and joining a DNA insert to a cut vector backbone to create recombinant DNA.

An in vitro technique that amplifies a target DNA segment through repeated cycles of denaturation, primer annealing, and extension by a thermostable DNA polymerase, doubling copy number each cycle.

A method that separates charged molecules such as DNA fragments or proteins through a gel under an electric field, with smaller or more highly charged molecules migrating faster.

An organism whose genome has been deliberately altered by introducing foreign DNA, commonly to produce a useful protein, improve a crop trait, or serve as a disease model.

A large vessel in which genetically engineered cells or microbes are cultured under controlled conditions to manufacture products such as insulin, enzymes, or antibiotics on an industrial scale.

The ability of the body to resist and eliminate pathogens, mediated by innate barriers and by adaptive responses involving B and T lymphocytes that create memory.

A Y-shaped protein produced by plasma cells that binds a specific antigen through variable regions, neutralising the target or marking it for destruction by other immune mechanisms.

A preparation of weakened, inactivated, or subunit antigen that primes the immune system to produce antibodies and memory cells without causing the full disease.

A protozoan parasite transmitted by female Anopheles mosquitoes that multiplies inside red blood cells and liver cells, causing the recurring fever and chills of malaria.

The feeding position an organism occupies in a food chain, such as producer, primary consumer, or secondary consumer, determining how energy flows through an ecosystem.

The unidirectional transfer of energy from sunlight through producers to successive consumers, with roughly ten percent passed to the next level and the rest lost as heat.

A graphical representation of numbers, biomass, or energy at successive trophic levels, which may be upright or inverted depending on the ecosystem being described.

A region with exceptionally high numbers of endemic species that has already lost a large share of its original habitat, making it a priority for conservation effort.

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

The net movement of water across a selectively permeable membrane from a region of higher water potential to one of lower water potential, driven by solute concentration differences.

Shrinkage of the protoplast away from the cell wall when a plant cell loses water in a hypertonic solution, causing visible collapse of the cell contents.

The free energy of water per unit volume, expressed in pressure units; pure water at atmospheric pressure has zero potential, and solutes lower it to negative values.

Loss of water vapour mainly through stomata in leaves, which drives the upward pull of the transpiration stream and cools the plant surface.

Pores in the leaf epidermis bounded by guard cells that open and close to regulate gas exchange and water loss, balancing carbon dioxide uptake against transpiration.

A wasteful process in which RuBisCO fixes oxygen instead of carbon dioxide, consuming energy and releasing carbon dioxide, and which is suppressed in C4 and CAM plants.

The functional unit of the kidney, comprising a glomerulus and tubule, where blood is filtered and useful solutes are reabsorbed while wastes are concentrated in urine.

Pressure-driven movement of water and small solutes from blood in the glomerulus into the Bowman's capsule, excluding cells and large proteins from the forming filtrate.

A rapid, self-propagating reversal of membrane voltage in a neuron caused by sodium influx followed by potassium efflux, transmitting an impulse along the axon.

A chemical released from a presynaptic terminal that diffuses across the synaptic cleft and binds receptors on the next cell, exciting or inhibiting it.