Grade 12 Life Sciences: Core Concepts and Terminology

Comprehensive vocabulary flashcards covering key terms and definitions from the Grade 12 Life Sciences curriculum, including molecular genetics, meiosis, vertebrate and human reproduction, environmental responses, homeostasis, plant responses, and evolution.

Nucleotide

The monomer or building block of nucleic acids (DNA and RNA), consisting of a phosphate group, a sugar molecule, and a nitrogenous base.

DNA (deoxyribonucleic acid)

A double-stranded, helical nucleic acid molecule made of nucleotides containing deoxyribose sugar that carries the hereditary genetic code for protein synthesis.

Transcription

The first stage of protein synthesis occurring in the nucleus, in which a segment of DNA serves as a template to form a complementary strand of messenger RNA (mRNA).

Translation

The second stage of protein synthesis occurring at ribosomes in the cytoplasm, where transfer RNA (tRNA) molecules transport specific amino acids to link via peptide bonds according to the mRNA codons.

Codon

A sequence of three consecutive nitrogenous bases on an mRNA molecule that codes for a specific amino acid.

Anti-codon

A sequence of three consecutive nitrogenous bases on a tRNA molecule that is complementary to a specific codon on mRNA.

DNA profiling

A laboratory technique that produces a unique pattern of bands of different lengths and thicknesses on X-ray film representing an individual's DNA.

Homologous chromosomes

A pair of chromosomes of identical size and shape that carry genes for the same characteristics at the same loci, with one chromosome inherited from the mother and one from the father.

Bivalent

A pair of homologous chromosomes that lie physically close together and in contact at points during Prophase I of meiosis.

Crossing over

The overlapping of non-sister chromatids of homologous chromosomes resulting in the exchange of genetic material during Prophase I, introducing genetic variation.

Chiasma

The physical point of overlap where non-sister chromatids touch and break to exchange genetic segments during crossing over.

Non-disjunction

An error during meiosis where homologous chromosome pairs in Anaphase I or sister chromatids in Anaphase II fail to separate, resulting in abnormal gametes.

Karyotype

A diagrammatic representation showing the number, shape, and arrangement of a complete set of chromosomes in the nucleus of a somatic cell.

Ovipary

A reproductive strategy in which eggs are laid and the embryo develops entirely outside the mother's body, receiving nourishment solely from yolk.

Ovovivipary

A reproductive strategy where eggs are fertilised internally and retained within the mother's body until hatching, with the embryo nourished by egg yolk rather than a placenta.

Vivipary

A reproductive strategy where fertilisation occurs internally, the embryo develops inside the mother's uterus, and nourishment is supplied directly through a placenta.

Amniotic egg

An egg containing extra-embryonic membranes (amnion, chorion, allantois, and yolk sac) surrounded by a protective shell, allowing terrestrial reproduction independent of water.

Amnion

An extra-embryonic membrane enclosing the amniotic cavity that produces amniotic fluid to cushion the embryo against mechanical shock, temperature fluctuations, and dehydration.

Allantois

An extra-embryonic membrane that collects nitrogenous waste products from the developing embryo and assists in gas exchange.

Chorion

An extra-embryonic membrane that enables gaseous exchange in shelled eggs and develops into the embryonic contribution to the placenta in mammals.

Precocial development

A pattern of development in which hatchlings emerge well developed with open eyes, down or fur, and the ability to move and feed immediately, requiring minimal parental care.

Altricial development

A pattern of development in which hatchlings emerge blind, naked, helpless, and immobile, requiring extensive parental care and feeding to survive.

Spermatogenesis

The process occurring in the germinal epithelium of the seminiferous tubules under the influence of testosterone, in which diploid cells undergo meiosis to form mature haploid sperm.

Oogenesis

The process in the ovaries whereby diploid cells in primary follicles undergo meiosis to form a single functional, mature haploid ovum and three degenerating polar bodies.

Acrosome

A cap-like structure at the anterior head of a sperm cell containing digestive enzymes that dissolve the outer layers of the ovum to enable fertilisation.

Graafian follicle

A fluid-filled ovarian structure containing a mature ovum that secretes oestrogen prior to ovulation.

Corpus luteum

A temporary endocrine structure formed from the ruptured Graafian follicle after ovulation that secretes progesterone to maintain the endometrium.

Allele

An alternative form or variation of a gene situated at the same locus on homologous chromosomes.

Complete dominance

A genetic condition where the dominant allele completely masks the phenotypic expression of the recessive allele in the heterozygous state.

Incomplete dominance

A pattern of inheritance in which neither allele is dominant, resulting in a heterozygous phenotype that is an intermediate blend of the parental traits.

Co-dominance

A pattern of inheritance in which two different alleles for a trait are equally dominant and both are fully expressed in the phenotype of a heterozygote.

Recombinant DNA technology

A biotechnological method where a specific gene is extracted from one organism using restriction enzymes and inserted into a bacterial plasmid to alter the host genome.

Synapse

The microscopic gap between the axon terminal of one neuron and the dendrites of an adjacent neuron across which chemical neurotransmitters diffuse to transmit an impulse.

Reflex arc

The neurological pathway travelled by an impulse from a sensory receptor via the spinal cord to an effector to bring about an automatic reflex action.

Accommodation

The process by which the ciliary muscles and suspensory ligaments alter the curvature and convexity of the eye lens to focus clear images on the retina from varying distances.

Pupillary mechanism

The antagonistic reflex action of the circular and radial muscles of the iris that adjusts pupil diameter to regulate the amount of light entering the eye.

Organ of Corti

The primary sensory receptor structure located in the middle chamber of the cochlea that converts sound vibrations in the endolymph into nerve impulses.

Cristae

Sensory receptors situated within the ampullae at the base of the semi-circular canals that detect sudden changes in the speed and direction of head movement.

Maculae

Sensory receptors located within the sacculus and utriculus of the inner ear vestibule that detect changes in the position of the head with respect to gravity.

Homeostasis

The physiological process by which organisms maintain a stable, constant internal environment within narrow limits despite changes in the external environment.

Negative feedback mechanism

A regulatory control system in which an initial change or imbalance triggers a physiological response that counteracts and reverses the change, restoring equilibrium.

Osmoregulation

The homeostatic regulation of water and solute concentrations in the blood and tissue fluids, largely controlled by antidiuretic hormone (ADH) acting on the kidneys.

Thermoregulation

The homeostatic process by which endothermic organisms regulate core body temperature to maintain it near $36.8^\circ\text{C}$.

Vasodilation

The widening of blood vessels in the skin in response to high temperatures, increasing blood flow to the skin surface to promote heat loss via radiation and conduction.

Vasoconstriction

The narrowing of cutaneous blood vessels in cold conditions, reducing surface blood flow and minimising body heat loss.

Auxins

Plant hormones produced primarily in the growing tips of shoots and roots that regulate cell division, cell elongation, apical dominance, and tropisms.

Apical dominance

The phenomenon whereby high concentrations of auxin produced at the stem apex inhibit the growth and development of lateral branches located close to the tip.

Phototropism

The directional growth movement of a plant organ in response to a unilateral light stimulus.

Geotropism

The directional growth movement of a plant in response to the downward pull of gravity.

Speciation

The evolutionary formation of one or more new species from an existing parent population following prolonged isolation and independent natural selection.

Punctuated equilibrium

An evolutionary theory proposing that species remain physically unchanged for long periods (stasis), interrupted by brief intervals of rapid evolutionary change.

Bipedalism

The habitual ability to walk upright on two lower limbs with an erect posture.

Foramen magnum

The large aperture at the base of the skull through which the spinal cord passes, positioned forward in humans to balance the skull upright on the vertical spinal column.

Prognathous

A cranial condition characterised by jaws that project or protrude outward significantly beyond the vertical plane of the upper face.

'Out of Africa' hypothesis

The scientific model stating that modern humans (Homo sapiens) originated exclusively in Africa and subsequently migrated outward to colonise all other continents.