Grade 12 Life Sciences: Core Concepts and Terminology

Comprehensive vocabulary flashcards covering the key terms, biological definitions, and anatomical structures from the Mind the Gap Grade 12 Life Sciences CAPS curriculum.

Nucleotide

The basic building block (or monomer) of nucleic acids, consisting of a phosphate group, a deoxyribose or ribose sugar, and a nitrogenous base.

DNA Replication

The process occurring during interphase by which a DNA molecule produces an exact copy (replica) of itself, doubling the genetic material for cell division.

Transcription

The first stage of protein synthesis occurring in the nucleus, where a strand of DNA unwinds and acts as a template for free RNA nucleotides to form mRNA.

Translation

The second stage of protein synthesis occurring on a ribosome in the cytoplasm, where tRNA molecules carrying specific amino acids bind by their anticodons to complementary codons on mRNA to build a polypeptide chain.

DNA Profiling

A pattern of dark bands representing specific DNA fragments unique to an individual (except identical twins), used in forensic investigations and paternity testing.

Homologous Chromosomes

A pair of chromosomes of similar size and shape, one inherited from each parent, carrying alleles for the same genes at the same locus.

Crossing Over

The exchange of genetic material between non-sister chromatids of a homologous chromosome pair occurring at points called chiasmata during prophase I of meiosis.

Non-Disjunction

The failure of homologous chromosome pairs to separate during anaphase I, or sister chromatids to separate during anaphase II, leading to gametes with abnormal chromosome numbers.

External Fertilisation

A reproductive strategy in which the sperm fertilises the egg outside the female body, typically requiring water to prevent the eggs from drying out.

Internal Fertilisation

A reproductive strategy where the male deposits sperm directly inside the reproductive tract of the female, allowing terrestrial reproduction without dependence on water.

Ovipary

A reproductive strategy where eggs are laid and develop outside the mother's body, obtaining nourishment from egg yolk.

Vivipary

A reproductive strategy where the embryo develops internally within the mother's uterus, receiving nutrients directly from the mother's blood via a placenta, followed by live birth.

Ovovivipary

A reproductive strategy where fertilised eggs are retained inside the female's body until they hatch, with embryos nourished entirely by yolk rather than a maternal placenta.

Precocial Development

A reproductive pattern where hatchlings are born relatively mature and mobile, with open eyes and the ability to feed themselves immediately, requiring minimal parental care.

Altricial Development

A reproductive pattern where hatchlings are born helpless, blind, immobile, and naked, requiring intensive parental care and feeding to survive.

Acrosome

A cap-like structure at the anterior tip of the sperm head containing digestive enzymes that break down the outer layer of the ovum during fertilisation.

Endometrium

The vascular inner lining of the uterus that thickens during the menstrual cycle to provide a site for embryo implantation and placenta formation.

Ovulation

The release of a mature ovum from a ruptured Graafian follicle in the ovary into the Fallopian tube, triggered by high levels of LH around day 14 of the menstrual cycle.

Corpus Luteum

A temporary endocrine structure developed in the ovary from the ruptured Graafian follicle after ovulation, responsible for secreting progesterone.

Gestation

The period of embryonic and foetal development within the uterus between fertilisation and birth, lasting approximately 39 to 40 weeks in humans.

Allele

An alternative form of a gene that occupies the same locus (relative position) on a homologous chromosome.

Complete Dominance

A genetic condition in which one dominant allele completely masks or blocks the phenotypic expression of a recessive allele in the heterozygous condition.

Incomplete Dominance

A form of inheritance where neither allele is completely dominant, resulting in a heterozygous individual showing an intermediate phenotype distinct from both homozygous parents.

Co-Dominance

A genetic condition in which both alleles of a gene pair in a heterozygote are fully and equally expressed in the phenotype.

Karyotype

A visual representation showing the number, size, and arrangement of all chromosomes in the nucleus of a somatic cell.

Cerebrum

The largest part of the brain that controls voluntary actions, higher intellectual processes, and interprets sensory inputs from sense organs.

Cerebellum

The region of the brain that coordinates all voluntary skeletal muscle movements, regulates muscle tone, and maintains equilibrium and balance.

Medulla Oblongata

The part of the brainstem that connects the spinal cord to the brain and regulates vital involuntary actions, such as heartbeat and breathing rate.

Reflex Arc

The neural pathway along which nerve impulses travel from a sensory receptor via the spinal cord to an effector to produce an automatic, rapid reflex action.

Accommodation

The process by which the ciliary muscles and suspensory ligaments alter the curvature of the eye lens to focus light rays from near or distant objects sharply onto the retina.

Pupillary Mechanism

An involuntary reflex that controls the diameter of the pupil through the antagonistic action of circular and radial iris muscles, regulating the amount of light entering the eye.

Organ of Corti

The receptor organ for hearing located inside the cochlea of the inner ear, converting mechanical sound waves into electrical nerve impulses.

Homeostasis

The physiological process of maintaining a relatively constant internal environment (blood and tissue fluid) within narrow limits to ensure optimal cellular functioning.

Osmoregulation

The homeostatic regulation of the water content and osmotic pressure in the blood and bodily fluids, mediated by antidiuretic hormone ($\text{ADH}$).

Vasodilation

The widening of arterioles supplying the surface capillaries of the skin during warm conditions, increasing peripheral blood flow to enhance heat loss.

Vasoconstriction

The narrowing of arterioles supplying the surface capillaries of the skin during cold conditions, diverting blood away from the skin surface to reduce heat loss.

Phototropism

The directional growth of a plant shoot toward a light source due to the unequal redistribution of auxins toward the darker side.

Geotropism

The directional growth of a plant organ in response to the pull of gravity, causing roots to grow downward and shoots to grow upward.

Natural Selection

The evolutionary mechanism proposed by Charles Darwin whereby organisms with traits best suited to their environment survive, reproduce, and pass their advantageous alleles on to the next generation.

Punctuated Equilibrium

A model of evolution proposing that species remain largely unchanged for extended periods of time (equilibrium), interrupted by brief periods of rapid speciation.

Speciation

The evolutionary formation of one or more new species from an existing ancestral population, typically resulting from geographic isolation and independent natural selection.

Foramen Magnum

The large opening in the base of the skull through which the spinal cord passes, positioned centrally/forward in bipedal hominins and further back in quadrupeds.

Prognathous

Having projecting or protruding jaws characteristic of non-human apes and early hominids, contrasted with the flatter, vertical face of modern humans.

Out of Africa Hypothesis

The theory that modern humans (Homo sapiens) evolved initially in Africa and subsequently migrated to populate Europe, Asia, and other continents.

Carbon Footprint

A measurement of the total amount of greenhouse gases, primarily carbon dioxide, emitted directly or indirectly by an individual, population, or organisation over one year.

Eutrophication

The enrichment of aquatic ecosystems with chemical nutrients such as nitrogen and phosphorus from fertilizers or sewage, causing rapid algal growth and subsequent dissolved oxygen depletion.

Food Security

The condition in which all people, at all times, have physical and economic access to sufficient, safe, and nutritious food to meet their dietary needs for an active, healthy life.