Grade 12 Life Sciences – Master Vocabulary

A comprehensive set of vocabulary flashcards covering the key terms, structures, processes and exam verbs found throughout the Grade 12 Life Sciences study guide.

Complementary Base Pairing

Specific hydrogen bonding: Adenine-Thymine and Guanine-Cytosine in DNA; Adenine-Uracil in RNA.

Transcription

Formation of mRNA from a DNA template in the nucleus to carry the genetic code to ribosomes.

mRNA (messenger RNA)

Single-stranded RNA copy of a gene that carries codons from the nucleus to the ribosome.

Translation

Decoding of mRNA codons at the ribosome when tRNA anticodons bring specific amino acids to build a protein.

Codon

Sequence of three mRNA bases that codes for one amino acid.

Anticodon

tRNA triplet complementary to an mRNA codon.

tRNA (transfer RNA)

RNA molecule that carries a specific amino acid and has an anticodon to pair with mRNA.

Peptide Bond

Chemical bond linking adjacent amino acids during protein synthesis.

Meiosis

Cell division in gonads producing four non-identical haploid gametes and introducing variation.

Synapsis

Pairing of homologous chromosomes during Prophase I of meiosis.

Bivalent

Structure of two homologous chromosomes joined during synapsis.

Crossing Over

Exchange of genetic material between chromatids of homologous chromosomes, producing recombinant chromosomes.

Chiasmata

Visible points where chromatids cross during crossing over.

Random Arrangement

Random orientation of homologous pairs on the equator during Metaphase I leading to variation.

Non-disjunction

Failure of homologous chromosomes or chromatids to separate, leading to aneuploidy.

Down Syndrome

Human trisomy 21 resulting from non-disjunction; individual has 47 chromosomes.

Diploid (2n)

Having two sets of chromosomes, e.g., somatic cells.

Haploid (n)

Having one set of chromosomes, e.g., gametes.

Gametes

Sex cells (sperm or ova) produced by meiosis and carrying a haploid chromosome set.

Spermatogenesis

Meiotic formation of four haploid sperm from diploid cells in the testes under testosterone influence.

Oogenesis

Formation of one mature ovum and three polar bodies from a diploid cell in the ovary, stimulated by FSH.

Fertilisation

Fusion of haploid nuclei of sperm and ovum in the fallopian tube to form a diploid zygote.

Zygote

Diploid cell formed after fertilisation; undergoes mitosis to form an embryo.

Blastocyst

Hollow ball of cells that implants into the endometrium.

Implantation

Attachment of the blastocyst to the endometrium about 6-7 days after fertilisation.

Graafian Follicle

Mature ovarian follicle that releases the ovum at ovulation and secretes oestrogen.

Corpus Luteum

Structure formed from the ruptured follicle; secretes progesterone to maintain endometrium.

Menstrual Cycle

28-day female reproductive cycle involving ovarian and uterine changes regulated by hormones.

FSH (Follicle-Stimulating Hormone)

Pituitary hormone that stimulates follicle development and oestrogen secretion.

LH (Luteinising Hormone)

Pituitary hormone that triggers ovulation and formation of the corpus luteum.

Oestrogen

Ovarian hormone that repairs/thickens endometrium and inhibits FSH via negative feedback.

Progesterone

Hormone from corpus luteum (and placenta) that maintains thick, vascular endometrium.

Ovulation

Release of a mature ovum from the Graafian follicle, typically on day 14.

Homeostasis

Maintenance of a constant internal environment through coordinated nervous and hormonal responses.

Thermoregulation

Control of body temperature via vasodilation, vasoconstriction, sweating and shivering.

Vasoconstriction

Narrowing of skin arterioles to reduce heat loss in cold conditions.

Vasodilation

Widening of skin arterioles to increase heat loss in hot conditions.

Osmoregulation

Regulation of water balance mainly by ADH and kidney tubule permeability adjustments.

ADH (Antidiuretic Hormone)

Hormone from posterior pituitary that increases water reabsorption in kidneys when blood water is low.

Aldosterone

Adrenal cortex hormone that increases sodium (and thus water) reabsorption and potassium excretion.

Insulin

Pancreatic beta-cell hormone that lowers blood glucose by promoting cellular uptake and glycogenesis.

Glucagon

Pancreatic alpha-cell hormone that raises blood glucose by converting glycogen to glucose in the liver.

Thyroxin

Thyroid hormone that raises basal metabolic rate; regulated by TSH via negative feedback.

Negative Feedback

Control mechanism where a change triggers responses that reverse that change, restoring norm.

Phototropism

Growth response of a plant shoot towards unilateral light, mediated by auxin redistribution.

Auxins

Plant hormones promoting cell elongation, apical dominance and positive phototropism.

Geotropism

Growth response to gravity; roots show positive geotropism while shoots are negative.

Gibberellins

Plant hormones stimulating stem elongation and seed germination.

Abscisic Acid

Plant hormone promoting dormancy, stomatal closure and abscission; antagonistic to gibberellins.

Natural Selection

Process where individuals with favourable heritable traits survive and reproduce more successfully.

Speciation

Formation of new species when populations are reproductively isolated and undergo independent evolution.

Gene Flow

Movement of alleles between populations through migration, reducing genetic differences.

Genetic Drift

Random change in allele frequencies, especially in small populations, due to chance events.

Polyploidy

Presence of extra whole chromosome sets; common speciation mechanism in plants.

Fossil

Preserved remains or traces of organisms from the past, providing evidence for evolution.

Bipedalism

Habitual upright walking on two legs, indicated by forward foramen magnum and short broad pelvis.

Foramen Magnum

Opening in the skull where spinal cord enters; its forward position indicates bipedalism.

Prognathous Jaw

Projecting lower face; reduced in human evolution towards a flatter face.

Sagittal Crest

Bony ridge atop skull for jaw-muscle attachment; present in apes, absent in modern humans.

Brow Ridge

Prominent bone above eye sockets; reduced through human evolution.

Out-of-Africa Hypothesis

Theory that modern humans evolved in Africa and later dispersed, replacing archaic humans elsewhere.

Chromosome

Condensed DNA molecule visible in cell division; carries genetic information.

Chromatid

One of two identical strands of a replicated chromosome joined by a centromere.

Centromere

Region joining sister chromatids and attachment site for spindle fibres.

Homologous Chromosomes

Pair of chromosomes with the same genes but possibly different alleles, one maternal, one paternal.

Chromatin

Uncondensed DNA-protein network present during interphase.

Mutation

Permanent change in DNA sequence or chromosome structure or number.

Gene Mutation

Change in one or a few nucleotides (substitution, deletion, insertion) altering a gene.

Chromosomal Mutation

Change in chromosome number or large segments (e.g., non-disjunction, translocation).

Haemophilia

Recessive sex-linked disorder causing impaired blood clotting; carried on the X chromosome.

Carrier

Heterozygous individual with one recessive allele for a disorder but phenotypically normal.

Co-dominance

Inheritance where both alleles in the heterozygote are fully expressed (e.g., AB blood group).

Incomplete Dominance

Inheritance where heterozygote shows an intermediate phenotype (e.g., snapdragon pink flowers).

ABO Blood Group

Human blood type system controlled by three alleles (IA, IB co-dominant; i recessive).

Phenotype

Observable traits resulting from genotype and environment.

Genotype

Genetic constitution of an organism for a particular trait.

Dihybrid Cross

Genetic cross tracking two gene pairs, yielding classic 9 : 3 : 3 : 1 ratio in F2 heterozygotes.

Test Cross

Cross of an individual showing the dominant phenotype with a homozygous recessive to determine genotype.

Punnett Square

Grid diagram used to predict genetic crosses and their offspring ratios.

Sensory Neuron

Nerve cell transmitting impulses from receptors to the CNS.

Interneuron

Neuron within CNS that links sensory and motor pathways for integration.

Motor Neuron

Neuron carrying impulses from CNS to effectors (muscles/glands).

Reflex Arc

Shortest neural pathway producing a quick, automatic response, bypassing conscious brain.

Medulla Oblongata

Brain‐stem region controlling heartbeat, breathing and reflexes like coughing.

Cerebellum

Brain region coordinating voluntary movement, posture and balance.

Cerebrum

Largest brain part responsible for higher functions like memory, reasoning and voluntary actions.

Meninges

Three protective membranes (dura, arachnoid, pia) surrounding brain and spinal cord.

Spinal Cord

CNS structure conducting impulses to/from brain and mediating spinal reflexes.

Retina

Light-sensitive inner layer of eye containing rods and cones.

Fovea (Yellow Spot)

Area of retina with highest cone density for sharp colour vision.

Blind Spot

Retinal area where optic nerve exits; lacks photoreceptors.

Optic Nerve

Nerve carrying visual impulses from retina to cerebrum (occipital lobe).

Pupil

Adjustable opening in iris through which light enters the eye.

Iris

Pigmented muscle controlling pupil diameter.

Lens

Elastic, transparent structure focusing light onto retina; shape changed by ciliary muscles.

Cornea

Transparent front layer of eye providing most refraction of incoming light.

Accommodation (eye)

Adjustment of lens curvature for near or distant vision via ciliary muscles and suspensory ligaments.

Pupillary Reflex

Automatic adjustment of pupil size to light intensity via radial and circular iris muscles.

Myopia

Short-sightedness where image focuses in front of retina; corrected with concave lens.

Hypermetropia

Long-sightedness where image focuses behind retina; corrected with convex lens.