Grade 12 Life Sciences Paper 1: Core Survival Concepts

Vocabulary study set based on the Grade 12 Life Sciences Paper 1 Survival Kit, reviewing core definitions across Human Reproduction, Nervous System, Sense Organs, Homeostasis, Endocrine System, and Plant Hormones.

Spermatogenesis

The process of forming male gametes (sperm cells) from diploid cells in the seminiferous tubules of the testes through meiosis under the influence of testosterone.

Scrotum

A skin sac that protects the testes and holds them outside the body at a temperature $2^\times\text{C}$ to $3^\times\text{C}$ below normal body temperature ($37^\times\text{C}$), providing the optimal temperature for sperm production.

Epididymis

A coiled tubular structure positioned against the testis where immature sperm cells mature and are stored.

Sperm duct (Vas deferens)

The tube that transports mature sperm cells from the epididymis to the urethra.

Seminal vesicle

An accessory gland that produces a nutrient-rich fluid that provides energy for sperm cell motility.

Prostate gland

A gland that secretes an alkaline fluid to neutralise acidic conditions produced in the vagina and urethra that would otherwise kill sperm cells.

Cowper's gland

A gland producing mucus that assists in the movement and lubrication of sperm cells.

Testosterone

A steroid hormone secreted by the testes responsible for stimulating the maturation of sperm cells and developing male secondary sexual characteristics (such as a beard, pubic hair, deep voice, and muscular body).

Acrosome

A cap-like structure at the anterior head of the sperm cell containing enzymes to digest the outer membrane of the ovum for fertilisation.

Oogenesis

The monthly process in females where diploid cells in the ovary undergo mitosis to form follicles, and under the influence of FSH after puberty, one enlarges and undergoes meiosis to yield a single surviving mature haploid ovum.

Fallopian tube

The muscular tube connecting the ovaries to the uterus that transports egg cells from the ovary and serves as the site of fertilisation.

Endometrium

The blood-vessel-rich inner lining of the uterus where the blastocyst implants and the placenta develops, which breaks down during menstruation if fertilisation does not occur.

Follicle-Stimulating Hormone (FSH)

A hormone secreted by the hypophysis (pituitary gland) that stimulates the development of a primary follicle into a mature Graafian follicle in the ovary.

Luteinising Hormone (LH)

A pituitary hormone that triggers the release of the ovum from the Graafian follicle (ovulation) and promotes the formation of the corpus luteum.

Oestrogen

A female sex hormone secreted by the Graafian follicle that starts the initial thickening and vascularisation of the endometrium.

Progesterone

A hormone secreted by the corpus luteum that thickens the endometrium further in preparation for pregnancy and inhibits FSH secretion to prevent new follicle maturation.

Corpus luteum

The temporary endocrine structure formed from the ruptured Graafian follicle following ovulation, which secretes progesterone.

Morula

A solid ball of cells formed by repeated mitotic divisions of the diploid zygote during its passage down the Fallopian tube.

Blastocyst

A hollow ball of cells containing an inner cell mass, derived from the morula, that implants directly into the endometrium of the uterus.

Stimulus

Any detectable change in the internal or external environment (such as light, sound, or temperature) that produces a response.

Impulse

An electrochemical message generated by receptor cells and carried along neurons across the nervous system.

Meninges

The three protective connective tissue membranes enclosing both the brain and the spinal cord.

Cerebrum

The largest brain region, responsible for controlling voluntary movements, higher thought processes (memory, judgment, learning), and interpreting sensory sensations.

Cerebellum

The lower rear portion of the brain that coordinates all voluntary movements and regulates muscle tension to maintain balance and posture.

Medulla oblongata

The lowest brainstem structure that transmits impulses between the spinal cord and brain, controlling involuntary autonomic functions like heartbeat, blood pressure, and breathing rate.

Corpus callosum

A tract of nerve fibers connecting the left and right cerebral hemispheres, facilitating communication between them.

Hypothalamus

The brain center that monitors the internal environment and acts as the control centre for hunger, thirst, sleep, body temperature, and emotions.

Sensory neuron (Afferent neuron)

A neuron that conducts nerve impulses from sensory receptors toward the central nervous system.

Motor neuron (Efferent neuron)

A neuron that conducts nerve impulses away from the central nervous system to effectors (muscles or glands) to bring about an action.

Interneuron (Relay neuron)

A neuron situated entirely within the central nervous system (spinal cord or brain) that connects sensory and motor neurons.

Receptor

A specialized sensory structure or cell capable of detecting a specific environmental stimulus and converting it into a nerve impulse.

Effector

A responsive muscle or gland that reacts when stimulated by a nerve impulse from a motor neuron.

Reflex action

A rapid, automatic, involuntary response to an environmental stimulus designed to protect the body against severe injury.

Reflex arc

The complete neural pathway traversed by impulses during a reflex action: receptor $\rightarrow$ sensory neuron $\rightarrow$ interneuron $\rightarrow$ motor neuron $\rightarrow$ effector.

Synapse

The microscopic junction across which a nerve impulse is chemically transmitted from the axon of one neuron to the dendrite of the next in one direction only.

Multiple sclerosis

A progressive nervous system disorder in which the myelin sheath of neurons degrades, impairing and slowing the transmission of nerve impulses.

Alzheimer's disease

A progressive brain disorder characterized by the degeneration of brain cells, resulting in severe memory loss and destruction of thinking skills.

Eye accommodation

The physiological adjustment of the curvature/shape of the crystalline lens via the ciliary muscles and suspensory ligaments to focus clearly on near or distant objects.

Pupillary mechanism

The reflex adjustment of pupil diameter by the antagonistic contraction and relaxation of the circular and radial muscles of the iris in response to light intensity.

Choroid

A deeply pigmented, vascular middle layer of the eyeball that reduces internal light reflection and provides nutrients and oxygen to retinal cells.

Yellow spot (Fovea centralis)

The specific area of the retina containing the highest concentration of cone photoreceptors, providing the sharpest and clearest vision.

Blind spot

The region on the retina where the optic nerve exits the eyeball, devoid of rods and cones, producing no image when light falls upon it.

Myopia (Short-sightedness)

A visual defect where the eyeball is too long or the lens is too rounded, causing light rays from distant objects to focus in front of the retina; corrected with concave lenses.

Hyperopia (Long-sightedness)

A visual defect where the eyeball is too short or the lens cannot become sufficiently convex, causing light rays from near objects to focus behind the retina; corrected with convex lenses.

Astigmatism

A refractive eye condition caused by an uneven, irregular curvature of the cornea or lens, leading to distorted and blurred images.

Cataracts

A visual defect where the crystalline lens of the eye turns cloudy and opaque, treated by surgically replacing the defective lens with a synthetic artificial lens.

Tympanum (Eardrum)

A taut membrane separating the outer ear from the middle ear that vibrates upon contact with incoming sound waves and transfers vibrations to the ossicles.

Auditory ossicles

Three tiny middle-ear bones (hammer/malleus, anvil/incus, stirrup/stapes) that amplify mechanical vibrations from the tympanic membrane and transmit them to the oval window.

Eustachian tube

A canal connecting the middle ear cavity to the pharynx, functioning to equalise air pressure on either side of the tympanic membrane.

Organ of Corti

The primary receptor organ for hearing situated within the cochlea, containing sensory hair cells that convert liquid pressure waves into nerve impulses.

Cristae

Sensory receptor structures located within the ampullae of the semicircular canals stimulated by changes in the direction and speed of head movements.

Maculae

Receptor organs situated in the sacculus and utriculus of the inner ear stimulated by changes in the static position of the head relative to gravity.

Round window

A membrane-covered opening in the middle ear that bulges outward to release fluid pressure from the cochlea, preventing echo formation.

Endocrine gland

A ductless organ that secretes chemical messengers (hormones) directly into the blood vessels to be carried to specific target tissues.

Exocrine gland

A gland that releases secretions through specialized ducts into cavities or external surfaces (e.g., salivary and sweat glands).

Homeostasis

The physiological process of maintaining a constant, stable internal environment within the body despite fluctuations in external conditions.

Negative feedback mechanism

A self-regulating control system operating in the body that detects deviations from normal physiological setpoints and initiates corrective mechanisms to restore homeostatic balance.

Thyroxin

An iodine-containing hormone secreted by the thyroid gland that regulates the basal metabolic rate, influences heart rate, and controls cellular growth.

Goitre

An enlargement of the thyroid gland resulting from iodine deficiency, leading to abnormally low thyroxin levels.

Insulin

A pancreatic hormone released when blood glucose levels are too high, stimulating liver and muscle cells to absorb glucose and store it as insoluble glycogen.

Glucagon

A hormone secreted by the pancreas when blood glucose levels drop below normal, stimulating the liver to convert stored glycogen back into glucose.

Glycogen

The insoluble storage polysaccharide synthesized in liver and muscle cells from surplus blood glucose.

Antidiuretic hormone (ADH)

A hormone produced by the hypothalamus and secreted by the hypophysis that increases the water permeability of kidney renal tubules during osmoregulation.

Aldosterone

A hormone secreted by the adrenal cortex that regulates blood sodium balance by stimulating the active reabsorption of sodium ions in the renal tubules.

Vasodilation

The widening of subcutaneous skin arterioles on a hot day, allowing increased blood flow to the surface to promote heat loss by radiation.

Vasoconstriction

The narrowing of cutaneous blood vessels in cold temperatures, diverting blood away from the skin surface to minimize heat loss.

Auxins

A class of plant growth hormones produced in apical tips that promote growth by stimulating cell elongation and division, directing tropic movements.

Gibberellins

Plant hormones responsible for breaking seed dormancy to trigger germination and promoting the growth of lateral side branches.

Abscisic acid (ABA)

A plant hormone that inhibits growth and cell division in roots and stems, promotes dormancy during cold winter months, and triggers abscission of leaves and ripe fruits.

Phototropism

The directional growth movement of a plant stem towards or away from a unilateral light stimulus due to the unequal redistribution of auxins.

Geotropism

The directional growth response of a plant organ (such as a root growing downward into soil) guided by the pull of gravity.