HSC Exam Practice

Sample response. A nutritional disease is a disease caused by nutrient deficiency, excess, or dietary imbalance — not by a pathogen, not by an inherited mutation. It differs from infectious disease (which is caused by a pathogen such as a bacterium or virus and may be transmitted between hosts) and from genetic disease (which results from an inherited or spontaneous mutation in DNA and is present from birth). Nutritional diseases are typically preventable through dietary modification.

Marking notes. 1 mark for defining nutritional disease (caused by nutrient deficiency, excess, or imbalance; not pathogenic); 1 mark for distinguishing from infectious disease (pathogen-caused; transmissible); 1 mark for distinguishing from genetic disease (inherited/mutational cause; present from birth/conception).

Sample response. Vitamin C is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase — enzymes that hydroxylate proline and lysine residues in procollagen. This hydroxylation is required for procollagen chains to form stable cross-linked triple-helix structures (collagen). Without vitamin C, collagen cannot form properly, and all connective tissues that depend on collagen — including gum tissue and the connective tissue of healing wounds — lose structural integrity. Gum tissue weakens and bleeds, and the formation of new collagen scaffolding in wounds is impaired, preventing normal healing.

Marking notes. 1 mark for naming prolyl hydroxylase and/or lysyl hydroxylase as the enzymes requiring vitamin C; 1 mark for stating that hydroxylation is required for collagen cross-linking/triple helix stability; 1 mark for connecting defective collagen to gum bleeding and impaired wound healing (with the mechanism — not just stating the symptom).

Sample response. Iodine is a structural component of thyroid hormones T3 and T4. When dietary iodine is insufficient, the thyroid gland cannot synthesise adequate T3/T4. Low T3/T4 levels are detected by the anterior pituitary via negative feedback — normally T3/T4 suppress TSH release, so when T3/T4 fall, TSH is no longer suppressed and TSH secretion increases. Elevated TSH stimulates thyroid follicular cell proliferation (more cells) and hypertrophy (larger cells), causing the entire gland to enlarge visibly — this is goitre. The enlarged gland still cannot restore T3/T4 to normal levels if iodine remains the limiting substrate.

Marking notes. 1 mark for identifying the mechanism (low iodine → insufficient T3/T4 synthesis); 1 mark for describing negative feedback correctly (low T3/T4 → pituitary releases more TSH); 1 mark for linking elevated TSH to thyroid cell proliferation/hypertrophy producing goitre.

Sample response. Type 1 diabetes: primary cause is autoimmune destruction of pancreatic beta cells (triggered by genetic predisposition and an environmental factor, e.g. viral infection). Mechanism: beta cells are destroyed → no insulin is produced → cells cannot take up glucose → chronic hyperglycaemia. Classification: autoimmune (immune) disease, though with a genetic predisposition component. Type 2 diabetes: primary cause is chronic dietary excess of refined carbohydrates and saturated fat combined with physical inactivity and genetic susceptibility. Mechanism: chronic hyperinsulinaemia → cells downregulate insulin receptors (insulin resistance) → beta cells eventually exhaust → insulin secretion declines → hyperglycaemia. Classification: multifactorial non-infectious disease, with nutritional excess as the primary modifiable driver.

Marking notes. 1 mark for T1D cause (autoimmune beta cell destruction, no insulin produced); 1 mark for T2D cause (dietary excess → insulin resistance, with genetic component); 1 mark for distinguishing the role of insulin (absent in T1D; present but cells resistant in T2D); 1 mark for classifying each disease type correctly (T1D = autoimmune; T2D = multifactorial/nutritional).

Sample response. Vegetarians: plant-based foods contain only non-haem iron, which is absorbed at only 2–10% efficiency compared to 15–35% for haem iron from meat; absorption is further inhibited by phytates in plant foods. Without dietary haem iron, meeting the daily iron requirement is difficult. Pregnant women: the developing foetus requires substantial iron for its own haemoglobin synthesis, increasing the mother’s iron demand significantly beyond baseline. Additionally, plasma volume expansion during pregnancy dilutes haemoglobin concentration. Both groups therefore have either reduced iron intake (vegetarians) or greatly increased iron demand (pregnant women) that can outpace dietary intake.

Marking notes. 1 mark for vegetarians (non-haem iron only; low bioavailability of plant-source iron); 1 mark for pregnant women (increased foetal iron demand / expanded plasma volume); 1 mark for connecting the specific factor (low bioavailability / high demand) to the mechanism of anaemia (insufficient haemoglobin synthesis).

Sample response. Atherosclerotic plaque builds progressively in arterial walls over years to decades: LDL infiltrates endothelium → oxidises → macrophages engulf oxidised LDL → foam cells form → plaque grows, narrowing the arterial lumen. This progressive narrowing may cause stable angina (pain on exertion) but does not immediately cause infarction. The acute event that converts chronic atherosclerosis into an emergency is plaque rupture: when the fibrous cap fractures, the lipid-rich core is exposed to flowing blood, rapidly activating the clotting cascade → thrombus (clot) forms → complete acute occlusion of the coronary artery → myocardial infarction as downstream cardiac muscle is deprived of oxygen.

Marking notes. 1 mark for describing plaque formation sequence (LDL → oxidation → foam cells → plaque/lumen narrowing); 1 mark for identifying plaque rupture as the acute event; 1 mark for explaining thrombus formation following rupture → complete arterial occlusion → infarction mechanism.

Sample response (a). The graph shows a positive relationship between HbA1c and 10-year cardiovascular risk: as HbA1c increases from ~4.6% to ~11.4%, 10-year CVD risk increases from approximately 6% to approximately 46%. The relationship is gradual at low HbA1c values (below the 6.5% T2D threshold, risk rises from ~6% to ~16%), then accelerates steeply above the threshold (from ~24% at 7.2% HbA1c to ~46% at 11.4% HbA1c). [Award 1 mark for identifying positive relationship with quantified values; 1 mark for describing the steeper acceleration above the T2D threshold.]

Sample response (b). Individuals with HbA1c above 7.0% have chronic hyperglycaemia (elevated average blood glucose). Glucose spontaneously undergoes non-enzymatic glycation — it binds to proteins in blood vessel walls including collagen and the glomerular basement membrane. Glycation stiffens and thickens vessel walls, impairing endothelial function. Additionally, chronic hyperglycaemia promotes oxidative stress and inflammatory signalling, further damaging endothelium [1 mark]. Damaged endothelium accelerates LDL infiltration and oxidation, accelerating atherosclerotic plaque formation beyond the rate caused by dietary saturated fat alone [1 mark]. Furthermore, hyperglycaemia-driven endothelial damage and plaque acceleration operate continuously over years — those with HbA1c >7.0% for prolonged periods accumulate significantly more arterial damage than normoglycaemic individuals, producing the substantially higher CVD risk at 10 years [1 mark].

Sample response (a). Three groups are below the 50 nmol/L deficiency threshold: South Asian Australian women indoors (31 nmol/L), Aboriginal Australians in remote communities (38 nmol/L), and Anglo-Australian women indoors (54 nmol/L — marginally above). The highest group is Anglo-Australian men outdoors (78 nmol/L) and the lowest is South Asian Australian women indoors (31 nmol/L). Percentage difference: (78 − 31) / 78 × 100 = 47/78 × 100 ≈ 60%. [1 mark for identifying the below-threshold groups with values; 1 mark for calculating the percentage difference correctly — accept 58–62%.]

Sample response (b). Both groups are primarily indoor workers, so UVB exposure is similarly limited. However, South Asian Australian women have significantly higher skin melanin content than Anglo-Australian women. Melanin in the skin competes with the vitamin D precursor 7-dehydrocholesterol for UVB absorption — the more melanin present, the lower the rate of UVB-driven conversion of 7-dehydrocholesterol to pre-vitamin D&sub3;, and consequently the lower the rate of vitamin D synthesis per unit of UVB exposure. Even the limited UVB exposure South Asian women receive (from commuting, windows, etc.) is less efficient at producing vitamin D, producing serum levels 23 nmol/L lower than the comparator group with identical indoor work patterns. [1 mark for identifying melanin as the biological variable; 1 mark for explaining the mechanism (melanin competes for UVB absorption, reducing 7-dehydrocholesterol conversion rate).]

Sample response. Deficiency nutritional diseases and dietary excess diseases represent two distinct mechanisms through which altered nutrient intake disrupts normal physiology. Both can be understood through the same nutrient → function → consequence framework, but they operate via opposite nutritional pathways.

Deficiency diseases result from the absence of an essential nutrient that performs a specific biochemical function. When vitamin C (ascorbic acid) is absent, the enzymes prolyl hydroxylase and lysyl hydroxylase cannot function, procollagen cannot be hydroxylated, collagen cross-linking fails, and all connective tissues dependent on collagen — gums, blood vessel walls, wound sites — lose structural integrity, producing the multisystem symptoms of scurvy. Similarly, iron deficiency impairs haemoglobin synthesis: iron is the central atom of the haem group; without it, red blood cells become small (microcytic) and pale (hypochromic) with reduced oxygen-carrying capacity, producing fatigue, pallor, and impaired cognition. In each case, one missing biochemical component disrupts function across every tissue that depends on it simultaneously.

Dietary excess diseases result from chronic metabolic overload: regulatory systems that function normally at physiological nutrient levels are overwhelmed by sustained excess over years to decades. Chronic excess of refined carbohydrates produces sustained hyperglycaemia and hyperinsulinaemia; target cells (liver, muscle, fat) progressively downregulate insulin receptors in response; insulin resistance develops; pancreatic beta cells exhaust trying to compensate; insulin secretion declines; blood glucose rises above 7.0 mmol/L — Type 2 diabetes. Chronic excess of saturated fat raises LDL cholesterol, which infiltrates arterial endothelium, oxidises, triggers macrophage recruitment and foam cell formation, and builds atherosclerotic plaques over years before causing clinically detectable narrowing or a plaque-rupture-triggered myocardial infarction.

Deficiency diseases typically produce symptoms faster than excess diseases because micronutrient body stores are limited. Vitamin C stores are depleted within 2–3 months of dietary deficiency, after which collagen synthesis fails body-wide with clinical manifestations appearing within weeks. By contrast, dietary excess diseases require years to decades of cumulative metabolic and vascular damage: atherosclerosis begins in young adulthood but heart attacks typically occur at 50–70 years; insulin resistance can precede T2D diagnosis by a decade or more. The body has mechanisms to buffer metabolic excess (adipose storage, insulin response) that delay overt disease far longer than the body can buffer micronutrient absence.

In Australia, dietary excess diseases (T2D, CVD) have become the dominant category of nutritional disease because the industrialised food supply has made calorie-dense, micronutrient-poor processed food cheap and ubiquitous, while sedentary lifestyles have reduced energy expenditure — the epidemiological transition from active, diverse traditional diets to processed Western diets has driven a chronic overnutrition pattern at population scale. Improved sanitation, vaccination, and antibiotics have largely controlled the infectious diseases that historically coexisted with nutritional deficiency, and food security overall has improved for most Australians. However, deficiency diseases remain significant in specific population groups: Aboriginal and Torres Strait Islander Australians in remote communities face iron deficiency anaemia (limited meat/vegetable access) and vitamin D deficiency (high skin melanin) simultaneously with T2D at triple the national rate — the double burden of malnutrition. Elderly Australians in residential care, food-insecure families, and recent immigrants also retain elevated deficiency disease risk, driven by food access constraints rather than overall national food abundance.

Marking notes. 1 mark — Defines the mechanism of deficiency disease (absent nutrient → specific biochemical function disrupted → predictable multi-system consequences). 1 mark — Names and applies at least one deficiency disease with correct biochemical mechanism (e.g. scurvy: vitamin C → prolyl/lysyl hydroxylase → collagen; or iron → haem → haemoglobin). 1 mark — Defines the mechanism of excess disease (chronic metabolic overload → dysregulation over years to decades). 1 mark — Names and applies at least one excess disease with correct mechanism (T2D: refined carbs → insulin resistance → beta cell exhaustion; or CVD: saturated fat → LDL → oxidation → foam cells → plaque). 1 mark — Explains why deficiency diseases produce faster symptoms (micronutrient stores deplete within months; excess diseases accumulate damage over years to decades). 1 mark — Explains the epidemiological shift in Australia (industrialised food supply → calorie-dense processed food → overnutrition; improved food security removes deficiency for most; sedentary lifestyle). 1 mark — Explains why deficiency diseases remain in specific groups (food access constraints, skin pigmentation, remoteness, Indigenous Australians — double burden). 1 mark — Response integrates both categories under the lesson’s overarching framework (nutrient → function → consequence) with precise terminology throughout and a coherent comparative structure.