Inquiry Question 2: Do non-infectious diseases cause more deaths than infectious diseases?
Investigate the causes and effects of non-infectious diseases in humans, including but not limited to: genetic diseases, diseases caused by environmental exposure, nutritional diseases and diseases caused by cancer
A focused answer to the HSC Biology Module 8 dot point on causes of non-infectious disease. Covers genetic, environmental, nutritional, lifestyle and age-related categories with named examples, distinguishing causal mechanisms and risk factors.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
NESA wants you to classify non-infectious diseases by cause and to provide named examples with mechanisms. The distinction from infectious disease (covered in Module 7) is the absence of a transmitted pathogen.
The answer
A non-infectious disease is a disease that is not caused by a pathogen and is not transmitted between hosts. The main causal categories are genetic, environmental, nutritional, lifestyle and age-related (degenerative). Cancer cuts across several categories and is often treated as its own group.
Genetic diseases
Caused by mutations in DNA. The mutation may be inherited from parents or arise de novo in a gamete or early embryo.
Mechanisms.
- Single-gene (Mendelian) disorders. One gene, one disease. Example: cystic fibrosis (autosomal recessive, CFTR gene), Huntington's disease (autosomal dominant, HTT gene), haemophilia A (X-linked recessive, F8 gene).
- Chromosomal disorders. Whole-chromosome abnormalities. Example: Down syndrome (trisomy 21), Turner syndrome (45,X).
- Polygenic and multifactorial. Many genes plus environment. Example: type 2 diabetes, schizophrenia, most cancers.
Environmental diseases
Caused by exposure to physical, chemical or biological agents.
Mechanisms.
- Chemical. Asbestos fibres cause mesothelioma; benzene exposure causes leukaemia; lead exposure causes neurological damage.
- Physical. UV radiation causes skin cancer (melanoma, basal and squamous cell carcinoma); ionising radiation causes various cancers and acute radiation syndrome.
- Air pollution. Particulate matter (PM2.5) causes chronic obstructive pulmonary disease (COPD) and ischaemic heart disease.
- Biological toxins. Aflatoxin from Aspergillus fungi on stored grain causes liver cancer.
Nutritional diseases
Caused by deficiency or excess of nutrients.
Deficiency examples.
- Scurvy. Vitamin C deficiency. Impaired hydroxylation of proline in collagen leads to bleeding gums, poor wound healing.
- Rickets. Vitamin D or calcium deficiency in children. Soft, deformed bones.
- Iron-deficiency anaemia. Low haemoglobin synthesis, fatigue, pallor.
- Kwashiorkor. Severe protein deficiency. Oedema, hepatomegaly, growth failure.
Excess examples.
- Type 2 diabetes. Chronic excess of refined carbohydrates and obesity drive insulin resistance.
- Cardiovascular disease. Excess saturated fats and salt contribute to atherosclerosis and hypertension.
- Obesity. Energy intake exceeding expenditure.
Lifestyle diseases
Caused by behavioural risk factors, often overlapping with nutritional and environmental categories.
Examples.
- Lung cancer. 80 to 90 percent of cases are caused by tobacco smoking. Tar contains polycyclic aromatic hydrocarbons that damage DNA in bronchial epithelium.
- Alcohol-related liver disease. Chronic alcohol consumption causes fatty liver, hepatitis and cirrhosis.
- Cardiovascular disease. Sedentary behaviour, smoking, poor diet, stress.
- Skin cancer. Sun exposure without protection.
Age-related (degenerative) diseases
Caused by cumulative cellular damage and reduced tissue repair with age.
Examples.
- Alzheimer's disease. Accumulation of amyloid-beta plaques and tau tangles in the brain.
- Osteoporosis. Reduced bone mineral density after menopause or with prolonged inactivity.
- Osteoarthritis. Wear of articular cartilage in load-bearing joints.
- Parkinson's disease. Progressive loss of dopaminergic neurons in the substantia nigra.
Cancer as a cross-cutting category
Cancer is uncontrolled cell division caused by accumulated mutations in genes regulating the cell cycle (oncogenes and tumour suppressor genes such as TP53).
It can be:
- Genetic. BRCA1/BRCA2 inherited mutations predispose to breast and ovarian cancer.
- Environmental. UV-induced melanoma, asbestos-induced mesothelioma.
- Lifestyle. Tobacco-induced lung cancer, alcohol-induced oral cancer.
- Infection-associated. Cervical cancer from HPV, liver cancer from hepatitis B (the trigger is infectious, but the cancer itself is not transmitted).
Effects on the individual and society
Individual effects. Pain, disability, reduced life expectancy, psychological impact, loss of income.
Societal effects. Health-care costs (non-infectious disease accounts for over 70 percent of Australia's disease burden), workforce productivity losses, demand for aged care and chronic disease services. Non-infectious disease now causes more deaths globally than infectious disease in every region except sub-Saharan Africa.
Examples in context
Example 1. Mesothelioma in former Wittenoom asbestos workers. Wittenoom in Western Australia mined crocidolite (blue) asbestos from 1943 to 1966. More than 2000 former workers and residents have since died of malignant mesothelioma, a cancer of the pleural lining caused exclusively by inhaled asbestos fibres. Fibres lodge in lung tissue, where they cannot be cleared by macrophages and slowly induce chronic inflammation and DNA damage in mesothelial cells over 20 to 50 years. The Western Australian Mesothelioma Registry reports incidence of around 6 per 100 000, the highest in the world. Mesothelioma is a textbook environmental non-infectious disease, with a single identifiable causal exposure rather than the polygenic multifactor causation typical of cardiovascular disease or type 2 diabetes.
Example 2. Type 2 diabetes and obesity in remote Aboriginal communities. The Northern Territory has the highest rate of type 2 diabetes in Australia, particularly in remote Aboriginal communities where prevalence reaches 27 percent of adults compared to 5 percent nationally. The causes are nutritional and lifestyle: rapid dietary transition from traditional bush tucker (low GI, high fibre) to processed foods (high refined sugars and saturated fats), combined with reduced physical activity and rising obesity. Underlying genetic predisposition (the "thrifty gene" hypothesis) and intergenerational health inequities compound the effect. NT Health's Mai Wiru community store nutrition strategy aims to reduce sugar consumption, illustrating how this category of disease requires structural rather than purely individual interventions.
Exam-style practice questions
Practice questions written in the style of NESA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2022 HSC2 marks[Data table: prevalence of chromosomal abnormalities (per 1000 births) rises with maternal age — 1.5 at age 20, 3 at 30, 8 at 35, 22 at 40, 38 at 45.] Outline the trend shown in the data.Show worked answer →
Full marks need the main features of the trend, not just 'it increases'. State that as maternal age increases, the prevalence of chromosomal abnormalities increases. Then add the key detail markers wanted: after the age of 30 there is a rapid increase — it is increasing at an increasing rate (the rate of increase itself gets steeper). 1 mark is given for merely identifying a trend; the 2nd mark requires that more detailed description of the changing rate. Source: NESA 2022 HSC Biology examination and marking guidelines.
2019 HSC8 marksDiseases are classified as infectious or non-infectious. Evaluate whether Alzheimer's disease should be classified as an infectious disease or a non-infectious disease. In your answer, include reference to the information and data provided throughout Question 33. [Stimulus: a cohort study linking untreated Herpes simplex virus (HSV) infection to higher dementia risk, and a table showing APOE genotypes (e2/e3/e4) altering Alzheimer's risk — e4/e4 making it 14.9× more likely.]Show worked answer →
This is an evaluate band-marked question; top marks need a clear, justified judgement plus correct disease-classification criteria and detailed use of BOTH data sets.
- Define the categories
- Infectious diseases are caused by pathogens passed between people, established as a cause via Koch's postulates. Non-infectious diseases do not spread person to person and arise from factors like the environment or inherited genes.
- Evidence it could be infectious
- The HSV cohort study shows untreated HSV infection is associated with higher dementia risk, and antiviral treatment lowers that risk — hinting at a viral cause. Note study strengths (large sample, long duration, matched controls) add validity.
- Evidence it could be non-infectious
- Alzheimer's results from build-up of amyloid protein; protein synthesis is gene-regulated, and the APOE table shows inherited alleles strongly change risk (e4/e4 = 14.9× more likely; e2 reduces risk) — an inherited genetic basis.
- Justified judgement
- Note the limits — correlation is not causation (Koch's postulates not met) and the study measured dementia, not specifically Alzheimer's. A valid conclusion is that it cannot be definitively classified from this information, as risk appears influenced by both a viral pathogen and genes.
Source: NESA 2019 HSC Biology examination and marking guidelines.
Practice questions
Original practice questions graded from foundation to exam level, each with a full worked solution. Try them before revealing the solution.
foundation2 marksDefine 'non-infectious disease' and state how it differs from an infectious disease.Show worked solution →
1 mark - definition. A non-infectious disease is a disease that is not caused by a pathogen and is not transmitted from one host to another; it arises from factors such as inherited genes, the environment, nutrition, lifestyle or ageing.
1 mark - the contrast. An infectious disease is caused by a pathogen (e.g. a virus, bacterium) that can be passed between people. The discriminator is the absence of a transmissible pathogen in non-infectious disease.
Naming one category without the no-pathogen / no-transmission point caps at 1 mark.
foundation3 marksIdentify the primary causal category of each disease and name the agent or mechanism responsible: (a) cystic fibrosis, (b) mesothelioma, (c) scurvy.Show worked solution →
- 1 mark - (a) cystic fibrosis
- Genetic - an autosomal recessive mutation in the CFTR gene (chromosome 7).
- 1 mark - (b) mesothelioma
- Environmental - inhaled asbestos fibres lodging in the pleural lining.
- 1 mark - (c) scurvy
- Nutritional - vitamin C deficiency, impairing collagen synthesis.
Each mark needs BOTH the category and the named agent/mechanism; a bare category ("genetic") with no named cause does not earn the mark.
foundation2 marksDistinguish between a 'cause' and a 'risk factor' for non-infectious disease, using one named example of each.Show worked solution →
1 mark - cause. A cause is a factor that is necessary for the disease - without it the disease does not occur. Example: the CFTR mutation is the cause of cystic fibrosis (no mutation, no disease).
1 mark - risk factor. A risk factor increases the probability of disease but does not deterministically produce it. Example: obesity is a risk factor for type 2 diabetes - it raises risk but not everyone obese develops the disease.
The mark hinges on "necessary" (cause) versus "raises probability" (risk factor), each tied to a valid example.
core4 marksExplain how exposure to a carcinogen can lead to the development of a tumour. Use ultraviolet (UV) radiation and skin cancer as your example.Show worked solution →
Award up to 4 marks for a clear causal chain linking the carcinogen to uncontrolled division.
- 1 mark - the carcinogen damages DNA
- UV radiation is a mutagen: it causes thymine dimers (covalent bonds between adjacent thymine bases) in the DNA of skin cells (melanocytes/keratinocytes).
- 1 mark - mutation in cell-cycle genes
- If the damage is not repaired, mutations accumulate in genes that control the cell cycle - oncogenes (e.g. BRAF) and tumour suppressor genes (e.g. TP53).
- 1 mark - loss of cell-cycle control
- These mutations remove the normal checkpoints that stop or repair a damaged cell, so the cell divides uncontrollably instead of being arrested or destroyed by apoptosis.
- 1 mark - tumour forms
- Continued uncontrolled division produces a mass of cells (a tumour); a malignant tumour can invade nearby tissue and metastasise.
A response that jumps from "UV causes cancer" to "tumour" without the mutation -> loss of control -> division steps caps at 2 marks.
core5 marksCompare genetic and environmental causes of non-infectious disease. In your answer refer to the origin of the cause, the role of inheritance, and one named example of each.Show worked solution →
Award up to 5 marks for a genuine comparison (both similarities and differences) supported by named examples.
- 1 mark - shared feature
- Both are categories of non-infectious disease: neither involves a transmissible pathogen, and both can ultimately act by damaging or altering the function of cells / DNA.
- 1-2 marks - origin of the cause
- A genetic cause originates from a mutation in the DNA sequence (inherited or de novo). An environmental cause originates from an external agent (chemical, physical or biological) the person is exposed to.
- 1 mark - role of inheritance
- Genetic disease can be passed to offspring through the gametes and follows inheritance patterns; a purely environmental disease is not inherited (though susceptibility may be).
- 1 mark - named examples
- Genetic: cystic fibrosis (CFTR mutation). Environmental: mesothelioma (asbestos exposure). (Accept other valid pairs.)
Note the overlap: many diseases (e.g. most cancers) are multifactorial, with an environmental trigger acting on a genetically susceptible person. Full marks need the origin contrast AND the inheritance point AND valid examples.
core4 marksA 60-year-old woman is diagnosed with type 2 diabetes. Her father had the same condition; she has a BMI of 32 and a sedentary office job. Analyse the causes of her disease and classify it.Show worked solution →
- 1 mark - genetic predisposition
- Her family history indicates an inherited susceptibility (variants in genes such as TCF7L2), raising her baseline risk.
- 1 mark - nutritional/lifestyle factors
- Excess energy intake, obesity (BMI 32) and sedentary behaviour drive insulin resistance.
- 1 mark - mechanism
- Insulin resistance causes chronic hyperglycaemia; impaired insulin signalling and high blood glucose damage blood vessels, kidneys, retinas and peripheral nerves.
- 1 mark - classification
- A multifactorial non-infectious disease combining genetic and lifestyle factors (note: this is type 2 - distinct from autoimmune type 1).
A complete answer integrates genes AND lifestyle and explicitly labels the disease multifactorial; listing factors with no mechanism or no classification caps below full marks.
exam7 marks'Non-infectious diseases place a greater burden on individuals and society than infectious diseases in developed countries.' Assess this statement, referring to the causes and effects of non-infectious disease and using named examples.Show worked solution →
"Assess" requires a judgement supported by evidence weighing both sides - not just a description.
- Causes and range (2-3 marks)
- Non-infectious diseases arise from genetic (cystic fibrosis, CFTR), environmental (mesothelioma, asbestos), nutritional (scurvy; type 2 diabetes from dietary excess), lifestyle (lung cancer from smoking) and age-related (Alzheimer's, osteoporosis) causes, with cancer cutting across categories. Their chronic, multifactorial nature means they often persist for years.
- Effects on individuals and society (2-3 marks)
- Individual: prolonged pain, disability, reduced life expectancy, psychological impact and loss of income. Societal: non-infectious disease accounts for over 70 percent of Australia's disease burden and the majority of deaths in developed countries; it drives health-care costs, lost workforce productivity and demand for aged and chronic-disease care. Because many are chronic, the cumulative burden is large and sustained.
- Judgement (1-2 marks)
- A supported conclusion: in developed countries the statement is well supported - non-infectious disease dominates the disease burden and mortality - but the picture differs globally (infectious disease still dominates in some low-income regions, e.g. sub-Saharan Africa), so the claim is context-dependent. An answer that lists effects without an explicit, justified judgement caps below full marks.
exam6 marksSome cancers have an infectious trigger yet are classified as non-infectious diseases. Explain this apparent contradiction, and discuss the implication for how such cancers are prevented. Use a named example.Show worked solution →
Target a sequenced response that resolves the classification and links it to prevention.
- Resolving the classification (2-3 marks)
- A disease is infectious only if the disease itself is transmitted between hosts by a pathogen. In cancers such as cervical cancer, the human papillomavirus (HPV) is transmitted and triggers the initial mutations, but the cancer (the tumour of uncontrolled cells) is not itself passed from person to person. The pathogen is an infectious trigger / risk factor; the resulting uncontrolled cell division is a non-infectious process. (Accept also hepatitis B -> liver cancer.)
- Mechanism link (1 mark)
- HPV proteins (E6/E7) inactivate tumour suppressor proteins (p53, Rb), removing cell-cycle control so cervical epithelial cells divide uncontrollably.
- Implication for prevention (2 marks)
- Because the trigger is infectious, prevention can target the pathogen: the HPV vaccine (e.g. Gardasil) prevents infection and so prevents most cervical cancers - a prevention route not available for purely genetic or environmental cancers. Screening (cervical screening test) also detects pre-cancerous change early.
Full marks need the transmitted-trigger-but-non-transmitted-disease distinction, the mechanism, AND the vaccine/prevention implication.