Monitoring and maintaining health
What you'll learn
- How diseases are grouped, spread, detected and prevented.
- How humans and plants defend themselves against pathogens.
- How vaccines, medicines, monoclonal antibodies and aseptic culturing are used.
- How lifestyle, stem cells, gene technology and the human genome link to future medicine.
Health and disease
Health and disease
Health is a state of physical and mental wellbeing. A disease is a condition that prevents the body or mind from working normally.
Disease can reduce health directly, but diseases can also interact. For example, one disease may weaken the immune system, making another infection more likely.
Communicable and non-communicable diseases
A communicable disease can be passed from one organism to another and is usually caused by a pathogen, which is a microorganism or virus that causes disease. A non-communicable disease cannot be passed directly between organisms.
Communicable diseases include infections such as influenza, tuberculosis and HIV. Non-communicable diseases include cardiovascular disease, many cancers, type 2 diabetes and some liver and lung diseases.
Not all microorganisms are harmful
Many microorganisms are useful, such as gut bacteria that help digestion and fungi used in food production. Only some microorganisms are pathogens.
When diseases interact
Two important GCSE examples are:
- HIV and tuberculosis (TB): HIV damages the immune system, so a person is less able to control TB bacteria.
- HPV and cervical cancer: some types of human papillomavirus (HPV) can infect cervical cells and increase the chance of changes that lead to cancer.
Linking HIV and tuberculosis
- HIV infects and damages important white blood cells, especially lymphocytes involved in immune responses.
- If TB bacteria enter the body, the weakened immune system is less able to destroy them.
- This means TB is more likely to become active, cause symptoms and spread to other people.
Pathogens and how communicable diseases spread
A virus is a very small pathogen that reproduces inside host cells. A bacterium is a single-celled microorganism; some bacteria are pathogens. A protist is a single-celled eukaryotic organism, and a fungus may be single-celled or made of thread-like hyphae.
Pathogens can spread in animals and humans by:
- droplets in the air, such as coughing and sneezing
- direct contact, including sexual contact
- contaminated food or water
- body fluids, such as blood
- vectors, which are organisms that carry pathogens between hosts, such as mosquitoes
In plants, pathogens can spread by wind, rain splash, soil, insect vectors, infected plant material and contaminated tools.
Examples you should know
For human infections, learn at least one example of each type:
- Viral: influenza or HIV.
- Bacterial: tuberculosis or salmonella food poisoning.
- Fungal: athlete’s foot.
A sexually transmitted infection (STI) is spread mainly by sexual contact. HIV is an STI; if untreated, it can lead to AIDS, where the immune system is severely damaged.
Plant disease examples include:
- Tobacco mosaic virus (TMV): a viral disease causing mosaic leaf discolouration and reduced photosynthesis.
- Erysiphe graminis barley powdery mildew: a fungal disease causing white powdery growth on barley leaves.
- Agrobacterium tumefaciens crown gall disease: a bacterial disease causing tumour-like galls on plants.
Estimating infected plants
A farmer randomly samples 80 barley plants. 12 show powdery mildew. The field contains about 6000 barley plants.
- Work out the infected proportion: p=1280=0.15p = \frac{12}{80} = 0.15p=8012=0.15.
- Apply that proportion to the whole field: estimated infected plants =0.15×6000= 0.15 \times 6000=0.15×6000.
- Calculate the estimate: 900 plants may be infected, assuming the sample was random and representative.
Detecting and preventing communicable disease
Antigens and DNA tests
An antigen is a molecule, often on the surface of a pathogen, that can be recognised by the immune system. DNA is genetic material; DNA tests can identify a pathogen by detecting its genetic sequence.
To reduce spread, you can break the chain of transmission. In humans this includes hygiene, clean water, safe food preparation, condoms, vaccination, isolating infected people and controlling vectors. In plants it includes removing infected plants, sterilising tools, using resistant varieties, controlling insect vectors and using suitable chemical treatments.
In separate Biology, you also learn plant defences. Physical plant defences include a waxy leaf cuticle, which reduces pathogen entry, and cell walls, which act as strong barriers. Chemical plant defences include antimicrobial substances, which kill or inhibit microorganisms.
This next detail is Higher Tier only and separate Biology: plant diseases can be identified in the field by observing symptoms and using microscopy, or in the lab by detecting the pathogen’s DNA or antigens.
Prevention is about breaking transmission
A prevention method works if it stops the pathogen entering, leaving, surviving outside, or moving between hosts.
Human defence systems
The body has non-specific defences, which act against many pathogens in the same general way. These include skin, blood clotting, mucus, cilia and stomach acid.
The immune system is the body’s defence network. White blood cells are adapted for defence: some engulf pathogens by phagocytosis, some make antibodies that bind to specific antigens, and some make antitoxins that neutralise toxins. Platelets are small blood fragments that help form clots, sealing wounds so pathogens cannot enter easily.
A vaccine contains dead, inactive or harmless parts of a pathogen, usually including antigens. It trains the immune system to make memory cells without causing the full disease.
Explaining vaccination
- The vaccine introduces harmless antigens, so lymphocytes recognise the pathogen without the person developing the serious disease.
- Lymphocytes produce antibodies and memory cells specific to those antigens.
- If the real pathogen enters later, memory cells produce antibodies faster, so the pathogen is destroyed before it causes serious symptoms.
Monoclonal antibodies
This section is Higher Tier only and separate Biology.
Monoclonal antibody
A monoclonal antibody is an identical antibody made by cloned cells. It binds to one specific antigen.
To make monoclonal antibodies, scientists inject a mouse with an antigen, collect lymphocytes that make the correct antibody, fuse them with tumour cells to make hybridoma cells, clone the hybridomas, then collect the antibodies they produce.
Uses include pregnancy tests, detecting disease markers such as prostate cancer markers, and potentially treating cancer by targeting cancer cells with drugs or radioactive substances.
How a pregnancy test uses antibodies
- If hCG is present in urine, it binds to monoclonal antibodies that are specific to hCG.
- The hCG-antibody complex moves along the test strip and is trapped by more antibodies at the test line.
- A coloured line appears because the antibodies carry a dye, showing that hCG has been detected.
Medicines, antibiotics and new drug testing
An antibiotic kills bacteria or stops them growing. An antiviral helps treat some viral infections by interfering with virus reproduction. An antiseptic reduces microorganisms on living tissue or surfaces.
Antibiotics do not treat viruses
Antibiotics target bacterial cell processes. Viruses reproduce inside host cells and do not have the same targets, so antibiotics do not cure viral infections like flu.
Potential new medicines are tested in stages. Preclinical testing uses cells, tissues and animals to check toxicity, effectiveness and dose. Clinical testing uses human volunteers, often starting with low doses in healthy people, then testing patients. Trials may use a placebo, which is a dummy treatment, and may be double-blind, meaning neither patients nor doctors know who has the real drug until the data are analysed.
Culturing microorganisms safely
In separate Biology, you need to understand aseptic technique, which means using methods that prevent contamination by unwanted microorganisms.
A culture is a population of microorganisms grown in a nutrient medium, often agar jelly. To culture safely, equipment and agar can be sterilised by autoclaving, an inoculating loop can be sterilised by flaming, benches can be cleaned with alcohol, and the Petri dish lid should be opened only slightly. School cultures are incubated below 25 °C to reduce the chance of growing human pathogens.
In antibiotic testing, a clear area around an antibiotic disc is called a zone of inhibition. A larger clear zone suggests the antibiotic was more effective, if all other variables were controlled.
Calculating the area of a clear zone
A clear zone has a diameter of 18 mm.
- Convert diameter to radius: r=182=9r = \frac{18}{2} = 9r=218=9 mm.
- Substitute into the circle area formula: A=πr2=π×92A = \pi r^2 = \pi \times 9^2A=πr2=π×92.
- Calculate the area: A≈254A \approx 254A≈254 square millimetres, using π≈3.14\pi \approx 3.14π≈3.14.
Non-communicable disease and lifestyle
A risk factor is something that increases the chance of developing a disease, but does not guarantee it. Many non-communicable diseases are caused by interactions between several factors, including genes, lifestyle and environment.
Examples include:
- Cardiovascular disease: linked to smoking, diet, inactivity, high blood pressure and inherited factors.
- Cancer: caused by changes in cells that lead to uncontrolled growth and division.
- Bronchitis: linked to smoking and air pollution.
- Cirrhosis: linked to alcohol misuse and some infections.
- Type 2 diabetes: influenced by diet, exercise, body mass and genetics.
Incidence means the number of new cases in a population over a time period. Scientists may compare incidence locally, nationally and globally, looking at lifestyle factors such as exercise, diet, alcohol and smoking.
Interpreting a lifestyle correlation
A graph shows that countries with higher smoking rates often have higher lung disease incidence.
- Identify the pattern: as smoking rate increases, lung disease incidence also tends to increase, so this is a positive correlation.
- Avoid overclaiming: correlation alone does not prove smoking is the only cause, because air pollution, age and healthcare access may also affect incidence.
- Strengthen the conclusion by looking for large samples, repeated data and evidence of a biological mechanism linking smoking to lung damage.
Treatments for cardiovascular disease can be lifestyle-based, medical or surgical. Lifestyle changes are low risk but need long-term commitment. Medicines such as statins can reduce risk but may have side effects. Surgery, such as fitting a stent or bypass, can be very effective but carries operation risks and costs.
Cancer is not simply inherited
Cancer results from changes in cells. Some inherited genes can increase risk, but lifestyle factors, random mutations and some infections, such as HPV, can also contribute.
Stem cells, gene technology and the genome
A stem cell is an unspecialised cell that can divide and develop into specialised cells. Stem cells may help replace damaged tissues, but risks include rejection by the immune system, infection, uncontrolled cell division and ethical concerns, especially around embryonic stem cells.
Gene technology means using or altering genes in medicine. Possible benefits include treating genetic disorders, producing targeted treatments and improving diagnosis. Risks include unexpected effects, privacy concerns, unequal access and ethical questions about changing genes.
The human genome is the full set of DNA in a human. Understanding it may help predict the likelihood of diseases and choose drugs targeted to a person’s genetic makeup.
Modern medicine is becoming more personalised
Genome information, stem cells and gene technology could allow treatments to be matched more closely to the patient, but benefits must be weighed against risks and ethical issues.
In the exam
- For communicable disease questions, always link pathogen → transmission route → prevention method.
- For data questions, describe the trend, quote figures if given, and say whether the evidence shows correlation or stronger support for causation.
- For treatment or technology questions, balance benefits against risks, then make a justified judgement.
Check yourself
- How are communicable and non-communicable diseases different?
- Why can HIV increase the risk of developing active tuberculosis?
- What aseptic steps stop contamination when culturing bacteria?
