Health, disease & the two big groups

Health is a state of complete physical and mental wellbeing, not just being free of disease. A disease is anything that stops the body working normally. Eduqas splits diseases into two great groups:

• Communicable diseases can be passed from one organism to another. They are caused by pathogens — e.g. influenza (flu).
• Non-communicable diseases cannot be spread between people. They tend to build up over time — e.g. cardiovascular disease, type 2 diabetes and many cancers.

Diseases can interact: one disease can raise the risk of another. For example, a person who is HIV-positive has a higher risk of some cancers (e.g. skin cancer), and diabetes increases the risk of cardiovascular disease.

Which group is it?

Pathogens & how they spread

A pathogen is a microorganism that causes communicable disease. There are four types:

• Viruses — tiny; reproduce inside the body's cells and burst them (e.g. HIV, influenza).
• Bacteria — living cells that reproduce rapidly and can release toxins (e.g. Chlamydia).
• Protists — single-celled organisms, often spread by a vector (e.g. Plasmodium, which causes malaria).
• Fungi — can affect plants and animals (e.g. ash dieback in trees).

Named diseases you must know

Eduqas names four communicable diseases — learn the pathogen, how it spreads and how to prevent it:

• HIV/AIDS — a virus; spread in body fluids. Prevented by not sharing needles and using protection during sex.
• Chlamydia — a bacterium; a sexually transmitted infection (STI). Prevented by using protection and by screening.
• Malaria — caused by a protist (Plasmodium); spread by the mosquito vector. Prevented by mosquito nets and controlling the vector.
• Ash dieback — a fungus that infects and kills ash trees; spread by spores in the wind.

Vector: an organism that carries a pathogen from one host to another without getting the disease itself — the mosquito is the classic example for malaria.

What kind of pathogen?

Tap a disease or feature, then tap the pathogen type it belongs to.

Your body's defences

The body fights pathogens in two ways. First come the non-specific defences that stop pathogens getting in at all:

• Intact skin — a physical barrier that keeps pathogens out.
• Blood clots — seal wounds quickly so pathogens can't enter through cuts.

If pathogens do get in, the immune system attacks them with white blood cells:

• Phagocytes — ingest and digest microorganisms (engulf them).
• Lymphocytes — a pathogen's surface antigens trigger lymphocytes to release antigen-specific antibodies and antitoxins. Antibodies also help activate phagocytes.

Which cell does the job?

Antibiotics & antibiotic resistance

Antibiotics (e.g. penicillin) cure bacterial disease by killing bacteria or stopping them growing — inside the body. They were originally made by living organisms such as fungi.

Nail this misconception: antibiotics do NOT kill viruses. Viruses reproduce inside your own cells, so a virus (like flu or the common cold) can't be treated with antibiotics.

Overusing antibiotics has led to antibiotic resistance: bacteria such as MRSA survive and multiply. To slow it, doctors avoid over-prescribing and patients must finish the full course. Bacteria are grown safely using aseptic technique (sterile inoculating, plating and incubating).

Will antibiotics help?

Testing antibiotics on bacteria

To compare antibiotics we grow bacteria on sterile nutrient agar, then add paper discs soaked in different antibiotics. Where an antibiotic works, no bacteria grow — leaving a clear ring called the zone of inhibition.

A bigger zone means a more effective antibiotic. We compare zones fairly by working out their cross-sectional area using A = π r².

Your turn — zone of inhibition

Your turn — percentage infected

How vaccines protect you

A vaccine contains antigens from a disease-causing organism (often a dead or weakened form). When you are vaccinated:

• The antigens stimulate your white blood cells (lymphocytes) to produce antibodies against that pathogen.
• Your body keeps memory cells, so if the real pathogen invades later you make antibodies quickly and don't become ill.

Nail this: a vaccine contains antigens (not the full active disease, and not the antibodies). Vaccines can protect against diseases caused by both bacteria and viruses.

Parents deciding whether to vaccinate weigh up scientific evidence, the media and public opinion. Science can only give the "balance of probability" — never a 100% guarantee.

What's in a vaccine?

Monoclonal antibodies

Monoclonal antibodies are made from activated lymphocytes that divide continuously, producing large numbers of identical antibodies — all specific to one antigen.

Because each one binds only its target, they are hugely useful:

• Diagnosis — detecting antigens, e.g. testing for Chlamydia or HIV.
• Tissue typing — checking a match for transplants.
• Monitoring — tracking the spread of malaria.
• Cancer treatment — supporting chemotherapy by targeting cancer cells.

Plant defences (linked idea): plants defend themselves with physical barriers (cellulose cell walls, a waxy leaf cuticle), mechanical defences against herbivores (hardened cells, stinging cells, trichomes) and chemical defences (enzymes and toxins).

Match each disease to its pathogen

Tap a disease on the left, then its matching pathogen type on the right.

Developing & testing new medicines

Before a new drug reaches patients it is tested in stages, to check it is safe and that it works:

Why so careful? Testing checks for side effects and the right dose. Large-scale, rigorous testing manages risk before a drug is approved for wide use.

Non-communicable disease & lifestyle

Non-communicable diseases can't be caught — they build up over time, usually from an interaction of lifestyle factors. Examples include:

• Cardiovascular disease, lung cancer and emphysema (linked to smoking).
• Skin cancer (linked to UV radiation from the sun/sunbeds).
• Type 2 diabetes (linked to diet, weight and exercise).
• Cirrhosis of the liver (linked to alcohol).

Lifestyle factors: exercise, diet, alcohol, smoking and exposure to UV radiation.

Treating cardiovascular disease — evaluate the options: statins lower blood cholesterol (long-term drug), angioplasty widens a blocked artery (a procedure), and lifestyle changes (better diet, more exercise) tackle the cause. Each has benefits and risks to weigh up.

The big ideas to know

You've covered the whole of Eduqas Topic 3 — health & disease, pathogens & defences, treating & preventing, and non-communicable disease. Press Finish to see your score.