Part 1 · What is a communicable disease?

Read the passage and table, then answer the questions.

Health is a state of complete physical, mental and social wellbeing. Things that damage health include disease, diet and stress. Diseases cause illness and can be communicable or non-communicable.

Part 2 · How pathogens spread

Read the passage about spread, then answer the questions.

Pathogens can spread through the air (droplet infection – breathing in pathogens from coughs and sneezes), through water (drinking contaminated water, or contaminated food/poor sanitation), and by direct contact (bodily fluids, e.g. sexual contact or shared needles, or touching surfaces).

Part 3 · Non-specific defences

Read the passage and look at the diagram, then answer the questions.

The body has non-specific defences that are always there to stop pathogens entering:

• the skin – a barrier
• the nose – hairs/cilia trap pathogens
• the trachea – mucus traps pathogens and cilia move it out
• the stomach – hydrochloric acid destroys swallowed pathogens
• tears – chemicals destroy microorganisms

Part 1 · How bacteria make us ill

Read the passage and look at the diagram, then answer the questions.

Bacterial pathogens are prokaryotic cells that cause disease by releasing toxins that damage cells, making you feel ill.

Once inside an organism they reproduce rapidly by binary fission (similar to mitosis):Triple only

• the DNA and ribosomes are replicated
• the cell grows
• then it divides into two identical cells (clones)

Part 2 · Examples of bacterial diseases

Read the table, then answer the questions.

Part 3 · Antibiotics

Read the passage about antibiotics, then answer the questions.

Antibiotics kill the bacteria that make us ill and can stop infections spreading. Antiseptics and disinfectants kill bacteria outside the body (e.g. to sterilise surfaces) but are too dangerous to use inside. Antibiotics cannot eradicate bacterial disease because bacteria evolve antibiotic resistance – they reproduce so quickly, and can copy and share plasmids carrying resistance genes. There are now antibiotic-resistant strains of gonorrhoea.

Part 1 · What is a virus?

Read the passage and look at the diagram, then answer the questions.

Viruses are not made of cells (they are acellular), so they are not considered living – they cannot reproduce on their own. They are about 100 times smaller than bacteria. A virus is genetic material (DNA or RNA) inside a protein coat. Viruses enter host cells and reproduce rapidly inside them before bursting out and damaging the cell, which makes you feel ill.

Part 2 · Measles

Read the passage about measles, then answer the questions.

Measles causes a fever and a red skin rash and can be fatal, especially in children. It spreads by droplet infection from coughs and sneezes. To prevent fatalities, young children are vaccinated against it. Someone with measles should be isolated to stop the spread.

Part 3 · HIV

Read the passage about HIV, then answer the questions.

HIV (human immunodeficiency virus) causes a flu-like illness.

It spreads by the exchange of body fluids:

• sexual contact
• sharing needles
• from mother to baby through breast milk

If not controlled with antiretroviral medication, HIV attacks the body's immune cells and can develop into AIDS – when the immune system is so weak it cannot fight other infections or cancer.

It can be prevented by:

• using condoms
• not sharing needles
• bottle-feeding babies

Part 1 · Vectors and malaria

Read the passage and look at the diagram, then answer the questions.

Vector-borne diseases are spread from one organism to another by a vector (e.g. fleas spread bubonic plague; aphids spread plant viruses). Malaria is caused by a protist (a unicellular eukaryotic microorganism). The parasite spends part of its life in mosquitoes and part in humans; by biting humans and drinking their blood, mosquitoes spread the protist – the mosquito is the vector. Infected humans get a high fever and damage to the liver and red blood cells, which the protist destroys as it replicates in them.

Part 2 · Preventing the spread of malaria

Read the passage about prevention, then answer the questions.

Malaria is widespread in tropical areas and kills around 660 000 people per year. It can be treated with antimalarial drugs, but these are becoming less effective as the protists evolve resistance.

The best strategies target the mosquito vector:

• using insecticides to kill mosquitoes (or repellent to avoid bites)
• using mosquito nets to prevent bites
• preventing mosquitoes breeding by removing standing water (their breeding habitat)

Part 3 · Evaluating disease data

Read the passage about evaluating data, then answer the questions.

When looking at disease data over time, consider:

• how and when the data was collected – numbers may be inaccurate, as not all cases or deaths are reported, especially in the past or in less-developed countries
• do not extrapolate beyond the data shown – you cannot assume patterns you cannot see
• the sample size – a small sample may be unreliable or not allow a valid conclusion

Part 1 · Plant diseases

Read the table about plant diseases, then answer the questions.

Part 2 · Preventing the spread

Read the passage about prevention, then answer the questions.

Plant viruses travel inside the plant through the xylem and phloem and can be spread by insect vectors that feed on the plant, on gardeners' hands/tools, or by infected leaves touching healthy ones.

Viral diseases cannot be cured, so to prevent the spread:

• kill insect vectors with insecticides
• disinfect tools and clean hands
• remove and burn infected plants

Rose black spot spreads by fungal spores carried in air or water and on tools/hands. Unlike viruses, the fungus can be killed with a fungicide spray; also remove and burn infected leaves.

Part 3 · Plant defences and ion deficiencyTriple only

Read the passage about defences, then answer the questions.

Plants defend themselves with physical barriers (cellulose cell walls, a tough waxy cuticle, and bark), chemical defences (antibacterial chemicals and poisons that deter herbivores), and mechanical defences (thorns, hairy stems/leaves, leaves that droop or curl when touched, and mimicry to look dangerous).

Plants can also be damaged by ion deficiency:

• magnesium deficiency causes chlorosis – magnesium is needed to make chlorophyll
• nitrate deficiency causes stunted growth – nitrate is needed for protein synthesis

Part 1 · Phagocytosis

Read the passage and look at the diagram, then answer the questions.

If a pathogen gets inside the body, the immune system launches a specific response using white blood cells, which travel in the blood. One way they protect us is phagocytosis: white blood cells called phagocytes have a large lobed nucleus that lets them stretch around bacteria, engulf them and digest them with enzymes. Once a phagocyte has ingested as many pathogens as possible, it dies (dead phagocytes make up mucus/pus).

Part 2 · Antibodies

Read the passage and look at the diagram, then answer the questions.

A second, very specific response is carried out by white blood cells called lymphocytes. They detect pathogens by the proteins on their surface called antigens. Lymphocytes produce antibodies – proteins that match the shape of the antigens and bind to them, helping to destroy the pathogen. Some lymphocytes become memory cells, which can produce these antibodies again quickly if you are reinfected with the same pathogen.

Part 3 · Antitoxins

Read the passage about antitoxins, then answer the questions.

When bacteria enter the body they produce toxins that damage cells and cause illness. Lymphocytes can also produce antitoxins, which bind to these toxins and prevent them from harming your cells (they neutralise them).

So white blood cells protect us in three ways:

• phagocytosis – engulfing pathogens
• producing antibodies
• producing antitoxins

Part 1 · What is a vaccine?

Read the passage about vaccines, then answer the questions.

Virus infections cannot be cured – there are no drugs that kill the virus without killing your own infected cells, which is also why antibiotics do not work against viruses (they cannot enter cells). The immune system is the only thing that can fight off a virus. A vaccine contains a small amount of dead or inactive pathogen (or its antigens). This makes the white blood cells (lymphocytes) produce antibodies and become memory cells, without you getting ill – so you become immune.

Part 2 · Primary and secondary responses

Read the passage and look at the diagram, then answer the questions.

Vaccines make the body produce memory cells, which remember how to make the antibodies for that specific pathogen. If the person is infected by the same pathogen later, the memory cells make lots of antibodies quickly (a secondary response) to destroy it before it makes the person ill. The first time (the primary response) is slower and makes fewer antibodies. A different pathogen has different antigens, so it would need a new primary response.

Part 3 · Herd immunity

Read the passage about herd immunity, then answer the questions.

Not everyone can be vaccinated (e.g. babies and people with immune deficiencies). To protect them, herd immunity is used: vaccinating most of the population means there are not enough infected people to pass the disease on to the vulnerable. Recently, some parents have chosen not to vaccinate their children, with no good evidence for this decision – causing a rise in deaths from once-rare viral diseases like measles.

Part 1 · Producing monoclonal antibodiesTriple only

Read the passage and look at the diagram, then answer the questions.

Monoclonal antibodies (mAbs) are antibodies produced to target one particular cell or chemical, because they are made from a single clone of cells.

They are made in these steps:

• inject a mouse with the antigen
• the mouse's immune system makes lymphocytes that produce a specific antibody
• the lymphocytes are combined with a tumour cell to make a hybridoma
• the hybridoma is cloned to make many cells that all produce the same antibody
• the antibodies are collected and purified

Part 2 · Uses of monoclonal antibodiesTriple only

Read the table of uses, then answer the questions.

Part 3 · Evaluating monoclonal antibodiesTriple only

Read the passage about pros and cons, then answer the questions.

Advantages of monoclonal antibodies:

• they can treat a wide range of diseases
• they target only the affected cells, so healthy cells are not harmed

Disadvantages:

• they create more side effects than expected (partly because they are produced using mice)
• they are not yet as widely used as people first hoped

Part 1 · Where drugs come from

Read the table of drug origins, then answer the questions.

Many drugs originated from plants (which make antibacterial chemicals and toxins to defend themselves) and from microorganisms. Most drugs are now made synthetically in the pharmaceutical industry, but some still start from a natural chemical.

Drug	Source and use	Source
Aspirin	From willow tree bark – a painkiller, also used to prevent heart attacks/strokes and reduce fever
Digitalis	From foxgloves – used to treat heart conditions (controls heart rate)
Penicillin	From Penicillium mould – the first antibiotic, discovered by Alexander Fleming in 1928

Part 2 · Painkillers

Read the passage about painkillers, then answer the questions.

Painkillers are drugs that relieve pain – examples include aspirin, paracetamol, ibuprofen and opiates (e.g. morphine and codeine). Painkillers, cough medicines and cold remedies do not cure the disease, because they do not kill the pathogen – they only relieve the symptoms caused by the pathogen (e.g. reducing fever, aches, pains or congestion).

Part 3 · Drug testing

Read the passage and look at the diagram, then answer the questions.

A new drug must be tested before use, and the results peer reviewed (checked by other scientists) before publication to prevent errors and bias.

Testing checks three things:

• toxicity – is it harmful?
• efficacy – does it work?
• dosage – how much is needed?

Pre-clinical testing uses cells and tissues, then animals.

Clinical trials then follow:

• Phase 1 tests low doses on healthy volunteers, to check for side effects
• Phase 2 tests on patients with the illness, to check efficacy and dosage

In a double-blind trial some patients get a placebo (no drug) and neither doctor nor patient knows who got which, to check the drug really works.