Health and Disease

Topic B6 of OCR Gateway Science A is called Global challenges because it takes the biology you have already met and points it at three of the biggest problems facing humanity: keeping people healthy, feeding a growing population, and protecting the environment we all depend on. This first lesson opens the health strand by asking a deceptively simple question — what does it actually mean to be healthy? — and then sorting the diseases that threaten health into two great families: communicable (infectious) diseases that can be passed on, and non-communicable diseases that cannot. Getting these definitions and categories secure now makes every later lesson on pathogens, the immune system, vaccines and lifestyle disease far easier to follow.

By the end of this lesson you should be able to define health as more than the absence of disease, distinguish communicable from non-communicable diseases with examples, explain how different conditions can interact so that one disease makes another more likely, and outline the main factors that affect a person's health.

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What Is Health?

It is tempting to think of health as simply "not being ill", but the widely used definition is broader and more useful:

Health is a state of physical, mental and social wellbeing, not merely the absence of disease.

Breaking that down:

• Physical wellbeing — your body works well: you can move, your organs function, you are free from injury and disease.
• Mental wellbeing — you can think clearly, cope with the normal stresses of life, and feel emotionally settled. Mental illnesses such as depression are genuine health conditions, not simply "feeling low".
• Social wellbeing — you have supportive relationships, somewhere safe to live, and the means to take part in everyday life.

A person can be free of any diagnosed disease and yet be unhealthy — for example, someone who is severely isolated, anxious, or living in poor housing. Equally, a person with a long-term managed condition such as well-controlled diabetes may enjoy good overall wellbeing. Recognising all three dimensions is the first big idea of B6.

Exam Tip: If a question asks you to "define health", the marks are for the whole definition — physical, mental and social wellbeing, and the phrase "not merely the absence of disease". Writing only "not being ill" is a common way to drop the marks.

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Communicable and Non-communicable Diseases

A disease is a condition that stops part of the body working properly. Diseases divide into two main categories.

Category	What it means	Can it be passed between people?	Examples
Communicable (infectious)	Caused by a pathogen (a disease-causing microorganism)	Yes — it can spread from person to person (or from another organism)	Measles, influenza, HIV/AIDS, tuberculosis, malaria, food poisoning
Non-communicable	Not caused by a pathogen; usually develops over a long time	No — it cannot be caught or passed on	Coronary heart disease, most cancers, type 2 diabetes, asthma, cirrhosis of the liver

The word communicable comes from the same root as "communicate" — these diseases can be communicated (passed on) from one host to another. The agent that causes them is a pathogen: a bacterium, virus, fungus or protist. You will study pathogens in detail in the next lesson.

Non-communicable diseases (NCDs), by contrast, are not caused by a pathogen and cannot be spread. They tend to develop slowly and are strongly linked to risk factors such as diet, exercise, smoking and inherited genes. They are the focus of Lesson 6.

Exam Tip: A very common trap is to assume "infectious = bacteria/viruses only". Pathogens also include fungi (such as athlete's foot) and protists (such as the malaria parasite). And remember: a disease being communicable tells you it is caused by a pathogen, but says nothing about how serious it is.

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How Diseases Interact

Diseases do not occur in isolation — having one condition can make a person more vulnerable to others. This idea of interactions between diseases is explicitly required by the specification, so learn a few clear examples.

Worked examples of interacting diseases:

1. A weakened immune system leads to more infections. If a pathogen or a condition damages the immune system, the body can no longer fight off other pathogens effectively. People with HIV, for example, become vulnerable to infections that a healthy immune system would easily defeat. This is why an immune problem rarely stays "just one disease".
2. Some viruses trigger cancers. Infection with certain types of the human papillomavirus (HPV) can cause changes in cells of the cervix that may develop into cervical cancer. Here a communicable infection raises the risk of a non-communicable disease — a direct link between the two categories.
3. Physical illness can lead to mental illness. Living with a severe, long-term physical illness can trigger depression and other mental health problems. The reverse can also happen: poor mental health can lead a person to neglect their physical health.
4. Immune reactions can trigger other conditions. Some immune responses caused by a pathogen can act as a trigger for allergies, such as skin rashes or asthma.

The lesson from all of these is that the body is a connected system: a problem in one part rarely stays contained, which is one reason preventing disease in the first place matters so much.

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Factors That Affect Health

Whether a person stays healthy depends on far more than chance. The main factors include:

• Diet. Too little food, or a poor balance of nutrients, weakens the body and the immune system; too much of certain foods raises the risk of NCDs such as heart disease and type 2 diabetes.
• Stress. Long-term stress is linked to both mental ill health and physical conditions such as high blood pressure.
• Life situation. Where and how someone lives matters enormously — access to clean water, good housing, healthcare and education all affect health. People in some parts of the world, or in poorer communities, face greater exposure to certain diseases and less access to treatment.
• Exposure to pathogens. Crowded or unsanitary conditions increase the chance of catching communicable diseases.
• Other substances and behaviours. Smoking, alcohol and a lack of exercise all raise the risk of disease (covered fully in Lesson 6).

These factors interact too. Poverty, for instance, can mean a poorer diet, more stress, worse housing and greater exposure to pathogens all at once — which is why health is so strongly linked to a person's wider circumstances.

Exam Tip: When a question asks for "factors that affect health", give a range (diet, stress, life situation, exposure to pathogens) rather than several versions of the same idea. Examiners reward breadth.

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The Cost of Ill Health

Disease does not only affect the individual who is ill. It also has a wider cost to society and the economy:

• Cost to health services. Treating disease — drugs, hospital stays, operations and long-term care — is expensive. Preventing disease (for example through vaccination or encouraging healthier lifestyles) is often far cheaper than treating it.
• Cost to families and communities. People who are seriously or chronically ill may be unable to work, study or care for others, which affects their families and reduces the number of people contributing to the economy.
• Research and prevention. Money is also spent on research into new treatments and on public-health measures such as clean water, sanitation and vaccination programmes.

This is one reason why prevention — stopping disease before it starts — is such an important idea in B6: keeping people healthy reduces suffering and the burden on health services and the wider economy.

Exam Tip: A question may ask why governments invest in prevention (such as vaccination or healthy-eating campaigns). A strong answer is that prevention reduces both the human cost (illness and suffering) and the financial cost of treating widespread disease.

How the Patterns of Disease Differ

The mix of diseases that affects people is not the same everywhere, and OCR expects you to appreciate this in broad, qualitative terms (you do not need to memorise figures).

• In wealthier countries with good sanitation, clean water, vaccination and healthcare, communicable diseases are largely controlled, so a large share of ill health is now caused by non-communicable diseases linked to lifestyle and ageing — such as heart disease and cancer.
• In poorer regions, or where there is conflict or poor sanitation, communicable diseases (such as those spread by unclean water or by vectors like the malarial mosquito) remain a major cause of ill health, alongside problems of poor nutrition.

These patterns can change over time: as a country develops clean water, sanitation and vaccination, the burden tends to shift from communicable towards non-communicable disease. This is why improving basic conditions — clean water, sanitation, vaccination and nutrition — has such a large effect on health worldwide.

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Common Misconceptions

Misconception	The correct idea
"Health just means not being ill"	Health is physical, mental and social wellbeing, not merely the absence of disease
"All diseases can be caught"	Only communicable diseases spread; non-communicable diseases cannot be passed on
"Mental illness is not a real health problem"	Mental wellbeing is part of health; conditions such as depression are genuine illnesses
"Infectious diseases are only caused by bacteria and viruses"	Pathogens also include fungi and protists
"One disease has no effect on any other"	Diseases interact — e.g. a weak immune system leads to more infections; HPV can lead to cervical cancer

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Model Answer — Defining and Categorising Disease

Question (6 marks): Explain what is meant by health, and describe the difference between communicable and non-communicable diseases. Use examples.

Mid-band response: "Health means being well and not having a disease. Communicable diseases can be passed from person to person, like flu. Non-communicable diseases cannot be passed on, like heart disease."

Examiner-style commentary: This earns marks for the basic distinction between the two disease types with one example each. It is held back by an incomplete definition of health ("not having a disease" misses the wellbeing dimensions) and by giving no cause for each disease category. To climb a band, give the full health definition and state that communicable diseases are caused by pathogens.

Stronger response: "Health is a state of physical, mental and social wellbeing, not just the absence of disease. Communicable (infectious) diseases are caused by pathogens and can spread between people — for example measles, which is caused by a virus. Non-communicable diseases are not caused by pathogens and cannot be passed on; they often develop slowly and are linked to lifestyle, for example coronary heart disease."

Examiner-style commentary: A clear, accurate answer with the full definition of health, the cause of each disease category, and a correctly classified example of each. To reach the top band, add that diseases can interact and give an example of that interaction.

Top-band response: "Health is a state of physical, mental and social wellbeing, and is not merely the absence of disease — a person can be free of any diagnosed illness yet be unhealthy because of poor mental or social wellbeing. Communicable diseases are caused by pathogens (microorganisms such as bacteria, viruses, fungi or protists) and can be passed on from one host to another; an example is measles, caused by a virus. Non-communicable diseases are not caused by pathogens, cannot be spread, and tend to develop over a long time in response to risk factors such as diet and smoking; an example is coronary heart disease. Importantly, the two categories can interact: infection with certain HPV viruses (communicable) can lead to cervical cancer (non-communicable), and a disease that weakens the immune system makes a person more vulnerable to further infections."

Examiner-style commentary: Full marks. The answer gives the complete definition of health with the wellbeing dimensions, defines and exemplifies both disease categories with their causes, and — crucially — shows that diseases interact, with a precise example linking the two categories. This is exactly the breadth and accuracy the top band requires.

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Exam Tips

• Learn the full definition of health: physical, mental and social wellbeing, not merely the absence of disease.
• Communicable = caused by a pathogen = can spread. Non-communicable = not caused by a pathogen = cannot spread.
• Be ready with at least one example of each disease type, and know its cause.
• Remember pathogens include fungi and protists, not just bacteria and viruses.
• Be able to give a worked example of diseases interacting (immune problem → more infections; HPV → cervical cancer; severe illness → depression).
• For "factors affecting health", give a range: diet, stress, life situation, exposure to pathogens.

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Summary

• Health is physical, mental and social wellbeing, not merely the absence of disease.
• Diseases are either communicable (infectious, caused by a pathogen, can spread) or non-communicable (not caused by a pathogen, cannot spread, often slow to develop and linked to lifestyle).
• Examples: communicable — measles, influenza, HIV, malaria, food poisoning; non-communicable — coronary heart disease, most cancers, type 2 diabetes.
• Diseases interact: a weakened immune system leads to more infections; HPV infection can lead to cervical cancer; severe physical illness can lead to depression.
• Health is affected by diet, stress, life situation, exposure to pathogens and behaviours such as smoking and alcohol, and these factors often act together.

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This content is aligned with OCR Gateway Science A GCSE Biology (J247), Topic B6 Global challenges. Refer to the official OCR specification document for the exact wording.