School BIOLOGY Notes: Non-communicable diseases and risk factors

Non-communicable diseases and risk factors

 Doc Brown's school biology revision notes: GCSE biology, IGCSE  biology, O level biology,  ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old students of biology

 What is a non-communicable disease?   Describe some examples on non-communicable diseases.   Explain some life-style risk factors associated with cancer.

Sub-index for this page

(a) Introduction to non-communicable diseases

(b) Examples of risk factors for non-communicable diseases and how different types of disease can interact

(c) Examples of non-communicable diseases and risk factors

(d) What are the human and financial costs of non-communicable diseases?

(e) More on problems with drugs and alcohol - lifestyle choices

(f) Measures of obesity  (one measure of healthiness and well-being)

(g) Evaluating data, statistics, graphs and correlation

See also communicable diseases  and  plant diseases

and Keeping healthy - our defences against pathogens, fighting infectious diseases, vaccination, monoclonal antibodies

(a) Introduction to non-communicable diseases

Non-communicable diseases cannot be transmitted between individual organisms e.g. cancer, diabetes, heart diseases (eg cardiovascular) or respiratory diseases of the lung.

Health is the state of an organism's well-being - physical or mental, but ill health is where there is a problem including suffering from some disease.

The World Health Organisation defines heath as "a state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity".

So, even if you are a very fit person, you are not necessarily healthy e.g. if you had mental health issues and/or lonely.

A disease is a medical condition where part of an organism (plant or animal) isn't functioning properly - in some way the organism is not as it should be.

The disease may take the form of cell damage to the host (plant or animal) which in some way impairs the healthy ('normal') structures or functions of the organism.

Most organisms, including ourselves, experience ill health at some point in their life.

If you have an increased chance of contracting a disease you are described as susceptible.

There are many causes of ill health in plants and animals e.g.

infection from a pathogen eg flue, malaria, salmonella,

mutation in an organism's genes (DNA) eg cancers,

an organism might suffer some deficiency eg lack of vitamins in human diet, lack of light on plant growth

an organism may experience mental or physical trauma triggered by some event eg depression, bereavement, serious accident,

the lifestyle of an organism can have consequences on your health eg links between: smoking and lung cancer, too much sugary/fatty food and obesity and/or diabetes,

All diseases show symptoms at some point in their development.

Symptoms are indications of disease in an organism - usually observable eg cough, rash, diarrhoea, leaf discolouration etc.

Sometimes symptoms do not show up immediately after infection - the virus or bacteria may multiply for days or weeks when sufficient of the pathogen is present to create visible symptoms.

This period of infection without symptoms is called the incubation period and may last hours, days, weeks or months - which is a bit scary, because you can't apply medical treatment to a medical condition you don't know you've got!

Diseases can be classified as communicable and non-communicable.

Communicable diseases are spread between individual organisms

Usually plants - animals, animals - people or person to person

See  communicable diseases  and  plant diseases

Non-communicable diseases cannot be transmitted between individual organisms e.g. cancer, diabetes, heart diseases (eg cardiovascular) or respiratory diseases of the lung.

These cannot be spread from person to person or between other animals and people.

They tend to last for a long time and slowly get worse over time, in the case of 'humans' they can be often linked to our lifestyles.

Examples are asthma, cancer and heart diseases.

If you are suffering from one non-communicable disease, your bodies defences may be weakened by it making you more susceptible to another disease - a 'knock on' effect reducing your body's ability to fight off a second disease.

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(b) Examples of risk factors for non-communicable diseases and how different types of disease can interact

Just a few general points as a 2nd introduction to non-communicable diseases - including when diseases coincide and cause other medical situations - physical conditions or mental health issues.

All diseases have risk factors.

Risk factors are anything that can be associated with an increase in likelihood of developing a non-communicable disease, but that doesn't been you will automatically contract the disease!

They can be often related to a person's lifestyle or whether they are exposed to a pollutant in the environment or place of work - air pollution has always been linked with bronchial and lung diseases including asthma.

Age or gender

Certain medical conditions become more likely to older you get - e.g. arthritis or Alzheimer's disease - these are unavoidable as the body ages, but susceptibility varies from one individual to another.

Males and females have different susceptibilities to certain non-communicable diseases.

Alcohol - a lifestyle choice

Too much a in your alcohol in your diet can cause liver damage e.g. cirrhosis of the liver (scarring of the live). This happens because alcohol is broken down by enzymes in the liver and some of the products of this process are toxic.

With excessive drinking over a long period time results in permanent liver damage - in some cases a liver transplant is required to keep the person alive - needs a donor - may not be available.

Heavy drinking raises blood pressure to increase the likelihood of cardiovascular disease.

Excessive drinking of alcohol can affect brain function, nerve cells are damaged and brain volume decreases.

High alcohol consumption is being linked to cancers of the bowel, liver, mouth and throat.

When pregnant women drink to much alcohol there is an increased risk of health problems for an unborn baby e.g. abnormal foetal brain development.


Quite a few diseases can be linked to genetic factors - what we become from our inherited genes, which may include particular mutated alleles.

Unfortunately, you can inherit faulty genes that you a person more susceptible to cancer or coronary heart disease.

e.g. mutations to the BRCA genes have been linked to increased chance of women developing breast cancer or ovarian cancer.

Immune system responses

The presence of a pathogen infection in your body can trigger an allergic reaction from your immune system e.g. asthma sufferers experience more intense symptoms or skin rashes.

You can also have problems if a disease you have lowers your immune system response and you become susceptible to another disease. See HIV virus infection as an example.

Other lifestyle choices and your personal situation


Lack of regular exercise is one of several factors that increase your chance of contracting cardiovascular disease - especially if you have a poor diet too rich in fatty and sugary foods leading to obesity - overweight.

Physically inactive people are more likely to develop high blood pressure and heart disease, and an increased risk of certain kinds of cancer.

See The human circulatory system - causes/treatment of cardiovascular disease


Eating a good balanced healthy diet helps maintain your body in good shape and your immune system to fight communicable disease infections and reduce the risk of contracting non-communicable diseases such as cardiovascular disease and cancers.

If you do not get the right balance of nutrients in your diet, you have a condition called malnutrition.

The poorer you diet (poor nourishment), the more susceptible you are to these kinds of diseases and mental health issues.

Eating a balanced nutritious diet, not too high in fats and sugars, plenty of minerals and vitamins from whole grains, fruit and vegetables.

Lack of vitamin C in your diet causes scurvy, a non-communicable disease with harmful consequences.

e.g. lack of vitamin C inhibits the body's ability to make collagen - an important protein found in bone and tendon tissue.

Symptoms of scurvy include painful joints and muscles and bleeding gums.

A diet too high in fat an sugar can lead to obesity - being overweight makes your more susceptible to non-communicable diseases such as cardiovascular disease and type 2 diabetes - the latter can often be dealt with by changing to a more healthy balanced nutritious diet.

Smoking - completely avoidable to reduce your chance of developing lung cancer.

BUT, smoking is now linked to cardiovascular disease and lung diseases including cancer.

Chemicals in tobacco smoke harm your blood cells and can damage the function of your heart and the structure and function of your blood vessels. This damage increases your risk of atherosclerosis - a disease in which a waxy substance called plaque builds up in the arteries.

Substances in tobacco smoke cause damage to lung tissue.

(i) Nicotine makes smoking addictive. You also breathe in carbon monoxide which displaces oxygen from haemoglobin - affects your breathing and lung function. Your lungs are also subjected to fine particulates that lodge in the alveoli of the lungs - the latter will affect the efficiency of lungs to deliver oxygen to the cells of your body. Cigarette smoking causes inflammation of the lining of the bronchi and bronchiole tubes in the lungs giving you chronic bronchitis - persistent cough, wheezing i.e. breathing problems!

(ii) Nicotine in cigarette smoke increases heart rate which increases blood pressure - increasing the chance of a heart attack, stroke or blood clot formation. Increased blood pressure damages the walls of arteries which contributes to the build up of fatty deposits on the walls of the arteries - leading to heart disease and circulation problems which further increase the risk of a stroke or heart attack when the blood supply to the brain or heart is cut off.

(iii) The cells in the lining of the lungs can be coated in tar (which also contains carcinogens) - leading to various serious lung conditions - breathing problems Inefficient oxygen intake), mutations of the DNA of lung cells to form tumours which can become cancerous. Smoking is now related to cancer of the lung, mouth, oesophagus and throat.

(iv) Smoking reduces the body's defences against particles you breathe in.

how respiratory system protects body ciliated cells goblet cells mucus traps dust particles cilia moves them along gcse biology igcse

Cells that line the trachea and bronchi have cilia and others produce mucus.

The cilia, hair-like structures, can move the mucous along from the lungs up to the nasal passage and back of the throat where it can be swallowed, coughed out or blow your nose, into a tissue!

Note that smoking can damage and paralyse the cilia reducing the ciliated cell's capacity to remove harmful particles, so another reason why smokers are more susceptible to respiratory diseases.

When pregnant women smoke there is an increased risk of health problems for an unborn baby.

I can't understand why anyone smokes cigarettes these days!

Access to your needs?

The risk of a non-communicable disease starting and progressing increases if you have limited access to good healthcare systems and health education.

When you have access to a quality healthcare system, your medical condition is more likely to be diagnosed and receive appropriate treatment.

Education provides you with knowledge about how non-communicable diseases develop and strategies for prevention e.g. diet and exercise.

Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.

Usually no problem in rich developed countries - your choices, BUT not so for people living in poorer underdeveloped countries - an undernourished body is more likely to be fatigued and more susceptible to the effects of infections and non-communicable diseases.

e.g. to help prevent or reduce the risk of non-communicable diseases in the first place - an you afford to buy healthy food? Is 'healthy shopping' readily available?

If you have contracted a non-communicable disease, do you have access to appropriate medicines?

Perhaps surprisingly?, non-communicable diseases are more likely with people of higher income in developed countries because they can afford to buy richer food higher e.g. in saturated fats - obesity related.

However, ALSO, people from poorer areas are poor likely to have a poorer diet (not balanced) and exercise less. Therefore in deprived areas, you find higher rates of cardiovascular disease, obesity, type 2 diabetes due to less healthy lifestyles.

Statistics and a note of caution!

Medical scientist do their best correlate data connecting risk factors with disease incidence.

However, correlation doesn't simply mean you can relate incidence to cause.

Just because you eat a poor diet and have little exercise doesn't mean to say you automatically get e.g. cardiovascular disease (CVD).

Your diet and lack of exercise does not cause CVD directly. What these two factors cause is high blood pressure and increase in the blood levels of bad LDL cholesterol - and it is these which actually cause the CVD.

Mental health and stress

If can develop a mental health condition such as depression while enduring some physical health problem e.g. lack of mobility reducing your ability to participate fully in everyday life.

If you are constantly under mental stress e.g. 'high-powered' job or caring for a very sick relative, then your physical well-being can be affected - ulcers can develop or a mental health condition like extreme anxiety - both of which are non-communicable.

When you are stressed, hormones are released, your blood vessels constrict (narrow) and your blood pressure is raised.

Stress can lead to depression, and increased risk of obesity and diabetes, also increasing the risk of cardiovascular disease, diabetes and Alzheimer's disease.

Obesity  (usually involves lifestyle factors)

Poor diet and 'over-eating' lead to excess weight in the body - obesity!

This increases your susceptibility to type 2 diabetes when your body is less responsive to your own insulin and reduced control of blood sugar levels - which can be very dangerous.

Obesity can also affect your breathing - reduces your respiratory function.

Obesity is a risk factor in other non-communicable diseases e.g. cardiovascular disease and type 2 diabetes.

Viral infection

Some types of cancer are triggered by particular viral infections.

This is a communicable disease causing the development of a non-communicable disease.


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(c) Examples of non-communicable diseases and risk factors

Cardiovascular disease

I've discussed this in detail on

The human circulatory system - including the causes and treatment of cardiovascular disease

See also the Keeping healthy - diet and exercise

and Respiration - aerobic and anaerobic in animals

Cancer - many types and many risk factors!

What is cancer?

Cells normally grow and divide by mitosis when the body needs new cells to replace old or damaged cells.

Cancer is caused by some genetic fault or change e.g. caused by a mutation, that leads to uncontrolled growth by cell division - these are known as cancerous cells and the body does NOT need them!

The extra mass of cancerous cells formed is called a tumour.

Most tumours are solid, but cancers of the blood like leukaemia are obviously not.

Tumours can be benign (non-cancerous) and not usually dangerous, or malignant (cancerous) which are potentially very harmful.

Benign tumours grow slowly and fill the space available.

A benign tumour stays in one place e.g. in a membrane and often has a capsule around it making it quite easy to remove surgically.

Benign tumours are not cancerous and the cancer cells do not invade other tissues of the body.

Because they are not cancerous, benign tumours are not usually harmful or dangerous to the body - but may be removed to stop the cancer from becoming malignant.

Malignant tumours keep growing faster then benign tumours, and spread to neighbouring healthy tissue.

Malignant cells can break away and spread to other parts of the body in the bloodstream.

* The same malignant cells can then invade healthy tissue and form secondary tumours in other parts of the body.

Therefore malignant tumours are highly dangerous forming potentially fatal cancers.

* As the malignant cells replicate they can invade surrounding tissue. Unfortunately, this malignant tumour can secrete hormone-like chemicals that stimulate blood vessels to grow around the tumour and supply it with food and oxygen so the cancerous cells further increase in number. Malignant cells can detach from the tumour and be transported away in the bloodstream. These malignant cells can 'squeeze' through a capillary wall and produce a secondary tumour in a different tissue.

For more on cell division see

Cell division - cell cycle - mitosis, meiosis, sexual/asexual reproduction, binary fission and cancer 


Risk factors associated with types of cancer

A large proportion of our ever increasing aging population will eventually suffer from cancer.

300 000 people are diagnosed with cancer in the UK every year, but it is estimated that 4 in 10 cases are preventable by making suitable lifestyle choices, and the earlier these choices are made the better!

We can get a cancer at any stage in our life, though as we get older our defensive immune system does decline in response to threats.

Cancer survival rates are continually increasing, particularly in richer developed countries with their comprehensive health care services, including early diagnosis from screening programmes and improved anti-cancer treatments.


A carcinogen is defined as a chemical substance or other agent capable of causing cancer in living tissue - usually a chemical that promotes changes in the structure and working of cell DNA.

e.g. chemicals in the home, industry or in the environment, ionising radiation e.g. from radioactive materials, lifestyle choices e.g. alcohol drinking or poor diet, ultraviolet radiation from over exposure to sunlight, viruses like HPV. More on these in the following notes.

A carcinogen causes cancer by damaging the DNA - that is causing a mutation in one or more of the chromosomes in the cells genome,

Mutations can occur by chance as cells are dividing, though most of these are not damaging because genetic errors are checked for in the cell cycle and repairs put in place!

Generally speaking you need several mutations to cause cancer cells to develop, which is why we become more susceptible to cancer as we get older - the repair systems become less effective!

Industrial practice and bad lifestyle habits have been responsible for some of the more common cancers in the past, particularly in men, but now we know more about the causes, things are improving for future generations e.g.

Sheets of the mineral asbestos were widely used in housing and factories for thermal insulation. Unfortunately, very fine asbestos fibres build up in the air passages of lungs. All forms of asbestos increase the risk of lung disease. The three types of asbestos-related lung disease are scarring (asbestosis), non-cancerous disease of the tissue of the lining of the surface of the lung (pleural disease), and lung cancer (of the lungs or their outer lining tissue - mesothelioma).

Several molecules in tobacco tar are carcinogenic, which you breathe down into your lungs when smoking.

Genetics - inheritance and mutations

Unfortunately, you can inherit faulty genes that make a person more susceptible to cancer.

Mutations in the BRCA genes have been linked to increased chance of women developing breast cancer or ovarian cancer - a good reason and argument for cancer screening programmes e.g. cervical smear test for cervical cancer or x-ray screening for breast cancer.

Ionising radiation - a powerful carcinogenic agent

Exposure to ionising radiation - uv, x-ray or gamma radiations, causes cell damage leading to cancer.

Ionising radiation is therefore described as carcinogenic.

Diet factors

Obesity - being overweight, is now being linked to cancers of the bowel, kidney and liver.

Too much fat and sugar in you diet is not good for your, excess calories the body doesn't need are converted into fat tissue.

Apparently, statistically, it is the 2nd biggest preventable cause of cancer, the 1st is smoking!


Osteoporosis a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D in your diet.


Too much red meat and processed meat in you diet is linked to an increase risk of bowel cancer.

Regular aerobic exercise can reduce your risk from some non-communicable diseases.

See the Keeping healthy - diet and exercise  gcse biology revision notes

and Respiration - aerobic and anaerobic in animals  gcse biology revision notes

doc b oil notesSmoking (see also carcinogens) some chemicals in tobacco smoke are carcinogenic

Giving up smoking, is a lifestyle choice to reduce your chance of developing lung cancer.

Statistically, stopping smoking is the biggest preventable cause of cancer.

There is clear evidence of a link between smoking and contracting lung cancer.

(Its a 'no-brainer' for me, and admit to smoking cheap nasty cigarettes from the age of 11 to 27!).

However, that's not the only cancer risk from smoking - it is being linked cancers in the cervix, bowel, mouth and stomach.

Ultraviolet light (uv) is a powerful carcinogenic agent.

The more uv light you are exposed too, including bright sunlight, the greater the chance developing skin cancer - uv damages skin cells including burns or causing mutations in the skin cell DNA.

Frequent users of sun beds are also increasing their risk of skin damage - the lamps emit uv radiation which can cause DNA damage leading to cancer.

People who work outside or live in particularly sunny climates, are at higher risk - though evolution has allowed many people to have developed extra melanin in their skin to increase uv protection - that's why so many people in sunny areas like Africa have a much darker skin than many northern European peoples.

Fair-skinned should use sun-blockers to protect their skin in bright sunlight.


Some types of cancer are triggered by particular viral infections. See also Communicable diseases

This is a communicable disease causing an increase in the likelihood of developing a non-communicable disease.

The hepatitis virus (hepatitis B and C strains) causes long-term infections in the liver where it inhabits the cells and this gives you an increased chance of developing liver cancer.

The chance of becoming infected with this communicable disease can depend on your lifestyle e.g. contracting hepatitis during unprotected sex or drug users sharing a needle.

The human papillomavirus (HPV virus) is a virus that can infect the human reproductive system.

HPV is a communicable pathogen infection, BUT, is linked to non-communicable diseases.

HPV infection occurs when the virus enters your body, usually through a cut, abrasion or small tear in your skin. The virus is transferred primarily by skin-to-skin contact. Genital HPV infections are contracted through sexual intercourse, anal sex and other skin-to-skin contact in the genital region.

It is thought that most cases of cervical cancer arise from HPV infections - one disease causes another.

The HPV virus causes cervical warts.

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(d) What are the human and financial costs of non-communicable diseases?

Millions of people die around the world every year from non-communicable diseases.

Non-communicable diseases decrease quality of life and life expectancy.

But, it isn't just the sufferers who are affected, but friends and family too.

There will be emotional strains and possibly financial strain too if the affected person is unable to work, reducing the family income. Homes may need to adapted if mobility is a problem.

There is also the extra burden and costs to health services - costs of providing the medical care and research into treating non-communicable medical conditions.

There are other costs too - if still in employment but unable to work properly for longer periods of time - the employer and ultimately the country has to bear the cost of reduced productivity in the workforce as a whole.

Millions of 'working days' are lost as a result of people with non-communicable diseases - and, as we have discussed, many of them are preventable, or there effects reduced, by thinking carefully and acting to adopt a more healthy lifestyle.

Non-communicable diseases are most common in the poorest areas, even in a rich developed country.

Here you find the greater levels of excessive alcohol consumption, obesity, poorer diet and smoking in the population. Not surprising in these same areas you find higher incidences of non-communicable diseases like cardiovascular diseases, liver disease or lung conditions.

This puts extra pressure on local health services.

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(e) More on problems with drugs and alcohol - lifestyle choices

  • Be able to define a drug as a chemical substance, such as a narcotic or hallucinogen, that affects the central nervous system, causing changes in psychological behaviour and possible addiction, despite their usefulness.
    • Drugs are dangerous if misused, which is why some drugs cannot be bought of the counter of a shop (e.g. local chemist) without a medical prescription from you doctor, but other drugs, like the painkiller paracetamol, can readily bought without prescription from your GP.
    • It can sometimes be difficult to state whether the addiction is a physical or mental dependence.
    • If some drugs are over used, you may become addicted to them, which means you have a physical craving for more of it, without which you can suffer withdrawal symptoms - extreme craving is symptomatic in itself of addition, and sometimes the body reacts physically in a negative way e.g. becoming very irritable, shaky hands.
    • Tolerance is another problem that arises when the body becomes used to a drug and progressively needs larger quantities of the drug to give the same effect. The increasingly higher dose rate can lead directly to addiction and examples range from legal drugs like alcohol and nicotine in tobacco and illegal use of cocaine and heroin.
    • Addiction can be cured by slowly decreasing the amounts of the drug administered, but most drug addicts required lots of support from e.g. the NHS in the UK, help groups and rehabilitation centres (politely referred to in pop songs as 'rehab').
  • Be able to describe the general effects of:
    • a) Painkillers that block pain nerve impulses, including morphine - yes it is a narcotic, but widely prescribed safely and legally!
      • If the nerve impulses to the brain are blocked, we do not experience a pain sensation and morphine molecules are very effective at doing this.
        • Morphine type drugs are amongst the strongest painkillers we use.
      • Different painkillers are more effective in particular situations and there maybe safer alternatives that are not as dangerous or addictive e.g.
        • paracetamol, an analgesic, is a good relatively safe painkiller for headaches.
        • Ibuprofen is a good anti-inflammatory drug for muscle pain and rheumatoid arthritis.
    • b) Hallucinogens that distort sense perception, including LSD.
      • When taken, hallucinogens create hallucinations in your mind so you experience distorted sounds and images because the normal processing of nerve impulse is interfered with.
    • c) Stimulants that increase the speed of reactions and neurotransmission at the synapse, including caffeine.
      • Stimulants increase the activity of the brain by increasing the amount of neurotransmitters at certain neurone synapses in the central nervous system i.e. they speed up your brain functions.
      • Stimulants increase your speed of reaction i.e. decrease your response time to a given physical or mental stimulus.
      • Many people take coffee to make them more alert and 'fully awake' in the morning because coffee is a rich source of the stimulant caffeine.
    • d) Depressants that slow down the activity of the brain (opposite of stimulants), including alcohol.
      • Depressants slow down your responses and increasing your reaction times to a physical or mental situation i.e. they slow down your brain functions.
      • 'Drink driving' is considered a dangerous activity and a serious criminal offence because a drunk (or not so drunk) driver is a danger to others and the driver himself/herself on the road.
      • There is a legal limit of alcohol in your blood which you must be below to 'legally drive' a car, and its pretty low!
  • Revise any experiments-investigations you did on reaction times e.g. the falling ruler experiment.
  • Be able to explain the effects of some chemicals in inhaled cigarette smoke, including:
    • a) Nicotine as an addictive drug which smokers can become dependant on and the more you smoke, the more you may become dependent on it - like it or not, smoking can become a drug addiction.
    • b) Tar as a carcinogen - several molecules (known collectively as carcinogens) in tobacco tar can cause mutations in the cells of the throat and lungs.
      • Such mutations can eventually lead to throat cancer, and, in particular, lung cancer - whose incidence correlates very highly with smokers.
    • c) Carbon monoxide reducing the oxygen-carrying ability of the blood - carbon monoxide combines more strongly with haemoglobin than does oxygen and is slower to be exhaled in the gaseous exchange in the lungs.
      • Consequently, smokers will have less oxygen in their circulatory system.
      • The effect can be damaging in pregnant women, where the foetus in the womb may receive less oxygen through the placenta causing babies to be underweight at birth.
  • Be able to evaluate data relating to the correlation between smoking and its negative effects on health.
  • Be able to evaluate evidence of some harmful effects of alcohol abuse:
    • a) in the short term -
      • blurred vision - at high intoxication levels you don't see things clearly as normal and your sense of balance is affected - difficulty walking, impaired memory, slurred speech, in fact most mental and physical activity is interfered with.
      • lowering of inhibitions - antisocial behaviour, from amusing to offensive actions you wouldn't normally do!
      • slowing of reactions - alcohol is a depressant and slows down brain activity - particularly dangerous for 'drink drivers'
    • b) in the long term -
      • liver cirrhosis - many people do not appreciate the poisonous nature of alcohol which can be toxic with a large intake of high % alcoholic drinks. In small quantities, the liver can metabolise the alcohol into harmless by-products. However, high 'doses' of alcohol can cause the death of liver cells and scarring the liver tissue, eventually restricting the blood flow to the liver. This inhibits the liver from doing its normal cleaning-filtering job of processing waste products from the body like urea. A build up of waste products like urea may harm the rest of your body.
      • brain damage - alcohol abuse is associated with widespread and significant brain lesions - permanent brain damage with potentially fatal consequences.
  • Be able to discuss the ethics of organ transplants when the organ is so damaged that a transplant is required to prolong life, including:
    • a) liver transplants for alcoholics -
      • Bearing in mind the acute shortage of organ donors (living or dead), should alcoholics with serious cirrhosis of the liver be given priority over someone who develops liver disease through no fault of their own?
      • A liver transplant patient should be expected to stop drinking before and after the liver transplant operation, otherwise why waste a valuable organ to be damaged by a transplant patient who will not stop drinking?
    • b) heart transplants for the clinically obese -
      • Obese people have a greater chance of dying during and after heart surgery and doctors can insist that the heart patient loses weight before major surgery is considered.
    • c) the supply of organs e.g.
      • Organs can be donated in advance by your own consent at your own death eg kidney donor card, though your family must be consulted too.
      • Organs can come from people killed in accidents or even from somebody declared brain dead, BUT without prior consent of the deceased, organ transplant consent must come from relatives.
      • Organs can be donated by living people e.g. we have two kidneys and we can donate one and live (with dietary care) very well on one kidney.
      • Unfortunately there is a great shortage of organ donors in the UK and so the medical profession is encouraging people to become organ donors in the event of their death.
      • The ethical issues are complex and whatever you think about whether a patient deserves an organ transplant, the medical profession basically decides on the basis of which patients are most likely to benefit from a transplant operation - sounds simpler than it sounds, it might not be just a medical opinion (the main factor), the likely patient's attitude post-operation might be taken into account too? (not sure on the last point? but alcoholics may be short on sympathy from the public? but the public doesn't decide!)
  • Know that drugs are chemicals that affect our body chemistry and alter the biochemistry of our system, mainly to our advantage, but not always!

  • Know that medical drugs are developed and must be tested before being used to relieve illness or disease.

    • Drugs like aspirin and paracetamol are relatively safe and widely used as analgesics (pain-killers).

    • Anti-cancer drugs are a big area of development in the pharmaceutical industry, though they often have side effects, and must be thoroughly tested before licensed for use.

  • Be aware that drugs may also be used recreationally as people like the effect on the body.

    • Note that knowledge of classification of drug types is not required. 

  • Know that some drugs are addictive, and not always those you think of as dangerous.

    • Drugs like heroin and cocaine are highly addictive, caffeine (in tea and coffee) and nicotine (in cigarette smoke and tar) are also addictive!

  • Know that some athletes take drugs to improve performance.

    • eg stimulants or steroids to build up muscle tissue.

  • Appreciate that people cannot make sensible decisions about drugs unless they know their full effects.

  • Given data-information, you are expected to use your acquired skills, knowledge and understanding to:

    • evaluate the effect of statins in cardiovascular disease,

    • evaluate different types of drugs and why some people use illegal drugs for recreation,

    • evaluate claims made about the effect of prescribed and non-prescribed drugs on health,

    • consider the possible progression from recreational drugs to hard drugs,

    • evaluate the use of drugs to enhance performance in sport and to consider the ethical implications of their use.

  • Appreciate that scientists are continually developing new drugs.

  • Know that when new medical drugs are devised, they have to be extensively tested and trialled before being used.

    • Know that new drugs are constantly being developed and must be tested in a series of stages to find out if they are safe and effective.

    • Know that new drugs are extensively tested for toxicity (serious side-effects), efficacy (capacity for producing the desired medical effect) and dose (effect of different amounts):

      • know drugs are tested in the laboratory, using cells, tissues first and then live animals, but drugs that affect the whole body eg a blood pressure reducing drug, a blood cancer drug etc., can only be satisfactorily tested in the end by using 'real people'.

        • A drug may tested on two or more live animals, to many people's objection (animal rights ethical issue) but many scientists would argue this reduces the risks when testing the drug with human volunteers.

      • know that clinical trials involve healthy volunteers and patients.

        • Very low doses of the drug are given at the start of the clinical trial to look for side-effects.

          • The first drug trials would be on healthy people, before doing further drug trials testing the drug on ill patients.

        • If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug - the dose that is most effective with little side-effects.

          • It should be noted that it is almost impossible to develop a drug that has no side-effects with anyone. I'm afraid we all have a slightly different body chemistry and a certain % of people will show some undesired reaction to the drug.

        • In some double blind trials, some patients are given a placebo, which does not contain the drug.

          • A placebo, which is delivered like the actual drug (eg look and taste), contains no medication and enables the clinicians to distinguish the effects of the drug from the volunteers who have not received the drug.

          • Its a sort of 'fair test' or 'blank check' idea should be familiar with in your school laboratory under the heading 'How Science Works'.

          • You can even do an extra check to avoid 'human bias' by doing a 'double-blind' drug trial in which the doctors or pharmaceutical scientist don't know who is or is not given the drug until all the results are collated. This hopefully avoids any prejudice on the part those conducting the trial.

        • Neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete.

    • You should understand that tissues and animals are used as models to predict how the drugs may behave in humans.

  • You should be aware of the use of statins in lowering the risk of heart and circulatory diseases.

    • Statins are prescribed drugs that help reduce cholesterol levels and research trials have shown they can have a significant effect in diabetic patients.

      • Increased cholesterol levels in your blood can lead to cardiovascular disease.

    • The statins drug trials were done using a large sample of people and half were given the drug and half were not.

      • Nobody knew who had the drug, half were given statins, but the other half, the control group, had a placebo - a substance containing NO medication.

    • Several independent studies like this 'blind trial' have shown that people treated with statins had reduced cholesterol levels.

  • Know that thalidomide is a drug that was developed as a sleeping pill in the 1950s. (on healthy 2 page too)

    • It was also found to be effective in relieving morning sickness in pregnant women.

    • Thalidomide had not been tested for use in pregnant women, in particular it was not tested for relieving morning sickness.

      • Also, it was not known that the drug could pass through the placenta and into the foetus, where unfortunately, it caused abnormal limb development.

      • Thousands of babies were affected and about half survived with missing limbs or malformed limbs.

    • Unfortunately, after many babies born to mothers who took the drug were born with severe limb abnormalities the drug was then banned.

    • As a result, drug testing has become much more rigorous in an attempt to reduce the incidence of serious side-effects from newly developed drugs..

    • More recently, thalidomide has been used successfully in the treatment of leprosy and other diseases.

  • You should be aware of the effects of misuse of the legal recreational drugs, alcohol and nicotine.

    • You should know and understand that the misuse of the illegal recreational drugs ecstasy, cannabis and heroin may have adverse effects on the heart and circulatory system.

    • Note that knowledge and understanding of the specific effects of recreational drugs on the body, except for cannabis are not required neither is knowledge of the legal classification of specific drugs required.

    • Drugs may be described as 'hard' or 'soft'. Hard drugs, like heroin, are generally more addictive and potentially harmful, but even soft drugs like cannabis are implicated with mental health effects, heart and circulatory problems and chemicals in the smoke and tar are carcinogenic - probably more than filter cigarettes.

  • Know that cannabis is an illegal drug.

    • Know that cannabis smoke contains chemicals which may cause mental illness in some people.

  • Appreciate that the overall impact of legal drugs (prescribed and non-prescribed) on health is much greater than the impact of illegal drugs because far more people use them.

    • Be Aware and be able to consider and discuss the benefits of medical drugs, the impact of non-medical drugs such as alcohol and the possible misuse of legal drugs.

    • Cannabis users consider such smoking as enjoyable, relaxing and stress relieving and choose to ignore well documented harmful side-effects.

    • Smoking is addictive, due to nicotine, and causes heart disease and lung cancer.

    • Alcohol, is a legal but addictive drug, which slows down the your reaction time to respond to a situation and the more alcohol you take in, the more your judgement is impaired and coordination is reduced. With large amounts of alcohol consumed you may become physically incapable of walking and become unconscious. Continuous excessive drinking (regular 'binge drinking') can result in brain damage and kidney disease.

      • From the millions of people who smoke and drink, eventually many will be suffer the serious side-effects. From days of work and anti-social behaviour and increase the cost to the NHS, our society pays quite a high price for these legal drugs!

  • Know that drugs change the chemical processes in peoplesí bodies so that they may become dependent or addicted to the drug and suffer withdrawal symptoms without them.

    • Know that heroin and cocaine are very addictive.

  •  Know there are several types of drug that an athlete can use to enhance performance.

    • Know that some of these drugs are banned by law and some are legally available on prescription, but all are prohibited by sporting regulations.

    • Know that examples of this type of drug include stimulants that boost bodily functions such as increasing heart rate; and anabolic steroids which stimulate muscle growth - bigger stronger muscles, all taken to make an athlete better at his/her sport.

      • However, apart from being illegal, banning these drugs hasn't prevented some athletes from using them, and are to compete in an unfair way (an ethical issue) AND they also run the risk of harmful side-effects eg steroids can cause high blood pressure.

      • Knowledge of the mode of action of steroids and other performance-enhancing drugs is not required.

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(f) Measures of obesity  (one measure of healthiness and well-being)


There is no such thing as the 'perfect weight', we come in all shapes and sizes, but there are limits within which we should be to be healthy!

In the medical profession, a doctor can't just simply that somebody is overweight, without reference to some kind of statistical index, usually by one/both of the ratios described below.

Equally healthy people can have quite different weights, but there are some reasonably good indicators as to when your weight is not what it should be 'ideally'.

In rich developed countries we are often dealing with 'overweight' people eating too much rich fatty food, but in poorer underdeveloped countries we are dealing 'underweight' people, particularly young children suffering from malnutrition.

Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.


The Body Mass Index

The body mass index is a 'rough' guide to help the medical profession decide whether is underweight, normal, overweight or obese.

The higher your BMI the more fat you are carrying - but not necessarily unhealthily.

Body Mass Index (BMI) = (body mass in kg) / (height in m)2

When measured, you then consult a table of BMI values to se where you fit in!

Table of BMI values (from https://www.vertex42.com/ExcelTemplates/bmi-chart.html)

Body mass index Weight description
less than 18.5 underweight
18.5 to 24.9 normal
25.0 to 29.9 overweight
30.0 to 40.0 moderately obese
over 40.0 very obese

If you eat too much fatty sugary foods and don't take enough exercise, most people will put on weight and too much of it. You are taking in too much energy rich food for your daily needs.

The excess energy releasing food is stored as fat and gives you a raised BMI value.

Having a higher than normal BMI value increases your risk of developing type 2 diabetes and cardiovascular disease.

For more on this see The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Note of caution: Having a high BMI is not always unhealthy e.g. sports people train hard to build up extra muscle which is heavier than fat, so they will tend to have higher than 'normal' BMI values and would not be classed as overweight.

The calculation is easy e.g. for a person with a body mass of 70.0 kg and a height of 1.80 m,

The BMI = m / h2 = 70 / 1.802 = 21.6 (3 sf), suggesting the person is 'normal'.

BUT, beware, we do come in all shapes and sizes, even people on healthy diets don't always 'fit in' with he BMI, but most doctors consider it a useful and reasonably accurate diagnostic tool.

Note from 2020 on the covid-19 flue pandemic: Research has shown that obese people are more likely to be seriously ill with the virus than non-obese people - more severe fever, more likely to be hospitalised and more likely to die!


The waist-to-hip ratio should also be taken into consideration (see below).


The waist-to-hip ratio

Comparing the circumferences of waist and hips is another measure of whether you are 'overweight' and concentrates around one area where we can accumulate to much fat.

This index is all about fat distribution.

waist-to-hip ratio = circumference of waist (cm) / circumference of hips (cm)

The higher your waist-to-hip ratio the more fatty tissue you are carrying around the middle of your body.

When measured, you then consult a table of BMI values to se where you fit in!

Make sure you measure both diameters with the same length units!

Table of waste-to-hip ratios (from https://www.healthline.com/health/waist-to-hip-ratio)

Health risk waist-to-hip ratio (women) waist-to-hip ratio (men
low less than 0.81 less than 0.96
moderate 0.81 to 0.85 0.96 to 1.00
high (overweight) over 0.85 over 1.00

If you are female and your waist-to-hip ratio is over 0.85 you are classed as overweight.

If you are male and your waist-to-hip ratio is over 1.00 you are classed as overweight.

If you are above the moderate waist-to-hip ratio values you are carrying too much fat around your 'middle' - referred to as abdominal obesity.

Having a higher than normal waist-to-hip ratio increases your risk of developing type 2 diabetes and suffering from cardiovascular disease.

For more on this see The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Again, beware, we do come in all shapes and sizes, but most doctors consider it a useful extra diagnostic tool.

The body mass index (BMI) should also be taken into consideration (see above).

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(g) Evaluating data, statistics, graphs and correlation (under development)

A correlation is a relationship between two random sets of data e.g. set A and set B for two variables.

A correlation does not automatically mean that A may affect B, B may affect A or both A and B are affected by a third variable.

Medical research scientists have to decide:

(i) whether links between possible causes and effects are valid, and

(ii) whether the link between treatments and cures is actually valid,

and this all about real correlation and just pure coincidence or a third unknown factor.

There is also the question of data collection and its evaluation and analysis.

(1) How reliable is the data and compared with an appropriate control group e.g. as in drug testing.

(2) How valid is the data - was it correctly measured and collected without bias? Where the results repeatable?

(3) How big was the sample size? Was it big enough for clear statistical significance?

(4) If repeated, how could a survey or set of experiment trials be improved?

(5) Where there any anomalies in the data? Can they be explained? Are they significant i.e. is the some unknown factor influencing the results in some way? Was sufficient time allowed for other possible effects to be clearly seen?

(6) What is the confidence of the conclusion? Have you proved the relationship between two variables?

(7) Could there be a bias in the interpretation of the results - vested personal or economic interests? I'm afraid this can happen in the pharmaceutical industry.

gcse biology graphs positive correlation negative correlation no correlation statistical data evaluation

Graph 1 A positive correlation graph

Despite the scatter of points (X), quite clearly, on average, an increase in variable B leads to an increase in variable A. The graph has a positive gradient.


(i) A plot of blood pressure versus weight shows this kind of correlation.

Obesity, is a problem for very overweight people because it can lead artery damage as the walls become thicker and stiffer and less flexible and elastic - anything that restricts blood flow will raise blood pressure.

Cardiovascular disease is a non-communicable medical condition.

The data points would be more scattered than graph 1, but the general trend would show a strong correlation.


Graph 2 A negative correlation graph

Again, despite the scatter of points (X), quite clearly, on average, an increase in variable B follows an decrease in variable A. The graph has a negative gradient - don't take the word negative to mean no correlation!


Graph 3 A no correlation graph

No particular pattern or correlation - just a scattered set of points (X).

There is no clear trend of A influencing B or B influencing A.

Graph 4 examples

(i) If variable A is time, years of the 20th century, the variable B could be quantity of cigarettes smoked (blue line) and the number of lung cancer cases (purple line). Lung cancer takes many years to develop and there is a 20 year lag between the two sets of data. This is good evidence for the connection between the non-communicable disease of lung cancer and smoking.

Graph 5 examples


Graph 6 examples

(i) Correlation of smoking and lung cancer. A = time, B blue = amount of smoking and B purple = lung cancer deaths. This has some similarities with graph 4, but in this case, although there is a lag, some other factor has intervened to bring both trends down. Hopefully, this is what will happen in the future. At the moment the two curves have just dropped a bit from their peak values. There has been a world-wide health campaign against smoking and some countries ban the advertising of cigarettes and it does seem to be having some effect.

Apparently during the Covid-19 corona flue pandemic in 2020. large numbers of people stopped smoking for fear it would make the more susceptible to this virulent and potentially deadly virus.

They hope, and quite correctly, it will help their lings to healthier, they are also more reluctant to go out to shops to buy cigarettes, others have lost their jobs and need to cut down on expenses.

Doctors in China have evidence that survival rates of non-smokers exceed that of smokers.

All in all, 2020 is a good time to stop smoking! and hope the two curves continue to fall.

Graph 7 examples

(i) Variable A could represent time in years. The purple B line could represent the number of people vaccinated in a population - increasing coverage. The blue B line could represent the fall in cases of the disease being vaccinated against - increasing immunisation of a population.

Graph 8 examples

Graph 8 is a typical graph for when a new vaccine is introduced to combat some disease.

A represents time in years. B represents the incidence of the disease in a given population.

Once the vaccine is developed and the immunisation programme instigated, the effect can be quite dramatic.

This happened in1940s with the development of a vaccine against diphtheria, producing a rapid decline in the number of cases.

Diphtheria is an acute and highly contagious bacterial disease causing inflammation of the mucous membranes, formation of a false membrane in the throat which hinders breathing and swallowing, and potentially fatal heart and nerve damage by a bacterial toxin in the blood. It is now rare in developed countries owing to immunization.

There other similar patterns for communicable diseases e.g. measles is an infectious viral disease causing fever and a red rash, typically occurring in childhood. This has been greatly minimised by the MMR vaccination of young children which is very effective at protecting people against measles, mumps, and rubella, and preventing the complications caused by these diseases.

Graph 9 examples

Graph 9 represents a trend that rises, reaches a peak and falls again to a similar start value.

If variable A represents a year in time, the blue graph line could represent the peak of some infection cases e.g. salmonella food poisoning tends reach a peak in the summer months. Warmer temperatures encourage the growth of salmonella bacteria in food causing the disease. Careless cooking and food storage add to the effect.

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General HUMAN BIOLOGY revision notes

See also cell biology index above

Introduction to the organisation of cells => tissues => organs => organ systems (e.g. in humans)

Examples of surfaces for the exchange of substances in animal organisms   gcse biology revision notes

See also Enzymes - section on digestion and synthesis  gcse biology revision notes

The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Homeostasis - introduction to how it functions (negative feedback systems explained)  gcse biology revision notes

Homeostasis - control of blood sugar level - insulin and diabetes  gcse biology revision notes

Homeostasis - osmoregulation, ADH, water control, urea and ion concentrations and kidney function, dialysis

Homeostasis - thermoregulation, control of temperature  gcse biology revision notes

The brain - what the different parts do and the dangers if damaged gcse biology revision notes

An introduction to the nervous system including the reflex arc  gcse biology revision notes

Hormone systems - Introduction to the endocrine system - adrenaline & thyroxine hormones  gcse biology revision

Hormone systems - menstrual cycle, contraception, fertility treatments  gcse biology revision notes

Respiration - aerobic and anaerobic in plants and animals.  gcse biology revision notes

Keeping healthy - communicable diseases - pathogen infections   gcse biology revision notes

Keeping healthy - non-communicable diseases - risk factors for e.g. cancers   gcse biology revision notes

Keeping healthy - diet and exercise  gcse biology revision notes

Keeping healthy - defence against pathogens, infectious diseases, vaccination, drugs, monoclonal antibodies

See also Culturing microorganisms like bacteria - testing antibiotics/antiseptics  gcse biology revision

Food tests for reducing sugars, starch, proteins and lipids  gcse biology revision notes

The eye - structure and function - correction of vision defects  gcse biology revision notes

Optics - lens types (convex, concave, uses), experiments, ray diagrams, correction of eye defects (gcse physics)

Doc Brown's School Biology Revision Notes

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