Revision Notes

15.2 Misused Drugs


  • Wines, beers and spirits contain an alcohol called ethanol
  • It is a depressant drug – it slows down signals in the nerves and brain
  • Because alcohol increases reaction times (meaning it increases the time taken to react to situations because it slows down signalling in the brain), there are legal limits for drinking and driving in many countries

Effects of alcohol:

Alcohol table, IGCSE & GCSE Biology revision notes


  • The liver removes alcohol from the bloodstream
  • it has enzymes that break down alcohol but the products of the reactions involved are toxic and over time, the liver can be irreparably damaged
  • In many people, alcohol can be a very addictive drug


  • Heroin is a powerful depressant drug
  • It reduces pain and slows down breathing
  • It is highly addictive and users quickly develop a tolerance for it, meaning they need larger and larger amounts in order to feel the same effects – this increases the risk of accidentally overdosing, which can cause death
  • This means they need more money to pay for the increased amounts of the drug they are taking; as the drug makes them less able to cope with everyday life and maintain a job, they may turn to crime in order to get the money they need
  • As it is so addictive, if a user stops taking heroin they suffer from significant withdrawal symptoms, such as nausea, muscle cramps, sweating, anxiety and difficulty sleeping
  • Heroin can be taken into the body in different ways; one of the most common is injecting with a syringe
  • As syringe needles cost money, heroin addicts may share needles which increases the risk of transmission of blood-borne infections such as HIV
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How does Heroin Affect the Nervous System?

  • In the brain there are many different chemical neurotransmitters that transfer nerve impulses across synapses
  • The neurotransmitters diffuse across the synapse and fit into receptor molecules on the postsynaptic membrane
  • One group of neurotransmitters is called endorphins which help to reduce sensations of pain, affect mood and reduce sensations of hunger and thirst
  • When it enters the brain, heroin is metabolised to morphine
  • Morphine molecules fit into some of the endorphin receptors and this is why taking heroin makes users feel so good
  • Taking heroin can reduce the production of natural endorphins and other neurotransmitters, which is why repeated use leads to the need for greater and greater amounts in order to get the same feelings

Tobacco & The Gas Exchange System

  • Smoking causes chronic obstructive lung disease, coronary heart disease and increased risks of several different types of cancer, including lung cancer
  • Chemicals in cigarettes include:
    • Tar – a carcinogen (a substance that causes cancer))
    • Nicotine – an addictive substance which also narrows blood vessels
    • Carbon monoxide – reduces the oxygen-carrying capacity of the blood

Lungs, CIE IGCSE BiologySection through a normal lung

Smokers lung, CIE IGCSE BiologySection through a smoker’s lung


  • Tar is a carcinogen and is linked to increased chances of cancerous cells developing in the lungs
  • It also contributes to COPD, which occurs when chronic bronchitis and emphysema, two different diseases which are frequently linked to smoking, occur together
  • Chronic bronchitis is caused by tar which stimulates goblet cells and mucus glands to enlarge, producing more mucus
  • It destroys cilia, inhibiting the cleaning of the airways, and mucus (containing dirt, bacteria and viruses) builds up blocking the smallest bronchioles
  • A smoker’s cough is the attempt to move the mucus but it damages the epithelia resulting in scar tissue, which narrows the airways and makes breathing difficult
  • Emphysema develops as a result of frequent infection, meaning phagocytes are attracted to the lungs where they release elastase – an enzyme that breaks down the elastin in the alveoli walls, to enable them to reach the surface where the bacteria are
  • Without adequate elastin, the alveoli cannot stretch, so they recoil and many burst
  • The breakdown of alveoli results in the appearance of large air spaces, reducing the surface area for gas exchange and making sufferers breathe more rapidly
  • As it progresses, patients become breathless and wheezy – they may need a constant supply of oxygen to stay alive

Emphysema in the lungs, IGCSE & GCSE Biology revision notesThe breakdown of alveoli in emphysema reduces the surface area for gas exchange

Carbon monoxide

  • Carbon monoxide binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen
  • This puts more strain on the breathing system as breathing frequency and depth need to increase in order to get the same amount of oxygen into the blood
  • It also puts more strain on the circulatory system to pump the blood faster around the body and increases the risk of coronary heart disease and strokes


  • Nicotine narrows blood vessels so will put more strain on the circulatory system and increase blood pressure
  • Narrow blood vessels are more likely to become clogged with fat, including cholesterol – if this happens in the coronary artery, this causes coronary heart disease
  • This means the heart muscle cells do not get sufficient oxygen and so less aerobic respiration takes place
  • To compensate the cells respire anaerobically, producing lactic acid which cannot be removed (due to lack of blood supply)
  • This creates a low pH environment in the cells causing enzymes to denature and eventually heart muscle cells will die
  • If enough die this can cause a heart attack
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Smoking & Lung Cancer: Is There a Link?

  • The majority of cases of lung cancer are caused by smoking

Graph correlation numbers of adults who smoke & lung cancer rates, IGCSE & GCSE Biology revision notesGraph showing correlation between numbers of adults who smoke and lung cancer rates over time

  • Note that as the general trend shows that as the numbers of adults who smoke decreases, so does the lung cancer rates a few years later (as cancer takes some time to develop)
  • The trend in the rate of developing lung cancer for women has been increasing, while in men it is decreasing
  • This is because numbers of female smokers – unlike men – continued to increase in the 1950s and 1960s before starting to fall
  • As cancer takes some years to develop, a fall in female rates of lung cancer is likely to occur later
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Performance-Enhancing Drugs in Sport

  • Hormones produced in the body help to control the way it develops and responds to changes
  • Some people take additional hormones to increase these effects
  • This is most commonly done to improve sporting performance
  • Testosterone is the hormone produced in the testes that affects the development of male secondary sexual characteristics
  • It is one of a group of hormones known as steroids which stimulate anabolic reactions to occur in the body (meaning the synthesis of large molecules from smaller ones), so it is known as an anabolic steroid
  • One of the effects of testosterone is to cause more proteins to be made in muscles so that muscles become larger and stronger
  • Taking anabolic steroids therefore increases muscle mass, helps athletes train harder and for longer periods of time, and can increase aggression which can give an edge when competing
  • The use of anabolic steroids in sports is banned as it gives an unfair advantage and also has serious side effects, including:
    • increases risk of heart disease
    • increases risk of liver damage
    • increases risk of kidney damage
    • affect the menstrual cycle in women
    • decreases the ability of the immune system to destroy pathogens

Exam Tip

Most questions about this section of the syllabus expect you to analyse data in a table or graph and discuss it to show the evidence for a link between smoking and lung cancer as shown in the notes above.

Keep your points concise and refer to the data as much as possible.

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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