IGCSE BIOLOGY CHAPTER 12: DRUGS

A drug is a substance that affects chemical reactions in the body. 12.1 WHAT IS A DRUG? A drug is a substance that affects chemical reactions in the body. Without drugs, many people would live much shorter lives or suffer great pain. Drugs used in medical care or to relieve mild pain are very useful to us. However, misuse of drugs cause harm to oneself and others.

12.2 ANTIBIOTICS KILL BACTERIA IN THE BODY Antibiotics are substances which kill bacteria but do not harm other living cells. Antibiotics are made by fungi. The first antibiotic discovered was Penicillin made by the fungus Penicillium. Penicillin kills bacteria by stopping them from making their cell walls.

12.2 ANTIBIOTICS KILL BACTERIA IN THE BODY The fungus Penicillium sometimes grow on decaying fruits

12.2 ANTIBIOTICS KILL BACTERIA IN THE BODY Penicillin in growth medium Bacteria without cell wall Bacteria grow in a medium with penicillin The antibiotic inhibits the enzyme that is responsible for the formation of cell wall Even when the formation of cell wall is stopped, the bacteria continue to grow The bacteria grow out of their cell walls The bacteria lose their cell walls and are easily damaged

12.2 ANTIBIOTICS KILL BACTERIA IN THE BODY The clear area around the antibiotic disc is where the bacterial growth is inhibited. The cloudy area is the region of bacterial growth

12.3 HEROIN IS AN ADDICITIVE DEPRESSANT Opium poppy produce a substance called opium which is a mixture of different chemicals. Some of the chemicals in opium are morphine and codeine. Both of these are used as painkiller. Opium is the raw material to produce heroin which is a painkiller. Heroin is an addictive drug.

12.3 HEROIN IS AN ADDICITIVE DEPRESSANT The dried latex of the fruit of the opium poppy is opium

12.3 HEROIN IS AN ADDICITIVE DEPRESSANT Heroin is a powerful depressant. This means that it slows down many functions of the brain. Heroin reduces pain, slows down breathing and the action of the hypothalamus. When a person takes heroin, it produces a feeling of euphoria (intense happiness).

12.3 HEROIN IS AN ADDICITIVE DEPRESSANT Video on heroin addiction:

12.4 ALCOHOL IS ALSO A POWERFUL DEPRESSANT People often drink alcoholic drinks because alcohol can make people feel more relaxed and release their inhibitions. Alcohol is quickly absorbed through the wall of the stomach and carried in the blood to all parts of the body. Alcohol breaks down in the liver but it takes a long time.

12.4 ALCOHOL IS ALSO A POWERFUL DEPRESSANT Effects on alcohol on the body Alcohol lengthens reaction time Alcohol can increase aggression in some people Large intakes of alcohol can kill

12.5 ALCOHOLISM IS A DANGEROUS DISEASE Alcoholism is a disease in which a person cannot manage without alcohol. An alcoholic drinks large quantities of alcohols regularly. This causes many parts of the body to be damaged because alcohol is poisonous to cells.

12.5 ALCOHOLISM IS A DANGEROUS DISEASE Health issues related to alcoholism Liver damage - Fibres growing in the liver (cirrhosis) Brain damage - Alcohol draws water out from the brain cells, causing them to shrink

12.5 ALCOHOLISM IS A DANGEROUS DISEASE Comparison between a normal liver and liver with cirrhosis

12.6 TOBACCO SMOKE CONTAINS IRRITANTS AND CARCINOGENS The main components of cigarette smoke are tar, nicotine, carbon monoxide and smoke particles. Components of cigarette smoke

Component in cigarette smoke 12.7 NICOTINE IS ADDICTIVE Component in cigarette smoke Effects Nicotine Causes addiction to smoking Causes vasoconstriction leading to hypertension Tar Causes lung cancer Carbon monoxide Reduces the delivery of oxygen to body cells by binding to haemoglobin inside the red blood cells Smoke particles Chemicals released by the white blood cells to remove the smoke particles damage the lungs * * The chemicals break down the walls of the alveoli. This causes emphysema. Emphysema reduces the total surface area for gaseous exhange.

12.7 NICOTINE IS ADDICTIVE A healthy lung has many small air spaces but a lung with emphysema has fewer but bigger air spaces

12.7 NICOTINE IS ADDICTIVE Cigarette smoke damages the cilia and stimulates the goblet cells to produce excessive mucus Mucus will be trapped in the lungs as there are fewer cilia to sweep it upwards towards the mouth The trapped mucus encourages the growth of bacteria which leads to lung infection. Besides that, it makes it harder for gaseous exchange between the alveoli and blood