1. IGCSE BIOLOGY
CHAPTER 12: DRUGS

2. 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.

3. 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.

4. 12.2 ANTIBIOTICS KILL BACTERIA IN THE BODY
The fungus Penicillium sometimes grow on decaying fruits

5. 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

6. 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

7. 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.

8. 12.3 HEROIN IS AN ADDICITIVE DEPRESSANT
The dried latex of the fruit of the opium poppy is opium

9. 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).

10. 12.3 HEROIN IS AN ADDICITIVE DEPRESSANT
Video on heroin addiction:

11. 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. 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

13. 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.

14. 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

15. 12.5 ALCOHOLISM IS A DANGEROUS DISEASE
Comparison between a normal liver and liver with cirrhosis

16. 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

17. 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.

18. 12.7 NICOTINE IS ADDICTIVE
A healthy lung has many small air spaces but a lung with emphysema has fewer but bigger air spaces

19. 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