B2 - Disease
• Pathogens are microorganisms that cause infectious
disease. Bacteria and viruses are the main pathogens.
• Bacteria are living cells and can multiply rapidly in
favourable conditions. Once inside the body, they release
poisons or toxins that can make us feel ill.
• Viruses can only reproduce inside host cells. Once inside,
they make hundreds of thousands of copies of themselves.
The first line of defence
The first line of defence is the
body’s natural barriers.
• chemicals in tears
• chemicals in sweat
• stomach acid.
• The skin
The skin covers the whole
body. It protects it from
physical damage, microbe
infection and dehydration.
The skin's dry, dead outer
cells are difficult for
microbes to penetrate.
White blood cells
If a pathogen manages to get into
the body, the second line of
defence takes over. This is called
active immunity. The white
blood cells have key functions in
Functions of the white blood
White blood cells can:
• ingest pathogens and destroy
• produce antibodies to destroy
• produce antitoxins that neutralise
the toxins released by pathogens.
• The pathogens are not the
disease - they cause the disease.
• White blood cells do not eat the
pathogens - they ingest them.
• Antibodies and antitoxins are not
living things - they are
There are several types of white blood cell, each with a
different function. But there are two main groups:
• phagocytes or macrophages
Phagocytes can pass easily through blood vessel walls into
the surrounding tissue and move towards pathogens or
toxins. They then either:
• ingest and absorb the pathogens or toxins, or
• release an enzyme to destroy them.
pathogens in a number
• They bind to them and
damage or destroy them.
• They coat pathogens,
clumping them together
so that they are ingested
easily by phagocytes.
• They bind to the
pathogens and release
chemical signals to
attract more phagocytes.
• BBC News item from
2006 about a five-year-
old girl who was born
without an immune
Vaccination involves putting a small amount of an inactive form of a
pathogen into the body. Vaccines can contain:
live pathogens treated to make them harmless
• harmless fragments of the pathogen
• toxins produced by pathogens
• dead pathogens.
These all act as antigens. When injected into the body, they
stimulate white blood cells to produce antibodies to fight the
• Because the vaccine contains only a weakened or harmless
version of a pathogen, the vaccinated person is in no danger of
developing a disease. If the person later becomes infected by the
pathogen, the required lymphocytes are able to reproduce rapidly
and destroy it.
• Some common diseases like influenza (flu) and the
common cold are caused by viruses. These mutate quickly,
which changes their surface proteins.
• Vaccinations can never be completely safe because side-
effect levels vary. A balance needs to be struck between
the advantages and disadvantages. For example:
• Using a vaccine may be much cheaper than treating a very
• The chance of falling seriously ill or dying from the disease
may be far greater than the chance of experiencing a
• Substances that kill bacteria or prevent their growth. They
do not work against viruses. It is difficult to develop drugs
that kill viruses without damaging the body’s tissues.
• Over time, bacteria can become resistant to certain
antibiotics. This is an example of natural selection. In a
large population of bacteria, there may be some that are
not affected by the antibiotic.
1. The drugs are tested using computer models and human
cells grown in the laboratory. Many substances fail this test
because they damage cells or do not seem to work.
2. Drugs that pass the first stage are tested on animals. In
the UK, new medicines have to be. A typical test involves
giving a known amount of the substance to the animals,
then monitoring them carefully for any side-effects.
3. Drugs that have passed animal tests are used in clinical
trials. They are tested on healthy volunteers to check they
are safe. The substances are then tested on people with
the illness to ensure they are safe and work.
The circulatory system
• thick outer walls
• thick layers of muscle and
• thin walls
• thin layers of muscle and
Blood vessels called the
supply blood to the
heart muscles. If they
become blocked, a
heart attack can
Causes of heart disease
• genetic factors, which show as a family history of heart
• lifestyle factors.
• lack of regular exercise
• stress leading to a fast heart rate
• drinking a lot of alcohol
• poor diet.
A lack of exercise and a diet high in salt and saturated
fat cause people to:
• become overweight
• have high blood pressure
• have high levels of cholesterol in their blood
• Polymers are large
molecules made by joining
many smaller molecules
together, end to end. The
smaller molecules are
• Short hydrocarbon molecules with only a few carbon atoms are
• Hydrocarbon molecules with between five and 12 carbon atoms
are usually liquids.
• Longer hydrocarbon molecules are solids.
• The separation of crude oil into different fractions through a
process called fractional distillation.
• The production of shorter hydrocarbon molecules from longer
ones by cracking.
• Monomers can join together to form polymers
Life Cycle Assessments
• Melting down
metals, plastics or
glass so they are
ready to make
• Using chemical
reactions to break
are ready for use.
Problems with polymers
• One of the useful properties of polymers is that they are
unreactive, so they are suitable for storing food and
chemicals safely. Unfortunately, this makes them difficult to
Most polymers, including polyethene and polypropene, are
Polymers can be burnt or incinerated. They release a lot of
heat energy, which can be used to heat homes or generate
Many polymers can be recycled. This reduces disposal
problems and the amount of crude oil used.
• An object can affect another
object that is some distance
away from it using
electromagnetic radiation. The
flow chart summarises how
The intensity of a beam
• the number of photons arriving and
• the energy each photon delivers.
The effect of distance
The intensity of a beam of electromagnetic radiation
decreases with distance from its source. This is because the
energy is spread over a larger surface area.
• Ionising radiation can break molecules into smaller
fragments. These charged particles are called ions. As a
result, ionising radiation damages substances and
materials, including those in the cells of living things. The
ions themselves can take part in chemical reactions,
spreading the damage. Ionising radiation includes:
• ultraviolet radiation (found in sunlight)
• X-rays (used in medical imaging machines)
• gamma rays (produced by some radioactive materials).
Information such as
computer data and
telephone calls can be
converted into infrared
signals and transmitted by
Microwave radiation can be
used to transmit signals
such as mobile phone calls
Radio waves are used to
transmit television and
radio programmes. Longer
wavelength radio waves are
reflected from an
electrically charged layer of
the upper atmosphere.
• radio waves
• infrared light
• visible light.
Microwave ovens protect users from the radiation by using:
• a metal case
• a metal mesh in the glass window of the door.
Mobile telephones communicate with their base stations using
low-intensity microwave radiation
Microwaves from the phone can penetrate body tissues to a depth
of a few centimetres. They are absorbed and give up their
energy to body tissues. This can cause a small amount of
heating, about 0.1°C - much less than if you were standing in
Ultraviolet light is part of the Sun’s spectrum of
electromagnetic radiation. It does not penetrate very far
into the body’s tissues, so its effects are seen mainly in the
skin and eyes. The eyes can develop cataracts, which
damage your sight. There are two main dangers to the
• short-term acute effects - sunburn
• long-term chronic effects – skin cancer
Plants use the energy in sunlight to make their own food by
• carbon dioxide + water → glucose + oxygen
• Photosynthesis releases oxygen into the atmosphere, and
removes carbon dioxide. This reverses the effect of respiration
• Absorbing ultraviolet light (Higher Tier)
Ultraviolet light splits oxygen molecules, O2, into separate oxygen
atoms. These react with other oxygen molecules to make ozone
molecules, O3. This is a reversible process.
• Ozone absorbs ultraviolet radiation. This prevents it from reaching
the ground and harming living organisms, especially animals.
• The Earth emits infrared
radiation. This is absorbed
by gases in the atmosphere
called greenhouse gases:
methane, water vapour and
carbon dioxide. These
absorb the radiation and
prevent it from escaping
into space. This greenhouse
effect keeps the Earth
warmer than it would
Processes that remove
carbon dioxide from
• photosynthesis by
• dissolving in the
Processes that return
carbon dioxide to the
• respiration by plants,
animals and microbes
• combustion (burning
wood and fossil fuels
such as coal, oil and
• thermal decomposition
of limestone (for
example, in the
manufacture of iron,
steel and cement).
• Global warming
• For thousands of years, the concentration of carbon dioxide
in the atmosphere remained much the same. But during the
past 200 years it has increased steadily
• Effects of global warming
Global warming could cause:
• climate change
• extreme weather conditions in some areas
• rising sea levels.