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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.
  These include:
• skin
• 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
  specialised proteins.
  There are several types of white blood cell, each with a
  different function. But there are two main groups:
• phagocytes or macrophages
• Lymphocytes

  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.
  Antibodies neutralise
  pathogens in a number
  of ways:
• 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
  ill person.
• The chance of falling seriously ill or dying from the disease
  may be far greater than the chance of experiencing a
  serious side-effect.

• 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.
                      Drug testing
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
• Arteries
• thick outer walls
• thick layers of muscle and
  elastic fibres.

• Veins
• thin walls
• thin layers of muscle and
  elastic fibres.
                           The heart

Blood vessels called the
coronary arteries
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.

•   smoking
•   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
  called monomers.
                          Crude oil
• 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.
               Synthetic polymers
• Monomers can join together to form polymers

Lycra                                           Gore-Tex
Modifying polymers
Life Cycle Assessments
                   Recycling can

                   • Melting down
                     metals, plastics or
                     glass so they are
                     ready to make
                     new objects.
                   • Using chemical
                     reactions to break
                     polymers down
                     into simpler
                     substances that
                     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
  dispose of.

• Biodegradable
  Most polymers, including polyethene and polypropene, are
  not biodegradable

• Incineration
  Polymers can be burnt or incinerated. They release a lot of
  heat energy, which can be used to heat homes or generate

• Recycling
  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
  this happens.
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
• 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).
Infrared light
  Information such as
  computer data and
  telephone calls can be
  converted into infrared
  signals and transmitted by
  optical fibres
  Microwave radiation can be
  used to transmit signals
  such as mobile phone calls
Radio waves
  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.
Non-ionising radiation
• radio waves
• microwaves
• 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
• Oxygen
  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
  otherwise be.
Processes that remove
  carbon dioxide from
  the air:
• 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.

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