Single Award - Disease and Body Defences (CCEA)

• Communicable diseases are infectious illnesses caused by microorganisms such as bacteria, viruses and fungi and can be passed from one organism to another.

• The body defends against pathogens using barriers like skin and white blood cells, which destroy microorganisms using antibodies and phagocytosis.

• Immunity develops when the body produces antibodies, either naturally through infection or artificially through vaccines, providing protection against future infections.

• Antibiotics can treat bacterial infections, but overuse can lead to antibiotic-resistant bacteria, making some diseases harder to control.

A communicable disease can be passed from one organism to another. It is also known as an infectious disease. It is caused by a microorganism – bacteria, virus or fungus.

A person free from both types of disease is described as being healthy.

Defence mechanisms help the body protect itself against the entry of microorganisms that cause communicable diseases.

These include:

• the skin, which is a barrier to microorganisms
• mucous membranes in the nose, ears and eyes which trap microorganisms
• blood clotting, which stops blood escaping and prevents the entry of microorganisms where the skin has been damaged

The entry of a microorganism may cause us to be sick while our body fights the infection.

If a microorganism does enter, white blood cells will kill them.

All cells have markers on their surface called antigens that have a specific shape.

Lymphocytes (white blood cells) make antibodies that are complementary to the antigen.

When the body recognises a foreign antigen, lymphocytes (white blood cells) produce antibodies, which are complementary in shape to the antigen.

An antibody will only work on one type of microorganism because of this complementary shape.

Antibodies attach to the antigen - an antibody-antigen reaction.

Antibodies immobilise microorganisms by clumping them together.

Immobilisation of the microorganism reduces symptoms and prevents the spread of infection.

The clump of microorganisms is then destroyed by phagocytosis.

Phagocytosis is when a phagocyte (another type of white blood cell) engulfs and digests the microorganisms.

Enzymes within the phagocyte digest the microorganism.

The infected individual will be sick while lymphocytes work to produce enough antibodies to provide immunity.

This is the primary response.

During this response, the body will also make memory lymphocytes that remain in the body for years.

If the same pathogen is encountered again, memory lymphocytes produce high numbers of antibodies very quickly.

This is the secondary response and it prevents the person getting sick again from that pathogen or disease.

The person is now immune from that disease.

Immunity means your body can fight off a disease. This happens when you have enough antibodies, which can protect you from getting sick from that disease.

There are two types of immunity:

This is when the body’s lymphocytes are activated and produce the specific antibodies needed to fight the pathogen.

Active immunity is:

• slow acting

• provides long-lasting protection

The primary response when a microorganism enters the body is described as natural active immunity.

Vaccines provide artificial active immunity.

This is when ready-made antibodies, from another source, are introduced to the body.

Passive immunity is:

• fast acting

• only lasts a short period of time (no memory lymphocytes are made)

Breastfeeding provides a baby with natural passive immunity.

Anti-venom provides artificial passive immunity after a poisonous bite.

Antibiotics are chemicals produced by fungi that kill or prevent the growth of bacteria.

Penicillin was the first antibiotic. It was discovered by Alexander Fleming in the 1920s when he noticed that bacteria didn't grow near a mould (fungus).

He concluded that the mould released a substance that prevented bacterial growth - this was penicillin.

In the 1940s, scientists Florey and Chain produced pure penicillin and began large-scale production of penicillin.

Since then, many more antibiotics have been discovered.

Penicillin and other antibiotics are produced commercially where fungi are grown in carefully controlled conditions (correct temperature, pH and nutrients) in fermenters.

Preclinical trials

Before a new drug can be made available for public use, it must undergo rigorous testing to ensure it is safe and effective.

There are various stages:

1. Preclinical Trials:

• conducted in laboratories
• involves in vitro testing - drug is tested on cells and tissue
• involves animal testing - drug is tested on animals to see how well the drug works on an entire living organism.

Preclinical trials are necessary to:

• check if the drug is toxic (poisonous)
• check how effective it is

2. Clinical Trials:

• drug is tested on small number of healthy volunteers first, then a larger group

Clinical trials are necessary to:

• assess how the drug works in humans (rather than other species)
• determine correct dosage required
• find out side effects if any

If these trials are successful, the drug can be licensed.

Some bacteria have developed resistance to antibiotics, meaning the drugs can no longer kill them.

The overuse of antibiotics is responsible for this process by allowing bacteria to mutate and become resistant.

Certain bacteria, known as superbugs (eg MRSA), are resistant to multiple antibiotics, making infections caused by them difficult to treat and posing serious health risks.

• Hygiene: regular handwashing and cleaning hospital environments.

• Controlled antibiotic use: prescribe antibiotics only when necessary.

• Isolation: keep patients infected with ‘superbugs’ separate to prevent spread.

• bacteria can mutate quickly

• resistant strains survive and multiply

• limited development of new antibiotics

Many people drink alcohol in moderation and are unlikely to suffer serious harm.

Binge drinking can cause harm to the individual and others. Binge drinking is when a large amount of alcohol is consumed over a short period of time.

Drinking alcohol excessively over a long period of time can damage the liver and other organs.

Drinking heavily during pregnancy can cause serious brain damage to the foetus, known as foetal alcohol syndrome.

Smoking bans have been effective at reducing passive smoking and encouraging people to stop smoking.

E-cigarettes help some quit smoking. Critics argue they may encourage non-smokers, especially children, to start using nicotine, causing health risks and long-term effects of vaping are not yet fully understood.