Preventing & Treating Disease

Learn how the body defends itself against pathogens and how science helps us stay healthy. GCSE Biology covers how vaccinations, antibiotics, and medicines are used to prevent and treat diseases. You’ll also explore the development of new drugs and why antibiotic resistance is a growing concern.

Pathogens and Disease

Pathogens are microorganisms that cause disease. These include bacteria, viruses, fungi, and protists. Once inside the body, they reproduce rapidly and may release toxins or damage cells, leading to symptoms.

The Human Defence System

The body has several layers of defence to stop pathogens entering or spreading:

• Physical barriers: Skin, mucus in the nose, and cilia in the airways trap or block pathogens.
• Chemical defences: Stomach acid destroys many harmful microbes.
• Platelets in the blood help clot wounds quickly to prevent infection.

The Immune System

If pathogens do get in, the immune system responds:

• White blood cells detect pathogens and act in three main ways:
• Phagocytosis – engulfing and destroying pathogens
• Producing antibodies – which target specific pathogens
• Producing antitoxins – which neutralise harmful toxins

Once the body has made antibodies for a pathogen, it can respond more quickly in the future.

Vaccination

Vaccines contain small amounts of inactive or dead pathogens. These stimulate the immune system to produce antibodies without causing illness.

Advantages of vaccination:

• Helps prevent serious diseases
• Protects entire populations through herd immunity
• Reduces the spread of infection

Disadvantages:

• Some people may have mild side effects
• Not all vaccines give full protection
• Rare allergic reactions can occur

Using Drugs to Treat Disease

Drugs help treat disease in two main ways:

• Painkillers relieve symptoms (e.g. paracetamol)
• Antibiotics (like penicillin) kill bacteria but do not work on viruses

Overuse of antibiotics can lead to antibiotic resistance, where bacteria evolve and become harder to treat.

Plants as a Source of Medicine

Many modern medicines were first discovered in plants. For example:

• Aspirin comes from willow bark
• Digitalis (used for heart conditions) comes from foxglove plants

Discovering and Developing New Drugs

Alexander Fleming discovered penicillin from mould – one of the first antibiotics.

New drugs are now developed in laboratories and must pass three stages:

1. Preclinical testing – on cells and animals
2. Clinical trials – on human volunteers to check safety
3. Double-blind trials – neither doctors nor patients know who gets the real drug vs a placebo

All drugs are tested for toxicity, efficacy (does it work?), and the correct dose.

Monoclonal Antibodies

These are identical antibodies made in a lab. They can be designed to:

• Target specific cells (e.g. cancer cells)
• Diagnose diseases
• Deliver drugs directly to the problem area

They have great potential but can cause side effects such as fever, low blood pressure, or allergic reactions.

Plant Diseases and Plant Defences

Plants can suffer from disease just like humans. Signs include:

• Discoloured leaves
• Spots or stunted growth
• Wilting or abnormal growth

Plant defences include:

• Physical: tough cell walls, waxy cuticles, bark
• Chemical: antimicrobial chemicals (like mint and witch hazel)
• Mechanical: thorns, curled leaves, mimicking other plants (e.g. to deter herbivores)

Also see Communicable Diseases, Non-Communicable Diseases

Links for learning

BBC Bitesize: Non-specific human defence systems
Study Mind: Disease Prevention
BBC Bitesize: The immune system
BBC Bitesize: Vaccinations
MME Revise: Vaccinations & Drugs
Revision World: Immunisation & Vaccinations
BBC Bitesize: Monoclonal Antibodies
BBC Bitesize: Plant defences
MME Revise: Plant disease