Health, Disease and the Development of Medicines

What you'll learn

This revision guide covers health, disease and how medicines are developed according to the Edexcel GCSE Biology specification. You'll learn the difference between communicable and non-communicable diseases, how they interact, and how the body defends itself against pathogens. You'll also understand how new medicines are developed, tested and used to treat disease.

Key terms and definitions

Health — a state of physical and mental wellbeing, not merely the absence of disease

Communicable disease — an infectious disease caused by pathogens that can be transmitted between individuals

Non-communicable disease — a disease that cannot be transmitted between individuals; often chronic and long-lasting

Pathogen — a microorganism that causes disease (includes bacteria, viruses, fungi and protists)

Antibody — a protein produced by white blood cells that binds to specific antigens on pathogens to destroy them

Antigen — a unique protein marker on the surface of cells, including pathogens, that triggers an immune response

Antibiotic — a drug that kills or inhibits the growth of bacteria without harming body cells

Placebo — an inactive substance given to a control group in a clinical trial to test the effectiveness of a new drug

Core concepts

Defining health and disease

Health is not simply the absence of disease. The World Health Organization defines it as complete physical, mental and social wellbeing. Several factors affect health:

• Physical factors: diet, exercise, disease, life situations (housing, pollution exposure)
• Mental factors: stress, social interactions, financial security
• Social factors: access to healthcare, education, clean water and sanitation

Diseases fall into two main categories. Communicable diseases are caused by pathogens and can spread from person to person or through vectors. Examples include tuberculosis (TB), HIV/AIDS, malaria and cholera. Non-communicable diseases cannot be transmitted and include cardiovascular disease, Type 2 diabetes, cancer and lung diseases such as COPD.

Interactions between diseases

Different diseases can interact within the body, making health outcomes worse:

Immune system deficiency leading to increased infection risk: HIV attacks and destroys white blood cells (specifically helper T-cells), weakening the immune system. This makes patients vulnerable to opportunistic infections like tuberculosis and pneumonia that a healthy immune system would normally fight off. AIDS (Acquired Immune Deficiency Syndrome) is the condition where the immune system is so damaged that the body cannot fight these infections.

HPV infection and cancer: Human papillomavirus (HPV) is a communicable disease that can lead to cervical cancer, a non-communicable disease. The virus causes changes to cervical cells that can become cancerous. The HPV vaccine, now routinely given to teenagers in the UK, prevents infection and significantly reduces cervical cancer risk.

Physical health problems affecting mental health: Chronic physical diseases often lead to depression and anxiety. For example, someone diagnosed with coronary heart disease may experience stress and worry, affecting their mental wellbeing.

Immune reactions triggered by pathogens causing allergies: Initial infection by certain pathogens can trigger the immune system to become oversensitive, leading to allergic reactions such as skin rashes or asthma.

The human defence systems

The body has several non-specific defences that work against all pathogens:

Physical and chemical barriers:

• Skin acts as a physical barrier; if cut, blood clots seal the wound
• Nose produces mucus that traps pathogens; cilia (tiny hairs) move mucus to the back of the throat to be swallowed
• Trachea and bronchi are lined with mucus and cilia to trap and remove pathogens
• Stomach produces hydrochloric acid (pH 2) that kills most ingested pathogens

The immune system provides specific defence against particular pathogens:

Phagocytosis: White blood cells called phagocytes engulf and digest pathogens. They detect pathogens, bind to them, engulf them in vesicles and destroy them using enzymes. This is a non-specific response.

Antibody production: White blood cells called lymphocytes produce antibodies specific to antigens on a pathogen's surface. Each pathogen has unique antigens. When lymphocytes encounter a pathogen:

1. They detect the pathogen's antigens
2. They produce specific antibodies that bind to these antigens
3. Antibodies clump pathogens together and mark them for destruction by phagocytes
4. Some lymphocytes remain as memory cells

Memory cells and immunity: After first exposure to a pathogen, some lymphocytes remain in the blood as memory cells. If the same pathogen enters the body again, memory cells rapidly produce large quantities of the correct antibody, destroying the pathogen before symptoms develop. This is immunity.

Antitoxin production: Some pathogens produce toxins that make you ill. Lymphocytes can produce antitoxins that neutralise these toxins.

Vaccination

Vaccination protects individuals and populations from serious diseases by establishing immunity without causing illness.

How vaccines work:

1. A vaccine contains dead or inactive forms of a pathogen
2. The pathogen's antigens stimulate lymphocytes to produce specific antibodies
3. Memory cells are created
4. If the live pathogen later infects the body, memory cells trigger rapid antibody production
5. The pathogen is destroyed before causing serious illness

Common vaccines in the UK: MMR (measles, mumps, rubella), DTaP (diphtheria, tetanus, pertussis), HPV, meningitis vaccines.

Herd immunity: When a large proportion of a population is vaccinated, the spread of disease is greatly reduced. This protects vulnerable individuals who cannot be vaccinated (babies, immunocompromised people). If vaccination rates fall below a threshold (typically 90-95%), disease outbreaks can occur.

Antibiotics and other medicines

Antibiotics are drugs that kill bacteria or inhibit their growth. They work by:

• Disrupting bacterial cell wall formation
• Interfering with bacterial protein synthesis
• Damaging bacterial DNA

Important points about antibiotics:

• They are only effective against bacteria, not viruses
• Viruses live and reproduce inside body cells, making them difficult to target without damaging host cells
• Different antibiotics work against different bacteria; doctors must prescribe the appropriate type

Antibiotic resistance is a growing global health concern:

• Random mutations in bacterial DNA can create resistance to antibiotics
• When antibiotics are used, resistant bacteria survive while non-resistant bacteria die
• Resistant bacteria reproduce, passing on resistance genes
• Overuse and misuse of antibiotics (not completing courses, using them for viral infections) accelerates resistance development
• MRSA (methicillin-resistant Staphylococcus aureus) is a significant problem in hospitals

Reducing antibiotic resistance:

• Only use antibiotics when necessary
• Complete the full prescribed course
• Doctors should avoid over-prescribing
• Agricultural use of antibiotics should be restricted
• Develop new antibiotics (though bacteria evolve resistance faster than new drugs are developed)

Painkillers and other treatments: Painkillers like paracetamol and ibuprofen treat symptoms but do not kill pathogens. The body's immune system must fight the infection.

Drug development and testing

New medicines must undergo rigorous testing before being approved for use. This ensures they are safe, effective and have an appropriate dosage.

Preclinical testing:

1. Computer modelling and cell cultures: Drugs are first tested on human cells and tissues grown in laboratories to check for toxicity and efficacy
2. Animal testing: Drugs are tested on live animals (typically mice and rats) to study effects on whole organisms, including toxicity and appropriate dosage

Animal testing remains controversial. Arguments supporting it include: necessary to protect human safety; animals are biologically similar to humans; strict regulations minimize suffering. Arguments against include: ethical concerns about animal welfare; animals are not identical to humans so results may not transfer.

Clinical trials involve testing on human volunteers:

Phase 1: Small numbers of healthy volunteers test the drug's safety and identify side effects. Very low doses are used initially.

Phase 2: Small numbers of patients with the target disease test whether the drug actually works (efficacy) and to determine the optimum dose.

Phase 3: Large numbers of patients test the drug more thoroughly. This uses:

• Double-blind trials: Neither patients nor doctors know who receives the drug or placebo until the trial ends, eliminating bias
• Placebo groups: Some patients receive an inactive substance (placebo) to compare against the drug's effects
• Randomisation: Patients are randomly allocated to drug or placebo groups to ensure fair comparison

If clinical trials show the drug is safe, effective and better than existing treatments, regulatory authorities (MHRA in the UK) may approve it for use.

Monoclonal antibodies: These are identical antibodies produced from a single clone of cells. They have medical applications including:

• Pregnancy tests (detecting hCG hormone)
• Diagnosing diseases by binding to specific antigens
• Treating some cancers by targeting cancer cells specifically
• Measuring hormone levels in blood tests

Production involves fusing a lymphocyte (produces antibodies) with a tumour cell (divides rapidly) to create a hybridoma cell that divides indefinitely while producing specific antibodies.

Worked examples

Example 1: A student investigated the effect of antibiotics on bacterial growth. They placed paper discs soaked in different antibiotics on agar plates covered with bacteria, then measured zones of inhibition (clear areas with no bacterial growth).

(a) Which antibiotic was most effective against this bacterium? [1 mark]

Answer: Antibiotic A ✓ (largest zone of inhibition shows most bacteria killed)

(b) Suggest why antibiotic D produced no zone of inhibition. [2 marks]

Answer: The bacteria are resistant to antibiotic D ✓ / The antibiotic cannot kill or inhibit the growth of this bacterial strain ✓

(c) The student wants to test whether antibiotic A works against a virus. Explain why this would not work. [2 marks]

Answer: Antibiotics only work against bacteria, not viruses ✓. Viruses reproduce inside body cells so antibiotics cannot target them without damaging human cells ✓

Example 2: Describe how vaccination prevents infection. [4 marks]

Mark scheme answer:

• Vaccine contains dead/inactive pathogen or antigens ✓
• Antigens stimulate white blood cells/lymphocytes to produce antibodies ✓
• Memory cells are produced ✓
• If live pathogen enters body, memory cells rapidly produce antibodies / secondary response is faster ✓
• Pathogen is destroyed before causing symptoms ✓

(Any 4 points)

Example 3: Explain why it is important that clinical trials for new drugs use a placebo. [3 marks]

Mark scheme answer:

• To compare the drug's effect against no treatment ✓
• Some patients may feel better due to psychological effects (placebo effect) ✓
• Ensures any improvement is due to the drug itself and not other factors ✓

Common mistakes and how to avoid them

• Confusing communicable and non-communicable diseases: Remember, communicable = contagious/infectious. Non-communicable diseases like cancer and heart disease cannot spread between people, even though some (like cervical cancer from HPV) may have infectious origins.

• Thinking antibiotics work on viruses: Antibiotics ONLY kill bacteria. Viral diseases like colds, flu and COVID-19 cannot be treated with antibiotics. Learn the difference: bacteria are living cells; viruses are not cells and reproduce inside host cells.

• Mixing up antigens and antibodies: Antigens are ON pathogens (the markers); antibodies are PRODUCED by white blood cells (the weapons). Antibodies bind to antigens.

• Not explaining the role of memory cells in vaccination: Simply stating "the body produces antibodies" gets few marks. You must explain that memory cells remain after vaccination and enable rapid antibody production upon re-infection.

• Vague answers about drug testing: Be specific about the stages: computer models → cells → animals → human trials. Know that double-blind trials and placebos eliminate bias.

• Confusing immunity with general health: Immunity is specific protection against particular pathogens due to antibodies/memory cells, not just "being healthy."

Exam technique for "Health, Disease and the Development of Medicines"

• "Explain" questions require reasoning: Simply describing what happens earns limited marks. Link cause and effect. For example, "Explain how antibiotic resistance develops" needs: mutation → survival advantage when antibiotics used → reproduction → spread of resistance, not just "bacteria become resistant."

• Use data effectively: When given graphs or tables about infection rates, vaccination coverage or antibiotic effectiveness, quote specific values and identify trends. "The zone of inhibition was 24mm" is better than "it was large."

• Command word precision: "Describe" = say what happens; "Explain" = say what happens AND why; "Suggest" = apply knowledge to unfamiliar contexts (you may not have learned the specific answer).

• Extended response (6-mark) questions: Plan your answer. Cover multiple points with detail. For drug development questions, work through the sequence logically. For disease interactions, give specific examples with mechanisms.

Quick revision summary

Health is complete physical and mental wellbeing. Communicable diseases are caused by pathogens and spread between individuals; non-communicable diseases cannot spread. The body defends against pathogens using physical barriers, phagocytosis, and antibody production by lymphocytes. Vaccination creates immunity through memory cells without causing illness. Antibiotics kill bacteria but not viruses; antibiotic resistance develops through natural selection. New drugs undergo preclinical testing (cells, animals) then clinical trials (humans) using placebos and double-blind protocols to ensure safety and efficacy before approval.