Disease and Immunity IGCSE Biology: Complete Guide with Memory Tips

🦠 Understanding Disease and Immunity in IGCSE Biology

Disease and immunity are crucial for understanding how organisms defend against pathogens. This guide covers immune responses, vaccines, and disease prevention.

🧠 Memory Tips

Pathogens: “Bacteria Viruses Fungi Protozoa”

• Bacteria: Single-celled prokaryotes
• Viruses: Need host cells to reproduce
• Fungi: Cause infections like athlete’s foot
• Protozoa: Single-celled eukaryotes

Immune Response: “Recognize Attack Remember”

• Recognize: Identify foreign antigens
• Attack: White blood cells respond
• Remember: Memory cells for future protection

White Blood Cells: “Phagocytes Lymphocytes”

• Phagocytes: Engulf pathogens
• Lymphocytes: Produce antibodies

📚 Key Concepts

Types of Pathogens

• Bacteria: Cause diseases like tuberculosis, cholera
• Viruses: Cause diseases like flu, HIV, COVID-19
• Fungi: Cause skin infections, thrush
• Protozoa: Cause malaria, sleeping sickness

Disease Transmission

• Direct contact: Touch, sexual contact
• Droplet infection: Coughing, sneezing
• Vector transmission: Mosquitoes, flies
• Contaminated food/water: Poor hygiene

Body’s Defense Systems

First Line Defense

• Skin: Physical barrier
• Mucus: Traps pathogens
• Stomach acid: Kills bacteria
• Tears: Contain lysozyme enzyme

Second Line Defense

• Phagocytes: Engulf and destroy pathogens
• Inflammation: Increases blood flow to infected area
• Fever: Raises body temperature to kill pathogens

Third Line Defense (Specific Immunity)

• Lymphocytes: B cells and T cells
• Antibodies: Specific proteins that bind to antigens
• Memory cells: Provide long-term immunity

Immune Response Process

1. Antigen recognition: Foreign substance detected
2. Lymphocyte activation: B cells or T cells respond
3. Antibody production: B cells make specific antibodies
4. Pathogen destruction: Antibodies neutralize pathogens
5. Memory formation: Memory cells remember antigen

Active vs Passive Immunity

• Active immunity: Body produces own antibodies (vaccination, infection)
• Passive immunity: Receive ready-made antibodies (breast milk, injection)

🎯 IGCSE Exam Focus

Common Questions

1. Compare different types of pathogens (6 marks)
2. Explain how vaccines work (5 marks)
3. Describe the immune response (8 marks)
4. Compare active and passive immunity (4 marks)

Key Processes

• Phagocytosis: How white blood cells engulf pathogens
• Antibody-antigen interaction: Lock and key mechanism
• Vaccination: Stimulating immune memory

💉 Vaccines and Prevention

How Vaccines Work

1. Weakened/dead pathogens injected
2. Immune system responds as if real infection
3. Memory cells formed without disease symptoms
4. Future protection against same pathogen

Types of Vaccines

• Live attenuated: Weakened living pathogens
• Inactivated: Dead pathogens
• Subunit: Parts of pathogens
• mRNA: Genetic instructions for antigen production

Disease Prevention

• Vaccination programs: Herd immunity
• Hygiene: Hand washing, food safety
• Quarantine: Isolate infected individuals
• Vector control: Eliminate disease carriers

🔬 Practical Applications

Antibiotics

• Function: Kill bacteria or stop growth
• Specificity: Only work against bacteria
• Resistance: Overuse leads to resistant strains
• Examples: Penicillin, streptomycin

Monoclonal Antibodies

• Production: From single clone of B cells
• Uses: Pregnancy tests, cancer treatment
• Advantages: Specific, consistent
• Applications: Medical diagnosis, research

Public Health Measures

• Sanitation: Clean water, sewage treatment
• Food safety: Proper storage, cooking
• Education: Health awareness programs
• Surveillance: Monitor disease outbreaks

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