Chapter 10: Diseases and Immunity - IGCSE Biology

Pathogens and Disease Transmission

Pathogens:

• Organisms that cause disease.
• Can be transmitted through direct or indirect contact.

Direct Contact:

• Involves person-to-person interaction.
• Examples: Chickenpox (by touch), HIV (sexual contact).

Indirect Contact:

• No direct human contact.
• Examples: Eating contaminated food, mosquito bites, inhaling infected droplets.

Body's Defenses Against Diseases

1. Skin:

   • Acts as a physical barrier.
   • Heals itself when wounded by forming a scab.

2. Nose:

   • Nose hairs filter out pathogens.

3. Mucus:

   • Traps pathogens before they enter the lungs.

4. Stomach Acid:

   • Hydrochloric acid in stomach kills consumed pathogens.

5. White Blood Cells:

   • Fight infections through phagocytosis and producing antibodies.
   • Types of white blood cells:
     • Phagocytes: Engulf and digest pathogens.
     • Lymphocytes: Produce antibodies.

Disease Prevention Methods

• Clean water supply: Prevents water-borne diseases like cholera and typhoid.
• Hygienic food preparation: Reduces foodborne pathogens.
• Good personal hygiene: Handwashing, covering mouth when coughing.
• Waste disposal and sewage treatment: Prevents disease spread via contaminants.

Active and Passive Immunity

Active Immunity:

• Develops after an infection or vaccination.
• Body produces antibodies in response to antigens.
• Example with lymphocytes reacting to specific antigens.
• Results in memory cells for long-term immunity.

Passive Immunity:

• Immediate, short-term immunity obtained from another individual.
• Examples: Antibodies passed from mother to fetus across the placenta or through breast milk.
• No memory cells are produced in passive immunity.

Vaccination

• Process involves introducing weakened pathogens or antigens to stimulate an immune response without causing disease.
• Promotes antibody production and memory cell formation for long-term protection.
• Herd immunity occurs when a large portion of the population is vaccinated, reducing the pathogen's ability to spread.

Examples of Diseases

Cholera:

• Caused by bacteria transmitted via contaminated water.
• Leads to severe diarrhea due to toxins produced by bacteria.
• Treatment includes oral rehydration therapy with salt and sugar solutions.

Key Takeaways

• Understanding how pathogens are transmitted helps in developing effective prevention strategies.
• The body has multiple defense mechanisms against pathogens.
• Active and passive immunity play crucial roles in protecting the body from diseases.
• Vaccinations are essential in controlling disease outbreaks through individual and herd immunity.

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This summary provides an overview of key concepts from Chapter 10 of the IGCSE Biology curriculum, focusing on diseases and the immune system. For further details, review specific sections as needed.