1. What are Infections and Pathogens?
Pathogens are microorganisms that cause infectious diseases. Main types:
Bacteria: single-celled organisms (e.g., Salmonella).
Viruses: smaller than bacteria, reproduce inside cells (e.g., HIV, measles).
Fungi: multicellular or unicellular, can cause diseases (e.g., athlete's foot, rose black spot in
plants).
Protists: single-celled eukaryotes, some are pathogens (e.g., malaria-causing protist).
2. How Do Diseases Spread ?
Direct contact: Touching contaminated surfaces, bodily fluids (e.g., HIV).
By water: Drinking/eating contaminated materials (e.g., cholera).
By air: Coughing, sneezing spreads droplets (e.g., measles).
Vectors: Organisms like mosquitoes carrying malaria.
3. Human Defence Systems
First Line Defense: Non-Specific Barriers
Skin: Physical and chemical barrier; produces antimicrobial secretions.
Nose: Mucus and hairs trap pathogens.
Trachea & Bronchi: Cilia and mucus trap and remove pathogens.
Stomach: Hydrochloric acid destroys ingested pathogens.
Second Line: Immune System (Specific Defense)
White Blood Cells (WBCs):
Phagocytes: Engulf and digest pathogens (phagocytosis).
Lymphocytes:
Produce antibodies specific to antigens on pathogens.
Pathogens are microorganisms that cause infectious diseases. Main types:
Bacteria: single-celled organisms (e.g., Salmonella).
Viruses: smaller than bacteria, reproduce inside cells (e.g., HIV, measles).
Fungi: multicellular or unicellular, can cause diseases (e.g., athlete's foot, rose black spot in
plants).
Protists: single-celled eukaryotes, some are pathogens (e.g., malaria-causing protist).
2. How Do Diseases Spread ?
Direct contact: Touching contaminated surfaces, bodily fluids (e.g., HIV).
By water: Drinking/eating contaminated materials (e.g., cholera).
By air: Coughing, sneezing spreads droplets (e.g., measles).
Vectors: Organisms like mosquitoes carrying malaria.
3. Human Defence Systems
First Line Defense: Non-Specific Barriers
Skin: Physical and chemical barrier; produces antimicrobial secretions.
Nose: Mucus and hairs trap pathogens.
Trachea & Bronchi: Cilia and mucus trap and remove pathogens.
Stomach: Hydrochloric acid destroys ingested pathogens.
Second Line: Immune System (Specific Defense)
White Blood Cells (WBCs):
Phagocytes: Engulf and digest pathogens (phagocytosis).
Lymphocytes:
Produce antibodies specific to antigens on pathogens.
