1. 31.1 KEY CONCEPT Germs cause many diseases in humans.

2. Germ Theory  Germ theory proposes that microorganisms cause diseases.  proposed by Louis Pasteur  led to rapid advances in understanding disease

3.  Disease-causing agents are called pathogens.

4. Pathogen Types  Bacteria are single-celled organisms.  cause illness by destroying cells  release toxic chemicals

5.  Viruses are genetic material surrounded by a protein coat. –force host cells to make more viruses –very small

6.  Fungi can be multicellular or single-celled. –take nutrients from host cells –occur in warm and damp places

7.  Protozoa are single-celled organisms. –use host cells to complete their life cycles –take nutrients from host cell –Ex: Malaria

8.  Parasites are multicellular organisms. –grow and feed on a host –possibly kill the host

9.  Vectors carry a pathogen and transmit it into healthy cells  Direct contact requires touching an infected individual.  kissing  sexual intercourse  hand shaking tick

10. 31.2 KEY CONCEPT The immune systems consists of organs, cells, and molecules that fight infections.

11. Many body systems protect you from pathogens.  The immune system is the body system that fights off infection and pathogens.  Many other tissues and systems help the immune system.  Skin is a physical barrier to infection.  Mucous membranes trap pathogens entering the body.  The circulatory system transports immune cells.

12. Immune Cell Types  White blood cells attack infections inside the body.  Phagocytes engulf and destroy pathogens.  T cells destroy infected cells.  B cells produce antibodies.

13.  Three types of proteins fight off invading pathogens. –Complement proteins weaken pathogen membranes. –Antibodies make pathogens ineffective. –Interferons prevent viruses from infecting healthy cells. antibody pathogens

14. Immunity prevents a person from getting sick from a pathogen.  In all immunity, pathogens are destroyed before you get sick.  Passive immunity occurs without an immune response.  mother ’ s milk  genetics  Active immunity occurs after a specific immune response