immune+system+homework-Faith

__PATHOGENS__
1. What is a pathogen? 2. What are the body's three lines of defense against pathogens? 3. Write a one paragraph summary of bacteria. 4. Write a one paragraph summary of viruses. 5. What is an emerging virus?
 * collective bacterias and viruses
 * Barriers to entry such as the skin and mucous membranes of body cavities act to prevent pathogens from gaining entrance into the body
 * first responders such as the phagocytic white blood cells act to prevent infection after such an invasion has occurred
 * specific defenses overcome an infection by killing the particular disease-causing agent that has entered the body. Specific defenses also protect us against cancer
 * Bacteria are single celled prokaryotes that do not have a nucleus. The main features of bacteria is a **bacillus**, a **coccus**, and a **spirillum**. The cell wall of some bacteria is surrounded by **capsule** that allow bacteria to stick to surfaces such as teeth. Bacteria are also independent cells that are metabolically competent.Their DNA is packaged in a chromosome that occupies the center of the cell. Many bacteria also have accessory rings of DNA called **plasmids**. Bacteria can reproduce rapidly under favorable condition and can double their number every 12 minutes. Growth of bacteria causes disease and also bacteria release molecules called **toxins** that inhibit cellular metabolism.
 * Viruses bridge that gap between the living and nonliving and are not composed of cells. Outside a host viruses are essentially chemicals that can be stored on a shelf. They replicate inside cells during a period of time they appear to be alive. They are obligate parasites and do not live independently. they also carry the genetic information needed to reproduce itself. Viruses gain entry into and are specific to a particular host cell because portions of the virus adhere in a lock-and-key manner with a receptor on the host ells outer surface. In large measure a virus relies on the host's enzyme and ribosome for its own reproduction.
 * When a certain infectious disease in humans is transported from one location to another
 * many are transmitted by vectors that are usually insects that carry disease from an infected individual to a healthy individual
 * diseases spread by insects may require massive efforts to control the vector population
 * viruses can emerge through acquisitions of new surface antigens

__**IMMUNE SYSTEM**__
6. What is an antibody? What do they do? 7. What is B Cell? 8. What is a Cytotoxic T Cell? 9. What is a Helper T Cell? 10. What is an antigen? How does the body respond to an antigen?
 * are proteins
 * they are produced by the body in response to the presence of a foreign substance called antigens
 * Lymphocyte that matures in the bone marrow and when stimulated by the presence of a specific antigen and gives rise to antibody-producing plasma cells
 * is a T cell that attacks and kills antigen-bearing cells
 * is a T cell that secretes cytokines that stimulate all kinds of immune system cells
 * a foreign substance usually a protein of a polysaccharide that stimulates the immune system to produce antibodies
 * the body reacts to it so that the body remains free of disease

**Pathogens**