Immune+System+hw-+kat

PATHOGENS 1. What is a pathogen? A pathogen is a human infectious disease that are caused by bacteria and viruses.

2. What are the body's three lines of defense against pathogens? The body's three lines of defense against pathogens are:
 * 1) Barriers to entry such as the skin and mucous membranes of body cavities. They prevent pathogens from gaining entrance into the body.
 * 2) First responders, such as the phagocytic white blood cells, act to prevent an infection after an invasion has occured.
 * 3) Specific defenses overcome an infection by killing the particular disease-causing agent that has entered the body. Specific defenses also protect us against cancer.

3. Write a one paragraph summary of bacteria. Bacteria are single celled prokaryotes, and they don't have a nucleus. There are three common shapes of the bacterial anatomy. One is **bacillus**, which is a rod shape, another is **coccus**, which has a spherical shape, and the last is **spirillum**, which is a curved shape. Bacteria have a cell wall that is made of amino-disaccharide, which the "cillin" antibiotics an interfere with the production of. The walls of of some bacteria are surrounded by a capsule, which allows the bacteria to stick to surfaces such as teeth. They also prevent phagocytic white blood cells from taking them up and destroying them. Bacterial features include **plasmids**, the accessory ring of DNA that carries resistant genes to antibodies, **sex pilus**, elongated hollow appendage used for DNA transfer to other bacterial cells, **fimbriae**, hairlike bristles that allow adhesion to surfaces, **flagellum**, allows the bacteria to move backwards, **ribosome, nucleoid, plasma membrane, cell wall, and capsule**.

4. Write a one paragraph summary of viruses. Viruses gap the bridge between the living and nonliving. Outside of the body, viruses are chemicals that can be stored on a shelf. But, viruses replicate inside cells, and during this period of time, the clearly appear to be alive. __Viruses are acellular__-- not composed of cells. They are obligate parasites and they do not live independently. Viruses cause disease, such as colds, flu, measles, chicken pox, polio, rabies, AIDS, genital warts, and genital herpes. Virus particles are about four time smaller than bacterium. A virus has two parts: an outer capsid composed of protein units and an inner core of nucleic acid. 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 cell's outer surface. Once inside the body, the nucleic acid codes for the protein units in the capsid. The virus also may have genes for special enzymes needed for the virus to reproduce and exit from the host cell. However, a virus relies on the host's enzymes and ribosomes for its own protection.

5. What is an emerging virus? Emerging viruses emerge by being transported from one location to another where it has never been before. Flu strains move from Southeast Asia to the United States every year. The West Nile virus is making headlines because it has changed its range, being transported into the United States and taking hold in bird and mosquito populations. SARS (severe acute respiratory syndrome) was transported from Southeast Asia to Toronto, Canada. Viruses can emerge because of the inability of the immune system to recognize a change in the virus that allows it to cause disease. Viruses that continually change their "faces", such as HIV, are far more difficult to eradicate.

IMMUNE SYSTEM 6. What is an antibody? What do they do? An antibody is a protein produced in response to the presence of an antigen, each antibody combines with a specific antigen.

7. What is B Cell? A B Cell produces plasma cells and memory cells. Plasma cells produce specific antibodies and memory cells are ready to produce antibodies in the future.

8. What is a Cytotoxic T Cell? A cytotoxic T Cell kills virus-infected cells and cancer cells.

9. What is a Helper T Cell? A Helper T Cell regulates immunity.

10. What is an antigen? How does the body respond to an antigen? An antigen is a foreign substance, which is usually a protein or a polysaccharide, that stimulates the immune system to produce antibodies.