Standard Set 10.  Physiology (Infection and Immunity)
Some bacteria, parasites, and viruses can cause human diseases because they either rob the body of
necessary sustenance or secrete toxins that cause injury.  The human body has a variety of mechanisms to
interfere with or destroy invading pathogens. Besides protection afforded by the skin, one of the most
effective means of defending against agents that harm the body is the immune system with its cellular and
chemical defenses. Students should develop a clear understanding of the components of the immune
system and know how vaccines and antibiotics are used to combat disease. They should also know that
acquired immune deficiency syndrome (AIDS) compromises the immune system, causing affected
persons to succumb to other AIDS-associated infections that are harmless to people with an intact
immune system.

10.  Organisms have a variety of mechanisms to combat disease. As a basis for
understanding the human immune response:
10. a.   Students know the role of the skin in providing nonspecific defenses against infection.
The skin serves as a physical barrier to prevent the passage of many disease-causing microorganisms.
Cuts and abrasions compromise the skin’s ability to act as a barrier. Teachers can use charts and
overhead projections to show the dangers and physiologic responses of a break in the skin.

10. b. Students know the role of antibodies in the body’s response to infection.
Cells produce antibodies to oppose antigens, substances that are foreign to the body. An example of an
antigen is a surface protein of a flu virus, a protein with a shape and structure unlike those of any human
proteins. The immune system recognizes that the flu virus structure is different and generates proteins
called antibodies that bind to the flu virus. Antibodies can inactivate pathogens directly or signal immune
cells that pathogens are present.

10. c. Students know how vaccination protects an individual from infectious diseases.
Several weeks are required before the immune system develops immunity to a new antigen. To overcome
this problem, vaccinations safely give the body a look in advance at the foreign structures. Vaccines
usually contain either weakened or killed pathogens that are responsible for a specific infectious disease,
or they may contain a purified protein or subunit from the pathogen. Although the vaccine does not cause
an infectious disease, the antigens in the mixture prompt the body to generate antibodies to oppose the
pathogen. When the individual is exposed to the pathogenic agent, perhaps years later, the body still
remembers having seen the antigens in the vaccine dose and can respond quickly. Students have been
exposed to the practical aspects of immunization through their knowledge of the vaccinations they must
receive before they can enter school. They have all experienced getting shots and may have seen their
personal vaccination record in which dates and kinds of inoculations are recorded. The review of a
typical vaccination record, focusing on the reason for the shots and ways in which they work, may serve
as an effective entry to the subject.
Students should review the history of vaccine use. Early literature provides descriptions of vaccine use
from pragmatic exposure, but the term vaccine is derived from the cowpox exudate that Edward Jenner
used during the 1700s to inoculate villagers against the more pathogenic smallpox. Louis Pasteur, noted
for his discov¬ery of the rabies treatment, also developed several vaccines. Poliovirus, the cause of
infantile paralysis (poliomyelitis), was finally conquered in the 1950s through vaccines that Jonas Salk and
Albert B. Sabin refined.

10. d. Students know there are important differences between bacteria and viruses with respect
to their requirements for growth and replication, the body’s primary defenses against
bacterial and viral infections, and effective treatments of these infections.
A virus, which is the simplest form of a genetic entity, is incapable of metabolic life and reproduction
outside the cells of other living organisms. A virus contains genetic material but has no ribosomes.
Although some viruses are benign, many harm their host organism by destroying or altering its cell
structures. Generally, the body perceives viruses as antigens and produces antibodies to counteract the
virus. Bacteria are organisms with a full cellular structure. They, too, can be benign or harmful. Harmful
bacteria and their toxins are perceived as antigens by the body, which in turn produces antibodies. In
some cases infectious diseases may be treated effectively with antiseptics, which are chemicals that
oxidize or in other ways inactivate the infecting organism. Antiseptics are also useful in decontaminating
surfaces with which the body may come in contact (e.g., countertops). Antibiotics are effective in treating
bacterial infections, sometimes working by destroying or interfering with the growth of bacterial cell walls
or the functioning of cell wall physiology or by inhibiting bacterial synthesis of DNA, RNA, or proteins.
Antibiotics are ineffective in treating viral infections.
Students might research infections caused by protists (malaria, amoebic dysentery), bacteria (blood
poisoning, botulism, food poisoning, tuberculosis), and viruses (rabies, colds, influenza, AIDS). They
might also investigate the pathogens currently being discussed in the media and study each infectious
organism’s re¬quirements for growth and reproduction. Teachers should review the dangers of
common bacteria becoming resistant to antibiotics through long-standing over-application, as shown by
the increasing incidence of drug-resistant tuberculosis and other bacteria. Using a commercially available
kit, teachers can demonstrate how antibiotics may act generally or specifically against bacteria. Agar
plates may be inoculated with different bacteria, and different antibiotic discs may be placed on these
plates to create a clear zone in which growth around the antibiotic discs is inhibited.

10. e. Students know why an individual with a compromised immune sys¬tem (for example, a
person with AIDS) may be unable to fight off and survive infections by microorganisms that are
usually benign.
When an immune system is compromised (e.g., through infection by the human immunodeficiency virus
[HIV]), it becomes either unable to recognize a dangerous antigen or incapable of mounting an
appropriate defense. This situation happens when the virus infects and destroys key cells in the immune

10. f.* Students know the roles of phagocytes, B-lymphocytes, and T-lymphocytes in the
immune system.
Phagocytes move, amoebalike, through the circulatory system, consuming waste and foreign material,
such as aged or damaged blood cells and some infectious bacteria and viruses. Two broad types of
lymphocytes (a class of white blood cells) originate in the bone marrow during embryonic life. One type
(the B-lymphocyte) matures in the bone marrow and gives rise to antibody-producing plasma cells that
are responsible for humoral immunity. Each mature B-lymphocyte can give rise to only a single type of
antibody, which itself may recognize only a single foreign antigen. The other type (the T-lymphocyte)
matures in the thymus gland during em¬bryogenesis and gives rise to “cytotoxic� (cell killing) and
“helper� T-lymphocytes. The cytotoxic T-cells are particularly useful for surveillance of intra-
cellular pathogens. Antibodies cannot reach the intracellular pathogen because of the cell mem¬brane,
but the infected cell can be identified and killed. Helper T-cells assist in organizing both the humoral and
cellular immune responses.