Systems II Writing Practice
1. The human immunodeficiency virus (HIV) that causes AIDS (acquired immunodeficiency
syndrome) attacks helper-T cells. In three or four sentences, explain why this makes it difficult for
the immune system to defend against the HIV. (2 pts)
The helper T cells have multiple jobs. First, they recognize foreign antigens on antigen presenting cells
(either an infected cell, or a macrophage that has phagocytized a pathogen.) Then, after copying itself a
number of times, it will activate both B- cells of the humoral response and Killer T-cells of the cell
mediated response. With low numbers of functional Helper T cells, as is the case in HIV, it is difficult for
the other cells of the immune system to mount a defense against the virus.
2. Humans live in a sea of germs protected by three lines of defense.
a. Describe the three lines of defense and how each protects us. (6 pts)
b. Compare and Contrast the role of T and B cells. (4 pts)
1st
Line
2nd Line
3rd Line



Description
Barriers, skin mucous
membranes, cilia, tears, sweat,
unfavorable pH
 Neutrophils,
macrophages, NK cells.
 Inflammatory response,
fever response
B-Cells & T-Cells
T-Cells
Originates from stem cells in bone marrow
mature in the Thymus
Located in lymph, lymph nodes and blood
Responsible for destroying infected cells
(killer T cells) and staying in reserve for
future infection (Memory T Cells)



Function
Prevents pathogens from
entering the body

Non-specific patrolling
cells that engulf/ induce
apoptosis in invading
cells.
 General response that aids
in WBC function.
Defense against specific
pathogens. Humoral response
neutralizes pathogens in blood
and lymph. Cell mediated
response destroys infected cells.
B-Cells
Originates and matures in the bone marrow
Located in lymph, lymph nodes, and blood
Responsible for neutralizing pathogens in
body fluids by secreting antibodies (effector
cells) and staying in reserve for future
infection (memory B cells.)
3. Andrea was telling her friend Jason why she had not been able to make it to biology class for
several days. “My throat has been so sore I could hardly swallow,” she croaked. “And the glands in
my neck are really sore and swollen.” Jason said, “We have been talking about this in class. They
are not really ‘glands,’ you know, and the reason they are sore is…” Complete Jason’s explanation.
They are lymph nodes. Lymph carries the microbes responsible for your sore throat to the lymph nodes,
where T and B lymphocytes are activated. Activated B cells proliferate and produce antibodies that are
carried by body fluids to sites of infection. T cells also travel to sites of infection. The rapid production of
lymphocytes makes your lymph nodes swollen and sore.
Circulatory
1. Using the following symbols, contrast single circuit and double circuit circulation pathways: (Your
goal is not to draw an anatomically-correct model, but a model of flow).
a. Triangle = lungs/gills
b. Circle = heart; draw lines to show chambers
c. Solid line = oxygenated blood
d. Dotted line = deoxygenated blood
i. Use a double-line to indicate high pressure flow; single line to indicate low-pressure
flow
e. Square = body tissue
f. On each line, do the following:
i. Place arrows to indicate direction of flow
ii. Place dots on the line to indicate location of valves