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BIOLOGY 250

Directions: Questions 1, 2, and 4 are short free-response questions that should
require about 5 minutes each to answer. Question 3 is a long free-response
question that should require about 20 minutes to answer. Question 5 includes
calculations that can be answered in a number grid. Read each question carefully
and write your response. Answers must be written out. Outline form is not
acceptable. It is important that you read each question completely before you begin
to write. (50 points possible)
Question 1: Exchange of Molecules (8 points)
Villi are small projections that line the inside of the small intestine. The villi are
covered in even smaller hair-like projections called microvilli, which increase the
surface area of the small intestine. The villi and microvilli function to absorb
nutrients from digested food into cells. Celiac disease is a condition in which the villi
that line the small intestine are damaged and may disappear as a result of an
adverse reaction to gluten. Predict how a reduction in the number of villi and
microvilli in the small intestine would affect the rate of absorption of nutrients. (4
points) Justify your response. (4 points)
When people with celiac disease consume gluten (a protein found in wheat, rye, and
barley), the body initiates an immune response that attacks the small intestine.
These attacks damage the villi, the little finger-like projections that surround the
small intestine, which facilitate absorption of nutrients. The villi of the intestinal tract
are protrusions of epithelial cells that significantly increase their surface area. When
the small intestine is completely smooth, there will be little chance of absorbing
nutrients. This quickly leads to nutritional deficiencies, no matter how much you eat.
What can justify this is that the function of the villi is to increase the surface area
with food to absorb nutrients.
Question