Contrary to their appearance, polar bears are not white. These arctic dwellers actually have black skin, and the peculiar composition of their guard hairs is responsible for their white appearance. The hair of mammals, including polar bears, is composed of keratin and has a three-layer structure. The outermost layer, the cuticle, is composed of translucent overlapping scales. Below the cuticle is the cortex, which contains bundles of keratin, air spaces, and the pigments that provide the color of the hair. The innermost layer, the medulla, is a structured open space filled with air. This final layer, which is found only in some mammals, is particularly well developed in polar bears. Since the cuticle is translucent, the cortex is devoid of pigment, and the medulla is a wide air space, polar bear hair is translucent. Light enters the hair and is trapped in the medulla, striking tiny light-scattering particles within it, rather than being absorbed by the bear's skin. This scattering of the light waves causes luminescence—an emission of light across the visible spectrum—and makes the polar bear appear white.

1. In the passage, the author is primarily concerned with

A. analyzing a pattern of reasoning
B. arguing against a traditional belief
C. providing an explanation for a phenomenon
D. persuading the reader to adopt a point of view
E. showing how new information has revised a previous view


2. Which of the following can be inferred from the passage regarding the composition and characteristics of polar bear hair

I. At least one characteristic of polar bear hair is not widely shared with other mammals.
II. The white pigmentation of polar bear hair is located in keratin bundles that reside in the cortex.
III. The interaction of the structure of hair and light makes the nearly clear hair of the polar bear appear white.

A. I Only
B. III Only
C. I and III Only
D. II and III Only
E. I, II, and III


3. According to the passage, each of the following is true EXCEPT:

A. The cortex of polar bear hair is composed of overlapping scales of keratin.
B. The cuticle of polar bear hair is located above the cortex and the medulla.
C. The guard hairs of the polar bear are composed of three layers.
D. The major component of polar bear hair is keratin.
E. The structure of the medulla is responsible for the polar bear's white appearance.