Question

passage
many individuals past the age of 45 develop osteoporosis, which makes the
bones less dense and is characterized by a net loss of calcium in the bones.
although osteoporosis occurs in men, it is more common in women. several
hypotheses have been proposed to explain the onset of osteoporosis.

dietary hypothesis
calcium from food is absorbed into the bloodstream by the small intestine.
vitamin d is necessary for this process. most americans ingest too little calcium
and vitamin d in their diet. in a study of individuals 18-25 years old. it was
shown thta the majority had significantly low levels of calcium in their blood.
when these individuals received daily supplements of 1,500 mg of calcium and
400 units of vitamin d, their blood calcium levels increased to normal levels. if
insufficient levels of calcium and vitamin d are supplied by the diet, dietary
supplements should be taken to avoid osteoporosis.

estrogen hypothesis
estrogens, hormones produced primarily in the ovaries in women and, to a
much lesser degree, in the adrenal glands in both sexes, and androgens,
produced in the testes in men, are required for the deposition of calcium into
bone. androgen levels in men remain relatively constant throughout life;
estrogen levels in women slowly decline after the onset of menopause (the time
when a womans ability to reproduce ends), which usually occurs between the
ages of 45 and 55. as a result, the bones of postmenopausal women lose
calcium.
scientists compared the bone density of 4 groups of postmenopausal women.
each group took a dietary supplement. the results are shown in the table.

group supplements change in bone density
a estrogen +2.3%
b 500 mg calcium -1.0%
c estrogen + 500 mg +2.3%
calcium

1 multiple choice 3 points
to accept the evidence presented in the dietary hypothesis, one must assume
that low blood levels of calcium are indicative of:
low bone levels of calcium.
high intestinal levels of vitamin d.
high blood levels of vitamin d.
low bone levels of estrogen.

2 multiple choice 3 points
one advantage of the estrogen hypothesis is that, of the three hypotheses, it
best explains why osteoporosis is more common in which of the following
groups?
men over the age of 45 rather than in men under the age of 45
women under the age of 45 rather than in women over the age of 45
men over the age of 45 rather than in women over the age of 45
women over the age of 45 rather than in men over the age of 45

3 multiple choice 3 points
according to the estrogen hypothesis, premenopausal women who have had
their ovaries surgically removed should exhibit:
gradual reduction in vitamin d levels in their blood.
gradual loss of calcium from their bones.
increased calcium levels in their bones.
increased estrogen levels in their blood.

Explanation:

1. For question 1: The Dietary Hypothesis links low dietary calcium/vitamin D to low blood calcium, and frames this as a precursor to osteoporosis (bone calcium loss). Thus, to accept its evidence, low blood calcium must signal low bone calcium.
2. For question 2: The Estrogen Hypothesis states estrogen (made in women's ovaries) supports bone calcium deposition, and estrogen drops after menopause (ages 45-55). This directly explains why osteoporosis is more common in women over 45 than men over 45, as men's androgen levels stay constant.
3. For question 3: The Estrogen Hypothesis ties estrogen levels to bone calcium retention. Premenopausal women with surgically removed ovaries lose their main estrogen source, so their bones will gradually lose calcium, mirroring postmenopausal calcium loss.

Answer:

1. low bone levels of calcium.
2. Women over the age of 45 rather than in men over the age of 45
3. gradual loss of calcium from their bones.