Exercise and Bone Tissue
During long space missions, astronauts can lose approximately 1 to 2 percent of their bone mass per month. This loss of bone mass is thought to be caused by the lack of mechanical stress on astronauts’ bones due to the low gravitational forces in space. Lack of mechanical stress causes bones to lose mineral salts and collagen fibers, and thus strength. Similarly, mechanical stress stimulates the deposition of mineral salts and collagen fibers. The internal and external structure of a bone will change as stress increases or decreases so that the bone is an ideal size and weight for the amount of activity it endures. That is why people who exercise regularly have thicker bones than people who are more sedentary. It is also why a broken bone in a cast atrophies while its contralateral mate maintains its concentration of mineral salts and collagen fibers. The bones undergo remodeling as a result of forces (or lack of forces) placed on them.
Q. What does the author say about bones?
A is correct because the final sentence states that bones experience “remodeling” or “changes” based on the “forces or lack of forces” – which is also referred to as mechanical stress in the paragraph – put on them. For this question and answer, it is necessary to read most of the passage because the keyword “bones” from the question is mentioned several times throughout. Since the keywords in option a are spaced out throughout the paragraph also, it might be necessary to go on to options b,c, and d and eliminate incorrect choices first. Option b has some keywords that help us located the sentence quickly – “1-2 percent” and “mass” – but the answer does not match what is written in the paragraph. For, it says “astronauts can lose 1- 2 percent…per month,” not that they do every month. Options c and d are untrue; the actual facts can be found by searching for the keywords “size”, “weight” and “thicker”.