Final answer:
Roger's regular weight-lifting likely results in bones with a higher mineral content, more active osteoblasts, and less osteolysis compared to his sedentary brother Steven. Weight lifting and other physical activities stimulate bone remodeling and the deposition of minerals like hydroxyapatite, which strengthen bones.
Step-by-step explanation:
The skeletal differences between Roger, who has been lifting weights seriously for years, and his twin brother Steven, who does not exercise regularly, could likely involve several factors related to bone remodeling, a process that strengthens and reshapes bones in response to physical stress. One reasonable hypothesis would be that Roger's osteoblasts are more active than Steven's. Osteoblasts are the cells responsible for building new bone tissue, and their activity is typically increased in response to the mechanical stress of weight lifting. Hence, one would expect Roger's skeleton to be denser and more robust than Steven's.
Additionally, it would not be unreasonable to hypothesize that Roger undergoes less osteolysis than Steven. Osteolysis is the breakdown of bone tissue by osteoclasts, and it is balanced by the work of osteoblasts in healthy, active individuals. Since Roger is more physically active, his bone remodeling should favor bone formation over breakdown. Furthermore, Roger's bones are likely to contain a higher combination of hydroxyapatite, a calcium phosphate mineral that is essential for bone strength and density since physical activity promotes more calcium deposition in bones to support the physical load.
Comparatively, misconceptions like those suggested in options a, b, and d are not supported by our understanding of bone physiology. A right-handed pitcher will not necessarily have thicker bones in one arm, but rather they may have denser bones due to repetitive use. A right-handed cyclist will not necessarily have thicker bones in one leg over the other. A broken bone can heal to be stronger at the fracture site due to bone remodeling, but it does not generally result in overall thicker bones. A bed-ridden patient typically experiences bone density loss, leading to thinner, not thicker, bones compared to an athlete.
In the context of skeletal muscle and smooth muscle differences with a sedentary lifestyle, skeletal muscles will atrophy due to disuse, while smooth muscles (which are not under voluntary control and are part of systems such as the digestive and cardiovascular systems) maintain their function and hence do not atrophy in the same way. Bone flexibility, strength, and mass will dramatically decrease without calcium and collagen, and while adding calcium back to decalcified bones may improve some aspects of strength and rigidity, without collagen, the bones may still be more brittle than normal.