Final answer:
In microgravity, osteocytes increase their rate of bone resorption, and the osteoblasts decrease their activity on bone formation, leading to potential bone density loss in astronauts.
Step-by-step explanation:
In microgravity environments, such as those experienced by astronauts, the body experiences physiological changes due to the lack of gravitational stress on the skeletal system. Osteocytes are cells that signal the remodeling process of bones by regulating mineral homeostasis. Typically, they help direct the uptake of minerals from the blood and release minerals into the blood as needed. However, in microgravity, the osteocytes increase their rate of bone resorption. On the other hand, osteoblasts, which are responsible for bone formation and mineralization, have a decreased level of activity in bone formation in these conditions, leading to a loss of bone density over time. This is a significant issue for long-duration space flight and requires countermeasures such as exercise and possibly medication to mitigate bone loss.
So, in answer to the student's question: In microgravity, osteocytes increase their rate of bone resorption while the osteoblasts decrease on the bone formation. Thus, the correct option is b) Increase; decrease.