The secretion of osteocalcin (in an inactive form) by osteoblasts is controlled by positive feedback.

Use information from Figure 1 to explain why this is positive feedback.

The acidic pH conditions created by osteoclasts cause the inactive form of the protein osteocalcin to change into the active form of osteocalcin.

Suggest how.

Binding of insulin leads to an increase in the rate of respiration in cells such as osteoblasts.

Explain how.