Final answer:
Basal phosphorylation of the insulin receptor is the phosphorylation that happens under normal physiological conditions without external insulin, necessary for maintaining receptor readiness.
Step-by-step explanation:
The basal phosphorylation of the insulin receptor refers to the phosphorylation that occurs under physiological conditions without the addition of exogenous insulin. It represents a regulatory background activity of the receptor that maintains a certain level of responsiveness and readiness for when insulin is present. In contrast, the phosphorylation that occurs in the presence of high insulin levels or due to exogenous insulin-induced phosphorylation tends to be above the basal level and leads to further downstream effects such as the translocation of the Glut4 transporter to the plasma membrane and increased glucose uptake. The latter processes are critical for lowering blood glucose levels and are important in the context of insulin resistance and diabetes mellitus type 2 where the phosphorylation activity of the insulin receptor may be impaired.