Final answer:
Cortisol is the molecule that would be expected to increase in the blood sample taken after an 8-hour sleep.
Step-by-step explanation:
Upon awakening after an 8-hour sleep, the molecule you would expect to see increased in the blood sample is cortisol. Cortisol is a stress hormone that is released during sleep and reaches its peak concentration in the morning. It is associated with the body's natural wake-up process and helps regulate various physiological processes.