Final answer:
During the hour that the blood sample is in the glass tube, it undergoes changes such as clotting and forming serum.
Step-by-step explanation:
In the context of this question, the subject is Biology. When a blood sample is collected in a glass tube, it undergoes certain changes during the hour it is in the tube. Over time, the blood clots and forms a gel-like substance called serum. After this hour, the serum can be separated from the blood cells through a process called centrifugation