Final answer:
Chief cells in the stomach secrete pepsinogen, which is converted to pepsin in the presence of HCl produced by parietal cells. The correct option is 1) Pepsin.
Step-by-step explanation:
Partial cells, more accurately referred to as chief cells, are primarily located in the basal regions of gastric glands and are responsible for secreting pepsinogen. Pepsinogen is the inactive proenzyme form of pepsin, an enzyme vital to the digestion of proteins.
The conversion of pepsinogen into its active form, pepsin, requires the presence of hydrochloric acid (HCl), which is produced by another class of cells known as parietal cells.
These parietal cells are highly differentiated epithelial cells found mainly in the middle region of the gastric glands and they not only produce HCl but also intrinsic factor, which is vital for the absorption of vitamin B12 in the small intestine.