Pepsin would have the greatest activity...
a.)when the pH of the chyme is greater than 3.
b.)immediately upon entering the duodenum.
c.)immediately upon secretion into the stomach.
d.)when the pH of the chyme is less than 3.
To determine which option is correct, let's discuss the conditions that affect the activity of pepsin.
Pepsin is an enzyme that plays a crucial role in the digestion of proteins in the stomach. It is produced and secreted in an inactive form called pepsinogen by the chief cells in the stomach lining. Pepsinogen is activated into pepsin when it comes into contact with the acidic environment of the stomach, specifically when the pH is below 5.
Based on this information, we can now evaluate the options:
a.) when the pH of the chyme is greater than 3: This statement suggests a less acidic environment, which is not favorable for pepsin activity as it requires an acidic environment to be activated. Therefore, this option can be ruled out.
b.) immediately upon entering the duodenum: Pepsin is primarily active in the stomach, but its activity decreases significantly in the duodenum due to the alkaline environment caused by the release of bicarbonate ions from the pancreas. Therefore, this option is also incorrect.
c.) immediately upon secretion into the stomach: This option suggests that pepsin is most active as soon as it is secreted into the stomach. Since pepsin activation requires an acidic environment, this option aligns with the requirements for pepsin activity. It is the correct answer.
d.) when the pH of the chyme is less than 3: This option correctly mentions the acidic pH, which is necessary for pepsin activity. However, it doesn't specify where this acidic pH is located. Pepsin activity occurs primarily in the stomach, not the chyme itself. Therefore, this option is not the most accurate.
In conclusion, the correct answer is c.) immediately upon secretion into the stomach. Pepsin is most active when it is secreted into the stomach due to the acidic environment that is present there.