Q.1
In most fishes, gastric digestion requires how much pH?
- Gastric Phase of Digestion in Fishes:
- In stomach-possessing fishes (gastric fishes), oxynticopeptic cells in the gastric mucosa secrete hydrochloric acid ($HCl$) and inactive pepsinogen.
- Hydrochloric acid lowers the gastric luminal pH to an intensely acidic range of $\le 2.0 - 4.0$ (pH 4 or less).
- This low pH is essential for two key biochemical processes:
- Denaturing quaternary and tertiary structures of ingested dietary proteins.
- Autocatalytically activating pepsinogen into active pepsin, whose optimum enzymatic activity occurs strictly at $pH \approx 1.5 - 3.0$.
- nalysis:
- (4 or less): Correct.
- Options 1 & 3: Characteristic of post-gastric intestinal digestion (pancreatic/bile neutral to alkaline $pH \approx 7.0 - 8.2$).
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