Animal Physiology

Step 1: Understanding the secretion of pepsinogen.
Pepsinogen is secreted as an inactive proenzyme from the chief cells in the gastric mucosa. It is converted into active pepsin upon exposure to hydrochloric acid (HCl) secreted by the oxyntic cells.

Step 2: Analyzing the options.
(A) P - chief cells, Q - hydrochloric acid, R - oxyntic cells: Correct — Pepsinogen is secreted by the chief cells and is activated by hydrochloric acid produced by the oxyntic cells.
(B) P - parietal cells, Q - enterokinase, R - chief cells: Incorrect — Parietal cells secrete HCl, not pepsinogen, and enterokinase is not involved in this process.
(C) P - oxynitic cells, Q - hydrochloric acid, R - parietal cells: Incorrect — Oxyntic cells produce HCl, not pepsinogen.
(D) P - peptic cells, Q - gastrin, R - oxyntic cells: Incorrect — Peptic cells do not secrete pepsinogen directly, and gastrin is not directly involved in the activation of pepsinogen.

Step 3: Conclusion.
The correct answer is (A) P - chief cells, Q - hydrochloric acid, R - oxyntic cells, as it describes the correct mechanism of pepsinogen activation.

Step 1: Understanding testis temperature regulation.
The testis needs to be kept at a temperature lower than the core body temperature for optimal sperm production. This is achieved by the scrotum, which hangs outside the body to provide a cooler environment.

Step 2: Analyzing the options.
(A) proximal tubule: Incorrect — The proximal tubule is part of the kidney, not involved in regulating testis temperature.
(B) loop of Henle: Incorrect — The loop of Henle is involved in kidney function, not temperature regulation of the testis.
(C) scrotum: Correct — The scrotum holds the testes outside the body, which helps in maintaining a lower temperature.
(D) seminal vesicles: Incorrect — Seminal vesicles produce seminal fluid, not involved in temperature regulation of the testes.

Step 3: Conclusion.
The correct answer is (C) scrotum.