The secondary messenger is often:

Correct Answer: A

Rationale: cAMP is a common secondary messenger in hormone signaling pathways.

Correct Answer: A

Rationale: Juxtaglomerular cells secrete renin to regulate blood pressure and filtration.

Correct Answer: D

Rationale: The small intestine is the primary site for nutrient absorption due to its large surface area and specialized structures like villi and microvilli.

Correct Answer: A

Rationale: Chyme is the semi-fluid mass of partly digested food expelled by the stomach into the duodenum.

Correct Answer: D

Rationale: Rennin is responsible for the digestion of milk protein. Rennin is present in the human body in its inactive form called prorenin. When we consume milk, it reacts with the hydrochloric acid present in the stomach. Hydrochloric acid activates the inert prorenin and converts it into active Rennin.