Which of the following is correct pairing site of action and substrate of rennin?

Options

A. Oral cavity - starch
B. Ileum - protein
C. Stomach - casein
D. Cuecum - cellulose

Answer

To solve the question regarding the correct pairing of the site of action and substrate of rennin, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of Rennin**: Rennin, also known as chymosin, is a proteolytic enzyme that plays a crucial role in the digestion of milk, particularly in infants.

2. **Identify the Source of Rennin**: Rennin is secreted by the chief cells located in the stomach. This is important as it tells us where the enzyme acts.

3. **Determine the Substrate of Rennin**: The primary substrate for rennin is casein, which is a protein found in milk. Casein is the main protein that needs to be digested when infants consume milk.

4. **Evaluate the Options**:
- **Option A**: Oral cavity, starch - Incorrect, as starch is not the substrate for rennin.
- **Option B**: Stomach, protein - This is vague; while rennin acts in the stomach on proteins, it specifically targets casein.
- **Option C**: Stomach, casein - Correct, as rennin acts in the stomach on casein.
- **Option D**: K-comb cellulose - Incorrect, as cellulose is not a substrate for rennin.

5. **Conclusion**: The correct pairing of the site of action and substrate of rennin is **Option C: Stomach, casein**.

### Final Answer:
The correct pairing site of action and substrate of rennin is **Stomach, casein**.