The inactive protoxin is activated in the gut of the insect by :

Options

A. Acidic pH
B. Alkaline pH
C. Low temperature
D. High temperature

Answer

### Step-by-Step Solution:

1. **Identify the Protoxin**: The question refers to an inactive protoxin that is activated in the gut of an insect. This protoxin is associated with the bacterium Bacillus thuringiensis (Bt).

2. **Understand the Role of Bacillus thuringiensis**: Bacillus thuringiensis is a bacterium that produces a protein known as a cryoprotein. This cryoprotein is secreted as an inactive form called protoxin.

3. **Conditions for Activation**: The activation of the protoxin occurs in the gut of the insect. It is important to note that the gut environment of insects has an alkaline pH, which is different from the acidic pH found in the human gut.

4. **Activation Process**: When the protoxin enters the insect's gut, the alkaline pH triggers a biochemical reaction that activates the protoxin, converting it into an active toxin.

5. **Effect of the Active Toxin**: The activated toxin is insecticidal and is particularly effective against certain pests, such as caterpillars. This is why Bacillus thuringiensis is commonly used in biological pest control.

6. **Conclusion**: Therefore, the inactive protoxin is activated in the gut of the insect by the alkaline pH of the gut.

### Final Answer:
The inactive protoxin is activated in the gut of the insect by the alkaline pH of the gut.

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