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Biology Question 109 – NEET-UG 2024

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Given below are two statements: Statement I : Bt toxins are insect group specific and coded by a gene cry IAc. Statement II : Bt toxin exists as inactive protoxin in B. thuringiensis. However, after ingestion by the insect the inactive protoxin gets converted into active form due to acidic pH of the insect gut. In the light of the above statements, choose the correct answer from the options given below:

Recall the basic characteristics and mechanism of action of Bt toxins produced by Bacillus thuringiensis.

Step 1: Evaluate Statement I✦ Active

Statement I claims that Bt toxins are insect group specific and coded by cry genes (e.g., cry IAc). This is a correct biological fact. Different cry genes produce toxins that are specific to different groups of insects, such as lepidopterans, coleopterans, and dipterans.

Step 2: Evaluate Statement II○ Expand

Statement II states that Bt toxin exists as an inactive protoxin in B. thuringiensis and is converted to an active form due to acidic pH in the insect gut. While it is true that Bt toxin is produced as an inactive protoxin and activated in the insect gut, the activation occurs under **alkaline pH** conditions, not acidic pH. The alkaline environment solubilizes the crystalline protoxin, which is then cleaved by proteases to release the active toxin.

💡 Teacher's Secret Hint

Remember that the insect gut environment is crucial for Bt toxin activation. The pH condition is a key detail.

Step 3: Determine the Correct Option○ Expand

Based on the evaluation, Statement I is true, and Statement II is false. Therefore, the option that correctly reflects this is 'Statement I is true but Statement II is false'.

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