B. thuringiensis form protein crystal at which phase of their life?

Options

A. Reproductive phase
B. Growth phase
C. Senescent phase
D. Embryonic phase

Answer

**Step-by-Step Solution:**

1. **Understanding Bacillus thuringiensis (Bt)**: Bacillus thuringiensis is a bacterium known for its ability to produce protein crystals that are toxic to certain insects. These protein crystals are referred to as Bt toxin.

2. **Identifying the Life Cycle Phases**: The life cycle of Bacillus thuringiensis includes several phases: growth phase, reproductive phase, senescent phase, and embryonic phase. We need to determine in which of these phases the protein crystals are formed.

3. **Focusing on the Growth Phase**: The formation of Bt toxin protein crystals occurs specifically during the growth phase of Bacillus thuringiensis. This is the phase when the bacterium is actively multiplying and preparing for sporulation.

4. **Sporulation Process**: During the growth phase, Bacillus thuringiensis undergoes sporulation, which is a process of forming spores. It is during this sporulation that the bacterium produces the protein crystals.

5. **Inactive Form of Toxin**: The protein crystals exist in an inactive form (protoxin) until they are ingested by an insect. Once ingested, the crystals become active and toxic to the insect.

6. **Conclusion**: Based on the information gathered, the correct answer to the question of when Bacillus thuringiensis forms protein crystals is during the growth phase.

**Final Answer**: Bacillus thuringiensis forms protein crystals during the growth phase.

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