The bacterial cell made competent to absorb the plasmid DNA by treating with a specific concentration of

Options

A. Calcium
B. Chloride
C. Zinc
D. Ethidium bromide

Answer

To answer the question regarding the bacterial cell made competent to absorb plasmid DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Competence**: Competence refers to the ability of a bacterial cell to take up foreign DNA, such as plasmid DNA, from its environment.

2. **Role of Calcium**: The process of making bacterial cells competent typically involves treating them with calcium ions. Calcium ions help to destabilize the cell membrane, making it more permeable to DNA.

3. **Specific Concentration**: The question asks for a specific concentration of a substance that facilitates this competence. The most commonly used substance for this purpose is calcium chloride (CaCl2).

4. **Mechanism of DNA Uptake**: When bacterial cells are treated with calcium chloride, they are often subjected to a heat shock procedure. This involves placing the cells on ice, then exposing them to a brief period of heat (usually around 42°C), and then returning them to ice. This heat shock creates a thermal imbalance that encourages the uptake of DNA.

5. **Final Answer**: Based on the above steps, the correct answer to the question is that bacterial cells are made competent to absorb plasmid DNA by treating them with a specific concentration of **calcium chloride** (Option B).