What are Gram-Negative bacteria?

Options

A. three layers
B. two layers
C. four layers
D. one layer

Answer

**Step-by-Step Solution:**

1. **Definition of Gram-Negative Bacteria**: Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining procedure. This characteristic is used to differentiate them from Gram-positive bacteria.

2. **Structure of Gram-Negative Bacteria**: Gram-negative bacteria have a complex cell structure that includes three main layers:
- **Cytoplasmic Membrane**: This is the innermost layer that surrounds the cytoplasm of the bacterial cell.
- **Cell Wall**: The cell wall is located outside the cytoplasmic membrane. In Gram-negative bacteria, this wall is relatively thin and is primarily composed of peptidoglycan.
- **Outer Membrane**: This is an additional layer found outside the cell wall. The outer membrane is unique to Gram-negative bacteria and is composed of lipopolysaccharides (LPS) on the outer side and phospholipids on the inner side.

3. **Comparison with Gram-Positive Bacteria**: Unlike Gram-negative bacteria, Gram-positive bacteria have a thicker cell wall made of peptidoglycan and do not possess an outer membrane. This structural difference is crucial for the classification of bacteria.

4. **Conclusion**: In summary, Gram-negative bacteria have three distinct layers: the cytoplasmic membrane, a thin cell wall, and an outer membrane. Therefore, they are characterized by having three layers in their structure.

**Final Answer**: Gram-negative bacteria have three layers: the cytoplasmic membrane, a thin cell wall, and an outer membrane.

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