A Level Biology Practice Exam

Which of the following best describes a characteristic of Gram negative bacteria?

1. They have a thick peptidoglycan layer

2. They appear purple when stained

3. They are typically more resistant to antibiotics

4. They lack genetic material

The correct answer is: They are typically more resistant to antibiotics

The characteristic that best describes Gram-negative bacteria is their increased resistance to antibiotics. This is primarily due to their unique cell wall structure, which consists of a thin layer of peptidoglycan surrounded by an outer membrane containing lipopolysaccharides. This outer membrane acts as an additional barrier to many substances, including certain antibiotics, making Gram-negative bacteria generally more resilient to treatment. In contrast, the presence of a thick peptidoglycan layer is typical of Gram-positive bacteria, which would lead to a different staining characteristic; these bacteria appear purple when subjected to Gram staining due to the retention of the crystal violet stain. Additionally, all bacteria contain genetic material, so the claim that Gram-negative bacteria lack genetic material is incorrect.