Which of the following structures is only found in some, but not all, bacterial species?

• A. Flagella
• B. Ribosomes
• C. Cell membrane
• D. Cytoplasm

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the basic structures common to all bacterial cells. These include ribosomes, the cell membrane, and cytoplasm, which are essential for fundamental cellular functions such as protein synthesis, maintaining cell integrity, and metabolic processes.
2. Step 2: Recognize that flagella are appendages used for motility, allowing bacteria to move in their environment. However, not all bacteria possess flagella; some are non-motile and lack this structure.
3. Step 3: Compare each option to determine which is universally present in bacteria and which is variable. Ribosomes, cell membrane, and cytoplasm are found in all bacteria, while flagella are only present in some species.
4. Step 4: Conclude that the structure only found in some bacterial species, but not all, is the flagella, as it is a specialized feature for movement rather than a fundamental cellular component.
5. Step 5: Summarize that the presence or absence of flagella can be used to differentiate bacterial species based on their motility capabilities.