Which of the following best describes the structure labeled 'A' in a typical bacterial photomicrograph?

• A. Chloroplast
• B. Nucleus
• C. Mitochondrion
• D. Cell wall

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the context of the question, which involves identifying a labeled structure 'A' in a bacterial photomicrograph. Recall that bacteria are prokaryotic cells, meaning they lack membrane-bound organelles such as a nucleus, mitochondria, and chloroplasts.
2. Step 2: Review the characteristics of the options given: Chloroplasts and mitochondria are organelles found in eukaryotic cells, not bacteria. The nucleus is also absent in bacteria because they have a nucleoid region instead.
3. Step 3: Recognize that the bacterial cell is surrounded by a rigid structure called the cell wall, which provides shape and protection. This structure is commonly visible in photomicrographs of bacteria.
4. Step 4: Conclude that the structure labeled 'A' is best described as the cell wall, since it is a defining feature of bacterial cells and is distinguishable under the microscope.
5. Step 5: Summarize that the correct identification relies on understanding bacterial cell anatomy and the absence of eukaryotic organelles in bacteria.