Which of the following is a characteristics of a bacteria except _______?

Analyze the question: The question asks for the statement that is NOT a characteristic of bacteria (the "except" option). Three options will be true of bacteria, and one will be false.

Explain the concept: Bacteria are prokaryotic, single-celled microorganisms. Key facts:

• They are microscopic, so they can only be seen under a microscope.
• They are very small, usually about 0.5 µm to 5 µm in size.
• They are classified by cell shape: cocci (spherical), bacilli (rod-shaped), spirilla (spiral), and vibrios (comma-shaped).
• Many are harmless or useful, but some are pathogens that cause diseases such as typhoid, cholera, tuberculosis and tetanus.

Step-by-step check of the options:

• A. They can be seen under a microscope. True. Bacteria are too small for the naked eye.
• B. They range from 0.5 µm in diameter. True. This is the typical lower size range of bacteria (the wording is incomplete, but it is a valid characteristic).
• C. They are grouped according to their cell shape. True. This is the basis of bacterial classification (cocci, bacilli, spirilla, vibrios).
• D. They do not cause disease. False. Many bacteria are pathogenic, for example Salmonella typhi (typhoid), Vibrio cholerae (cholera) and Mycobacterium tuberculosis (TB).

Answer: Option D is the statement that is not a characteristic of bacteria, so it is the "except" answer.

Exam tip: In "except" questions, test each option and look for the one that is false. Words like "do not", "never" and "all" are often warning signs. Here, remembering that bacteria can cause disease immediately exposes option D.