Approximately what size range do most microorganisms that live on and in the human body fall into?

• A. 1–10 millimeters
• B. 0.1–1 centimeters
• C. 0.2–10 micrometers
• D. 20–100 nanometers

Answer: (C)

Verified step by step guidance

1. Understand the units of measurement used to describe microorganism sizes: millimeters (mm), centimeters (cm), micrometers (\( \mu m \)), and nanometers (nm). Recall that 1 mm = 1000 \( \mu m \), 1 cm = 10 mm, and 1 \( \mu m \) = 1000 nm.
2. Recognize that most microorganisms living on and in the human body are microscopic and typically measured in micrometers (\( \mu m \)), which is a unit suitable for bacteria, fungi, and protozoa.
3. Recall typical size ranges for common microorganisms: bacteria usually range from about 0.2 to 10 micrometers, while viruses are smaller, often measured in nanometers (20–100 nm). Larger organisms like parasites or human cells are measured in micrometers to millimeters.
4. Compare the given options with these typical size ranges: 1–10 millimeters and 0.1–1 centimeters are too large for most microorganisms; 20–100 nanometers is typical for viruses but not for most microorganisms living on/in humans; 0.2–10 micrometers fits the size range of most bacteria and other microorganisms.
5. Conclude that the size range 0.2–10 micrometers is the most appropriate for most microorganisms living on and in the human body.