Question

a single red blood cell has an average diameter of $7.5 \times 10^{-6}$ meters. which two units of measurement are most appropriate to use when discussing this size? \\(\circ\\) millimeters and centimeters \\(\circ\\) micrometers and nanometers \\(\circ\\) kilometers and meters \\(\circ\\) liters and grams

Explanation:

Step1: Recall unit conversions

We know that \(1\) meter \( = 10^{3}\) millimeters \( = 10^{2}\) centimeters \( = 10^{6}\) micrometers \( = 10^{9}\) nanometers, and \(1\) kilometer \( = 10^{3}\) meters. Also, liters are for volume and grams for mass, so option with liters and grams is invalid.

Step2: Analyze the given diameter

The diameter of red blood cell is \(7.5\times 10^{- 6}\) meters. Let's convert it to other units:

• To micrometers: Since \(1\) meter \(=10^{6}\) micrometers, then \(7.5\times 10^{-6}\) meters \(=7.5\times 10^{-6}\times10^{6}\) micrometers \( = 7.5\) micrometers.
• To nanometers: Since \(1\) meter \( = 10^{9}\) nanometers, then \(7.5\times 10^{-6}\) meters \(=7.5\times 10^{-6}\times10^{9}\) nanometers \(=7.5\times 10^{3}\) nanometers \( = 7500\) nanometers.
• For millimeters: \(1\) meter \( = 10^{3}\) millimeters, so \(7.5\times 10^{-6}\) meters \(=7.5\times 10^{-6}\times10^{3}\) millimeters \(=7.5\times 10^{-3}\) millimeters (very small, not appropriate as primary for this size).
• For kilometers: \(1\) kilometer \( = 10^{3}\) meters, so \(7.5\times 10^{-6}\) meters \(=7.5\times 10^{-9}\) kilometers (extremely small, not appropriate).

So the units micrometers and nanometers are appropriate as the diameter is around micrometer range and can also be expressed in nanometers.

Answer:

B. Micrometers and nanometers