Scale bar converts image measurement to actual cell size

Steps:

• Locate the scale bar on the electron micrograph, showing 1 μm equals 2 mm.
• Measure the cell's maximum length on the image as 1.34 mm.
• Calculate actual length: measured length divided by scale (1.34 mm / 2 mm per μm) = 0.67 μm.
• Confirm this as the maximum dimension.

Why B is correct:

• Scale bar formula (actual size = image size / magnification scale) directly yields 0.67 μm for the cell length.

Why the others are wrong:

• A ignores scale, treating image size as actual (5.0 μm too large).
• C misapplies half the scale factor, underestimating length.
• D reverses scale calculation, overestimating by 10x.

Final answer: B