A student uses a light microscope fitted with a camera to take photomicrographs of two different specialised cells: a root hair cell from a growing root tip, and a human sperm cell. (a) The actual length of the root hair cell is 0.8 mm. In its photomicrograph, this cell has been…

IGCSE Biology 0610: Magnification, Image Size and Converting mm to Micrometres

The magnification formula can be rearranged to find an image size when the actual size and the magnification are both known:

image size = actual size × magnification

For the root hair cell, the actual length is 0.8 mm and the magnification of the photomicrograph is ×60:

0.8 mm × 60 = 48 mm

So the length of the root hair cell in the photomicrograph is 48 mm.

The magnification formula is:

magnification = image size ÷ actual size

Both lengths for the sperm cell are already given in millimetres, so they can be divided directly:

image size = 9 mm actual size = 0.06 mm

9 mm ÷ 0.06 mm = 150

So the magnification of the second photomicrograph is ×150.

There are 1000 micrometres (μm) in every millimetre (mm), so to convert from mm to μm, multiply by 1000:

0.8 mm × 1000 = 800 μm

So the actual length of the root hair cell is 800 μm.