Recognise cell-theory statements and calculate sizes from magnification or scale bars.
Method and worked examples
Cell theory states that organisms consist of cells, cells are the basic structural and functional units of life, and new cells arise from existing cells. Cells contain hereditary material and exchange matter with their surroundings. A single characteristic such as movement is not enough to identify something as living: a moving car is not cellular.
Magnification equals image size divided by actual size, using the same units. One millimetre equals 1000 micrometres. A scale bar stays proportional when an image is resized, whereas a printed magnification label may become inaccurate. Resolution means distinguishing close points; enlarging a blurred image does not reveal additional structures.
Example 1
A cell is 20μm long. Its image is 10mm long. Find magnification.
Convert 10mm to 10000μm. Magnification =1020000=500×.
Example 2
A 2μm scale bar measures 8mm; a bacterium measures 12mm. Find its length.
Length =(812)×2=3μm. Both image measurements use the same units.
Watch out:Magnification enlarges the image; resolution determines which separate structures can be distinguished.
Cell theory and microscopic scale | Year 11 Biology | Ascent Arcade