What is spectrum?

The electromagnetic spectrum is a vast band of energy frequencies extending from radio waves to gamma waves. When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. It is represented by frequency (in Hertz) or Wave length (in meter). 

Largest and smallest cells in human body.

Cells are measure in Microns. The human ovum is typically around between 120 to 150 micro meters which is the largest cell in the human body. it is visible to the human eye under a microscope.