Final answer:
Spectrophotometry is the technique that uses the relative transmission and/or absorption of portions of the light spectrum. It is used to measure the amount of light absorbed or transmitted by a substance as a function of wavelength.
Step-by-step explanation:
The relative transmission and/or absorption of portions of the light spectrum are the basis for spectrophotometry. Spectrophotometry is a technique used to measure the amount of light absorbed or transmitted by a substance as a function of wavelength. It is commonly used in biology and chemistry to determine the presence and concentration of substances in a sample.