Final answer:
A spectrophotometer is the instrument that measures the absorbance of light at a specific wavelength, useful in determining the absorption spectra of photosynthetic pigments in plants.
Step-by-step explanation:
The instrument that measures the absorbance of light at a specific wavelength is a spectrophotometer. A spectrophotometer works by shining light through a sample and determining the amount of light absorbed at a particular wavelength. It is essential in research such as analyzing photosynthetic organisms, where scientists may use a spectrophotometer to generate absorption spectra for different pigments extracted from leaves. This allows scientists to identify which wavelengths of light the organism can absorb. Other methods, such as various types of chromatography, are used to separate the pigments based on their relative affinities to solid and mobile phases, but do not directly measure light absorbance.