In 1883, theodor engelmann devised an experiment to find out which wavelengths of light were most used by photosynthetic organisms. he placed a strip of algae on a microscope slide, and then projected a spectrum of light on the slide. a suspension of oxygen-loving" bacteria was also placed on the slide. based on an understanding of the light reactions of photosynthesis, predict the most likely outcome of the experiment."

Oxygen loving bacteria are accumulated only in two areas in the slide, at its ends, areas rich in oxygen

Explanation:

A prism decomposed the light in different wavelengths between 400 and 700 nm.  Plants only absorbed some wavelenghts, one that peaks at about 440nm and the other around the 660 nm, as their particular Chlorophyls used to work.

Electrons from a reaction center from a photosystem (PSII) containing a particular chlorophyl , are launched to higher levels of energy when this is excited by light wavelength (680 nm) and travel by a molecular chain to an acceptor of electrons, forming ATP.  To refill the electrons in the reaction center, H2O is hydrolyzed, and their e- reach the reaction center.  In this step O2 is also produced.

A second photosystem (PSI) is also excited from another similar reaction center, whose electrons are used to produce reducing power in the form of NADPH.  This photosystem I also acts as acceptor of the electrons coming from PSII