Passage VI

Plants produce food by photosynthesis, summarized as follows:

Light can be described by a wavelength, measured here in nanometers (nm). Each color of the rainbow has its own range of wavelengths. Plants contain cells with colored pigments that absorb various wavelengths of light. Researchers conducted 3 studies to examine the role of light's wavelengths and plant pigments on photosynthesis.

Study 1

A prism was used to shine a rainbow of colors on living algae. Bacteria that require oxygen for survival were added to the algae. Most of the bacteria were found around the region of algae exposed to red and orange light. A smaller number were found in the blue light region and a few were also found in other regions.

Study 2

The effect of different colors of light on photosynthesis was tested by exposing groups of bean plants to light of specific wavelengths. Sugar production of each group of plants was measured and used as an estimate of the rate of photosynthesis at each wavelength. Figure 1 shows the action spectrum of photosynthesis, which is the effect of light of different wavelengths on photosynthesis.

Study 3

Solutions of 3 different photosynthetic pigments, isolated from plant cells, were each exposed to light of a specific wavelength. Figure 2 shows the absorption spectrum, which is the percentage light absorbance of various wavelengths for each pigment.

Figures adapted from Claude A. Villee, Eldra P. Solomon, and P. William Davis, Biology. ©1985 by CBS College Publishing.