Why are plants green?

Chlorophyll is the pigment responsible for making plants green and it is found in the chloroplasts of plant cells. It is responsible for capturing light energy from the Sun and using it to drive photosynthesis in the chloroplast.

The Science Department recently purchased a spectrophotometer which allows students to expose samples of solutions to many different wavelengths of light and then measure how much of the light a solution absorbs.

In order to utilise the spectrophotometer, the Gr 12 Higher Level Biology class recently asked the question: "Does the chlorophyll from different plants show similar absorbance spectra?"

To answer this question they extracted the chlorophyll from diffent green leaves and exposed the chlorophyll solution to different wavelengths of light using the spectrophotometer.

The results of their experiment are shown in the graph below. Each line represents the absorbance spectrum of one type of chlorophyll. As it shows, the chlorophyll samples all showed peaks of absorbance at wavelengths in the blue and red areas of the visible spectrum. The difference in height of the peaks is due to the different concentrations of chlorophyll in each sample. The low level of absorbance in the green area explains why plants are green - they absorb red and blue light but reflect green light!