Ask A Scientist© Biology Archive

 
Question:  How is chlorophyll released from the chloroplasts?  Why is chlorophyll 
green?  Why do leaves on trees change color?
barnas

Answer:
I'm not sure that I understand your first question. Chlorophyll is produced within 
the chloroplast and stays in the chloroplasts to function in collecting light energy 
for the plant to use for growth.  Chlorophyll is a pigment, which means it absorbs 
visible light.  Because of its particular molecular structure, it absorbs mostly red 
and blue light.  Therefore, if you shine white light (which contains all of the colors), 
red and blue light will be absorbed and the other colors will be transmitted or 
reflected.  The colors that are left over are perceived by the human eye as green. 
Leaves on trees change colors as pigments (including chlorophyll) begin to break down.  
Leaves typically contain chlorophyll, anthocyanins (red and blue), and carotenoid 
pigments (yellow and orange).  As chlorophyll breaks down, the leaf color will reflect 
the pigments that are still present in the leaf. -Brian