Chapter 8.2, Problem 7MI

Summary Introduction

To analyze:

The change in color of leaves in the fall.

Introduction:

A colored molecule that absorbs light is called a pigment. Pigments are present in the membranes of thylakoids of chloroplasts. Pigments differ in their ability to absorb specific wavelengths of light. Most important light absorbing pigment is chlorophyll. There are many types of chlorophyll but two most common ones are chlorophyll a and chlorophyll b.

Answer to Problem 7MI

In the fall season, trees stop producing chlorophyll in their leaves. Other pigments become visible giving leaves wide variety of colors such as red, yellow and purple.

Explanation of Solution

Chlorophylls absorb mostly in the violet blue region of the visible light spectrum and reflect green light. That is why chlorophyll containing parts of plants appear green in color.

Besides chlorophyll there are other pigments called accessory pigments that trap additional light energy from other areas of visible spectrum. Carotenoid such as beta- carotene is an accessory pigment that reflects light in red, yellow and orange regions.

Chlorophyll is the most abundant pigment in the leaves and so it hides the effect of other pigments. However in autumn, in certain parts of United States, leaves display a myriad of colors like red, yellow, orange and purple. As trees prepare to lose their leaves before winter, the chlorophyll molecules break down and leaves stop producing more chlorophyll, thereby revealing the colors of other pigments.