From Seed to Seed:
Sunlight is made up of all the colors of light-shown by the colors in a rainbow-and each of these colors has a different wavelength. When light hits a surface, it can be reflected, transmitted, or absorbed. The color that we see when we look at an object is the color of the wavelength that is being reflected. For example, an object that appears white is reflecting all wavelengths, whereas an object that appears black is absorbing all wavelengths and reflecting none. It is logical to conclude, then, that a leaf appears green because it is reflecting green and absorbing all other colors.
The green pigment chlorophyll is contained in the cell's chloroplasts and is responsible for absorbing light from the sun. When chlorophyll is exposed to light, it is bombarded by photons. When an individual chlorophyll molecule absorbs a photon, the energy of that photon pushes the outermost electron-a negatively charged subatomic particle-to a new, larger orbit. When this happens, the molecule is said to be in an "excited," or energized, state. The molecule has acquired the energy of the photon.
This is only the very beginning of the process. The chlorophyll molecule
does not remain in the excited state for very long-only for about one
thousand-millionth of a second! But this is enough time to trigger a series
of reactions in which this outer electron is transferred from one chlorophyll
molecule to another in a process called electron transfer. Eventually,
the electron reaches a collection center, known as the "reaction center."
By doing this, the chlorophyll is, essentially, "harvesting" the sun's
The plant may then take these simple sugars and combine them into long
chains, forming the large molecules of starch and cellulose. Plants store
food in the form of starch, and cellulose is incorporated into the structure
of cell walls.
Made possible by a grant from Oracle Corp.
Copyright 2001, National Gardening
For questions regarding this web site, contact Webmaster