wavelength: distance between adjacent waves
electromagnetic spectrum: range of types of electromagnetic energy from gamma waves to radio waves
pigment: chemical compound that determines a substance's color
paper chromatography: laboratory technique used to observe the different pigments in a material
photosystem: cluster of chlorophyll and other molecules in a thylakoid
Summary
-Sunlight is a form of electromagnetic energy
-Electromagnetic energy travels in waves that can be compared to ocean waves rolling onto a beach
-Visible light—those wavelengths that your eyes see as different colors—makes up only a small fraction of the electromagnetic spectrum
-Shorter wavelengths have more energy than longer wavelengths
-When light shines on a material that contains pigments, three things can happen to the different wavelengths: they can be absorbed, transmitted, or reflected
-The chloroplasts convert some of this absorbed light energy into chemical energy. But the chloroplast pigments do not absorb green light well
-As the solvents move up the paper strip, the pigments dissolve in the solvents and are carried up the strip
-Each photosystem contains a few hundred pigment molecules, including chlorophyll a, chlorophyll b, and carotenoids
-Each time a pigment molecule absorbs light energy, one of the pigment's electrons gains energy—the electron is raised from a low-energy "ground state" to a high-energy "excited state."
-The electron transport chain connecting the two photosystems releases energy, which the chloroplast uses to make ATP
-The second photosystem can be thought of as the "NADPH-producing photosystem."
-This photosystem produces NADPH by transferring excited electrons and hydrogen ions to NADP+.
Concept Check 8.2
1. Explain why a leaf appears green.
A leaf appears green because the green light is not absorbed. When light shines on a material that contains pigments, three things can happen to the different wavelengths: they can be absorbed, transmitted, or reflected. The chloroplasts convert some of this absorbed light energy into chemical energy. But the chloroplast pigments do not absorb green light well.
2. Describe what happens when a molecule of chlorophyll a absorbs light.
When a molecule of chlorophyll a absorbs light, the molecule excited due to the light energy and transfers the light to another molecule.
3. Besides oxygen, what two molecules are produced by the light reactions?
Besides oxygen, hydrogen ions and NADPH is released.
Besides oxygen, hydrogen ions and NADPH is released.
4. Where in the chloroplast do the light reactions take place?
Light reactions take place in the thylakiod membrane in the chloroplast.
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