Concept 8.2- Summary and Concept Check.
The light reactions convert light energy to chemical energy.- Sunlight is a form of electromagnetic energy, which travels in waves.
-A wavelength is the distance between two adjacent waves.
-Range of types of electro magnetic energy is called an electromagnetic spectrum.
-Visible light is only a very small fraction of the electromagnetic spectrum. (approximately 400 nanometers, violet to about 700 nm red)
-Short wavelengths have more energy than longer wavelengths.
-Wavelengths are shorter than those of visible light to have energy to damage organic molecules like protein and nucleic acids.
Example) Ultraviolet Light (UV) is harmful to your skin made of protein.
Pigments and Color:
-substance's color is due to chemical compounds called pigments.
-Three things can happen to wavelengths:
1) they can be absorbed
2) they can be transmitted.
3) they can be reflected.
- leaf's chloroplasts absorb blue-violet and red-orange light very well, and they convert some absorbed light energy into chemical energy.
-Leaves look green for chloroplasts do not absorb green light well, and green light passes through the leaf.
You can easily observe the pigments in a green leaf by using a laboratory technique called paper chromatography:
Step One: press the leaf onto strip of filter paper to deposit a "stain"
Step Two: Seal the paper in a cylinder containing solvents.
Step Three: As the solvents move up the paper strip, the pigments dissolve in the solvents carried up the trip
Step Four: Examine the speed of which the travel up the paper and how strongly they are attracted to the paper, to examine which color is which.
-Photosystems: Chlorophyll and other molecules are arranged in it.
- Each photosystem contains few hundred pigment molecules. (chlorophyll a, chlorophyll b, and carotenoids)
- Each time a pigment absorbs energy, one of the pigment's electrons gain energy, and low energy is boosted up into high- energy.
-This electron transfer excites an electron in receiving a molecule, and the electron falls back to the ground state (low energy) and transfers the energy to another molecule that is next to it.
- Two photosystems are involved with light reactions.
-The first photosystem traps light energy and transfers the light- excited (high with energy) to an electron transport chain.
*This process is thought of as the "water-splitting photosystem" because the electrons are replaced by splitting of a molecule of water, and releases water as a waste product.
- Electron Transport chain connects the two photosystems together and releases energy, and the chloroplast use this energy to create ATP.
- The second photosystem is thought of as the "NADPH-producing photosystem" because the photosystem produces NADPH by transferring excited electrons and hydrogen ions to NADP+.
- Light reactions convert light energy to the chemical energy of ATP and NADPH.
Concept Check 8.2-
1) Explain why a leaf appears green.
A leaf appears green because the pigments in the leaf do not absorb green light, and it reflects/transmits green light from the leaf.
2) Describe what happens when a molecule of chlorophyll a absorbs light?
When chlorophyll a absorbs light, it mainly absorbs blue-violet, and red light and reflects green light.
3) Besides oxygen, what two molecules are produced by the light reactions?
Besides oxygen, NADPH and ATP are molecules produced by the light reactions.
4) Where in the chloroplasts do the light reactions take place?
In the Thylakoid membranes (located surrounding the interior place) is where the chloroplasts' light reactions take place.
Key Terms 8.2-
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 its food at the expense of a host organism.
Photosystem: Cluster of chlorophyll and other molecules in a thylakoid.
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