Summary 8.2

The light reactions convert light energy to chemical energy

-sunlight is electromagnetic energy
-travels in waves, can be compared to ocean waves
-distance between waves is wavelength
-short wavelengths to long wavelengths
-electromagnetic spectrum shows the different kinds of electromagnetic waves
-visible light is only small fraction
-visible light is around 400 nanometers to 700 nanometers
-wavelengths shorter damage proteins and nucleic acids
-UV can cause skin cancer
-pigments give color to an object
-light can be transmitted, reflected or absorbed
-pigments in leaf absorb blue-violet and red-orange
-giving off green light
-paper chromatography, can see pigments of leaf
-press leaf onto filter paper
-seal paper under a cylinder with solvents
-pigments will separate onto the filter paper
-photosystems include clusters of thylakoid membranes and chlorophyll
-a few hundred pigment molecules in each cluster
-are like light gathering panels
-everytime light is absorbed, electron gains energy
-“ground state” to “excited state”
-unstable during “excited state”
-energy is transferred to neighboring molecule
-like dominos, energy is transferred and received on and on
-energy trapped from “excited” electrons can make ATP and NADPH
-first photosystem captures light and transfers “excited” electrons to electron transport chain
-“water-splitting photosystem”
-electrons replaced by splitting water molecule
-electron transport chain inbetween two photosystems give off energy
-hydrogen pumped across membrane, difference; respiration-food, photosynthesis-light excited electron
-second one NADPH production photosystem
-electrons and hydrogen ion sent to NADP+
-light energy “bumps” electrons to excited state
-light reactions convert light into ATP and NADPH
-no sugar produced, late produced by Calvin Cycle

Concept Checks
1. A leaf appears green because the pigment inside the leaf absorb blue-violet and red-orange light very well, but it does not absorb the green light effectively. Thus, the green light is reflected and it is the color the leaf appears to be.

2. When the molecule of chlorophyll a absorbs sunlight, it absorbs the blue-violet and red-orange light while it reflects the green light.

3. The light reactions also produce ATP and NADPH.

4. The light reaction takes place inside the thylakoid membranes of the chloroplasts