1. PHOTOSYNTHESIS Chapter 7
creating energy-rich organic molecules from light
PHOTOSYNTHESIS
The photosynthesis rxn is:
anabolic (building)
endergonic (energy-storing)
redox

2. PHOTOSYNTHESIS
Summative equation

3. LIGHT Electromagnetic (aka radiant) energy
Long wavelength
Low frequency
Low energy
Short wavelength
High frequency
High energy
Photosynthesis employs visible light wavelengths

4. Light Energizes Electrons
e- absorb specific wavelengths
e- jump to more distant orbit
fall back, emitting light & heat
Look familiar?

5. Light Energizes Electrons
to ETC
If the excited e- are in chlorophyll, or other plant pigments, the e- doesn’t fall back - it gets transferred to an electron transport chain

6. Pigments Absorb Different Wavelengths
• In plants, chlorophyll a is the primary pigment, unable to absorb (thus transmitting) green
• In fall, chlorophyll production stops and accessory pigment transmission is visible - yellow, reds, until production stops

7. Wavelength Is Key to Psn Productivity
Photosynthetic rate is greatest at red, blue wavelengths

8. Granum - stack of thylakoids
CHLOROPLASTS contain CHLOROPHYLL and other PIGMENTS
Light
Reflected
Absorbed
light
Granum - stack of thylakoids
Transmitted
Stacking pigments maximizes absorption
Analgous to a multijunction solar cell
Light passing through is trapped by pigments in next thylakoid - except green!

9. Pigments are Within in the Thylakoid Membrane

10. Pigments are Grouped into Photosystems
• Accessory pigments shuttle energy, in form of excited e-, to the reaction center, containing chlorophyll a
• Focuses the energy, like an antenna

11. Photosynthesis labs Chromatography Leaf disc assay Spectrometry
Uses the distance the pigments travel in solvent to differentiate between them
Photosynthesis labs
Leaf disc assay
As O2 is produced in psn, the discs rise
carotene
xanthophyll
chlorophyll
Show Bozeman video on labs
Spectrometry
• chlorophyll electrons, excited by light, are captured by a blue dye turning the solution lighter in the process
• the more excited the electrons, the quicker the solution loses color, and the more light is transmitted through the sample.