1. Photosynthesis also requires light catching pigments
Light and Pigments
Photosynthesis also requires light catching pigments
These photosynthetic pigments are designed to capture the energy from light that is in a specific range of wavelengths

2. Most common pigment is chlorophyll
Other pigments exist in most plants to capture energy in other wavelengths

3. Other pigments…
xanthophyll is yellow in color, but is hidden by the green in chlorophyll
beta carotene is orange
chlorophyll gets broken down when the temperature goes down, so other pigments can be seen in the autumn leaf colors

4. The Reactions of Photosynthesis
Inside a chloroplast
Thylakoids – membrane sacs that contain clusters of pigment molecules called photosystems
Grana – stack of thylakoids
Stroma – area outside the thylakoids

5. Light dependent reactions happen inside thylakoids; makes sense, that’s where the photosynthetic pigments are
Light independent reactions happen in the stroma; they are not in the way of the light-dependent reactions

6. NADPH
The process of capturing sunlight results in the formation of high energy electrons (electrons that have jumped to another level; they will give off lots of energy on their way back towards the nucleus of the atom)
These high energy electrons require special carrier molecules

7. NADP+ is a carrier molecule
nicotinamide adenine dinucleotide phosphate
accepts a pair of high energy electrons along with a hydrogen ion: H+
creates NADPH – carries the high energy electrons elsewhere in the cell, so there energy can be used to drive other reactions

8. Light-dependent reactions
require light
turn ADP and NADP+ into high energy carriers ATP and NADPH

9. How does it work?
Light is absorbed by pigments in Photosystem II (discovered after Photosystem I)
Absorbed light increases energy in electrons which are passed on to the electron transport chain
New electrons (to replace the ones the chlorophyll passed on) come from water

10. High-energy electrons travel from Photosystem II to Photosystem I on the e- transport chain; drives the transport of H+ across the membrane of the thylakoid
Photo. I reenergizes high energy electrons & transfers them to NADP+ which becomes NADPH after picking up H+

11. Process creates a charge difference across the thylakoid membranes; restoring the charge balance drives ATP creation
ATP synthase helps with facilitated diffusion of hydrogen ions, but uses their passage to create ATP

12. The Calvin Cycle
ATP & NADPH are not stable enough to store energy for a long time
The Calvin Cycle converts less stable, high energy molecules into high energy sugars
Calvin cycle is light-independent

13. How does it work?
six carbon dioxides enter cycle
combine with six 5-carbon molecules which split creating twelve 3 carbon molecules
3 carbon molecules are then converted to high energy form using the energy from ATP and NADPH

14. How does it work? (cont.)
2 of the twelve 3-carbon compounds are converted to similar molecules and combined to form a 6-carbon sugar
The remaining ten 3-carbon compounds are recombined into 5-carbon compounds and re-enter the cycle

15. Plants use 6-carbon sugars for energy for growth and repair, and to construct complex carbohydrates like cellulose