1. Photosynthesis: Light Reactions and the Calvin Cycle

2. Photosynthesis Review…
There are two types of reactions that occur in photosynthesis.
Light dependent reactions
Light independent reactions (dark reactions, Calvin cycle)

3. Light Dependent Reactions:
Responsible for ATP and NADPH
Occurs in the grana (photosynthetic membranes) of chloroplasts
Grana contain chlorophyll and other pigments

4. Light Dependent Reactions:
4 Processes of Light Reactions:
Light Absorption
Electron Transport
Oxygen Production
ATP Formation (ENERGY!!)

5. 1. Light Absorption
Grana contain pigment clusters called photosystems.
Photosystems capture the energy of sunlight.
When light hits the thylakoid (single pancake) in the chloroplast, energy is transferred into the electrons in the chlorophyll, causing the electrons to jump to a higher energy level.
Excited electrons then jump from chlorophyll molecules to other nearby molecules in the thylakoid membrane, where electrons are used to power the second stage of photosynthesis.

6. 2. Electron Transport Electron transport chain: The electron carriers
Electron transport: Series of electron carriers in the grana of chloroplasts that transfer high-energy electrons.
Located in the thylakoid membrane.

7. 3. Oxygen Production
When the electrons jump to a higher energy level, they must be replaced by other electrons.
These “other electrons” come from water molecules.
The water molecules are split into 4 H+, O2, and 4 high-energy electrons.
This replaces the electrons and produces oxygen to be breathed by animals.

8. 4. ATP Production
When the water molecules are split, hydrogen ions accumulate inside the thylakoids, setting up a concentration gradient that provides the energy to make ATP.

9. Calvin Cycle (Light Independent, Dark Reactions)
Occur in the stroma of chloroplasts
Does not depend directly on the energy from sunlight
Uses CO2 given off by animals to form complex molecules
Carbon fixation– the transfer of CO2 to organic compounds
Forms a cycle of steps called the Calvin Cycle