1. Quaestio: What happens during light dependent reactions?
Nunc Agenda: Write the formula for photosynthesis

2. Quaestio: How do plants capture the sun’s energy?
Nunc Agenda: What do you think photolysis means?

4. The Plant Cell

5. Chloroplast Structure
Chloro- = green
-plast = body
Thylakoid
Photosynthetic membrane
Contains chlorophyll
Grana
Stacks of thylakoids
Stroma
Fluid inside the thylakoid

6. Leaf cross section
Vein
Mesophyll
Stomata
CO2 O2
Chloroplast
Mesophyll cell
5 µm

10. Chlorophyll Photosynthetic pigment Captures light energy
Causes electrons to become excited (high energy)
Absorbs both red and blue light, reflects green
Makes photosynthesis work

13. Reflected

15. Paper Chromatography Can Separate The Plant Pigments

16. Photosynthesis overview
2 main reactions
Light dependent reactions
Captures and transfers energy
Light-independent reactions (dark reactions)
Uses energy from first stage to make sugars

17. Light-dependent reactions overview
First set of photosynthetic reactions
Only takes place when light is present
Uses energy from the sun to produce ATP for production of glucose
Takes place in and across thylakoid membrane
Water is split and oxygen is produced
Process called: photolysis

18. Photolysis
Photolysis: The splitting of molecules by means of light energy.
In photosynthesis, the photolysis of water is an integral part of the light reactions. The splitting of water releases oxygen and hydrogen.
Scientists have confirmed that the O2 released from photosynthesis comes from water by tracing the path of the isotope oxygen-18. Photolysis is responsible for the release of oxygen from photosynthetic organisms.

20. Light dependent reactions

21. Details
Energy from the sunlight is used to produce oxygen and create ATP and NADPH (energy carriers)
Contain clusters of chlorophyll and proteins called photosystems
Generate high energy electrons

23. Photosystem details
Groups of molecules in the membrane of the thylakoid called photosystem I and photosystem II
These photosystems contain pigments that capture the light energy
All this energy is transferred to a single electron which becomes raised to a high energy state.

27. Details cont (occurs in membrane of thylakoid)
Photosystem II
Produces High energy electrons
Water is split to replace electrons  oxygen released
Electron Transport Chain (ETC)
A series of chemical reactions that use the energy of electrons to make ATP
Transports electrons to photosystem I
H+ ions pumped into thylakoid space
ATP forms
H+ ions cascade through ATP synthase

28. Photolysis

29. …Continued Photosystem I
Electrons from photosystem II are re-energized by light energy
NADPH produced
When photosystem I receives electrons from photosystem II, the energy of the electrons is used to transform the molecule (NADP+) into NADPH

31. animation

34. Light dependent reactions

39. What comes next? Light- independent reactions
“dark reactions”
The ATP and NADPH produced is transported to the stroma where it powers the production of glucose

40. Summary for Photosystems
1. Photosystems are in place only for the light reactions.
2. Photosystem II generates ATP from ADP, while Photosystem I generates NADPH from NADP.
3. ATP and NADPH are high-energy products (chemical energy) used to power the dark reactions.
4. The photosystems (and light reactions) happen in the thylakoid membranes of the grana in the chloroplasts.
5. In the light reactions (aka photochemical reactions), water goes in, gets split (to supply electrons), and gaseous oxygen (O2) goes out.

41. Questions:
What are the roles of chloroplasts and chlorophyll in photosynthesis?
How do the two photosystems work together to capture energy from sunlight?
What is the main purpose of the light-dependent reactions?
Create a flow chart showing the light dependent reactions.

42. Photosystem II  ETC  photosystem I  ATP +. NADPH
Photosystem II  ETC  photosystem I  ATP NADPH to light independent reactions