1. 4.1-Capturing Solar Energy: Light Dependent Reactions
SBI4U1

3. Photosynthesis Overall Chemical Equation:
6CO2 (g) + 6H2O (l) + energy  C6H12O6 (s) + 6 O2 (g)
Simply stated…
Carbon dioxide + water with addition of energy from the sun yields glucose + oxygen.

4. Photosynthesis…
-Photosynthesis transforms radiant energy of sunlight into chemical energy
-Photosynthesizing agents/organisms use approx. 2% of the sun’s energy.
Photosynthesis allows plants to:
Make glucose
Converted to cellulose in cell walls
Starch for energy storage

5. Two sets of reactions that make up photosynthesis…
“Photo” = light
“Synthesis” = rxns that synthesize carbohydrate
Rx. 1- Light Dependent Reaction:
Light energy is trapped and used to generate ATP and NADPH( similar to NADH in Cell. Resp)
Rx. 2- Light Independent Reaction
Energy from ATP and reducing power of NADPH are used to make glucose

6. Light Dependent Rxn: rxn that uses solar energy to generate ATP and NADPH (similar to NADH)
Light Independent Rxn: rxn that uses the energy of ATP and reducing power of NADPH to make a high energy organic molecule
*Note: cyanobacteria, algae and plants all carry out photosynthesis, but we are just going to focus on plants for simplicity

7. Structure of the Chloroplasts
Photosynthesis factory
3-8µm in length and 2-3µm in diameter
Outer and inner membranes enclose a space filled w/ protein rich semi-liquid material called stroma
Thylakoids are within the stroma
Flattened discs
Stacked thylakoids are called grana, unstacked thylakoids are called lamellae

8. Levels of Organization in a Plant Leaf
Carbon dioxide and water that are used to synthesize glucose through photosynthesis are taken up by the leaf and then enter into plant cells and chloroplasts. Water enters the leaf through veins, and carbon dioxide enters via openings called stomata.

9. Grana

10. Inside the thylakoid sac is the thylakoid lumen
Water filled
Chlorophyll and ETC proteins are embedded in thylakoid membrane
Chlorophyll is a green coloured pigment that absorbs light
Common Forms of chlorophyll:
chlorophyll a and chlorophyll b

11. Why Chlorophyll Appears Green
Leaves appear green because chlorophyll molecules in leaf cells reflect green and yellow wavelengths of light and absorb other wavelengths (red and blue).
This absorbance spectrum for three photosynthetic pigments shows that each pigment absorbs a different combination of colours of light.

12. Light is absorbed in packets of energy called photons
Absorption of Light
Light is absorbed in packets of energy called photons
Wavelengths (colour) of light are related to energy
Shorter wavelength  more energy
Longer wavelength  less energy
Electrons can absorb a photon only if it carries exactly enough energy to allow the electron to move up to another allowed energy level.

13. Pigment: compound that absorbs visible light
E.g. Chlorophyll a and chlorophyll b
Chlorophyll a absorbs at nm and nm
Chlorophyll b absorbs at nm and nm
Both types of chlorophyll reflect green

14. Photosystems
Protein based complexes composed of clusters of pigments that absorb light energy in the thylakoid membrane

15. Light reactions of photosynthesis occur in the thylakoid membrane
When a pigment molecule absorbs a photon, the molecule passes the energy to the chlorphyll a molecules.
Light reactions of photosynthesis occur in the thylakoid membrane
Divided into 3 parts
Photoexcitation: e- gets excited
Electron transport: e- transferred to e- carriers, and protons pump into lumen
Chemiosmosis: formation of ATP

16. Photosystems are made up of two parts:
Antenna complex
Made up of chlorophyll molecules and other pigments
Absorbs a photon and transfers energy from pigment to pigment until it reaches chlorophyll a in reaction centre

17. Reaction Centre: Transmembrane protein complex Contains chlorophyll a
e- absorb energy and passes e- to an electron acceptor

18. The Reaction Centre
The antenna complex is also sometimes referred to as the light-harvesting complex because it gathers (harvests) energy from light so that the energy can be directed to the P680 molecule in the reaction centre.

19. There are 2 Photosystems: Photosystem One - PS I:
Primary pigment is chlorophyll a.
Absorption peak at 700nm
Called P700
Photosystem Two - PS II:
Primary pigment is chlorophyll b
Absorption peak at 680nm
Called P680

20. Arrangement of Photosystem I and Photosystem II
In the light-dependent reactions, photosystem II passes electrons to photosystem I via an electron transport system, which contains the b6-f complex. This complex acts as a proton pump to produce a proton gradient across the thylakoid membrane. The electrons lost from the reaction centre of photosystem II are replenished by the oxidation of water. Photosystem I uses the electrons to reduce NADP+ to NADPH.

21. PSI and PSII work together to produce ATP and NADPH
PSII passes electrons to PSI via an electron transport system (w/ b6-f complex  proton pump)
e- lost from PSII are replenished by oxidation of H2O
PSI uses e- to reduce NADP+ to NADPH
Animation:

22. It is called photophosphorylation
ATP synthesis in light-dependent rxns is the same as in aerobic respiration
It is called photophosphorylation
Using photons to drive phosphorylation of ADP to produce ATP via chemiosmosis

23. They works together to make ATP
PSI and PSII, an electron transport system, and ATP synthase enzyme are in the thylakoid membrane
They works together to make ATP
Animation:

24. Making ATP by Chemiosmosis
Photosystem I, photosystem II, an electron transport system, and the ATP synthase enzyme are embedded in the thylakoid membrane of chloroplasts. ATP synthesis by chemiosmosis in chloroplasts occurs in a way that is very similar to the way it occurs in mitochondria.

25. Cyclic Photophosphorylation

26. Cyclic Phosphorylation
In cyclic photophosphorylation, an electron in P700 is excited by a photon and begins taking the same path that it took in noncyclic photophosphorylation. However, the electron is not used to reduce NADP+ but instead is passed back to the b6-f complex, where the energy is used to generate the proton gradient.

27. Chloroplast produce more ATP through cyclic photophosphorylation
Only PSI
Photon excited an e- from P700 in PSI
it follows the same path as in noncyclic
e- is not used to reduce NADP+
It is passed back to b6-f complex
Creatinfga proton gradient to generate ATP, but not NADPH
Believed to be used by early bacteria

28. Learning Expectations...
Reactants and products of photosynthesis
Structure and function of chloroplasts
Chlorophyll a vs. chlorophyll b
Photosystems (PSI vs. PSII)
ATP production and chemiosmosis in plants
Cyclic vs. noncyclic photophosphorylation
** there are a lot of details here, re-watching the animations may be beneficial**