1. Light dependent reaction
photoexcitation, photolysis, photosystems, photophosphorylation, electron carriers, higher energy level, NADP, ATP

2. Learning outcomes
Be able to explain how photolysis of water produces protons, electrons and oxygen. C
Be able to explain how light energy excites electrons in chlorophyll B
Be able to explain how energy from these excited electrons generates ATP and reduced NADP for the independent reaction B
Be able to explain how the production of ATP involves electron transfer associated with the electron transfer chain in chloroplast membranes and movement of H ions B/A

3. Pigments and photosystems
Chloroplasts contain photosynthetic pigments to absorb the light energy
Pigments are chlorophyll a, chlorophyll b and carotene
The pigments are found in the thylakoid membranes attached to proteins.
The protein and pigment are called a photosystem
Two photosystems used by plants to absorb light are PSI ( 700nm wavelength) and PSII ( 680nm wavelength)

4. Photosynthesis Photosynthesis can be split into two stages
The light-dependent reaction
The light-independent reaction – AKA the Calvin Cycle

5. Photosynthesis

6. Light dependent reaction
This reaction needs light energy
Takes place in the thylakoid membranes
Light energy absorbed by photosynthetic pigments in the photosystems and converted to chemical energy
Light energy is used to add inorganic phosphate to ADP to form ATP
And reduce NADP to form reduced NADP
ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction
During the process H2O is oxidised to O2

7. Analogy

8. Light dependent reaction

9. Light dependent reaction
Light reactions occur mostly in the thylakoid stacks of the grana. Here, sunlight is converted to chemical energy in the form of ATP (free energy containing molecule) and NADPH (high energy electron carrying molecule). Chlorophyll absorbs light energy and starts a chain of steps that result in the production of ATP, NADPH, and oxygen (through the splitting of water). Oxygen is released through the stomata. Both ATP and NADPH are used in the dark reactions to produce sugar.
The purpose of the light-dependent reactions is to harness energy from the Sun and use it to make ATP and NADPH.  In the process water is split into hydrogen ions, electrons and oxygen atoms. This is called photolysis. The hydrogen ions and electrons are captured by NADP+ to form NADPH and oxygen gas is formed. 
Light energy excites electrons on PSII and boosts them to a higher energy level where they are received an electron acceptor.
The electrons are passed from the acceptor along a series of electron carriers to PSI. As energy is lost by the electrons it is used to convert ADP to ATP.
Light energy excites the electrons at PSI boosting them to an even higher energy level where they are received by another electron acceptor.
Meanwhile photolysis has occurred allowing electrons to replace those lost at PSII. The protons from the water molecule combine with electrons from the second electron acceptor and so reduce NADP.
Oxygen is lost as a waste product.
This method of ATP production is called non-cyclic photophosphorylation. Therefore, electrons are passed from water to NADP. For each pair of electrons one ATP molecule is produced.
Cyclic photophosphorylation uses only photosystem I and produces ATP alone.   Excited electrons are passed down the electron transport chain to move hydrogen ions back to PSI again producing ATP in the process. No NADPH is produced.

10. Photophosphorylation and photolysis
In the light-dependent reaction, the light energy absorbed by the photosystems is used for three things:
Making ATP from ADP and Pi – this is known as photophosphorylation
Making reduced NADP from NADP
Splitting water into protons( H+ ions), electrons and oxygen. This is called photolysis

11. Things to do Using the information from The animation From the diagram
From textbooks
Produce a summary piece that will enable you to remember the sequence of events, the new vocabulary and the end products of the light dependent reaction
photoexcitation, photolysis, photosystems, photophosphorylation, electron carriers, higher energy level, NADP, ATP

12. http://highered. mheducation. com/olcweb/cgi/pluginpop. cgi
and Noncyclic Photophosphorylation
What is the difference between cyclic noncyclic photophosphylation?

13. Light-dependent reaction

14. 1

15. Non-cyclic photophosphorylation
Produces ATP, reduced NADP and O2
Photosystems in the thylakoid membranes are linked by electron carriers
Electron carriers are proteins that transfer electrons
The photosystems and their electron carriers form an electron transport chain – a chain of proteins through which excited electrons flow

16. Light energy excites electrons in chlorophyll
Light energy is absorbed by PSII
Light energy excites electrons in chlorophyll
The electrons move to a higher energy level
These high energy electrons move along the electron transport chain to PSI

17. Photolysis of water produces protons ( H+ ions), electrons and O2
As the excited electrons from chlorophyll leave PSII to move along the electron transport chain, they must be replaced
Light energy splits water into protons (H+ ions), electrons and oxygen
H2O H+ + 1/2 O2

18. Energy from the excited electrons makes ATP
The excited electrons lose energy as they move along the electron transport chain
This energy is used to transport protons into the thylakoid so that the thylakoid has a higher concentration of protons than the stroma. This forms a proton gradient across the membrane
Protons move down their concentration gradient, into the stroma, via an enzyme ATP synthase. The energy from this movement combines ADP and Pi to form ATP
Chemiosmosis is the name of the process where the movement of H+ ions across a membrane generates ATP – this also occurs in respiration

19. Generation of reduced NADP
Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level
Finally, the electrons are transferred to NADP, along with a proton (H+ ion) from the stroma, to form reduced NADP

20. Cyclic photophosphorylation
Only uses PSI
Cyclic because the electrons used aren’t passed to NADP, but passed back to PSI via electron carriers
Electrons recycled and used repeatedly to flow through PSI
Produces small amounts of ATP

21. Things to do Using the information from The animation From the diagram
From textbooks
Produce a summary piece that will enable you to remember the sequence of events, the new vocabulary and the end products of the light dependent reaction
photoexcitation, photolysis, photosystems, photophosphorylation, electron carriers, higher energy level, NADP, ATP

22. The best ones will include for vocab..
Be able to explain how photolysis of water produces protons, electrons and oxygen. C
Be able to explain how light energy excites electrons in chlorophyll B
Be able to explain how energy from these excited electrons generates ATP and reduced NADP for the independent reaction B
Be able to explain how the production of ATP involves electron transfer associated with the electron transfer chain in chloroplast membranes and movement of H ions B/A
Photoexcitation – what is it (B) Photolysis – what happens and why (C) Photosystems – what are these, which comes first and why do they have those numbers (B) Photophosphorylation – your exam board loves this. What does it mean? (C/B)

23. The best ones will include for explanation..
Be able to explain how photolysis of water produces protons, electrons and oxygen. C
Be able to explain how light energy excites electrons in chlorophyll B
Be able to explain how energy from these excited electrons generates ATP and reduced NADP for the independent reaction B
Be able to explain how the production of ATP involves electron transfer associated with the electron transfer chain in chloroplast membranes and movement of H ions B/A
Electron carriers – what are these, what are their names and why role do they play? (B) What is the fundamental purpose of the light dependent reaction? (B) Where precisely does it take place? (B/A) What role do the H ions play? (A)

24. Plenary
Test your understanding of the light dependent reaction and the products with some exam questions
Mark your own and award yourself a grade based on the learning outcomes
Make a note of what you need to do to improve your grade
Write an equation(s) for photosynthesis that better reflects the process of the light dependent reaction.