1. Photosynthesis Honours1

2. 2 stages of Photosynthesis (HL)
Light Stage
Dark Stage 2

3. Light Stage (HL) This takes place in the grana of the chloroplast
It involves the very fast movement of electrons and is not controlled by enzymes
Light is absorbed by a range of pigment clusters found in the chloroplast (almost all colours of light are absorbed but green is normally reflected) 3

4. Light Stage (HL)
This light energy is transferred to the electron that has been passed to the chlorophyll
This chlorophyll is in the pigment cluster and is strategically placed near an electron acceptor
The pigment cluster absorbs as much light energy as possible and passes it to the chlorophyll which passes it to the electron
The energised electron is passed to the electron acceptor which can the send it on one of two pathways 4

5. Learning Check Where does the light stage occur?
Why is it called the light stage?
Where do the electrons supplied to the chlorophyll come from?
What absorbs the light energy?
What is the chlorophyll strategically placed near?
How many possible pathways can the electron be passed on? 5

6. Electron Flow Pathway 1 (HL)
In pathway 1 the electrons pass from the first electron acceptor to a series of other electron acceptors and back again to the chlorophyll
As the electrons are passed around they lose energy
This energy is used to join a phosphate to ADP to form high energy ATP
Water is also formed in this process 6

7. Electron Pathway 1 (HL) ADP + Energy + P ATP + Water
The addition of phosphate to ADP is called phosphorylation
Because the electron travel in a cycle and returns to its original chlorophyll this process is called Cyclic Phophorylation 7

8. Learning Check
Where does the electron go to from the chlorophyll in pathway 1?
What happens to the electron as it is moved around?
What is phosphorylation?
Why is this pathway called cyclic phosphorylation?
What are the end products of pathway 1? 8

9. Electron Pathway 2 (HL)
2 high energy electrons at a time are passed from chlorophyll to the electron acceptor and then along another series of electron acceptors
In this case the electrons do not return to the original chlorophyll
They lose energy as they pass from electron acceptor to electron acceptor and this energy is used to make more ATP 9

10. Electron Pathway 2 (HL)
Eventually the 2 electrons are passed to combine with NADP+ to form NADP-
The chlorophyll molecule is now short of electrons and gains more from the splitting of water
The splitting of water using light energy is called Photolysis 10

11. (HL)
The protons that were stored in the proton pool are attracted to NADP- and combine with it to form NADPH
Because the electrons start at a chlorophyll and finish at NADPH and form ATP on their way this pathway is known as Non cyclic photophosphorylation
Non cyclic photophosphorylation 11

12. Learning Check
Where do the electrons move to from the chlorophyll in pathway 2?
What happens to the electrons as they are moved around?
What is the final destination of the electrons and what does this form?
What is attracted to NADP-?
What was the original source of these substances?
What is photolysis? 12

13. The light stage occurs in the granum of the chloroplast
Light stage (HL)
Light Stage
Phosphorylation
Making ATP
Photolysis
Splitting water
The light stage occurs in the granum of the chloroplast 13

14. Phosphorylation (HL) Hydrogen ions join with NADP-1:
Chlorophyll traps sunlight 5:
Hydrogen ions join with NADP-
To form NADPH 2:
Electrons are energised 4:
Other electrons join with NADP
To form NADP- 3:
Electrons lose energy to ADP
Which joins with P to form ATP 14

15. Photolysis (HL) The splitting of water
Hydrogen ions H+
Electrons E-
Oxygen 02
Used to convert NADP To
NADPH
By product
Excreted through leaf
Go back to chlorophyll 15

16. End Products of the Light Stage (HL)
There are 3 end products of the light stage
ATP this will provide energy for the dark stage
NADPH this will provide protons + energised electrons for the dark stage
Oxygen is made when water is split 16

17. Learning Check What are the 3 end products of the light stage?
Where do each of these products come from?
What will happen to each of these products? 17

18. Dark Stage (HL)
This may also be called the light independent stage as it can occur in the light but does not need to use it
It takes place in the stroma of the chloroplast
It is controlled by enzymes and therefore can be affected by temperature 18

19. Dark Stage (HL)
Carbon dioxide from the air enters the chloroplast where they combine with protons + electrons to form glucose
This needs energy and protons + electrons 19

20. Dark Stage (HL) It uses energy got from breaking down ATP into ADP + P
It uses hydrogen ions and electrons got from breaking down
NADPH into NADP+ + 2 electrons + H+ 20

21. Dark Stage (HL)
Remember the addition of electrons to anything is known as reduction
Carbon Dioxide is reduced to glucose 21

22. Dark Stage (HL) CO2 is reduced Oxygen atom is removed Hydrogen ions
are added
Electrons are
added
Glucose is formed
C6H1206 22

23. Learning Check
Why can the dark stage more accurately be called the light independent stage?
What part of the chloroplast does the dark stage take place in?
Why is the dark stage affected by temperature?
What gas is reduced to glucose?
Where does the energy for this come from?
What else is needed to reduce the gas? Where do these items come from? 23

24. Main events in photosynthesis (HL)
Light energy is absorbed by chlorophyll
Water is split
The electrons are passed to chlorophyll
The protons are stored in the chloroplasts
The oxygen is released
Sunlight transfers energy to electrons
The high energy electrons, stored protons( the hydrogen ions) and carbon dioxide are used to make glucose 24

25. Summary of photosynthesis
cyclic
phosphorylation
Non-cyclic
phosphorylation
Reduction of CO2
To glucose

26. Syllabus Can you?...... Explain the role of ATP
Explain the production of ATP from ADP
Explain the role of NADP+ in trapping & transferring electrons & H ions.
Explain the Light Stage/Dark Stage
State the two-pathway system of electron carriage.
1. Direct to chlorophyll
2. Trapped by NADP+ 26

27. Role of ATP and NAD
Honours 27

28. What you will learn The energy role of ATP and ADP.
Revision of catabolic and anabolic reactions
The role of NAD and NADP in biological reactions
Chloroplast structure and function. 28

29. Energy Carriers
ATP , NADP+ and NAD+ play a vital role in trapping and transferring energy in cellular activities 29

30. ADP and ATP
If another phosphate is added to ADP it forms ATP (Adenosine Triphosphate)
Extra energy is also added as there is an extra bond between the last two phosphate groups
Addition of a phosphate like this is called Phosphorylation
ATP is rich in energy and stores this energy carrying it around in the cell 30

31. ADP and ATP
ADP is an abbreviation for Adenosine Diphosphate this is a molecule found in the cells of all organisms
It is made of the base adenine , a 5 carbon sugar called ribose and 2 phosphate groups
ADP is a low energy molecule 31

32. ADP and ATP
ATP cannot store energy for very long it breaks down releasing energy and converting back to ADP
Most cells release energy from ATP 10 million times every second! This energy is used for cellular reactions 32

33. Learning Check What do ADP and ATP stand for?
What base is found in ATP and ADP?
What sugar is found in ATP and ADP?
Which is a higher energy molecule?
How does ADP become ATP?
This process is called p
How is the energy in ATP released? 33

34. NADP+ and NADPH
NADP+ is a low energy molecule involved in photosynthesis
NADP+ can combine with 2 high energy electrons and a proton to form NADPH
NADPH is a very high energy molecule
It’s energy is used to form glucose in photosynthesis 34

35. NADP+ and NAD NAD+ is used in respiration
It can combine with 2 high energy electrons and a proton to form NADH which is very high in energy
Remember P for photosynthesis, NADP+ is used in photosynthesis NAD+ in respiration 35

36. These electrons, protons and energy are used by cells
Both NADH and NADPH release energy and protons when they break down into NAD+ and NADP+
These electrons, protons and energy are used by cells 36

37. Learning Check Is NADP+ used in photosynthesis or respiration?
What combines with NAD+ and NADP+ to form NADH and NADPH?
What do NADH and NADPH provide for reactions in cells?
How do they provide these things? 37

38. The ATP cycle is like natures rechargeable battery
Catabolism e.g respiration
Anabolism e.g photosynthesis

39. The making of ATP using light energy is called photophosphorylation
Chloroplasts
The making of ATP using light energy is called photophosphorylation
Chloroplast
Spliting water
Stroma
Where the dark stage occurs
Granum
Thylakoid disc (chlorophyll captures the light energy)
Carbohydrates (glucose)

40. Syllabus Can You?
Explain the role of ATP and describe how it is formed from ADP + P
Explain the role of NADP+ in trapping and transferring electrons and hydrogen ions in cell activities 40

41. END