1. Topic 2.9 and 8.3
Photosynthesis

2. SL Topic
2.9 Photosynthesis

3. Light striking the plant is converted into chemical energy  glucose
Photosynthetic organisms produce foods
Primary production

4. Chloroplasts are the Chlorophyll  photosynthetic pigment
only green component of a plant

5. Light provides energy  photosynthesis,
light absorbed by chloroplasts partly determines rate of photosynthesis
Useful colors  Red and Blue
Absorption correlates to action (run photosynthesis)
Green not useful since not absorbed (reflected)
Absorption and Action spectra vary for different plants
Different pigments
Relative amounts of those pigments

6. Stages of photosynthesis
First stage: Light Dependent Reactions
Chlorophyll absorbs light energy and convert it to chemical energy (ATP)
Photolysis occurs to release needed electrons, separating oxygen (waste) from hydrogen
Oxygen
ATP
Chlorophyll
Water
Light independent reactions
Electrons
Hydrogen ions
Hydrogen

7. Stages of Photosynthesis
Second stage: Light independent reactions
6 CO H2O  C6H12O6 + 6 H2O + 6 O2
Inorganic compound
Organic compound
Carbon Fixation
ATP and hydrogen used as chemical energy to convert CO2 and H2O into glucose

8. Measuring the rate of photosynthesis
Rate of cell respiration is consistent day and night  at low levels
Directly measure the rate of oxygen production or carbon dioxide intake
Measure biomass (indirect measure)
As a plant photosynthesizes, it should increase in biomass.
correction is made for cell respiration

9. Effects of Environmental Factors
Enzymes, etc. already working at their maximum rate
Positive correlation between light intensity and photosynthesis rate in this area of the graph

10. Effects of Environmental Factors
Enzymes and other proteins become denatured
Increased molecular collisions

11. Effects of Environmental Factors
Rate of reaction reaches a plateau unless light or temperature is also increased.
Positive correlation

12. HL Topic
8.3 Photosynthesis

13. The Chloroplast
All photosynthetic processes occur within the chloroplast
Occur only in algae and plant cells
Contains double membrane, own DNA and 70s ribosomes
Grana
Made up of numerous stacked thylakoids
Thylakoids
Flattened membrane sacs
Used in the absorption of light (1st step of photosynthesis)
Stroma
Fluid (like cytosol), within the chloroplast
Contains many enzymes and chemicals necessary for photosynthesis

15. Process of Photosynthesis
6 CO H2O  C6H12O6 + 6 H2O + 6 O2
Light
Water occurs on both sides because 12 molecules are consumed and 6 are produced

16. Light Dependent Reaction
Occurs in the thylakoids/grana
Light supplies the energy  Sun
Pigments
Absorbed light
Different pigments absorb different wavelengths of light
Chlorophylls
Carotenoids
Organized on the membranes of the thylakoids
Photosystems:
Chlorophyll a molecules
Accessory pigments
A protein matrix

17. Light Dependent Reaction
Reaction Center contains:
A pair of chlorophyll molecules
A matrix protein
A primary electron acceptor

18. 2. Electron is captured by the primary acceptor
1. A photon of light is absorbed by a pigment in photosystem II  transferred to other pigment  reaches chlorophyll a (P680)  causes an excitement of electrons into a higher energy state

19. 3. Photolysis: Driven by energy of light  water is split by an enzyme to produce electrons, H+, and an oxygen atom  electrons supply chlorophyll a

20. 4. Excited electrons pass from primary acceptor down an electron transport chain (losing energy at each exchange)
Three electron carriers

21. 5. Energy lost from electron movement  drives chemiosmosis (think respiration)  phosphorylation of ADP to ATP

22. 7. Electrons are passed down a second electron transport chain
8. Enzyme NADP reductase catalyzes the transfer of an electron to NADP+
2 electrons are required to fully reduce NADP+ to NADPH
7. Electrons are passed down a second electron transport chain
6. Photon of light is absorbed by pigment in photosystem I  chlorophyll a (P700) accepts energy  increases energy in an electron  de-energized electron from photosystem II fills void

23. Final Products NADPH + ATP Oxygen Release
Supply chemical energy for the light-independent reaction
Oxygen Release
Step 3

24. Chemiosmosis Comparison
Respiration Chemiosmosis
Photosynthesis Chemiosmosis
1. Involves an ETC embedded in the membranes of cristae
1. Involves an ETC embedded in the membranes of thylakoids
2. Energy is released when e- are exchanged from one carrier to another
3. Released energy is used to actively pump H+ into the intermembrane space
3. Released energy is used to actively pump H+ into the thylakoid space
4. H+ come from the matrix
4. H+ come from the stroma
5. H+ diffuse back into the matrix through the channels of ATP synthase
5. H+ diffuse back into the stroma through the channels of ATP synthase
6. ATP synthase catalyzes the oxidative phosphorylation of ADP to form ATP
6. ATP synthase catalyzes the photophosphorylation of ADP to form ATP

25. A mechanical analogy for the light reactions

26. How Do these Fit Spatially?
THYLAKOID MEMBRANE
STROMA
THYLAKOID SPACE

27. So how is ATP synthesized?

28. Light-Independent Reaction
Occurs within the stroma (cytosol-like) region of the cholorplast
ATP and NADPH produced in light-dependent reaction provide the energy and reducing power
Product = GLUCOSE 

29. Calvin Cycle
1. Ribulose biphosphate (RuBP), 5C compound, binds to CO2 through an enzyme, rubisco  carbon fixation  unstable 6C compound 6
CO2 from the air
Rubisco
CO2 Fixation 6 6
RuBP
Unstable intermediate
2. 6C breaks down into two 3C compounds  glycerate-3-phosphate 12
Glycerate-3-phosphate
12 ATP
3. Glycerate-3-phosphate are acted on by ATP and NADPH (from LD reactions) to form triose phophate (TP)  reduction reaction
12 NADPH
12 ADP
12 Pi
12 NADP+ 12
Triose phosphate

30. Calvin Cycle 5. In order to regain RuBP, the cycle uses 6 ATP
CO2 from the air
5. In order to regain RuBP, the cycle uses 6 ATP
Rubisco
CO2 Fixation 6 6
4. TP may go one of two directions: 1) leave cycle  sugar phosphates, or 2) continue cycle to reproduce originating compound: RuBP
RuBP
Unstable intermediate
6 ADP 12
6 ATP
Glycerate-3-phosphate
12 ATP
12 NADPH 10
Triose phosphate
12 ADP
12 Pi
12 NADP+ 12 2
Triose phosphate
Triose phosphate
Sugar

31. Calvin Cycle TP is the pivotal compound
Produce simple sugars (glucose), disaccharides (sucrose),or polysaccharides (cellulose or starch)
Most is used to regain starting compound, RuBP

34. Summary Light-Dependent Light-Independent Occurs in the thylakoids
Occurs in the stroma
Uses light energy to form ATP and NADPH
Uses ATP and NADPH to form TP
Splits water in photolysis to provide replacement electrons and H+, and to release O2 to the atmosphere
Returns ADP, inorganic phosphate, and NADP to the light-dependent reaction
Includes 2 ETC and photosystems I and II
Involves the Calvin Cycle

35. Chloroplast Chloroplast Structure Function Allowed
Extensive membrane surface area of the thylakoids
Allows greater absorption of light by photosynthesis
Small space (lumen) within the thylakoids
Allows faster accumulation of protons to create a concentration gradient
Stroma region similar to the cytosol of the cell
Allows an area for the enzymes necessary for the Calvin cycle to work
Double membrane on the outside
Isolated the working parts and enzymes of the chloroplast from the surrounding cytosol

36. Factors Affecting Photosynthesis
Potential limiting factors:
Temperature
Light intensity
Carbon dioxide concentration
Rate Limiting Step
One part of photosynthesis is slowed, all parts are slowed

37. Light Intensity (why?)

38. Carbon Dioxide Concentration (why?)

39. Temperature (why?)

40. Cyclic Photophosphorylation
Light energized electrons from photosystem I flow back to the cytochrome complex  creating more ATP