1. Photosynthesis

2. What is photosynthesis?
Conversion of light energy into chemical energy
Chlorophyll is the main photosynthetic pigment

3. White light Light from the sun is composed of a range of wavelengths
Chlorophyll a and b absorb red ( nm) and blue ( nm) wavelengths
Green ( nm) light is transmitted or reflected by chlorophyll

4. Absorption vs. Action
Absorption spectrum shows the quantity of each wavelength of light absorbed by a specific pigment
Action spectrum is the summation the individual absorption spectra of the various pigments
Y axis is the rate of photosynthesis
The maximum rate are at the blue end and red end of the visible spectrum

6. So how does photosynthesis work?
Light dependent reaction
Energy absorbed by chlorophyll/protein complex is used to produce ATP
Photolysis of water: Energy absorbed by chlorophyll is used to split water molecules, forming oxygen and hydrogen
H2O  2 H+ + 2 e- + 1/2 O2

7. So how does photosynthesis work?
Light independent reaction
Carbon dioxide absorbed for use in photosynthesis
Inorganic carbon dioxide molecules to organic form via fixation
Use hydrogen (from photolysis) and ATP

8. What factors affect the rate of photosynthesis?
Limiting factors
Temperature:
Increased molecular collisions
Enzymes denature
Light intensity:
Visible light (especially red and blue) is essential for activity of chlorophyll during the light-dependent reactions
Positive correlation between light intensity and photosynthesis
Enzymes already working at max rate
Carbon dioxide concentration:
CO2 is essential for Calving cycle for the production of carbohydrates
Positive correlation between CO2 concentration and photosynthetic rate

9. Photosynthetic rate O2 production CO2 uptake Biomass increase
Place plant in an enclosed volume
Monitor the change in gaseous O2 over time
O2 is produced by the photolysis of water
Monitor the change in gaseous CO2 over time
CO2 is consumed during the Calvin cycle
CO2 dissociates from bicarbonate, making the pH increase
CO2 + H2O   H2CO3  H+ + HCO3- 
monitor the change in pH of the water over time
Measure organic content of plants before and after experiment
Organic content of plants is measured by removing water through dehydration, usually in an oven.

10. To do today
How much energy do you use? Try the Ecological Footprint Survey here. We will compare the results with the class so take a screenshot of your responses, put them on a goolge doc and then in the Ecological Footprint folder.
Try the color of the light spectrum & growth. Which wavelength of light is the best for plant growth?
Next class: Mind Map Draft
Learning log: 3.7 & 3.8 (HL also: 7.5, 8.1, 8.2) - May 23rd.

11. HL ONLY: Light Dependent Reactions

12. Chloroplast

14. Light dependent vs. independent
Light independent
Occurs in thylakoid
Occurs in stroma
Uses light energy to form ATP and NADPH
Uses ATP and NADPH to form triose phosphate
Splits water in photolysis to provide replacement electrons and H+ and to release oxygen to the atmosphere
Returns ADP, inorganic phosphate and NADP to the light dependent reaction
Includes two electron transport chains and photosystems I and II
Involves the Calvin Cycle
Damon et al., 2007

15. Photosystem (I and II): Light harvesting unit in photosynthesis, made up primarily of chlorophyll a molecules, accessory pigments, a protein matrix

16. Oxidation and Reduction
Reactions concerned with the e- transfer
Oxidation: gain of oxygen, loss of e- and H+
Reduction: loss of oxygen, gain of e- and H+
OIL RIG

18. Light Dependent Reaction Production of ATP
Photoactivation of photosystem II:
photons of visible light absorbed by pigments, esp. chlorophyll a, at 680 nm
chlorophyll a is reduced as it gains energy
chlorophyll a oxidized when excited e- move to electron transport system
Photolysis of water:
H2O  2 H+ + 2 e- + 1/2 O2
2 electrons: replace electrons lost by chlorophyll a to ETS
O2: lost to environment as a waste product
H+: used to create ATP

19. Light Dependent Reaction Production of ATP
electron transport system: proteins embedded in thylakoid membrane transfer energy along a pathway in a series of redox reactions
some energy used to pump H+s from stroma to thylakoid interior

20. Light Dependent Reaction Production of ATP
ATP phosphorylation:
ADP + P  ATP
Chemiosmosis = coupling of ATP synthesis to electron transport
H+ movement across the membrane causes release of energy, which is used by ATP synthase to create ATP
Therefore: H+: remains in the thylakoid interior, lowering pH and contributing to the chemiosmotic gradient --> ATP phosphorylation
H+ diffuse down chemiosmotic gradient from thylakoid interior (pH = 4) through proton channel and into stroma (pH = 8)

21. Light Dependent Reaction Production of NADPH
electron transport system: proteins embedded in thylakoid membrane transfer energy along a pathway in a series of redox reactions
Electrons passed from PSII  PSI  NADP

22. Light dependent reaction Production of NADPH
Photoactivation of photosystem I:
photons of visible light absorbed by pigments, esp. chlorophyll a, at 700 nm
chlorophyll a is reduced as it gains energy
chlorophyll a oxidized when excited e-s move to electron transport system
Reduction of NADP+  NADPH + H+:
gain of 2 e-s from ETS
NADP reductase
NADPH is used to make carbohydrates

23. Light Dependent Reaction Production of ATP
non-cyclic photophosphorylation:
one-way flow of 2 e- from water to PsII to ETS to PsI to NADP+
2 main products: 1) NADPH + H+ 2) ATP
cyclic photophosphorylation:
cyclic flow of e-s from PsI to ETS back to PsI
1 main product: ATP
When light is not a limiting factor, NADPH tends to accumulate in stroma and there is a shortage of NADP+

25. HL ONLY: Light Independent Reactions

27. Calvin Cycle
ribulose bisphosphate carboxylase (rubisco): an enzyme with ribulose bisphosphate (RUBP) to form 2 molecules of glycerate 3-phosphate (GP)
RUBP + CO2 –Rubisco---> 2 GP
Reduction of GP to triose phosphate (G3P):
reduction, driven by energy from ATP and NADPH + H+
products of light-dependent reactions provide energy to reduce GP to G3P
Animation:

28. Light Independent Reactions
regeneration of RuBP:
83% of 3-carbon TP is used to regenerate 5-carbon RuBP
using energy from ATP
synthesis of carbohydrates and other products:
enzymes convert G3P to various products
monosaccharides: glucose, fructose
disaccharides: sucrose
polysaccharides: starch
other products: lipids, amino acids, nucleic acids

29. Structure and Function of Chloroplasts
Chloroplast interior separated into thylakoids and stroma
Thylakoids are the site of light dependent reactions
large surface area to maximize light absorption
small space inside thylakoids allows for proton accumulation (pH = 4) , creating a chemoiosmotic gradient
Stroma is the site of light independent reactions
stroma (pH = 8) basic where Calvin cycle enzymes function optimally

30. Structure and Function of Chloroplasts
Membranes & Proteins
Thylakoid membranes hold photosystem pigments (hydrophobic)
Photolysis enzymes on inner surface of thylakoid membrane for splitting water into oxygen and hydrogen
Proteins in thylakoid membranes allow electron transport/ ETC between PsII and PsI.
Some proteins between PSII and PSI pump protons into the thylakoid interior contributing to the chemiosmotic gradient
NADP reductase bound to outer thylakoid membrane allowing reduction of NADP to NADPH for Calvin cycle
ATP synthase transmembrane complex bound across thylakoid membrane allow ATP production in stroma

31. Structure and Function of Chloroplasts
chloroplast DNA allows for protein synthesis
chloroplast ribosomes allow for protein synthesis
chloroplast starch granules allow for storage of photosynthetic products

32. Light dependent vs. independent
Light independent
Occurs in thylakoid
Occurs in stroma
Uses light energy to form ATP and NADPH
Uses ATP and NADPH to form triose phosphate
Splits water in photolysis to provide replacement electrons and H+ and to release oxygen to the atmosphere
Returns ADP, inorganic phosphate and NADP to the light dependent reaction
Includes two electron transport chains and photosystems I and II
Involves the Calvin Cycle
Damon et al., 2007

33. To do
Calvin’s Lollipop apparatus data base question p. 397 Q 1 -3 (section 8.3 photosynthesis)
Watch photosynthesis animations here