1. Chapter 4
Photosynthesis

2. Photosynthesis is the process by which certain organisms use light energy
To make sugar and oxygen gas from carbon dioxide and water
What does it need? (Input)
What does it make? (Output)
Light
energy
PHOTOSYNTHESIS 6
CO2 +
H2O
Carbon dioxide
Water
C6H12O6 O2
Glucose
Oxygen gas

3. Trophic Roles Autotrophs  Producers of the biosphere:
produce organic molecules from CO2 & inorganic raw materials
Heterotrophs  consumers

4. Learning Target
1. Describe Oxidation & Reduction reactions

5. REDOX Reactions
LEO the Lion Says GER

6. REDOX Reactions Oxidation Reduction CO2 + H2O + energy → C6H12O6 + O2
When a compound loses electrons
Reduction
When a compound gains electrons
CO2 + H2O + energy → C6H12O6 + O2
CO2 is reduced to form glucose
Water is oxidized to form O2

7. Photosynthesis is a redox process, as is cellular respiration
Photosynthesis is a redox process, as is cellular respiration
In photosynthesis
H2O is oxidized and CO2 is reduced
Reduction
Oxidation
6 O2
6 H2O
6 CO2 
C6H12O6
Figure 7.4A, B

8. Learning Check
If H2O is losing electrons than it is being reduced/oxidized
Co2 is being reduced/oxidized, which means it is gaining/losing electrons.

9. Photosynthesis Overview
Light reactions
Depend on light
Occur in Thylakoid Membrane
Light Independent (“Dark”) reactions
Does NOT need light
Occurs in the Stroma

10. Learning Target
Compare & contrast the structure & function of mitochondria & chloroplast
15. Determine what factors affect the process of photosynthesis & cellular respiration

11. Location, location, location
Where does the Light Dependent Reaction occur? The Light Independent reaction?

12. Chloroplast Structure
Found in mesophyll
1 mesophyll cell may have 30 chloroplasts
Stomata regulate passage of CO2, O2 and H2O

13. Learning Check Where does the Light Dependent Reaction occur?
The Light Independent reaction?
What factors could affect the process of photosynthesis?

14. Learning Targets
11. Describe the purpose of Chlorophyll & Accessory pigments.

15. Pigments Pigments Absorb light energy Boost e- become unstable!
Chlorophyll
Chlorophyll a  main pigment  blue-green
Chlorophyll b  accessory pigment  yellow-green
Other accessory pigments  absorb different wavelengths of light
Carotenoids  yellow-orange
Xanthophyll yellow
Rhodophyll  red
Fucoxanthin  brown
Why are plants green?
Why are plants changing color?

16. Photosystems
Pass energy  reaction center (chlorophyll a molecule)  transfers energy to primary electron acceptor
antenna pigments are primarily chlorophyll b, carotenoids & xanthophyll

17. Learning Check
What is the purpose/function of pigments?

18. Photosynthesis Overview
Light reactions
light energy  chemical energy (ATP and NADPH) and produce O2
Light Independent (“Dark”) reactions
Using ATP and NADPH from the light reactions form sugar from CO2

19. Learning Target
6. Explain how electron transport chains (ETC) establish an electrochemical gradient across membranes.
7. Contrast Chemiosmosis in Cellular Respiration and Photosynthesis

20. ETC, Chemiosmosis & ATP Synthase
Powers ATP synthesis in light reactions
electrons (e-) are passed along a chain of proteins (called the ETC) in the membrane  H+ pumped into Thylakoid space (chemiosmosis)
H+ diffuse back across the membrane through ATP synthase  powers the phosphorylation of ADP to produce ATP (photophosphorylation)

21. Photophosphorylation http://vcell. ndsu. nodak

22. Learning Check!
ETC uses the energy of e- being passed along to pump _______ from the ________ into the thylakoid _______
Chemiosmosis is the movement of ______ to create a ________concentration.

23. Learning Target
3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 14. Summarize how energy is transferred during photosynthesis and cellular respiration.

24. Electron Carriers NAD+ NADP+ ADP  ATP
Reacts with C-H bonds to become NADH
NADP+
Reacts with free e- and H+ ions
ADP  ATP
diffusion of H+ through ATP Synthase

25. LDR Inputs? Outputs? Two types: Noncyclic Photophosphorylation

26. Non-cyclic photophosphorylation

32. Learning Target 12. Describe the connection between PS2 & PS1

33. Cytochrome complex synthase reductase
LIGHT
REACTOR
NADP+
ADP
ATP
NADPH
CALVIN
CYCLE
[CH2O] (sugar)
STROMA
(Low H+ concentration)
Photosystem II
H2O
CO2
Cytochrome
complex O2 1
1⁄2 2
Photosystem I
Light
THYLAKOID SPACE
(High H+ concentration)
Thylakoid
membrane
synthase Pq Pc Fd
reductase
+ H+
NADP+ + 2H+ To
Calvin
cycle P 3 H+
2 H+
+2 H+

34. Light Dependent RXN animation

35. Cyclic Photophosphorylation
Primitive  used by bacteria
Electron boosted out of P1  ETC  returned to P1
Electron drives proton pumps chemiosmosis  ATP

36. Learning Targets
3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle. 4. Explain the role of NADH, FADH2, and NADPH. 15. Summarize how energy is transferred during photosynthesis and cellular respiration.

38. Calvin Cycle/Light Independent Reactions
Occur in the dark or the light
Light independent reactions
3 steps
Carbon fixation
Reduction
Regeneration of RuBP

39. Step 1: Carbon Fixation RuBP (ribulose bisphosphate)
5 C sugar
Catalyzed by Rubisco (RuBP carboxylase)
Adds CO2
Creates an unstable 6 C molecule that splits
Creates PGA (3 C moleucle

40. Step 2: Reduction PGA gets phosphorylated by ATP (gets it’s energy)
Reduced by NADPH (gets it’s e-)
Produces G3P (PGAL)
some G3P  glucose
most G3P  regenerate RuBP

41. Step 3: Regeneration of RuBP
1 G3P moves out to eventually become glucose
G3P  rearranged into RuBP
Requires input of 3 ATP
Takes 6 turns of cycle  1 glucose

43. Alternative mechanisms: Photorespiration
C3 plants  rice, wheat, soybeans
Uses Co2 directly to make PGA
On hot, dry days they close their stomata
no CO2 taken in and O2 builds up
rubisco substitutes O2 for CO2
Creates a 2 C compound
2 C compound gets broken down  releases CO2 & water
Called photorespiration
Uses light, releases CO2 and water
Doesn’t make glucose

44. Alternative mechanisms: C4 Plants
Sunny ecosystems
C is fixed into 4 C molecule
Carbon fixed outside cells (in bundle sheath cells  very efficient  requires extra ATP
Only fixes C, not oxygen
Donates the carbon to Calvin Cycle
Balances out photorespiration & saves water
Corn and sugarcane are a C4 plants

45. Alternative mechanisms: CAM Plants
Crassulacean acid metabolism  Hot/dry climates
Orchids, cacti, pineapple etc.
Stomates open at night to reduce water loss  evaporation
CO2 is fixed into a 4 C compound, used later