1.
AP BIOLOGY PHOTOSYNTHESIS Part 1: Photosynthesis & Chloroplast Structures

2. Organisms capture and store free energy to use in biological processes to grow, reproduce and maintain homeostasis
Organisms can do this in different ways

3. Autotrophs: capture free energy from physical sources in environment
Photosynthesis: capture free energy from sunlight
Example: plants
Chemiosynthesis: capture free energy from small inorganic molecules present in the environment
Bacteria in thermal vents in bottom of ocean where there is no oxygen
Heterotrophs: capture free energy present in carbon compounds produced by other organisms
Examples: animals, fungi

4. History of Photosynthesis
First evolved in prokaryotic organisms
Evidence supports that bacterial photosynthesis was responsible fro the production of our oxygenated atmosphere
This process led to the evolution of eukaryotic photosynthesis

5. Photosynthesis Overview
Sunlight + 6CO2 + 6H2O  C6H12O6 + 6O2

6. PHOTOSYNTHESIS HAPPENS IN CHLOROPLASTS
THYLAKOIDS
= sac-like
photosynthetic = stack of thylakoids
membranes
inside chloroplast
GRANUM (pl. grana)
Image from BIOLOGY by Miller and Levine; Prentice Hall Publishing©2006

7. SPACES THYLAKOID SPACE (lumen) STROMA cytoplasm
Gel-filled space inside chloroplast surrounding
thylakoid sac
Gel-filled space
Inside the
thylakoid
sac
cytoplasm
Gel-filled space OUTSIDE chloroplast but inside the cell membrane

8. Light Dependent Reactions
Photosynthesis Lecture 2

9. Photosynthesis Light reactions Calvin cycle light-dependent reactions
energy production reactions
convert solar energy to chemical energy
Make ATP & NADPH
Calvin cycle
light-independent reactions
sugar production reactions
use chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

10. pigments Plants gather the sun’s energy with
light absorbing molecules called
_______________.
pigments
By: VanderWal

11. The main energy absorbing molecule in green plants is
The main energy
absorbing molecule
in green plants is
__________________
CHLOROPHYLL a

12. CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW
CAROTENOID PIGMENTS appear ORANGE, RED, and YELLOW
Carotene
appears orange
Xanthophyll
appears yellow

13. Pigments of photosynthesis
Chlorophyll & other pigments
embedded in thylakoid membrane
arranged in a “photosystem”
structure-function relationship

14. Light: absorption spectra
Photosynthesis gets energy by absorbing wavelengths of light
chlorophyll a
absorbs best in red & blue wavelengths & least in green
other pigments with different structures absorb light of different wavelengths

15. WHY ARE PLANTS GREEN? We “see” reflected light
Light wavelengths that are reflected
bounce back to your eyes . . .
so leaves “LOOK” green.
Image modified from:

16. WHY DON’T WE SEE THE OTHER PIGMENTS?
Carotenoids are usually hidden by
the presence of chlorophyll

17. In the fall chlorophyll production shuts down and other pigments “show”

18. Photosystems of photosynthesis
2 photosystems in thylakoid membrane
Photosystem II
Occurs first
Photosystem I
Occurs second
Chlorophylls absorb free energy from light to boost its electrons to a higher energy level in photosystems I and II of the Light Dependent Reactions (LDR) which is used to create ATP and NADPH as part of the electron transport chain (ETC)

19. ETC of Photosynthesis Photosystem II Photosystem I
Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide

20. Light Dependent reactions
Electron Transport Chain
membrane-bound proteins in organelle
electron acceptors
NADPH
proton (H+) gradient across inner membrane
ATP synthase enzyme
Not accidental that these 2 systems are similar, because both derived from the same primitive ancestor.

21. Chloroplasts transform light energy into chemical energy of ATP
use electron carrier NADPH
ETC of Photosynthesis
Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide

22. LIGHT DEPENDENT REACTIONS
ETC produces from light energy
ATP & NADPH
go to Calvin cycle (light independent reacitons)
PS II absorbs light
excited electron passes from chlorophyll to “primary electron acceptor”
need to replace electron in chlorophyll
enzyme extracts electrons from H2O & supplies them to chlorophyll
splits H2O
O combines with another O to form O2
O2 released to atmosphere

23. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thylakoid membrane is established
The hydrogen ions that split off water must be removed from the thylakoid space
These hydrogens are used in the synthesis of ATP from ADP and inorganic phosphate via ATP synthase that is embedded in the thylakoid membrane

24. ETC of Photosynthesis to the Calvin Cycle 3 1 H+ 4 H+
PS II absorbs light
Excited electron passes from chlorophyll to the primary electron acceptor
Need to replace electron in chlorophyll
An enzyme extracts electrons from H2O & supplies them to the chlorophyll
This reaction splits H2O into 2 H+ & O- which combines with another O- to form O2
O2 released to atmosphere
Chlorophyll absorbs light energy (photon) and this moves an electron to a higher energy state
Electron is handed off down chain from electron acceptor to electron acceptor
In process has collected H+ ions from H2O & also pumped by Plastoquinone within thylakoid sac.
Flow back through ATP synthase to generate ATP. 4 H+
ADP + Pi
ATP

25. ETC of Photosynthesis to the Calvin Cycle 3 1 2 H+ 4 H+ ATP ADP + Pi

26. $$ in the bank… reducing power
ETC of Photosynthesis
electron carrier 6
to the Calvin Cycle 5
Need a 2nd photon -- shot of light energy to excite electron back up to high energy state.
2nd ETC drives reduction of NADP to NADPH.
Light comes in at 2 points.
Produce ATP & NADPH
$$ in the bank… reducing power

27. ETC of Photosynthesis split H2O Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide
split H2O

28. MAKING ATP moves the electrons runs the pump pumps the protons
forms the gradient
drives the flow of protons through ATP synthase
attaches Pi to ADP
forms the ATP H+
ADP + Pi
ATP

29. Noncyclic Photophosphorylation
Light reactions elevate electrons in 2 steps (PS II & PS I)
PS II generates energy as ATP
PS I generates reducing power as NADPH
1 photosystem is not enough.
Have to lift electron in 2 stages to a higher energy level. Does work as it falls.
First, produce ATP -- but producing ATP is not enough.
Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle!

30. Cyclic photophosphorylation
PS I doesn’t pass electron to NADP… it cycles back to ETC & makes more ATP, but no NADPH
coordinates light reactions to Calvin cycle
Important in maintaining proportion of ATP & NADPH for Calvin
Calvin cycle uses more ATP than NADPH X

31. Photophosphorylation
cyclic
photophosphorylation
noncyclic
photophosphorylation

32. Experimental evidence
Where did the O2 come from?
radioactive tracer = O18
6CO2
6H2O
C6H12O6
6O2
light
energy  +
Experiment 1
6CO2
6H2O
C6H12O6
6O2
light
energy  +
6CO2
6H2O
C6H12O6
6O2
light
energy  +
Experiment 2
Proved O2 came from H2O not CO2 = plants split H2O

33. LIGHT DEPENDENT REACTION
Requires ______________
Molecules embedded in ________________________
Made up of __________________
connected by ______________________
& ___________________
Uses light energy to change
ADP + P → _______
NADP+ + 2e- + H + → _________
Breaks apart ______ molecules and releases _____________
LIGHT
THYLAKOID membranes
PHOTOSYSTEMS II & I
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
ATP
NADPH
H20
oxygen

34. LIGHT REACTIONS summary
Where did the energy come from?
Where did the electrons come from?
Where did the H2O come from?
Where did the O2 come from?
Where did the O2 go?
sunlight
From chlorophyll; replaced by H2O
In through roots
Made when water splits
Out through stomata

35. LIGHT REACTIONS summary
Where did the H+ come from?
Where did the ATP come from?
What will the ATP be used for?
Where did the NADPH come from?
What will the NADPH be used for?
Split off of water
Produced by ATP synthase during light rxns
Make sugar in Calvin cycle
Receives e-’s at end of ETC
Make sugar in Calvin cycle
…stay tuned for the Calvin cycle

36. Light Independent Reactions
Photosynthesis Lecture 3

37. PHOTOSYNTHESIS Light-Dependent Reaction Light & Water Oxygen
ATP
NADPH
(CH2O)n
Carbon Dioxide
Light-Independent Reactions
CALVIN CYCLE

38. CALVIN CYCLE ____________ require ____________
(also called _________________________)
____________ require ____________
Happens in _________ between thylakoids
NADPH donates _______________
ATP donates _________________
CO2 donates ______________
to make __________________________
LIGHT INDEPENDENT
DOES NOT
LIGHT
STROMA
Hydrogen ions + electrons
ENERGY
Carbon & oxygen
glucose

39. Calvin Cycle *
See Calvin cycle animation
X 2

40. To make one glucose molecule C6H12O6 the Calvin cycle uses
_____ molecules of CO2
_____ molecules of ATP
_____ molecules of NADPH 6 18 12
Campbell concept check 10.3

41. CALVIN CYCLE summary Where does the C in glucose come from?
Where does the H in glucose come from?
Where does the O in glucose come from?
Where does the ADP & NADP+ go?
CO2
From H2O via NADPH
CO2
Back to light reaction to recharge

42. STOMA (pl. STOMATA)
GUARD CELLS

43. PROBLEMS ON HOT DRY DAYS
If stomata are open to receive CO results in water loss
On hot, dry days if plant shuts stomata to conserve water photosynthesis slows

44. PHOTORESPIRATION C3 ____ plants (Ex: rice, wheat, soybeans)
(1st product of carbon fixation has 3 C’s- 3PG)
On hot, dry days when plant shuts stomata
plant switches to ______________________
Rubisco adds O2 to Calvin cycle instead of CO2
Product broken down by mitochondria/peroxisomes to release CO2
COUNTERPRODUCTIVE:
Makes NO ATP
Makes NO sugar
Uses ATP
Decreases photosynthesis by siphoning molecules from Calvin cycle
PHOTORESPIRATION

45. ALTERNATIVE METHODS of CARBON FIXATION
______ plants (Ex: corn & sugarcane
Spatial separation of steps for carbon fixation and calvin cycle in different types of cells
______ Crassulacean acid metabolism (Ex: succulents, cactus, pineapple,)
Temporal separation of steps, carbon fixation and calvin cycle occur in same cell one at night and other during day
WAYS TO AVOID DECREASE IN PHOTOSYNTHESIS DUE TO PHOTORESPIRATION
CAM
SEE ANIMATION

46. CALVIN CYCLE found in BUNDLE SHEATH CELLS in C4 plants*
PEP CARBOXYLASE
________________________ adds CO2 to make a 4 carbon molecule before entering Calvin Cycle