1. AP Biology 2007-2008

2. Photosynthesis:
Life from Light and Air
AP Biology 2007-2008

3. Energy needs of life
 All life needs a constant input of energy
 Heterotrophs (Animals)
 get their energy from “eating others”
consumers  eat food = other organisms = organic molecules
 make energy through respiration
 Autotrophs (Plants)
 produce their own energy (from “self”)
 convert energy of sunlight
producers
 build organic molecules (CHO) from CO2
 make energy & synthesize sugars through
AP Biology photosynthesis

4. How are they connected?
Heterotrophs
making energy & organic molecules from ingesting organic molecules
glucose + oxygen → carbon + water + energy
dioxide
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
oxidation = exergonic
Autotrophs Where’s
making energy & organic molecules from light energy the ATP?
carbon + water + energy → glucose + oxygen
dioxide
6CO2 + 6H2O + light → C6H12O6 + 6O2
energy
AP Biology reduction = endergonic

5. What does it mean to be a plant
 Need to…
 collect light energy ATP
 transform it into chemical energy
 store light energy
 in a stable form to be moved around
glucose the plant or stored
 need to get building block atoms
CO2
from the environment H 2O
 C,H,O,N,P,K,S,Mg
N
 produce all organic molecules K P
needed for growth …
 carbohydrates, proteins, lipids, nucleic acids
AP Biology

6. Plant structure
 Obtaining raw materials
 sunlight
 leaves = solar collectors
 CO2
 stomates = gas exchange
 H2O
 uptake from roots
 nutrients
 N, P, K, S, Mg, Fe…
 uptake from roots
AP Biology

7. stomate
transpiration
AP gas exchange
Biology

8. Chloroplasts
cross section absorb
leaves of leaf
sunlight & CO2
CO2
chloroplasts
in plant cell
chloroplasts
chloroplast contain
chlorophyll make
AP Biology energy & sugar

9. chloroplast
H+ H +H + H++
+ +
Plant structure H H
+ +
+ H H H
ATP H+ H
thylakoid
 Chloroplasts
 double membrane
 stroma outer membrane inner membrane
 fluid-filled interior
 thylakoid sacs
stroma
 grana stacks
 Thylakoid membrane
contains thylakoid
granum
 chlorophyll molecules
 electron transport chain
 ATP synthase
 H+ gradient built up within
thylakoid sac
AP Biology

10. Photosynthesis
 Light reactions
 light-dependent reactions
 energy conversion reactions
 convert solar energy to chemical energy
 ATP & NADPH
It’s not the
 Calvin cycle Dark Reactions!
 light-independent reactions
 sugar building reactions
 uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
AP Biology

11. chloroplast thylakoid
H+ H+ +
H+ H+H + H+H+H +
+
H+ H H
Light reactions + ++H H
+H H
+
H H H + H+H+H +
+
+
ATP H
 Electron Transport Chain
 like in cellular respiration
 proteins in organelle membrane
 electron acceptors
 NADPH
 proton (H+)
gradient across
inner membrane
 find the double membrane!
 ATP synthase
enzyme
AP Biology

12. ETC of Respiration
Mitochondria transfer chemical energy from food molecules
into chemical energy of ATP
 use electron carrier NADH
generates H2O
AP Biology

13. ETC of Photosynthesis Chloroplasts transform light energy
into chemical energy of ATP
 use electron carrier NADPH
generates O2
AP Biology

14. The ATP that “Jack” built
photosynthesis respiration
sunlight breakdown of C6H12O6
H+
H+ H+ H+
H+ H+
H+ H+
 moves the electrons
 runs the pump
 pumps the protons
 builds the gradient
 drives the flow of protons
through ATP synthase ADP + Pi
 bonds Pi to ADP ATP
H+
 generates the ATP
AP Biology
… that evolution built

15. Pigments of photosynthesis
How does this
molecular structure
fit its function?
 Chlorophylls & other pigments
 embedded in thylakoid membrane
 arranged in a “photosystem”
 collection of molecules
AP 
Biology
structure-function relationship

16. A Look at Light
 The spectrum of color
V I B G Y O R
AP Biology

17. Light: absorption spectra
 Photosynthesis gets energy by absorbing
wavelengths of light
 chlorophyll a
 absorbs best in red & blue wavelengths & least in green
 accessory pigments with different structures
absorb light of different wavelengths
 chlorophyll b, carotenoids, xanthophylls
Why are
plants green?
AP Biology

18. Photosystems of photosynthesis
 2 photosystems in thylakoid membrane
 collections of chlorophyll molecules
 act as light-gathering molecules
 Photosystem II
reaction
 chlorophyll a center
 P680 = absorbs 680nm
wavelength red light
 Photosystem I
 chlorophyll b
 P700 = absorbs 700nm
wavelength red light
antenna
AP Biology pigments

19. ETC of Photosynthesis
chlorophyll a
Photosystem II
chlorophyll b
Photosystem I
AP Biology

20. ETC of Photosynthesis
sun
1
e
e
Photosystem II
P680
AP Biology chlorophyll a

21. Inhale, baby!
ETC of Photosynthesis
chloroplast thylakoid
+H H
+ +
H H H + H+H+H +
+ + +
H +H H
+H+ H
+
H+ H+H + H+H+H +
+
ATP H +H H
Plants SPLIT water!
H H
1 O
2
e
e O H
H
O
+H
e- H+
e-
e e
fill the e– vacancy
Photosystem II
P680
AP Biology chlorophyll a

22. ETC of Photosynthesis
chloroplast thylakoid
H+ H+ +
H+ H+H + H+H+H +
+
H+ H H
+H+ H
+
H+ H+H + H+H+H +
+
ATP H+ H H
e
e 3
1
2
e H+
e
4 ATP
H+ to Calvin Cycle
H+
H+ H+ H+
H+ H
+
H+ H+
energy to build
carbohydrates
Photosystem II
P680 ADP + Pi
chlorophyll a ATP
AP Biology
H+

23. ETC of Photosynthesis
e
e
e cy
e ca
n
sun
– va
e
5 e
th
e
l
fil
e
e e
Photosystem I
P700
Photosystem II
chlorophyll b
P680
AP Biology chlorophyll a

24. ETC of Photosynthesis
electron carrier
e
e
6
e
e
N
5 Cal ADPH
vin
Cyc to
sun le
Photosystem I
P700
Photosystem II
chlorophyll b
P680 $$ in the bank…
AP Biology chlorophyll a reducing power!

25. ETC of Photosynthesis
sun sun
e
e
e
e
H +
H H H+ H+ H +
+ +
O +
H+
+ H+ H+
H to Calvin Cycle
H
split H2O
ATP
AP Biology

26. ETC of Photosynthesis
 ETC uses light energy to produce
 ATP & NADPH
 go to Calvin cycle
 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
AP Biology  and we breathe easier!

27. Experimental evidence
 Where did the O2 come from?
 radioactive tracer = O18
Experiment 1
6CO2 + 6H2O + light → C6H12O6 + 6O2
energy
Experiment 2
6CO2 + 6H2O + light → C6H12O6 + 6O2
energy
Proved O2 came from H2O not CO2 = plants split H2O!
AP Biology

28. 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
ATP
AP Biology

29. Cyclic photophosphorylation
 If PS I can’t pass electron
to NADP…it cycles back
to PS II & makes more
ATP, but no NADPH
 coordinates light
reactions to Calvin cycle
 Calvin cycle uses more
ATP than NADPH
ATP
18 ATP +
12 NADPH
→ 1 C6H12O6
AP Biology

30. Photophosphorylation
cyclic
photophosphorylation
NADP
NONcyclic
photophosphorylation
ATP
AP Biology

31. Photosynthesis 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?
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?
AP Biology …stay tuned for the Calvin cycle

32. You can grow if you
Ask Questions!
AP Biology 2007-2008

33. Ghosts of Lectures Past
(storage)
AP Biology 2007-2008

34. Stomates
AP Biology