1. Ch 8 AP Biology Converting Solar Energy to Chemical Energy
Photosynthesis
6 CO H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O
Ch 8 AP Biology
Converting Solar Energy to Chemical Energy

2. Autotrophs vs. Heterotrophs
Autotrophs: photosynthesis (or chemosynthesis) and Cellular Respiration
Photoautotrophs: free energy source: light
Chemoautotrophs: energy source: chemicals
Types of Autotrophs:
Plants
Algae
Cyanobacteria
Protists
Bacteria
Heterotrophs:
Eat other organisms to obtain energy.
Cellular Respiration (or fermentation) only

3. Chloroplast: Site of photosynthesis
Double Membrane
Chlorophyll
Green pigment, absorbs sunlight, reflects back green and yellow light
Stroma
fluid in chloroplast
Thylakoid
pancake like structure (increases surface area)
Grana
stacks of thylakoids
Leaf
interior cells: mesophyll
Stomata: pores in leaf for gas exchange
Chloroplast
Mesophyll
5 µm
Outer
membrane
Intermembrane
space
Inner
Thylakoid
Granum
Stroma
1 µm

4. Anatomy of a leaf

5. Light and Pigments Pigments absorb visible light:
Chlorophyll a: light reactions absorbs violet, blue and red
Accessory pigments
Chlorophyll b: absorbs blue & orange
Carotenoids: absorbs blue
Electromagnetic Spectrum
Light energy
Lower wavelength, higher E
10_07LightAndPigments_A.swf
Photons are particles of light, light travels as both energy and a particle. E=mc2
Light
Reflected
Chloroplast
Absorbed
light
Granum
Transmitted
Figure 10.7

6. Spectrophotometer or Colorimeter measures wavelength of light absorbed by pigments
Shine white light through a prism, separate colors
Pick a color to shine through a sample
Measure transmission of that color
High transmission = low absorption & 1/X
Notice the wavelengths for each pigment

7. Photosynthesis 6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2
Light Reactions
Occur in the thylakoid membranes of the chlorplasts
Absorb light (free) energy & convert it to ATP, NADPH & O2
10_05Photosynthesis.mpg
Calvin Cycle (Dark Reactions or light independent Rxns)
Occur in the stroma
Uses Energy from the light reactions to make food!

8. Figure 10.5 H2O CO2 [CH2O] O2 (sugar) Light NADP  ADP + P CALVIN
LIGHT REACTIONS
CALVIN
CYCLE
Chloroplast
[CH2O]
(sugar)
NADPH
NADP 
ADP
+ P O2
Figure 10.5
ATP

9. Light Reactions (photosystem I & II)
Thylakoid Membranes
Solar Energy + H2O  ATP + NADPH + O2
ATP + NADPH will be used in the Calvin Cycle
O2 is given off by the autotroph as a by product (water is source of Oxygen)
H2O is split by photons of light to provide electrons for the electron transport chain
NADP + is the equivalent to NAD + in Respiration (it carries electrons (reduced) to be used later in photosynthesis to power an H+ pump)
Remember: a photon of light that is higher E than an e- can excite the e- ,when the e- falls back down E is released when this happens in the chloroplast, the E is captured in the redox reaction.

10. Light Reactions

11. Photosystems Linear Electron flow
Photosystem II (P680)
Red part of visible light
Absorbs light E
Enzymes splits H2O & 2e- are used in photosystems, O2 from 2 water molecules is given off
Passes the E through electrons, down an ETC (chemiosmosis)
The E is used to make ATP
Photosystem I (P700)
Far red part of visible light
Catches the e- from PSII and uses solar energy to excite the e- again.
The exergonic “fall” of e- down the ETC is now used to make NADPH
Study Figure 8.16 on page 167 for an explanation of ETC

12. Linear or Non-cyclic Flow

13. Cyclic Electron Flow
Cyclic Flow
Uses only PSI, no NADPH is made, ATP made is sent to Calvin Cycle
Likely an evolutionary leftover, used in some photosynthetic prokaryotes and all eukaryotes tested to date.

14. Calvin Cycle uses the ATP, NADPH & CO2 to make sugar
1. Carbon Fixation
CO2 attached to RuBP by the rubisco enzyme
RuBP splits in half to form 2 three carbon molecules
2. Reduction
ATP & NADPH used to make G3P (1 used to make glucose, one used in regeneration)
3. Regeneration of acceptor RuBP
RuBP is regenerated so that it is ready to accept more CO2
9ATP + 6NADPH + 3CO2  1/2 Glucose (G3P) the cycle turns twice for every glucose made

15. Process Where? Input Output
1. Light Reactions
Thylakoid Membrane
Sunlight + H2O
ATP + NADPH + O2
2. Dark Reactions
Stroma
ATP + NADPH + CO2
Glucose
TOTAL
Chloroplast
Sunlight + H2O + CO2
Glucose + O2

16. Alternative Pathways Photorespiration C4 plants CAM Plants
Plants close Stomata in hot dry climates to conserve water and energy
Starves the Calvin Cycle of CO2

17. Photorespiration An evolutionary remnant or a protection mechanism?
C3 plants – “normal photosynthesis”
Rubisco will bind O2 and CO2 at its active site
If CO2 is limited O2 will bind in its place in the Calvin cycle
NO ATP or glucose is produced
Energy is used
Decreases photosynthetic production by preventing the formation of 3-phosphoglycerate molecules

18. C4 Plants: alternative form of Carbon Fixation
C4 plants minimize the cost of photorespiration
By incorporating CO2 into four carbon compounds in mesophyll cells = a physical separation
These four carbon compounds are exported to bundle sheath cells, where they release CO2 used in the Calvin cycle

19. CAM Plants: CAM-TIME Desert plants – cactus, pineapple etc.
Conserve H2O by closing the stomata during the day when hot and opening stomata at night, a time separation
Fix CO2 into organic acids at night and store it in vacuoles then use the organic acids in the morning when the light reactions make ATP and NADPH

20. C4 vs. CAM Plants Both minimize photorespiration & optimize Calvin Cycle
Partially close stomata to conserve H2O
CO2 fixation w/ PEP carboxylase
DAY
Completes Calvin Cycle immediately
Bundle sheath cells
CAM
Close stomata completely during day to conserve H2O – open at night
CO2 fixation w/ PEP carboxylase
NIGHT
Stores organic acids in vacuole until morning then completes Calvin cycle
CAM-TIME

21. Non Cyclic Electron Flow
Concept Maps & Summary
Photosystem II
Electron Transposrt
Photosystem I
Light Reactions
Carbon Fixation
Reduction
CO2 regeneration
Calvin Cycle
Non Cyclic Electron Flow
Cyclic Electron Flow