1. How do photoautotrophs use light to make their own food?
Photosynthesis
How do
photoautotrophs
use light to make
their own food?

2. Autotrophs Literally means “self-feeders”
Include all plants, some bacteria, archaea, and protists (algae)
make organic food molecules (e.g. glucose) from inorganic raw materials (e.g. water and carbon dioxide)

3. Leaf Section Chloroplast http://iusd.k12.ca.us/uhs/cs2/
images/Leaf%20Cross-section.jpg
Chloroplast

4. How can carbon dioxide get into the leaf?
Leaf Structure
Through tiny holes on leaf surface called stomata
Oxygen produced from photosynthesis can also escape out of leaves through stomata

5. lab bench Stomata Regulation of Guard Cells Closed Stomate

6. A. Open stoma B. Closed stoma

7. How can we tell if a plant is actively photosynthesizing?

8. Photosynthesis and oxygen atoms
6 CO H2O  C6H12O6 + 6H2O + 6O2
No label
6 CO H2O  C6H12O6 + 6H2O + 6O2
Label

9. Redox reactions… Which one is photosynthesis?
reduction
6 CO H2O  C6H12O6 + 6H2O + 6O2
oxidation
oxidation
C6H12O6 + 6O2  6 CO2 + 6 H2O
reduction

11. Electromagnetic Spectrum
Spectrum.png/350px-Electromagnetic-Spectrum.png

12. Green plants are green because…
Chlorophyll reflects green light, but absorbs light in the red, orange, blue, indigo and violet wavelength range
Other pigments absorb light of different wavelengths, e.g. carotenoids are yellow-orange pigments

13. Chlorophyll embedded in a photosystem

14. Two photosystems Chemiosmosis
Photosystem I was discovered first and the chlorophyll a of its reaction center absorbs light best at 700 nanometers (far-red zone)
Photosystem II reaction center chlorophyll absorbs best at 680 nm (red zone)
Chemiosmosis

15. Electron flow in the light reactions

16. Two types of photosystems cooperate in the light reactions
Photon
ATP
mill
Photon
Water-splitting
photosystem
NADPH-producing
photosystem

17. Two stages of Photosynthesis
Light Reactions
takes place in thylakoid membranes (grana) of chloroplasts
Dark Reactions (Calvin Cycle)
takes place in the stroma (thick fluid inside chloroplasts)

18. I. Light Reactions Input: Output: H2O (from roots) O2 NADP+
ADP and Phosphate
photons (packets of light energy)
Output: O2
NADPH (carrying electrons)
ATP

19. Light Reactions of photosynthesis Noncyclic Photophosphorylation

20. Light Reactions Animations
Light Dependent Reactions
Light Reaction Light Reaction
Light Reaction
NonCyclic Photophosphorylation
Cyclic Light Reaction

21. Cyclic Photophosphorylation

22. II. Calvin Cycle Output: Input:
G3P (glyceraldehyde 3-phosphate) used to make glucose
NADP+
ADP and Phosphate
Input:
CO2
ATP
NADPH
RuBP (ribulose biphosphate: a 5-carbon sugar)

25. Calvin Cycle Carbon is reduced to glucose (carbon fixation)
Electrons and protons are added to carbon
NADP+ is regenerated so it can be reused in the Light Reactions

26. Calvin Cycle Animations
Calvin Cycle Calvin Cycle
Calvin Cycle Dark Reactions
Interactive Photosynthesis

28. Alternate Mechanisms of Carbon Fixation
C3 plants like rice, wheat, and soybeans
Rubisco can accept O2 instead of CO2
resulting in photorespiration Stomates on hot dry days
decrease carbon dioxide in leaf starves Calvin Cycle
oxygen concentrations in the leaf overtake CO2
photorespiration occurs decreasing photosynthetic
output taking organic material away from
Calvin Cycle

29. C3 95 percent of the plant species on earth
The equation for the Calvin Cycle:
CO2 (Carbon dioxide in from stomata) + RuBP (Ribulose bisphosphate already in plant) + the enzyme RUBISCO (Ribulose bisphosphate carboxylase) “fixes” carbon from the atmosphere  2PGA (phospholygerate)
PGA enters Calvin cycle in Mesophyll cells  more RuBP (to fix more CO2) + sugar (CH2O)
C3 are inefficient at CO2 fixation because RUBISCO has a greater affinity for oxygen than CO2
Mesophyll cells are packed with RUBISCO
Stomata open during day (CO2, oxygen, and water can all flow out)
Photorespiration undoes CO2 assimilation
2PGA  CO2 + RuBP
increases when there is lots of O2, low levels of CO2, and increased temperature

30. C4 crop plants—sugar cane and corn
2nd most prevalent photosynthetic type
C4 plants—carbon fixation and photosynthesis split between the mesophyll cells and bundle sheath cells.
The equation:
In mesophyll (carbon fixation):
CO2 + PEP (phosphoenol pyruvate) + PEP carboxylase fixes carbon  OAA (oxaloacetic acid) OAA diffuses to bundle sheath cells
In bundle sheath (Calvin Cycle):
OAA  malic acid and aspartic acid is decarboxylated  CO2 + pyruvate
Then the Calvin Cycle CO2 + RuBP + the enzyme RUBISCO  2PGA  RuBP + CH2O
Pyruvate with ATP is moved back to mesophyll and turned into PEP (to fix more CO2)

31. C4 Photosynthesis

32. C4 Feature of many grasses (i.e. big blue stem back campus), corn,
and many arid/semi arid shrubs
Calvin cycle in bundle sheath cells where there is no oxygen
to be bound by RUBISCO
Very high concentration of CO2 in bundle sheath cells
PEP carboxylase has a high affinity for CO2 so plants must open
their stomata less to get CO2 and hence lose less water
(especially important in arid regions)
Low levels of photorespiration and higher net photosynthesis
than C3 because of low photorespiration
Costly adaptation because it requires lots of ATP (energy)—
however, benefits outweigh energy costs.
Stomata are open during the day
Fixation and the Calvin cycle are physically separate C4