1. Using Light to Make Food
Photosynthesis
Using Light to Make Food

2. photosynthesis
Transformation of sun’s energy into useable energy (energy of chemical bonds) by autotrophs

3. Where? When?

4. Light facts Radiant energy from sun = 1 million Hiroshima bombs
1/3 of sun’s energy reflected back to space
Less than 1% captured by photosynthesis

6. Light facts, cont’d… Described as “waves” or particles
Electromagnetic spectrum shows all wavelengths
Absorbtion spectrum shows photons capable of being “captured”

7. How to capture light

9. 2 steps to photosynthesis
Light RXN
Generates NRG to drive the making of glucose
Light Independent RXN
Uses NRG of Light RXN to grab Carbon dioxide from the atmosphere and make glucose

11. Light Reaction Capture light at PSII and PSI
Splitting water generates H+/e-
ETC & the proton pump makes ATP (chemiosmosis or photophosphorylation)
H+/e- carried by NADP for use in next step
O2 released as waste

12. Light Independent Reaction
Also known as Dark RXN, Calvin Cycle, carbon fixing cycle, and C3 cycle
This is where glucose is made

14. *CO2 is “grabbed” by a 5-sugar compound, RuBP – carbon fixation
*NADPH wagons dump H+/e-
H+ are needed to build CHO molecules
CO2 + H+/e- makes PGAL, then glucose

15. PGAL is an intermediary step in respiration
Recall…
Glucose breaks down to PGAL (then to Pyruvate)
Therefore PGAL is a key link in the breakdown and build up of organic molecules

16. Most PGAL continues the cycle to regenerate RuBP so the cycle can go again
**1 PGAL drops out of the cycle and goes on to make organic compounds
Glucose
Proteins
lipids

17. It takes 6 turns of the cycle to make enough PGAL to make 1 molecule of glucose

19. Rate of photosynthesis
If you change input, you change output

21. Stomata, open and closed
Figure 7.2x2

22. Plant Dilemmas
Keeping stomata open to bring in CO2 also means the plant is losing water
Loss of water is BAD
Without CO2, no glucose can be made – that’s BAD
What’s a plant to do???

23. Alternative pathways C4 pathway & CAM pathway
“stockpile” CO2 during evening or when stomata are partially closed to be used later
Stomata can be closed to stop the loss of water during times of water shortage

24. This molecule can then donate CO2 to the Calvin cycle
Special cells in C4 plants—corn and sugarcane—incorporate CO2 into a four-carbon “storage” molecule
This molecule can then donate CO2 to the Calvin cycle
4-C compound
CALVIN CYCLE
3-C sugar
Figure 7.12B

25. The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism
They open their stomata at night and make a four-carbon compound
It is used as a CO2 source by the same cell during the day
4-C compound
Night
Day
CALVIN CYCLE
3-C sugar
Figure 7.12C

26. Respiration Photosynthesis
step by step break down of organic compounds
Photosynthesis
step by step build up of organic compounds

27. It takes energy to make energy…
Flow of energy in universe is constantly cycled
Stored in chemical bonds
Released from chemical bonds

28. Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A & B

29. Photosynthesis removes CO2 (greenhouse gas) and adds O2 (used to make ozone (O3)

30. This lets harmful UV rays thru, increasing GW
Industrial chemicals called CFCs “eat ozone”, causing dangerous thinning of the ozone layer
This lets harmful UV rays thru, increasing GW
Sunlight
International restrictions on these chemicals are allowing recovery
Southern tip of South America
Antarctica
Figure 7.14B