1. Ch 10 NOTES (part 1): Photosynthesis in Nature

2. 10.1 – Photosynthesis converts light energy to the chemical energy of food.

3. PHOTOSYNTHESIS:
● PHOTOSYNTHESIS = the capture of light energy & the conversion of this energy to stored chemical energy (in the form of sugar)
-AUTOTROPHS: “producers”; capable of producing their own food PHOTOAUTOTROPHS: use light energy to synthesize food (e.g. plants)

5. ● Photosynthesis occurs in plants, algae, certain other protists, and some prokaryotes
● These organisms feed not only themselves but also the entire living world… thank you plants! 

6. Plants Unicellular protist Purple sulfur bacteria Multicellular algae
Cyanobacteria
40 µm

8. ● HETEROTROPHS: “consumers”; live on compounds produced by other organisms
-animals that eat plants or other animals
● Almost all heterotrophs, including humans, depend on photoautotrophs for food and oxygen

9. **some heterotrophs are:
-decomposers: live on dead matter

10. Chloroplasts: The Sites of Photosynthesis in Plants
● Leaves are the major locations of photosynthesis
● Their green color is from CHLOROPHYLL, the green pigment within chloroplasts
● Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast
● Through microscopic pores called STOMATA, CO2 enters the leaf and O2 exits

12. CHLOROPLASTS: ● organelles in which photosynthesis occurs
● found primarily in leaves (about 500,000
per mm2)
● contain green pigment CHLOROPHYLL
(absorbs light energy)
● found mainly in mesophyll (tissue inside leaf)
● a typical mesophyll cell has chloroplasts

14. Leaf cross section
Vein
Mesophyll
Stomata
CO2 O2
Mesophyll cell
Chloroplast
5 µm
Outer
membrane
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
Inner membrane
1 µm

15. ● CO2 enters and O2 leaves through STOMATA
● water is delivered to leaves from the roots via veins

16. CHLOROPLAST: ● enclosed by 2 membranes
● STROMA = fluid within the chloroplast
● THYLAKOID MEMBRANES are interconnected & contain the thylakoid space, or lumen (are usually in stacked columns called GRANA)
● chlorophyll is stored in the thylakoid membranes

18. PATHWAYS OF PHOTOSYNTHESIS
● TOTAL equation for photosynthesis:
6CO H2O + light  C6H12O6 + 6O2 + 6H2O
energy
● NET EQUATION:
6CO H2O + light  C6H12O O2

19. The Splitting of Water
● Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules

20. Tracking Atoms Through Photosynthesis:
Reactants:
6 CO2
12 H2O
Products:
C6H12O6
6 H2O
6 O2

21. Photosynthesis as a Redox Process
● Photosynthesis is a redox process in which water is oxidized and carbon dioxide is reduced

22. (the required energy boost comes from light energy)
● like respiration, photosynthesis is a series of redox reactions…BUT, the electron flow is reversed!…the electrons increase in potential energy as they move from water  sugar… an uphill process!
(the required energy boost comes from light energy)

23. Two Stages of Photosynthesis:
1) the LIGHT REACTIONS
2) the CALVIN CYCLE
(a.k.a. the “dark reactions”
or light-independent
reactions)

24. The Two Stages of Photosynthesis: A Preview
● Photosynthesis consists of the light reactions (the photo part) and the Calvin cycle (the synthesis part)

25. LIGHT REACTIONS: ● convert solar energy  chemical energy
● light is absorbed by chlorophyll and drives a transfer of electrons and H from water to an acceptor called: NADP+
● water is split and O2 is produced as a “waste product”
● NADP+ is reduced to NADPH…ALSO, ATP is generated via phosphorylation of ADP
(photophosphorylation!)

27. CALVIN CYCLE:
● CO2 from air is incorporated into organic molecules by carbon fixation
● NADPH and ATP from the light reactions power the production of sugar
● also called: the “dark” reactions or light-independent reaction

28. ● Light reactions occur in the THYLAKOIDS
Locations of the Photosynthesis Reactions:
● Light reactions occur in the THYLAKOIDS
● Calvin cycle occurs in the STROMA

29. H2O
Light
LIGHT
REACTIONS
Chloroplast

30. H2O
Light
LIGHT
REACTIONS
ATP
NADPH
Chloroplast O2

31. H2O CO2 Light NADP+ ADP + CALVIN CYCLE LIGHT REACTIONS ATP NADPH
Chloroplast
[CH2O]
(sugar) O2