Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy. It occurs in two stages - the light-dependent reactions in which ATP and NADPH are produced, and the light-independent Calvin cycle where glucose is formed. Chlorophyll and other pigments in chloroplasts absorb light which is used to power electron transport and generate energy carriers. C4 and CAM plants have evolved adaptations to limit photorespiration and water loss compared to C3 plants.

1. Photosynthesis
6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O

2. Synthesizes energy-rich organic molecules (glucose) from energy-poor
molecules (CO2, H2O).
Uses CO2 as carbon source & light energy as energy source.
Directly or indirectly supplies energy to most living organisms.

3. The major
“Play-as”
Fig. 10.4

4. Photosynthesis occurs in chloroplasts in eukaryotic
organisms:
• Light dependent reactions occur in the thylakoid
membranes of the grana and yield ATP and NADPH
(obtained by reducing NADP with H2O). O2 is a waste
product
2. The Calvin cycle occurs in the space between grana
called stroma

5. Fig. 10.6

6. l Photo = light
l synthesis = putting together
l = production of sugar (glucose = C6H12O6)
using E from solar radiation (photons), CO2
and H2O
l Photons = fixed quantity of light E
l Utilized by most plants, some bacteria,
some protists

7. Nutritional categories
1. Autotrophs – require no organic nutrients. All can
“fix” or reduce CO2 into glucose via the Calvin Cycle:
6CO2 + 12 NADPH + 18 ATP
C6H12O6 + 12 NADP + 18 ADP + 18 P
They can then synthesize all other organic constituents
from this glucose

8. Autotrophs
• Photoautotrophs – use light energy to generate both
the ATP and NADPH for the Calvin cycle.
(photosynthetic organisms)
B) Chemoautotrophs – cannot use light. Use respirations
of inorganic substrates like reduced sulfur compounds,
nitrogen compounds, and iron to generate the ATP and
NADPH for the Calvin cycle (all chemosynthetic organisms
are bacteria)

9. 2. Heterotrophs – require at least 1 organic nutrient.
Heterotrophs are dependent upon autotrophs, usually the
photosynthetic organisms, for a source of fixed carbon
(ie carbohydrates) and other nutrients
Photoautotrophs are considered “producers” in an
ecosystem. Heterotrophs are considered as “consumers”
All life is therefore either directly or indirectly dependent
upon the energy of the sun

10. l In eukaryotes, takes place in chloroplasts
l Plants - chloroplasts in leaves, other green
parts
l Contain chlorophyll
l = green pigment
l captures/absorbs light E

11. Electromagnetic Spectrum
Nm = nanometer = 10-9 m
0.0000000001 m Fig. 10.7
Based on Wavelength
Short wavelength = high E Long wavelength = low E

12. Electromagnetic Spectrum
l Range = wavelengths of less than 1 nm
(gamma rays) to wavelengths of more than
1 km (radio waves)
l gamma = high E
l radio = low E

13. Visible Light
l Drives photosynthesis
l = light detectable by human eye
l 380-750 nm
l Ranges from violet red
l ROY G BIV backwards
l red, orange, yellow, green, blue, indigo,
violet

14. l Blue and red most important in
photosynthesis
l Why?
l Colors (wavelengths) absorbed by
chlorophyll
l Why is chlorophyll green?

15. l Light can be:
l reflected, transmitted, absorbed
l reflected - “bounces” off of pigment
l = color that you see
l transmitted - goes through pigment
l absorbed - captured by pigment
l don’t see

16. Fig. 10.7+8

17. l Different pigments absorb different
wavelengths of light
l pigment = substance that absorb visible
light
l Wavelengths absorbed, disappear
l black = all wavelengths absorbed
l white = all wavelengths
reflected/transmitted

18. Photosynthetic Pigments in
Plants
l Chlorophyll a
l Chlorophyll b
l = yellow-green
l absorbs slightly different wavelength
l Carotenoids
l = yellow & orange
l Phycocyanins
l = blue and purple

19. l Chlorophyll a = primary pigment
l Chlorophyll b, carotenoids and
phycocyanins = accessory pigments
l Expand range of wavelengths available for
photosynthesis

20. Absorption and action
spectra for photosynthesis
Fig. 10.10

21. Chloroplast Structure
l Lens-shaped
l surrounded by double membrane
l divided into 3 compartments by system of
membranes

22. Chloroplast Structure
l 1. Intermembrane space
l = space between the 2 outer membranes
l 2. Thylakoid space
l thylakoids = flattened membranous sacs
inside chloroplast
l Stacks of thylakoids = grana
l chlorophyll embedded within thylakoid
membrane

23. l membrane separates thylakoid space
l = area inside of thylakoids
l from stroma
l 3. Stroma
l = thick fluid outside/surrounding thylakoids

24. Fig. 10.11

25. l Photosynthesis
l - light (kinetic) E → chemical (potential) E
l E stored in bonds of glucose molecules
l Breaking bonds releases E

26. Photosynthetic Process
l 2 stages
l 1. Light Dependent Reactions
l - require sunlight
l 2. Light-Independent Reactions (Calvin Cycle)
l - don’t require sunlight

27. l 1. Light Reactions
l convert light energy to chemical energy
l energy stored in bonds of ATP & NADPH
l - adenosine triphosphate
l - Nicotinamide adenine dinucleotide
phosphate

28. Light energy harvesting occurs via photosytems in
thylakoid membranes:
ADP + P + NADP + H2O + light energy
ATP + NADPH + O2
Involves 2 photosytems interconnected by an
electron transport chain

29. Light Rxns.
l Require sunlight = light dependent rxns.
l Occur in thylakoid membranes of
chloroplasts
l Thylakoid membranes contain photosystems
l = light harvesting units
l consist of reaction center, antenna
molecules, and e- acceptors

30. Example of a photosystem
Fig. 10.13a

31. Excitation of an isolated chlorophyl molecule
Fig. 10.12

32. l Reaction Center = single, specialized chlorophyll
a molecule + primary e- acceptor
l Antenna molecules = all other photosynthetic
pigment molecules
l (chlorophyll b, carotenoids, phycocyanins)
l e- acceptor molecules = molecules that accept
electrons from “excited” chlorophyll molecules

33. How photosystems work
l 1. Antenna molecules absorb photons
l 2. Pass energy from molecule to molecule
until rxn. center reached
l 3. Chlorophyll a molecule in rxn center
donates excited e- to primary e- acceptor

34. Photosystems
l Chlorophyll a molecule at rxn. center loses
e- to primary e- acceptor
l = electron transfer
l e- excited
l boosted to higher energy state

35. l Transfer of e- from chlorophyll a to primary
acceptor = redox rxn.
l = reduction/oxidation rxn.
l Reduction = gain of e- = more negative chg
l Oxidation = loss of e- = more positive chg
l primary acceptor gains e- (reduced)
l chlorophyll a loses e- (oxidized)
l = first step of light rxns.

36. l Thylakoid membrane contains 2 types of
photosystems
l - photosystem I
l - photosystem II
l each has characteristic rxn. center
l systems cooperate

37. l Photosystem I
l rxn. center absorbs light having wavelength
of 700 nm
l = P700
l Photosystem II
l absorbs light having wavelength of 680 nm
l = P680

38. l 2 systems cooperate to generate ATP &
NADPH
l ** = PRIMARY FUNCTION OF LIGHT
REACTIONS **

39. Non-cyclic electron flow generates ATP and NADPH
Fig. 10.14

40. Non-cyclic e- flow
“mechanical
analogy”
Fig. 10.15

41. Chemiosmosis of ATP
Fig. 10.18

42. Chemiosmosis in mitochondria and chloroplasts:
10.17

43. Light Independent Reactions
CO2 fixation via the Calvin Cycle (recall from previous
Notes)
6CO2 + 12 NADPH + 18 ATP
C6H12O6 + 12 NADP + 18 ADP + 18 P
See Fig. 10.17 for normal C3 pathway:

44. Calvin
Cycle
Fig. 10.19

45. Calvin
Cycle
6 CO2’s yield
1 glucose
Occurs in
Stroma
Catalyzed by
Rubisco
(RuBP)

46. Photorespiration:
- CO2 enter the plant leaf openings called stomata
-these openings are surrounded by guard cells which
when flaccid close the opening
-During dry conditions, stoma are thus closed and CO2
becomes limiting
-The Rubisco enzyme then reacts with O2 rather than
CO2 and photorespiration occurs instead of CO2
fixation

47. Photorespiration:
- Photorespiration wastes fixed carbon by converting
ribulose biphosphate into only 1 glyceraldehyde
phosphate plus 1 glycolic acid (CH2OHCOOH)
-this glycolic acid is removed from the cycle and is
Wasted
-plants evolved photosynthetic pathways to prevent
this wasteful process

48. C4 Plants and the C4 Photosynthetic Pathway:
-Occur/originated in tropics, Mediterranean
-Adapted to hot/arid environment
-Adaptations save water, prevent photorespiration

49. l Initial enzyme = PEP (phosphoenolpryuvate),
fixes C into 4 C molecule (oxaloacetate)
l Rubisco not involved initially
l - eliminates photorespiration
l C stored in 4 C molecule in mesophyll cells
l Calvin cycle occurs in nearby cells
l = bundle sheath cells

50. l Mesophyll cells shuttle C to bundle sheath
cells
l Allows photosynthesis to occur even if
stomates closed
l Examples: corn, sugarcane, Bermuda grass

51. C4 anatomy and pathway:
Fig. 10.20

52. l C4 can handle heat, drought, high light
l C3 more efficient if water is available and
under lowlight
conditions

53. CAM Plants
l = Crassulacean Acid Metabolism
l - Cacti, pineapples, succulents
l Open stomates at night
l - lets in CO2, minimizes water loss
l CO2 incorporated into organic acids (stored)
l Used in light rxns during day while
stomates closed

54. Comparison of
C4 and CAM
Fig. 10.21