Photosynthesis occurs through two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, chlorophyll absorbs sunlight and uses it to convert water to oxygen and produce ATP and NADPH. The Calvin cycle then uses ATP and NADPH to incorporate carbon dioxide into organic molecules to produce glucose. There are three types of photosynthesis - C3, C4, and CAM - that differ in how they incorporate carbon dioxide and their adaptations for water efficiency. C3 photosynthesis occurs in most plants while C4 and CAM photosynthesis have evolved in plants as adaptations for hot and dry conditions.

1. Photosynthesis
Light-Dependent Reactions
Calvin Cycle
Observe the animations
highlighted above

2. Fig. 10-2
(a) Plants
(c) Unicellular protist
10 µm
1.5 µm
40 µm(d) Cyanobacteria
(e) Purple sulfur
bacteria
(b) Multicellular alga
• Photosynthesis occurs
in plants, algae, certain
other protists, and
some prokaryotes
– These organisms feed
not only themselves but
also most of the living
world
BioFlix: PhotosynthesisBioFlix: Photosynthesis

3. Structures of Photosynthesis
• Chloroplasts are structurally similar to and
likely evolved from photosynthetic bacteria
• Leaves are the major
locations of
photosynthesis
• Their green color is from
chlorophyll, the green
pigment within
chloroplasts
• CO2 enters and O2 exits
the leaf through
microscopic pores called
stomata

4. Fig. 10-3a
5 µm
Mesophyll cell
Stomata
CO2 O2
Chloroplast
Mesophyll
Vein
Leaf cross section
• Chloroplasts
are found
mainly in cells
of the
mesophyll, the
interior tissue
of the leaf
– A typical
mesophyll
cell has 30–
40
chloroplasts
• Thylakoid
• Grana
• Stroma

5. The Photosynthesis Equation
6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O

6. Reactants:
Fig. 10-4
6 CO2
Products:
12 H2O
6 O26 H2OC6H12O6

7. • Light-
dependent
reactions
– Occurs in
Thylakoid
– Used H2O
and light to
produce ATP,
NADPH, and
O2
– NADPH is an
electron
carrier
• Calvin cycle
– Occurs in stroma
– uses carbon dioxide, ATP, and NADPH to
produce sugars

8. The Goal of Photosynthesis is to form high energy
sugars.
This requires transforming light energy into usable
chemical energy (ATP)
• ATP is form by the process of:
• Photophosphorylation –
– The production of ATP using energy derived
from the redox reactions of an electron
transport chain.

9. Redox Reactions
• A chemical reaction involving the transfer of
one or more elections from one reactant to
another; also called oxidation/reduction
reactions
• InIn oxidationoxidation, a, a
substance losessubstance loses
electrons, or iselectrons, or is
oxidizedoxidized
• InIn reductionreduction, a, a
substance gainssubstance gains
electrons, or iselectrons, or is
reduced (thereduced (the
amount ofamount of
positive chargepositive charge
is reduced)is reduced)

10. Fig. 9-UN1
becomes oxidized
(loses electron)
becomes reduced
(gains electron)

11. Fig. 9-UN2
becomes oxidized
becomes reduced

12. The Two Stages of Photosynthesis:The Two Stages of Photosynthesis: A PreviewA Preview
• The light reactions (in the
thylakoids):
– Split H2O
– Release O2
– Reduce NADP+
to
NADPH
– Generate ATP from
ADP by
photophosphorylation
• The Calvin cycle (in the
stroma) forms sugar from
CO2, using ATP and
NADPH
• The Calvin cycle begins
with carbon fixation,
incorporating CO2 into
organic molecules
• Photosynthesis consists of the light reactions (the
photo part) and Calvin cycle (the synthesis part)

13. Light
Fig. 10-5-1
H2O
Chloroplast
Light
Reactions
NADP+
P
ADP
i
+

14. Light
Fig. 10-5-2
H2O
Chloroplast
Light
Reactions
NADP+
P
ADP
i
+
ATP
NADPH
O2

15. Light
Fig. 10-5-3
H2O
Chloroplast
Light
Reactions
NADP+
P
ADP
i
+
ATP
NADPH
O2
Calvin
Cycle
CO2

16. Light
Fig. 10-5-4
H2O
Chloroplast
Light
Reactions
NADP+
P
ADP
i
+
ATP
NADPH
O2
Calvin
Cycle
CO2
[CH2O]
(sugar)

17. The light reactions convert solar energy to the
chemical energy of ATP and NADPH
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 10-7
Reflected
light
Absorbed
light
Light
Chloroplast
Transmitted
light
Granum
• Chloroplasts
are solar-
powered
chemical
factories
– Their
thylakoids
transform
light energy
into the
chemical
energy of
ATP and
NADPH

18. The Nature of Sunlight
• Light is a form of electromagnetic energy
• The electromagnetic spectrum is the entire range of
electromagnetic energy, or radiation
• Visible light consists of wavelengths (including those
that drive photosynthesis) that produce colors we can
see
WavelengthWavelength is theis the
distancedistance betweenbetween
crests of wavescrests of waves
WavelengthWavelength
determines the typedetermines the type
of electromagneticof electromagnetic
energyenergy

19. UV
Fig. 10-6
Visible light
Infrared
Micro-
waves
Radio
wavesX-raysGamma
rays
103
m
1 m
(109
nm)106
nm103
nm1 nm10–3
nm10–5
nm
380 450 500 550 600 650 700 750 nm
Longer wavelength
Lower energyHigher energy
Shorter wavelength

20. Light and Pigments
• Pigments –
light
absorbing
chemicals
• Chlorophyll –
principle
pigment in
plants
– Chlorophyll a
– Chlorophyll b
– Carotenoids
– Xanthophyll

21. Why do leaves change colors?
• Chlorophyll
a
• Chlorophyll
b

22. Component of a Chloroplast
• Thylakoid – Saclike
photosynthetic
membranes
– Light-dependent
reactions occur here
• GranumGranum – Stack of– Stack of
thylakoidsthylakoids
• StromaStroma – Region– Region
outside the thylakoidoutside the thylakoid
membranemembrane
– Reactions of the CalvinReactions of the Calvin
Cycle occur hereCycle occur here

23. The Light-Dependent Reactions
• Photophosphorylation is the process of
creating ATP using a Proton gradient
created by the Energy gathered from
sunlight.
• ChemiosmosisChemiosmosis is the process of usingis the process of using
Proton movement to join ADP and Pi. ThisProton movement to join ADP and Pi. This
is accomplished by enzymes calledis accomplished by enzymes called ATPATP
synthasessynthases oror ATPasesATPases..

24. NADP+
+ e-
+ Energy  NADPH
• NADP+ (Nicotinamide
adenine dinucleotide
phosphate)
– Electron, hydrogen, and energy
carrier

25. Light-Dependant
Reactions

26. 1. Photosystem II
• Chlorophyll absorbs lightChlorophyll absorbs light
• Electrons on a chlorophyll molecule (p680)Electrons on a chlorophyll molecule (p680)
absorb energy from light and becomeabsorb energy from light and become
“energized”“energized”
• High-energy (“energized”) electrons are passedHigh-energy (“energized”) electrons are passed
on to the electron transport chainon to the electron transport chain
– Electrons are passed to pheophytin molecule then toElectrons are passed to pheophytin molecule then to
plastoquinone Qa then to plastoquinone Qb then to ETC.plastoquinone Qa then to plastoquinone Qb then to ETC.
• Chlorophyll’s electrons are replenished by theChlorophyll’s electrons are replenished by the
breakdown of Hbreakdown of H22OO
• HH22O is broken down into 2H+ ions, OO is broken down into 2H+ ions, O22, and 2 e-., and 2 e-.
Electrons are used to replenish chlorophyll’s lostElectrons are used to replenish chlorophyll’s lost
electrons.electrons.

27. 2. Electron Transport Chain
• The molecules of the electron transports
chain use high-energy electrons to push
H+ ions from the stroma into the inner
thylakoid space.

28. 3. Photosystem I
• Chlorophyll absorbs light-energy and re-Chlorophyll absorbs light-energy and re-
energized the electrons from photosystemenergized the electrons from photosystem
II.II.
• NADP+ picks up these high-energyNADP+ picks up these high-energy
electrons and H+ to become NADPH.electrons and H+ to become NADPH.

29. 4. Hydrogen Ions
• ChemiosmosisChemiosmosis
• Electrochemical GradientElectrochemical Gradient
• Hydrogen ions build up inside the thylakiodHydrogen ions build up inside the thylakiod
membrane.membrane.
– High concentration of H+ inside the membrane (StrongHigh concentration of H+ inside the membrane (Strong
Positive Charge)Positive Charge)
– Low concentration of H+ outside the membraneLow concentration of H+ outside the membrane
(Negative Charge)(Negative Charge)
– Provides the energy to form ATPProvides the energy to form ATP

30. 5. ATP formation
• H+ work to reach equilibrium.H+ work to reach equilibrium.
• Pass through the ATPsynthasePass through the ATPsynthase
• Movement of H+ ions through theMovement of H+ ions through the
ATPsynthase powers ATP productionATPsynthase powers ATP production

31. Do Now…Do Now…
• What is the function of NADPH?What is the function of NADPH?
• How is light energy converted into chemical energyHow is light energy converted into chemical energy
during photosynthesis?during photosynthesis?
• Can the complete process of photosynthesis take placeCan the complete process of photosynthesis take place
in the dark? Explain your answer.in the dark? Explain your answer.
• Explain what happens to a molecule of water in the lightExplain what happens to a molecule of water in the light
dependant phase of photosynthesis.dependant phase of photosynthesis.
• If OIf O22 is a waste/byproduct of photosynthesis, track whereis a waste/byproduct of photosynthesis, track where
it came from to where it exits the plant.it came from to where it exits the plant.

32. CalvinCycleCalvinCycle

33. The Calvin CycleThe Calvin Cycle
1.1. 6 CO6 CO22 molecules enter the cycle.molecules enter the cycle.
2.2. Enzyme “rubisco” combines 6 5-carbon (RuBp)Enzyme “rubisco” combines 6 5-carbon (RuBp)
molecules with the carbon from COmolecules with the carbon from CO22 and forms themand forms them
into 12 3-carbon moleculesinto 12 3-carbon molecules
3.3. 12 ATP and 12 NADPH form the12 ATP and 12 NADPH form the
12 3-carbon molecules into12 3-carbon molecules into
12 High-energy 3-carbon molecules (G3P)12 High-energy 3-carbon molecules (G3P)
4.4. 2 (G3P)of the 12 3-carbon molecules are combined to2 (G3P)of the 12 3-carbon molecules are combined to
form a 6-carbon sugarform a 6-carbon sugar
5.5. 6 ATP molecules are used to convert the 10 remaining6 ATP molecules are used to convert the 10 remaining
3-carbon molecules back into the 6 5-carbon3-carbon molecules back into the 6 5-carbon
molecules the cycle began with (RuBp)molecules the cycle began with (RuBp)

34. CalvinCycleCalvinCycle

35. Factors Affecting Photosynthesis
• Water supply
• Amount of sunlight
• Temperature

36. Types of Photosynthesis
• C3 Photosynthesis
• C4 Photosynthesis
• CAM Photosynthesis

37. C3 Photosynthesis : C3 plants.
• Called C3 because the CO2 is first incorporated into a 3-
carbon compound.
• Stomata are open during the day.
• RUBISCO, the enzyme involved in photosynthesis, is
also the enzyme involved in the uptake of CO2.
• Photosynthesis takes place throughout the leaf.
• Adaptive Value: more efficient than C4 and CAM plants
under cool and moist conditions and under normal light
because requires less machinery (fewer enzymes and
no specialized anatomy)..
• Most plants are C3.

38. C4 Photosynthesis : C4 plants.
• Called C4 because the CO2 is first incorporated into a 4-carbon
compound.
• Stomata are open during the day.
• Uses PEP Carboxylase for the enzyme involved in the uptake of CO2.
This enzyme allows CO2 to be taken into the plant very quickly, and
then it "delivers" the CO2 directly to RUBISCO for photsynthesis.
• Photosynthesis takes place in inner cells (requires special anatomy
called Kranz Anatomy)
• Adaptive Value:
• Photosynthesizes faster than C3 plants under high light intensity and
high temperatures because the CO2 is delivered directly to RUBISCO,
not allowing it to grab oxygen and undergo photorespiration.
• Has better Water Use Efficiency because PEP Carboxylase brings in
CO2 faster and so does not need to keep stomata open as much (less
water lost by transpiration) for the same amount of CO2 gain for
photosynthesis.
• C4 plants include several thousand species in at least 19 plant families.
Example: fourwing saltbush pictured here, corn, and many of our
summer annual plants.

39. CAM Photosynthesis : CAM plants. CAM stands for
Crassulacean Acid Metabolism
• Called CAM after the plant family in which it was first found
(Crassulaceae) and because the CO2 is stored in the form of an acid
before use in photosynthesis.
• Stomata open at night (when evaporation rates are usually lower) and are
usually closed during the day. The CO2 is converted to an acid and
stored during the night. During the day, the acid is broken down and the
CO2 is released to RUBISCO for photosynthesis
• Adaptive Value:
– Better Water Use Efficiency than C3 plants under arid conditions due to
opening stomata at night when transpiration rates are lower (no sunlight, lower
temperatures, lower wind speeds, etc.).
– May CAM-idle. When conditions are extremely arid, CAM plants can just leave
their stomata closed night and day. Oxygen given off in photosynthesis is
used for respiration and CO2 given off in respiration is used for
photosynthesis. This is a little like a perpetual energy machine, but there are
costs associated with running the machinery for respiration and
photosynthesis so the plant cannot CAM-idle forever. But CAM-idling does
allow the plant to survive dry spells, and it allows the plant to recover very
quickly when water is available again (unlike plants that drop their leaves and
twigs and go dormant during dry spells).
• CAM plants include many succulents such as cactuses and agaves and
also some orchids and bromeliads