Light energy is converted to chemical energy through photosynthesis. In the light-dependent reactions, light is absorbed by chlorophyll in the thylakoid membranes which generates excited electrons. These electrons are used to produce ATP and NADPH. In the light-independent reactions that occur in the chloroplast stroma, CO2 is fixed into carbohydrates using ATP and NADPH produced in the light reactions. The structure of the chloroplast, including the thylakoid membranes, is adapted to efficiently carry out these photosynthetic reactions.

1. Essential idea: Light energy is converted into chemical energy
8.3 Photosynthesis
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2. Understandings
Statement Guidance
8.3 U.1 Light-dependent reactions take place in the
thylakoid membranes and the space inside them.
8.3 U.2 Light-independent reactions take place in the
stroma.
8.3 U.3 Reduced NADP and ATP are produced in the light-
dependent reactions.
8.3 U.4 Absorption of light by photosystems generates
excited electrons.
8.3 U.5 Photolysis of water generates electrons for use in
the light-dependent reactions.
8.3 U.6 Transfer of excited electrons occurs between
carriers in thylakoid membranes.
8.3 U.7 Excited electrons from Photosystem II are used to
contribute to generate a proton gradient.
8.3 U.8 ATP synthase in thylakoids generates ATP using the
proton gradient.
8.3 U.9 Excited electrons from Photosystem I are used to
reduce NADP.
8.3 U.10 In the light-independent reactions a carboxylase
catalyzes the carboxylation of ribulose
bisphosphate.

3. Statement Guidance
8.3 U.11 Glycerate 3-phosphate is reduced to triose
phosphate using reduced NADP and ATP.
8.3 U.12 Triose phosphate is used to regenerate RuBP and
produce carbohydrates.
8.3 U.13 Ribulose bisphosphate is reformed using ATP.
8.3 U.14 The structure of the chloroplast is adapted to its
function in photosynthesis.
Understandings

4. Applications and Skills
Statement Guidance
8.3 A.1 Calvin’s experiment to elucidate the
carboxylation of RuBP.
8.3 S.1 Annotation of a diagram to indicate the
adaptations of a chloroplast to its
function.

5. 8.3 U.1 Light-dependent reactions take place in the thylakoid
membranes and the space inside them.
• Double outer membrane
• Thylakoids is the internal
membranes called which
is the location of the light
dependent reaction
• Grana are stacks of
thylakoids
• Stroma cytoplasm that
surrounding the
thylakoids and grana. This
is the location of the light
independent reaction.

6. Light energy converted into chemical energy
• Producers contain chlorophyll
• Chlorophyll can trap light
energy (photons).
• The chlorophyll convert this
energy into chemical energy.
• The chemical energy is
transferred as bond energy
(electrons)and is transferred in
turn to other chemical energy
stores called carbohydrates,
lipids and protein.
• These molecules are called
organic molecules.
8.3 U.1 Light-dependent reactions take place in the thylakoid
membranes and the space inside them.

7. 8.3 U.1 Light-dependent reactions take place in the thylakoid
membranes and the space inside them.
• Chlorophyll in the thylakoid
membrane is excited by light
absorption.
• Electrons (e-) in the chlorophyll
are energized to an excited
state.
• e- captured by primary electron
acceptor
 Redox reaction  e- transfer
 As e- is transferred from one
enzyme to the next it drop
to a ground state
• H2O is split to replace e-  O2
formed

8. 8.3 U.2 Light-independent reactions take place in the stroma.
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• Energy captured from the electron is transferred to NADPH
and ATP and move from the thylakoid into the stroma of the
chloroplast.
• Carbon dioxide will be converted into glycerate 3-
phosphate (G3P) a triose phosphate using NADPH and ATP.

9. 8.3 U.3 Reduced NADP and ATP are produced in the light-dependent
reactions.
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•At the same time water is
split into oxygen, hydrogen
ions and free electrons are
produced:
2H2O 4H+ + O2 + 4e-
(photolysis)
•The electrons then react
with a carrier molecule
(NADP), changing it from its
oxidized state (NADP+) to its
reduced state (NADPH):
NADP+ + 2e- + 2H+ NADPH + H+

10. 8.3 U.3 Reduced NADP and ATP are produced in the light-dependent
reactions.
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12. 8.3 U.4 Absorption of light by photosystems generates excited electrons.
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• Pigments in the thylakoid
membrane absorb light at
certain wavelengths
• The light energy causes
electrons held by pigments to
raise to higher energy states.
This converts the light energy
into a form of chemical energy.
• These excited electrons are
passed from pigment to
pigment until the reach a
molecule called the reaction
center.
• The reaction center pass the
electrons to electron acceptors
in the thylakoid membrane

13. 8.3 U.9 Excited electrons from Photosystem I are used to reduce NADP.
• A pair of excited electrons
e- pass from the reaction
center of thylakoid into a
small electron transport
chain (ETC).
• At the end of the ETC the
electrons are passed to
NADP in the stroma.
• In addition NADP picks up
two protons (H+) and is
reduced to NADPH.
• NADPH will be used to fix
carbon from carbon dioxide
into a carbohydrate.

19. 8.3 U.5 Photolysis of water generates electrons for use in the light-
dependent reactions.
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• Photosystem II must
replace excited
electrons given away
by chlorophyll
• With the help of an
enzyme in the reaction
center, water
molecules in the
thylakoid space are
split and electrons from
them are given to the
chlorophyll at the
reaction center.

20. 8.3 U.6 Transfer of excited electrons occurs between carriers in thylakoid
membranes.

21. 8.3 U.6 Transfer of excited electrons occurs between carriers in thylakoid
membranes.

22. 8.3 U.6 Transfer of excited electrons occurs between carriers in thylakoid
membranes.

23. 8.3 U.6 Transfer of excited electrons occurs between carriers in thylakoid
membranes.

24. 8.3 U.6 Transfer of excited electrons occurs between carriers in thylakoid
membranes.

25. Protons Build up Inside Thylakoids
8.3 U.7 Excited electrons from Photosystem II are used to contribute to
generate a proton gradient.

26. Proton motive force generated by:
(1) H+ from water
(2) H+ pumped across by cytochrome
(3) Removal of H+ from stroma when NADP+ is reduced
8.3 U.7 Excited electrons from Photosystem II are used to contribute to
generate a proton gradient.

27. 8.3 U.8 ATP synthase in thylakoids generates ATP using the proton
gradient.
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• ATP Synthase located
in the thylakoid
membranes allows the
protons to diffuse back
down the
concentration gradient
to produce ATP.
• The generation of ATP
using energy released
by the movement of
H+ is called
chemiosmosis and is
called
photophosphorylation

28. 8.3 U.8 ATP synthase in thylakoids generates ATP using the proton
gradient.
http://www.uncommondescent.com/wp-content/uploads/2015/02/atpsynthase.gif

29. Calvin Cycle: Uses ATP and NADPH to convert CO2 to sugar
• Uses ATP, NADPH, CO2
• Produces 3-C sugar G3P
(glyceraldehyde-3-phosphate)
Three phases:
1. Carbon fixation
2. Reduction
3. Regeneration of RuBP
(CO2 acceptor)

30. The Three phases of
The Calvin Cycle LIR:

31. 1. Carbon Fixing phase
•Adds carbon dioxide to 5C
ribulose bisphosphate
(RuBP)
•Catalyzed into RUBISCO;
ribulose bisphosphate
carboxylase
8.3 U.10 In the light-independent reactions a carboxylase catalyzes the
carboxylation of ribulose bisphosphate (RuBp).

32. 2. Reduction phase
•Citrate is made and broken to
form 2 phosphoglycerate (PGA)
•PGA is rearranged and
phosphorylated by ATP
•NADPH reduces the backbone
further to form glyceraldehyde-3-
phosphate (G3P)
8.3 U.11 Glycerate 3-phosphate is reduced to triose phosphate using
reduced NADP and ATP.

33. 3. Regeneration of RuBP:
– G3P is rearranged,
– & phosphorylated
– With further investment of
ATP…
– To make RuBP, a
bisphosphorylated compound
• Alternatively,
– G3P is shuttled out of the
cycle to produce glucose and
other carbohydrates
elsewhere
8.3 U.12 Triose phosphate is used to regenerate RuBP and produce carbohydrates.
8.3 U.13 Ribulose bisphosphate is reformed using ATP.

34. 8.3 A.1 Calvin’s experiment to elucidate the carboxylation of RuBP.
http://www.intechopen.com/books/photosynthesis
/the-path-of-carbon-in-photosynthesis-mannosideshttp://bancroft.berkeley.edu/Exhibits/Biotech/Images/3-9lg.jpg

35. 8.3 A.1 Calvin’s experiment to elucidate the carboxylation of RuBP.

36. 8.3 A.1 Calvin’s experiment to elucidate the carboxylation of RuBP.
• A timer and a quick acting valve
were used to catch algae at
various stages of the light
independent reaction.
• Hot methanol kills algae; stops
photosynthesis.
• Radioactive carbon (C14) allows
the carbon containing
intermediates to be identified.
• The carbon compounds were
separated at each advancing
stage by chromatography and
identifying (results to the right).
http://5e.plantphys.net/images/ch08/wt0802a.png

37. 8.3 U.14 The structure of the chloroplast is adapted to its function in
photosynthesis.
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• Outer membrane Consists of
inner and outer phospholipid
bilayers. The membrane helps
increase the concentration of
enzymes, increasing the rates
of reaction inside the
chloroplast.
• Thylakoids A flattened
membrane sac inside the
chloroplast increasing surface
area and concentration of
enzymes, used to convert
light energy into chemical
energy.

38. 8.3 S.1 Annotation of a diagram to indicate the adaptations of a
chloroplast to its function
http://www2.victoriacollege.edu/dept/bio/CoonsWebPages/ch5cell/taL22600_05_11b.jpg

39. 8.3 S.1 Annotation of a diagram to indicate the adaptations of a
chloroplast to its function
• Chloroplast double membrane- Creates a compartment in
which enzymes and other components can be concentrated
• 70S Ribosome allows for the synthesis of proteins
• Stroma Matrix
• Circular DNA source for protein synthesis and mitosis
• Granum stack of thylakoids
• Thylakoids membrane/space increase surface area for light
absorption, which generates electron flow, with the space
providing and area to create a proton gradient

40. 8.3 S.1 Annotation of a diagram to indicate the adaptations of a
chloroplast to its function
http://www2.victoriacollege.edu/dept/bio/CoonsWebPages/ch5cell/taL22600_05_11b.jpg