The document introduces photosynthesis, including that it occurs in chloroplasts in plant leaves. It absorbs light energy to produce sugars from carbon dioxide and water. This involves two phases - the light-dependent reaction where ATP and NADPH are produced, and the light-independent Calvin cycle where carbon is fixed into glucose using ATP and NADPH. Plants are green due to chlorophyll, which absorbs most colors of light except green, which it reflects, making the plant appear green.

1.  Why are plants so important?
 Why are plants green?
 Which are the main pigments in a plant?
 What plants produce?
 Which materials are used to poduce organic materials?
 What do they release during this process?
 What is the name of this process?

4. Aim: to introduce the students to the process
of photosynthesis
Objectives:
 Recognize the importance of photosynthesis for our
survival;
 Identify the reactants and products of photosynthesis;
To draw the absorption and action spectrum of
photosynthesis
Explain and illustrate the two phases of photosynthesis.

5. Light Energy Harvested by Plants & Other
Photosynthetic Autotrophs

6. What is photosynthesis?
Photosynthesis is the process by which autotrophic
organisms use light energy to make sugar and oxygen gas
from carbon dioxide and water

7. Photosynthesis in Overview
 In this process plants and other autotrophs store the
energy of sunlight into sugars.
 Requires sunlight, water, and carbon dioxide.
 Overall equation:
6 CO2 + 6 H20  C6H12O6 + 6 O2

8. Where does photosynthesis take place?
Occurs in the
leaves of plants
in organelles
called
chloroplasts.

9. Leaf

10. The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Granum Inner
membrane
Grana Stroma Thylakoid
Stroma Thylakoid compartment

11. Chloroplast Structure
 Have 2 membranes
 A “bi-bilayer!”
 The inner membrane is
called the thylakoid.
 The thylakoid is folded
and looks like stacks of
coins called granum
(grana singular).
 The stroma is the space
surrounding the
granum

12. Why are plants green?

13. Why are plants green?
Different wavelengths of visible light are seen by
the human eye as different colors.
Gamma Micro- Radio
X-rays UV Infrared
rays waves waves
Visible light
Wavelength (nm)

14. The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.
Sunlight minus absorbed
wavelengths or colors
equals the apparent color of
an object.

15. Why are plants green?
Transmitted light

16. Why are plants green?
Plant Cells
have Green
Chloroplasts
The thylakoid
membrane of the
chloroplast is
impregnated with
photosynthetic
pigments (i.e.,
chlorophylls,
carotenoids).

17. THE COLOR OF LIGHT SEEN IS THE COLOR
NOT ABSORBED
 Chloroplasts absorb
light energy and
convert it to chemical Light
Reflected
light
energy
Absorbed
light
Transmitted Chloroplast
light

18. During fall what causes pigments
to change colour?

19. Fall Colours
 In addition to the chlorophyll pigments, there are
other pigments present.
 During the fall, the green chlorophyll pigments
are greatly reduced revealing the other pigments
(carotenoids and xantophylls)

20. Pigments
 Chlorophyll A is the most important photosynthetic
pigment.
 Other pigments called antenna or accessory pigments
are also present in the leaf.
 Chlorophyll B
 Carotenoids (orange / red)
 Xanthophylls (yellow / brown)
 These pigments are embedded in the membranes of
the chloroplast in groups called photosystems.

21. Different pigments absorb light
differently

24. Chlorophyll in the chloroplasts
 Chlorophyll molecules
are embedded in the
thylakoid membrane
 Act like a light
“antenna”
 These molecules can
absorb sunlight
energy.

25. Photosystem
• Reaction centre
(chlorophyll a & electron
acceptor)
• Light-harvesting complex
(pigment molecules
bounded to proteins)

26. Harvesting light
There are two types of
reaction centre:
 Photosystem I is
arranged around a
chlorophyll a
molecule with
absorption peak of
700 nm.
 Photosystem II is
arranged around a
chlorophyll a
molecule with
absorption peak of
680 nm.

27. Photosynthesis occurs in 2 phases:
 The light reactions
convert solar energy Light Chloroplast
to chemical energy NADP
 Produce ATP & ADP
NADPH +P
Calvin
Light cycle
reactions
• The Calvin cycle makes
sugar from carbon
dioxide
– The ATP and NADPH are
used to assemble sugars
and other organic
compounds

28. Excitation of chlorophyll
in a chloroplast Loss of energy due to heat
causes the photons of light to be
less energetic.
e Excited
2 state Less energy translates into
longer wavelength.
Fluorescene Heat Transition toward the red end of
the visible spectrum.
Light
Light
(fluorescence)
Photon
Ground
state
Chlorophyll
molecule
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution

29. 1. Light Reaction (Electron Flow)
 Occurs in the Thylakoid membranes
 During the light reaction, there are two possible
routes for electron flow.
A. Noncyclic Electron Flow
B. Cyclic Electron Flow

30. B. Noncyclic Electron Flow
 Occurs in the thylakoid membrane
 Uses PS II and PS I
 P680 rxn center (PSII) - chlorophyll a
 P700 rxn center (PS I) - chlorophyll a
 Uses Electron Transport Chain (ETC)
 Generates O2, ATP and NADPH

31. Noncyclic Photophosphorylation
 Photosystem II regains electrons by splitting water,
leaving O2 gas as a by-product
Primary
electron acceptor
Primary
electron acceptor
Photons
Energy for
synthesis of
PHOTOSYSTEM I
PHOTOSYSTEM II by chemiosmosis

32.  Two types of photosystems
cooperate in the light
reactions
ATP
mill
Water-splitting NADPH-producing
photosystem photosystem

33. In the light reactions, electron transport chains
generate ATP, NADPH, & O2
 Two connected photosystems collect photons of light
and transfer the energy to chlorophyll electrons
 The excited electrons are passed from the primary
electron acceptor to electron transport chains
 Their energy ends up in ATP and NADPH

34. B. Noncyclic Electron Flow
 ADP + P  ATP (photophosphorylation)
 NADP+ + H  NADPH (source of energized
electrons)
 Oxygen comes from the splitting of H2O, not CO2
H 2O  1/2 O2 + 2H+

35. A. Cyclic Electron Flow
 Occurs in the thylakoid membrane.
 Uses Photosystem I only
 P700 reaction center- chlorophyll a
 Uses Electron Transport Chain (ETC)
 Generates ATP only
ADP + P ATP

36. A. Cyclic Electron Flow
Reaction Center => 700 nm
2e-
2e-
2e-
2e-

37. The Hill reaction
 Hill placed cells of the green alga Chlorella into water
containing the heavy isotope 18O
 He was able to show that the Oxigen given off in
photosynthesis was na isotope 18O which must have
come from water.

38. When Hill repeated the experiment with CO2 containing the heavy
18O instead, the oxygen given off was normal 16O
Photolysis
H2O + Energy  ½ O2 + 2H+ + 2e-

39. The production of ATP by chemiosmosis in photosynthesis
Thylakoid
compartment
(high H+) Light Light
Thylakoid
membrane
Antenna
molecules
Stroma ELECTRON TRANSPORT
(low H+) CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

40. Chemiosmosis powers ATP synthesis in the
light reactions
 The electron transport chains are arranged with the
photosystems in the thylakoid membranes and pump H+ into
the thylakoid space
 The flow of H+ back through the membrane is harnessed
by ATP synthase to make ATP
 In the stroma, the H+ ions combine with NADP+ to form
NADPH
Video

41. Calvin Cycle
 Calvin Cycle (light-independent) occur in the stroma:
 Carbon fixation
 Carbon dioxide is “fixed” into the sugar glucose.
 ATP and NADPH molecules created during the light
reactions power the production of this glucose.

42. The Calvin Cycle

43. Carbon Fixation:
 (3) CO2 molecules enter
 Rubisco attaches the Co2 to RuBP
 The 6C product immediately splits into 2x glycerate 3-
phosphate

44. Reduction
 6 ATP and 6 NADPH used
 Some of the triose phosphate
molecule are linked to form
Glucose phosphate

45. Regenerate RuBP
Use 3 more ATP
Video

46. The light-independent stage
 CO2 combines with a five-carbon compound, ribulose
biphospate (RuBP)
 The unstablr 6-carbon compound breaks down to form 2
molecules of 3-carbon glycerate 3-phosphate
 ATP is used to phosphorylate the 2 molecules of GP
forming 2 molecules of glycerate biphosphate

47. The light-independent stage
 NADPH reduces each molecule of glycerate
biphosphate to glyceraldehyde 3-phosphate (GALP)
 For every six molecules of GALP formed, five are used
in a series of reactions to regerate RuBP.
 One of six GALP molecules is converted to glucose and
other carbohydrates, aminoa cids and lipids

48.  A Photosynthesis Road Map
Chloroplast
Light
Stroma
Stack of NADP
thylakoids ADP
+P
Light Calvin
reactions cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds
Video
Video Video

49.  http://www.youtube.com/watch?v=-
37Rrw1vEsw&feature=related
 http://www.youtube.com/watch?v=ixpNw6mx3lk&fea
ture=related
 http://www.youtube.com/watch?v=yGYUnDFmJdM&f
eature=related
 http://www.youtube.com/watch?v=kzLz2EcSPnQ&fea
ture=related
 http://www.youtube.com/watch?v=isyksgQPnVY&feat
ure=related
http://www.youtube.com/watch?v=mYbMP
wmwx88&feature=related