Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of glucose. It occurs in two stages: the light-dependent reactions and the Calvin cycle. In the light reactions, solar energy is absorbed and used to convert water to oxygen and energy carriers like ATP and NADPH. In the Calvin cycle, the energy from the light reactions drives the reduction of carbon dioxide and production of glucose. Chlorophyll, located in chloroplasts, absorbs light and drives these reactions. Plants are green because chlorophyll reflects green light while absorbing other wavelengths.

1. PHOTOSYNTHESIS
6.1

2. • The main form of energy from the sun is in
the form of electromagnetic radiation
• Visible radiation (white light) used for
photosynthesis
• Remember : ROY G. BIV?

3. The electromagnetic spectrum

4. • A Red Object absorbs the blue and green wavelengths and reflects the red wavelengths

5. Why are
plants
green?

6. • pigment a compound that absorbs light
– different pigments absorb different wavelengths of white
light.
• chlorophyll is a pigment that absorbs red & blue light
(photons) so green is reflected or transmitted.
• Chlorophyll is located in the chloroplasts.
So, Plants are green because the green wavelength is
reflected, not absorbed.

7. 2 types of chlorophyll
• Chlorophyll a – involved in light reactions
• Chlorophyll b – assists in capturing light
energy – accessory pigment
• Carotenoids – accessory pigments – captures
more light energy
– Red, orange & yellow

8. The electromagnetic wavelengths and the wavelengths that are
absorbed by the chlorophyll

9. During the fall, what
causes the leaves to
change colors?

10. Fall Colors
• 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 are pigments that are
either red, orange, or yellow

12. Photosynthesis is -
• conversion of light energy into chemical energy
that is stored in organic compounds
(carbohydrates > glucose)
• Used by autotrophs such as:
– Plants
– Algae
– Some bacteria (prokaryotes)

14. • glucose - energy-rich chemical produced through
photosynthesis
– C6H12O6
• Biochemical pathway – series of reactions
where the product of one reaction is consumed
in the next
– E.g. photosynthesis product is glucose which is used
in cellular respiration to make ATP
(carbohydrate)

15. Remember Redox Reaction
reduction/oxidation
The transfer of one or more
electrons from one reactant to
another
Two types:
1. Oxidation is the loss of e-
2. Reduction is the gain of e-

16. Oxidation Reaction
The loss of electrons from a
substance or the gain of oxygen.
glucose
6CO2 + 6H2O  C6H12O6 + 6O2
Oxidation
Carbon
dioxide
Water
Oxygen

17. Reduction Reaction
The gain of electrons to a
substance or the loss of oxygen.
glucose
6CO2 + 6H2O  C6H12O6 + 6O2
Reduction

18. Photosynthesis equation
Light energy
6CO2 + 6H2O C6H12O6 + 6O2
Chlorophyll
Reactants: Carbon dioxide and water
Products: glucose and oxygen which is a
byproduct

19. Where does
photosynthesis
take place?

20. Plants
• Mainly occurs in the leaves:
a.stoma - pores
b.mesophyll cells
Stoma
Mesophyll
Cell
Chloroplast

21. Mesophyll Cell of Leaf
Cell Wall
Nucleus
Chloroplast
Central Vacuole
Photosynthesis occurs in these cells!

22. Stomata (stoma)
Pores in a plant’s cuticle through which
water vapor and gases (CO2 & O2)
are exchanged between the plant and
the atmosphere.
Guard Cell
Guard Cell
Carbon Dioxide
(CO2)
Oxygen
(O2)
Found on the underside of leaves
Stoma

23. Chloroplast
Organelle where photosynthesis takes place.
Granum
Thylakoid
Stroma
Outer Membrane
Inner Membrane
Thylakoid stacks are connected together

24. Parts
Chloroplasts double membrane organelle that absorbs
light energy
Thylakoids – flattened sacs contain pigment - chlorophyll
Grana (pl: granum) – layered thylakoids (like pancakes)
Stroma – solution around thylakoids
Stomata – pore on underside of leaf where O2 is
released and CO2 enters
Stroma : chloroplast :: cytosol : cytoplasm

25. Thylakoid
Thylakoid Membrane
Thylakoid Space
Granum
Grana make up the inner membrane

26. What do cells
use for
energy?

27. Energy for Life on Earth
• Sunlight is the ULTIMATE
energy for all life on Earth
• Plants store energy in the
chemical bonds of sugars
• Chemical energy is released as
ATP during cellular respiration

28. Structure of ATP
• ATP stands for adenosine triphosphate
• It is composed of the nitrogen base
ADENINE, the pentose (5C) sugar
RIBOSE, and three PHOSPHATE groups
• The LAST phosphate group is bonded
with a HIGH ENERGY chemical bond
• This bond can be BROKEN to release
ENERGY for CELLS to use

29. Removing a Phosphate from ATP
Breaking the LAST PHOSPHATE bond
from ATP, will ---
– Release ENERGY for cells to use
– Form ADP (adenosine diphosphate)
– Produce a FREE PHOSPHATE GROUP

30. High Energy Phosphate Bond

31. FREE PHOSPHATE can be re-attached to
ADP reforming ATP
Process called Phosphorylation

32. Phosphorylation

33. Photosynthesis
1. Light Reaction -
Produces energy from solar power
(photons) in the form of ATP and
NADPH.
2. Calvin Cycle
• Also called Carbon Fixation or
Carbon Cycle, Uses energy (ATP
and NADPH) from light reaction to
make sugar (glucose).
SUN

34. • 3 stages of photosynthesis-

35. Stages:
• STAGE 1 - LIGHT REACTIONS - energy from sun is
used to split water into H+ an O2
• STAGE 2 – energy is converted to chemical energy
& stored in ATP & NADPH in stroma
• STAGE 3 - CALVIN CYCLE where carbon is fixed into
glucose

36. Light Reaction (Electron Flow)
• Occurs in the Thylakoid membranes
• 2 possible routes for electron flow:
Use Photosystem I and Electron
Transport Chain (ETC) and generate
ATP only
• OR use Photosystem II and
Photosystem I with ETC and
generate O2, ATP and NADPH

38. Photosynthesis animation
• http://www.mhhe.com/biosci/genbio/biolink/
j_explorations/ch09expl.htm

39. ELECTRON TRANSPORT - LIGHT REACTIONS in 5
steps

40. Photosystem I and II
• Step 1 – light excites e- in photosystem II
• Step 2 – e- move to primary e- acceptor Step 3 –
e- move along electron transport chain (etc)
• Step 4 – light excites e- in photosystem I
• Step 5 – e- move along 2nd (etc)
• End – NADP+ combine H+ to make NADPH

41. Light reaction animation
• http://www.science.smith.edu/departments
/Biology/Bio231/ltrxn.html

42. Electron transport chain song
• Play the "Come On Down (The Electron
Transport Chain)" song performed by Sam
Reid.

43. Photolysis –photo-chemical splitting of water (restoring
photosystem II)

44. Chemiosmosis – synthesis of ATP
• Powers ATP synthesis
• Takes place across the thylakoid
membrane
• Uses ETC and ATP synthase
• H+ move down their concentration
gradient forming ATP from ADP
• Concentration of protons is greater in thylakoid
than stroma

46. Chemiosmosis
H+ H+
ATP Synthase
H+ H+ H+ H+
H+ H+
high H+
concentration
H+
ADP + P ATP
PS II PS I
E
T
C
low H+
concentration
H+
Thylakoid
Space
Thylakoid
SUN
(Proton Pumping)

47. The Calvin Cycle
6.2

48. Calvin Cycle -
• Biochemical pathway in photosynthesis that
produces organic compounds using ATP & NADPH
• Carbon fixation – carbon atoms from CO2 are
bonded or ‘fixed’ into carbohydrates
• occurs in stroma

50. Calvin Cycle
• Carbon Fixation
• C3 plants (80% of plants on earth)
• Occurs in the stroma
• Uses ATP and NADPH from light
reaction as energy
• Uses CO2
• To produce glucose: it takes 6 turns
and uses 18 ATP and 12 NADPH.

51. Chloroplast
Granum
Thylakoid
STROMA– where Calvin Cycle occurs
Outer Membrane
Inner Membrane

52. Calvin Cycle (C3 fixation)
6CO2
6C-C-C-C-C-C
6C-C-C 6C-C-C
6C-C-C-C-C
12PGA
RuBP
12G3P
(unstable)
6NADPH 6NADPH
6ATP 6ATP
6ATP
C-C-C-C-C-C
Glucose
(6C)
(36C)
(36C)
(36C)
(30C)
(30C)
(6C)
6C-C-C 6C-C-C
C3
glucose

53. Calvin Cycle
Remember: C3 = Calvin Cycle
C3
Glucose

54. Step 1 -
• CO2 diffuses fr cytosol & combines with RuBP
which splits into pair of PGA

55. Step 2 -
• PGA gets phosphate gr fr ATP gets proton fr
NADPH to become PGAL
• Reaction produces: ADP, NADP+ & phosphate
to be used again

56. Step 3 -
• PGAL converts back to RuBP
• Allows Calvin cycle to continue

57. Alternates:
• C3 plants – use Calvin cycle exclusively
– Form 3-carbon compounds
• C4 pathway – evolved in hot, dry climate
– Form 4-carbon compounds
– Partially close stomata
– E.g. Corn, sugar cane, crabgrass
• CAM – open stomata at night, close in day
– Grow slow, lose less water
– E.g. cactus, pineapple

58. C4 Plants
• Hot, moist
environments
• 15% of plants
(grasses, corn,
sugarcane)
• Photosynthesis
occurs in 2 places:
– Light reaction -
mesophyll cells
– Calvin cycle - bundle
sheath cells

59. C4 Plants
Mesophyll Cell
CO2
C-C-C
PEP
C-C-C-C
Malate-4C sugar
ATP
Bundle Sheath Cell
C-C-C
Pyruvic Acid
C-C-C-C
CO2
C3
Malate
Transported
glucose
Vascul
Tissu

60. CAM Plants
• Hot, dry environments
• 5% of plants (cactus and ice
plants)
• Stomates closed during day
• Stomates open during the night
• Light reaction - occurs during
the day
• Calvin Cycle - occurs when CO2 is
present

61. CAM Plants
Night (Stomates Open) Day (Stomates Closed)
Vacuole
C-C-C-C
Malate
C-C-C-C
Malate Malate
C-C-C-C
CO2
CO2
C3
C-C-C
Pyruvic acid
ATP
C-C-C
PEP
glucose

62. Rate of photosynthesis is effected by -
light intensity, CO2 or temperature
• High intensity or high CO2 = high rate
– Growth graph levels off (plateau)
• High temp = initial high rate but peaks
– Rate drops when stomata closes

63. Recap
• Photosynthesis converts light energy into chemical
energy thru series of biochemical pathways
• Electrons excite in photosystem II – move along ETC to
photosystem I
• electrons are replaced when water is split
• oxygen is byproduct
• ATP synthesized across thylakoid
• Calvin cycle – carbon is fixed & sugar produced
• 3 turns produce PGAL (PGAL keeps cycle going
• Other pathways – C3, C4, CAM

64. References
• www.biologyjunction.com