1. Photosynthesis Photosynthesis The Photosynthesis Song -
Intro Video –
Photosynthesis the Movie -
Photosynthesis

2. Objectives
Summarize how energy is captured from sunlight during the light dependent reactions of photosynthesis.
Analyze the function of electron transport chains during the light dependent reactions of photosynthesis.
Relate the Calvin cycle to carbon dioxide fixation in photosynthesis.
Identify three environmental factors that affect the rate of photosynthesis.

3. Using the Energy in Sunlight
Plants, algae, and some bacteria capture 1% of the sunlight that reaches earth and convert it to chemical energy through the process of photosynthesis.

4. History of the Discovery of Photosynthesis
The following people all contributed to the discovery of photosynthesis.
Van Helmont (1600’s)
Priestley (1700’s)
Ingenhousz (1779)
Mayer (1845)
Ruben and Kamen (1941)
Melvin Calvin (1948)
Rudolph Marcus (1992)

5. Jan van Helmont
He wondered where the mass of a tree came from- perhaps the soil?
To find out, he did an experiment where he weighed a seedling and a pot of soil. After 5 years, he reweighed them both.
The soil was the same mass but the tree had gained mass. Where did it come from?
He concluded it came from the water!

6. Joseph Priestley (1700’s) He put a jar over a candle and found?
The candle went out!
But when he placed a living plant under the jar with the candle, it stayed lit longer. Why???
The plant produced….OXYGEN!

7. Jan Ingenhousz
He did the same experiment as Priestley, but in the dark and in the light.
It only worked in the light, proving that plants need light to make oxygen!

8. Photosynthesis is…
The process where plants, algae and some bacteria convert light energy into chemical energy (glucose), using water and carbon dioxide and releasing oxygen gas as a byproduct.

9. A. Introduction
1. Location: chloroplasts (in plants and algae) or folds in cell membrane (in photosynthetic prokaryotes, cyanobacteria)

10. Stages of Photosynthesis
Stage 1 Light-dependent reaction
Chlorophyll pigments capture light energy
Thylakoid membranes
Stage 2 Light-dependent reaction
Light energy converted to chemical energy. Production of ATP and NADPH
2 H+ + NADP+ --> NADPH + H+ in photosynthesis
Stage 3 Light-independent reaction
Reduction of CO2 to glucose:
using ATP + NADPH + H+ to synthesize organic compounds (glucose) from CO2 (carbon fixation); process called Calvin cycle;
Stroma
© Teachable and Louise Edgeworth. Some rights reserved.

11. the carbon + oxygen from CO2 and the H from H2O produce the glucose
3. Overall process:
6CO2 +
12H2O +
light
chlorophyll
C6H12O6 +
6O2 +
6 H2O
the carbon + oxygen from CO2 and the H from H2O produce the glucose
the oxygen from H2O is released as oxygen gas

13. LIGHT AND PIGMENTS Light has different wavelengths.
You can only see visible light.

14. Visible spectrum
Sunlight contains a mixture of all the wavelengths (colors) of visible light.
When sunlight passes through a prism, the prism separates the light into different colors.

15. light energy travels in wave packets called photons
visible light has a wavelength of 380 nm (violet) to 750 nm (red) (ROYGBIV)
short wavelengths [violet] is high energy
long wavelengths [red] is low energy

16. Pigments
Pigments are light-absorbing molecules which absorb only certain wavelengths and reflect all of the others.
Chlorophyll is the pigment in plants that makes them appear green.
GREEN is reflected, while all other colors are absorbed.
Long carbon-hydrogen tail called phytol tail/chain (hydrophobic)
A ring of C, N and lots of double bonds, Mg trapped in middle, called porphyrin ring

17. chlorophyll a (primary light absorbing pigment in all
chlorophyll a (primary light absorbing pigment in all photosynthetic organisms) and chlorophyll b absorb photons of blue-violet λ and red-orange λ
green λ are reflected (that is why leaves appear green)
and green is transmitted so leaves look green from underneath

18. Absorbs mostly blue and red light and reflects green and yellow light.
Thus, the plant looks green.
Chlorophyll

19. Carotenoids
Pigments in plants that absorb blue and green light and reflect yellow and orange.

20. Autumn Colors
In the fall, as it gets colder, chlorophyll gets broken down because photosynthesis cannot occur in the winter. Why?
Chorophyll is broken down into these other pigments.
Water freezes!
And if water freezes, it cannot do its part in photosynthesis.

22. Inside a Chloroplast

23. CHLOROPLAST STRUCTURE
Period 0 stopped here

24. Thylakoids
Are disk shaped structures containing clusters of pigments embedded in their membranes.
This is where the Light-Dependent Reactions occur.

25. Great Animation of Photosynthesis!

26. Overview of The Light-Dependent Reactions
Where do they occur?
What are they?
The Thylakoid Membranes where there is chlorophyll!
The light-dependent reactions use water, produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH.

27. Light-dependent reaction
Chlorophyll molecules are arranged on the thylakoid membranes in groups called PHOTOSYSTEMS.
There are two types of photosystems PSI and PSII.
© Teachable and Louise Edgeworth. Some rights reserved.

28. Thylakoid membranes
Electron carrier molecules and ATP synthase are also located on the thylakoid membranes.
© Teachable and Louise Edgeworth. Some rights reserved.

29. Overview of The Light-Dependent Reactions
What part of the photosynthesis equation is involved?
Water (H2O) is broken apart for its electrons.
Oxygen gas (O2) is given off as a waste product.

30. Glucose

31. The energy captured in the light-dependent reaction is used for:
Direct synthesis of ATP – a process called photophosphorylation.
Splitting water into H+ ions and OH- ions – a process called photolysis.
© Teachable and Louise Edgeworth. Some rights reserved.

32. STEPS OF THE LIGHT DEPENDENT REACTIONS

33. B. Light Reactions 1. Photoexcitation
e- are normally stable in their ‘ground state’, the lowest possible energy level
when a photon strikes a chlorophyll molecule, the e- have energy added to them and are in a state of ‘excitation’
an excited e- has more energy than one in a ground state, but it will return to the ground state in 1 billionth of a second

34. if left alone, the e- returns to the ground state and
if left alone, the e- returns to the ground state and releases energy (heat + light)
instead of the e- from chlorophyll releasing heat + light, they are captured by a primary e- acceptor (chlorophyll is oxidized, e- acceptor is reduced)

35. 2. Photosystems
photosystems = a group of pigments that work together to capture light
the antenna complex consists of several hundred pigment molecules that capture light of different wavelengths and pass energy to the reaction center
the reaction center is a chlorophyll a pigment that takes all the energy and uses it to excite an electron
the excited e- is transferred to an e- acceptor (chlorophyll is oxidized, primary e- acceptor is reduced)

37. 3. Sources of electrons: a) bacteria:
photosystem I contains chlorophyll P700 (max. absorption at 700 nm λ)
the photosystem I does not have enough energy to break water,
however it does have enough energy to break H2S
but H2S is rare; only found in sulphur springs
6CO2 + 12H2S + light energy  C6H12O6 + 6H2O + 12S

38. Sulphur springs

39. b) algae and plants
photosystem II contains chlorophyll P680 (max. absorption at 680 nm λ)
photosystem II does have enough energy to break water
electrons are then passed to photosystem I
6CO2 + 12H2O + light energy 
C6H12O6 + 6H2O+ 6O2
c) photosystem I and II are used to produce ATP + NADPH + H+

40. 4. Photolysis (the breaking of water by sunlight)
the Z protein (in the thylakoid space) uses energy from light to split H2O
2 e- are given to photosystem II
2 H+ are released in the thylakoid space and create an electrochemical gradient
O2 leaves the chloroplast as waste

41. 5. Electron Transport System
a series of proteins that move electrons and protons to produce high energy compounds

42. photosystem II 3. cytochrome b6-f 5. photosystem I 7. NADP reductase
PROTEINS
Z –protein
photosystem II cytochrome b6-f photosystem I NADP reductase
PQ plastoquinone PC plastocyanin ferredoxin 8. ATP synthase
2H+
stroma
P680
P700
ADP +Pi
2H+
ATP
NADP+
NADPH + H+
2H+ 8 1 2 3 5 7 4 z 6
2e-
2e-
H20
2H+
½ O2 + 2H+

43. 5. Electron Transport System
a) occurs in the thylakoid membrane
b) photon strikes photosystem II and excites 2e- of chlorophyll P680, 2e- passed to electron acceptor called plastoquinone (PQ)
c) 2e- from Z protein replace the missing 2e- from chlorophyll P680
d) PQ takes 2e- from photosystem II and moves with them to b6-f complex
e) b6-f complex takes 2e- and passes them onto plastocyanin which allows 2H+ to pass from the stroma into the thylakoid space;
f) this creates an electrochemical gradient

44. g) Pc takes 2e- and moves with them to photosystem I
g) Pc takes 2e- and moves with them to photosystem I (these replace 2e- lost when photosystem I was struck by a photon)
h) photosystem I transfers 2e- to ferredoxin (Fd) (an e- acceptor)
i) Fd transfers 2e- to NADP reductase
j) NADP reductase passes on the 2 e- to NADP+
k) (NADP+ + 2H e-  NADPH + H+)

45. 6. Types of Electron Transport Systems
a) non-cyclic phosphorylation
normal process as described in notes
involves both P700 and P680 and transfers e- from H2O to NADP+ to produce
1 NADPH + H+ and 2 ATP needed to make glucose
H2O + photons + 2ADP + 2Pi + NADP+  ½O2 + 2ATP + NADPH + H+
but demand for ATP and NADPH + H+ is not always in a 2:1 ratio

46. b) cyclic phosphorylation
happens in all plants when extra ATP is needed
the process produces only ATP and not NADPH + H+
one of the proteins [Fd] in the thylakoid membrane shifts in order for the cycle to flow

47. Cyclic phosphorylation
stroma
P700
ADP +Pi
2H+
ATP
2H+ 6 6
2e- 1 3 7 8 2 5 z 4
2H+
PROTEINS
Z –protein
photosystem II cytochrome b6-f photosystem I NADP reductase
PQ plastoquinone PC plastocyanin ferredoxin 8. ATP synthase

48. photosystem I (P700) is involved, but not photosystem II (P680)
electrons from P700 are excited but eventually return to P700 (H2O & NADP+ are not involved)
P700  Fd  b6-f complex  protein C  P700
b6-f complex pumps H+ ions across the thylakoid membrane, creating an electrochemical gradient which is used to make ATP

49. Summary of Light dependent reaction
Pigments in the thylakoids of chloroplasts absorb light energy.
Electrons in the pigments are excited by light and move through electron transport chains in thylakoid membranes.
These electrons are replaced by electrons from water molecules, which are split by an enzyme.
Oxygen atoms from water molecules combine to form oxygen gas.
Hydrogen ions accumulate inside thylakoids, setting up a concentration gradient that provides the energy to make ATP.

50. Light Dependent Reactions

51. Review of Light Dependent Reactions!

53. Pigment molecules absorb energy at which stage of photosynthesis?
The beginning of the Light-Dependent Reactions!

54. At which stage of photosynthesis is light energy stored as ATP and NADPH?
The end of the Light-Dependent Reactions!

55. At which stage of photosynthesis are excited electrons passed along an electron transport chain?
Light-Dependent Reactions!

56. Where do the light-dependent reactions occur?
The thylakoid membranes!

57. What goes into the light-dependent reactions?
Light excites the electrons of chlorophyll.
Water is split to replace lost e-’s in chlorophyll.
ADP gets a phosphate group to become ATP.
NADP+ gets hydrogen ions to become NADPH.

58. What is produced in the light-dependent reactions?
ATP and NADPH go into the Calvin Cycle.
Oxygen gas is released into the atmosphere.

59. Light Reactions Animation

60. light reaction animation on moodle
Photosynthesis Animation by John L. Giannini
photosynthesis tutorial