1. Biology: Life on Earth (Audesirk)
Chapter 9
Biology: Life on Earth (Audesirk)
Photosynthesis
Chapter 7

2. Chapter 7
This is CHAPTER 9 in your text…….ignore the “chapter 7” title at the top of each powerpoint page.

3. What Is Photosynthesis?
Chapter 7
What Is Photosynthesis?
Photosynthesis is the ability to capture sunlight energy and convert it to chemical energy
Most forms of life on Earth depend on the chemical energy produced by photosynthetic organisms

4. The Photosynthetic Equation
Chapter 7
6CO2
carbon
dioxide
+ 6H2O
water
+ light energy 
sunlight
C6H12O6
glucose
(sugar)
+ 6O2
oxygen
Photosynthesis occurs in plants, algae, and some prokaryotes
Photosynthetic organisms are autotrophs (“self- feeders”)
Photosynthesis in plants occurs within chloroplasts

5. Gases, Sugar, and Water Cycle
Chapter 7
Production of carbon compounds like glucose (photosynthesis) is linked with energy extraction (in cellular respiration)
Water, CO2, sugar, and O2 cycle between the two processes
Photosynthesis and cellular respiration are interconnected

6. Interconnections: Photosynthesis & Respiration
Biology: Life on Earth (Audesirk)
Interconnections: Photosynthesis & Respiration
Chapter 7
Photosynthesis, this chapter
Takes in water and carbon dioxied, and in the presence of light energy at a chloroplast, will create sugar and oxygen
Cellular respiration, next chapter, will reverse the process.
Both processes create ATP…remember…the energy molecule from chapter 6??
Chapter 7

7. Adaptations for Photosynthesis
Chapter 7
Leaves
Chloroplasts
Let’s look at your diagrams

8. Structures of Photosynthesis
Biology: Life on Earth (Audesirk)
Structures of Photosynthesis
Chapter 7
Use for zoomed out locations of each structure…details follow next…
Chapter 7

9. Leaves
Chapter 7
Flattened leaf shape exposes large surface area to catch sunlight
Upper and lower leaf surfaces of a leaf comprise the epidermis
Waxy, waterproof cuticle on outer surfaces reduces water evaporation

10. Leaf Anatomy
Chapter 7
Adjustable pores called stomata allow for entry of air with CO2
Inner mesophyll cell layers contain majority of chloroplasts- many per cell “photosynthesis tissue”
Vascular bundles (veins) supply water and minerals to the leaf while carrying sugars away from the leaf

11. Internal Leaf Structure
Chapter 7
Internal leaf structure is crucial to photosynthesis since photosynthesis occurs primarily in the leaves of land plans

12. Biology: Life on Earth (Audesirk)
Leaf Structure
Chapter 7
Upper Epidermis
Mesophyll Cells
Stoma (plural = stomata) = adjustable pores of lower epidermis
Mesophyll (middle – leaf - ) = contains the most chloroplasts
Veins/vascular bundles carry water and minerals to mesophyll and sugars out to other plant parts
Lower Epidermis
Vein
Stoma
Chapter 7

13. Anatomy of a Chloroplast
Chapter 7
Mesophyll cells have chloroplasts each
Chloroplasts are bounded by a double membrane composed of the inner and outer membranes

14. Anatomy of a Chloroplast
Chapter 7
The stroma is the semi-fluid medium within the inner membrane. Contains the enzymes needed for the reactions of photosynthesis. Location of light independent reactions of photosynthesis.
Disk-shaped sacs called thylakoids found within the stroma in stacks called grana. Chlorophyll found in thylakoids. Involved in ATP synthesis or light dependent reactions of photosynthesis
Find these on YOUR diagram

15. Chloroplast Structure
Biology: Life on Earth (Audesirk)
Chloroplast Structure
Chapter 7
Stroma = semifluid medium
Thy = disk shaped membrane sacs
Grana (singluar = granum) = stacks of thy
Thylakoids
Stroma (space)
Granum
Inner & Outer Membranes
Chapter 7

16. Chapter 7

17. REVIEW EQUATION FOR PHOTOSYNTHESIS:
Chapter 7
REVIEW EQUATION FOR PHOTOSYNTHESIS:

18. End of Photosynthesis Lecture #2 Quiz tomorrow!!!!!
Chapter 7
End of Photosynthesis Lecture #2 Quiz tomorrow!!!!!

19. Chapter 7
Photosynthesis Lecture #3 Introduction to the light dependent reactions of photosynthesis

20. Chapter 7
In the light dependent reactions, the radiant energy from sunlight is used to make ATP and to reduce the electron acceptor molecule NADP+, forming NADPH. The light energy captured by photosynthesis is temporarily stored within these two compounds.

21. Light dependent reaction equation
Chapter 7
Water + NADP+ + ADP + P yields Oxygen + NADPH + ATP How many of each??????

22. Chapter 7
Because life on our planet depends on light, it is important to understand the nature of light and how it permits photosynthesis to occur

23. Chapter 7
Light is a very small portion of a vast, continuous spectrum of radiation called the electromagnetic spectrum. Light travels in waves A wavelength is the distance from one wave peak to the next The different colors of light correspond to different regions of the visible spectrum and are identified by their wavelengths. Violet light has the shortest wavelength and red light has the longest

24. Colors of the visible spectrum
Chapter 7
ROY G BIV

25. The Energy in Visible Light
Chapter 7
The sun radiates electromagnetic energy
Packets of energy called photons have different energy levels
Short-wavelength photons are very energetic
Longer-wavelength photons have lower energies
Energy of photons is inversely proportional to the wavelength of light

26. Light, Chloroplast Pigments, & Photosynthesis
Biology: Life on Earth (Audesirk)
Light, Chloroplast Pigments, & Photosynthesis
Chapter 7
Gamma Rays
X-Rays UV
Infrared
Micro- waves
Radio Waves
Visible Light
Light that we can see ranges from 400 to 750 nm in wavelength…the distance from on peak of the wave to the next peak
Shorter wavelengths = more energy…passing by faster
Violet is most energetic…reverse rainbow order…red least energy
400
450
500
550
600
650
700
750
Wavelength (nanometers, nm)
Chapter 7

27. Photons interact with atoms Raises electrons to higher energy levels
Chapter 7
Photons interact with atoms
Raises electrons to higher energy levels
Excites or energizes the electrons
When this occurs, one of two things can happen:
Electron returns to original state and energy is lost as heat OR
The excited electron leaves the atom and is accepted by the electron acceptor molecule. (this is what occurs in Photosynthesis)

28. Pigments are substances that absorb visible light
Chapter 7
Pigments are substances that absorb visible light
Different pigments absorb different wavelengths of light

29. Light Captured by Pigments
Chapter 7
Action of light-capturing pigments
Absorption of certain wavelengths (light is “trapped”)
Reflection of certain wavelengths (light bounces back). Light we see
Transmission of certain wavelengths (light passes through)

30. Light Captured by Pigments
Chapter 7
Absorbed light drives biological processes when it is converted to chemical energy
Common pigments found in chloroplasts include:
Chlorophyll a and b- absorbs light in the blue and red regions. Green NOT absorbed
Accessory pigments such as carotenoids- yellow and orange

31. Light Captured by Pigments
Chapter 7
Light Captured by Pigments
Chlorophyll a and b absorb violet, blue, and red light but reflect green light (hence they appear green)
Carotenoids absorb blue and green light but reflect yellow, orange, or red (hence they appear yellow-orange)
Pigment absorbs visible light

32. Biology: Life on Earth (Audesirk)
Absorption Spectra
Chapter 7
Visible Light
400
450
500
550
600
650
700
750 20 40 60 80
100
% Light Absorption
Collectively
Chlorophyll
What color light do plants use? Blue/violet…absorption is highest here…they keep and use that light
What color do we “see” plants? Green (sometimes yellow, orange, red)…plants reject and reflect that light back to our eyes
Carotenoids
Phycocyanin
400
450
500
550
600
650
700
750
Wavelength (nanometers)
Chapter 7

33. Why do leaves “change color” in the fall??
Question
Chapter 7
Why do leaves “change color” in the fall??

34. Answer
Chapter 7
 Leaves change color due to a lack of chlorophyll. Chlorophyll is used in photosynthesis and gives leaves their green color. As the days shorten, trees stop producing chlorophyll, allowing other pigments to take over

35. Activity completed here
Chromatography
Chapter 7
Activity completed here

36. Lecture #4 Light Dependent Reactions of Photosynthesis
Chapter 7
Lecture #4 Light Dependent Reactions of Photosynthesis

37. Overview of Photosynthesis
Biology: Life on Earth (Audesirk)
Overview of Photosynthesis
Chapter 7
Light-Dependent Reactions (in thylakoids)
H2O O2
Water starts the process…H+ is taken in to make NADPH and the electrons get energized. Oxygen is released
Dark reactions actually make the sugar in the final step.
Depleted Carriers (ADP, NADP+)
Energized Carriers (ATP, NADPH)
Light-Independent Reactions (in stroma)
Glucose
CO2
Chapter 7

38. 2 phases of photosynthesis
Chapter 7
Photosynthesis happens in two phases: 1. the light dependent reactions which convert light energy into chemical energy (produces ATP) 2. the light independent reactions- produce simple sugars from the ATP of the light dependent reactions

39. Light dependent reactions
Chapter 7
OVERVIEW:
Occurs in thylakoid membranes of chloroplast
Requires sunlight and water
Includes photosystems II and I and the electron transport chain
End products are ATP, NADPH, and oxygen

40. NADPH
Chapter 7
Nicotinamide adenine dinucleotide phosphate Energy storage compound similar to ATP “electron acceptor” Donates electrons for use in the Calvin Cycle (light independent reactions, or “dark” reactions)

41. Biology: Life on Earth (Audesirk)
The Photosystems
Biology: Life on Earth (Audesirk)
Chapter 7
There are 2 in the Light Reactions. Both energize electrons using sunlight. The green areas are chlorophyll molecules
ETC are a series of enzymes that pass the electrons down
Chapter 7

42. Light-Dependent Reactions
Chapter 7
Steps of the light reactions: PHOTOSYSTEM II
Accessory pigments in Photosystems absorb light and pass the energy of the light to reaction centers containing chlorophyll
Reaction centers receive energized electrons…

43. Light-Dependent Reactions
Chapter 7
Energized electrons then passed down a series of electron carrier molecules (Electron Transport Chain). The ETC is a series of proteins embedded in the thylakoid membrane. Page 226
Energy released from passed electrons used to synthesize ATP from ADP and phosphate

44. Chapter 7

45. Second photosystem is named PHOTOSYSTEM I
Chapter 7
After the electrons have traveled down the ETC, they are re-energized in a second photosystem and passed down a second ETC
Second photosystem is named PHOTOSYSTEM I

46. PHOTOSYSTEM I
Chapter 7
At the bottom of this second ETC, the electrons are still very energized
The electrons are transferred to the stroma of the chloroplast by an electron carrier molecule called NADP+
NAPH+ combines with two electrons and one H+ to become NADPH
NADPH stores the energy- does not use it. Energy will be used in the light independent reactions

47. Steps (summary) Chapter 7 Photosystem II Water and light in
Energized electrons (energy) passed to reaction centers containing chlorophyll
Oxygen released
Electron transport chain- proteins pass along electrons of H+
*#3 and #4 are known as PHOTOLYSIS when two molecules of water are split to form oxygen, H+, and electrons)
Photosystem I
Light absorbed
nd ETC of H+
NADPH created in stroma
ATP synthetase creates ATP “Photophosphorylation”
NADPH and ATP fuel Calvin Cycle (otherwise known as light INDEPENDENT reaction)

48. Thylakoid Structure & Light-Dependent Reactions
Biology: Life on Earth (Audesirk)
Chapter 7
Thylakoid Structure & Light-Dependent Reactions
Arrow starts
#1 water comes into photosystem II. Is split apart. Oxygen is released into the air. Light is collected by the chlorophyll
#2 high energy excited electrons are ejected out of the reaction center
#3 electrons are passed to the electron transport system
#4 some of the electron’s energy is used to drive some ATP synthesis
#5 light strikes photosystem I
#6 the electron is energized again and ejected from the reaction center
#7 Electrons passed along another electron transport system
#8 the electrons are captured as molecules of NADPH are created from NADP+ and H+
Chapter 7

49. Chapter 7

50. Chapter 7
End lecture here

51. PHOTOLYSIS
Chapter 7
Reaction taking place in the thylakoid membranes of a chloroplast during light dependent reactions where two molecules of water are split to form oxygen, hydrogen ions, and electrons

52. PHOTOLYSIS
Chapter 7
Replaces the electrons lost at the beginning of photosystem II (first photosystem)
Does this so chlorophyll can absorb additional light and continue producing ATP
Figure 9.6 page 228

53. PHOTOLYSIS
Chapter 7
Equation page 228.
KNOW it

54. PHOTOLYSIS Products: ½ molecule of oxygen Two electrons
Chapter 7
Products:
½ molecule of oxygen
Two electrons
Two hydrogen ions

55. Oxygen is released into the air Electrons are returned to chlorophyll
Photolysis
Chapter 7
Oxygen is released into the air
Electrons are returned to chlorophyll
Hydrogen ions are pumped into thylakoid where they accumulate high concentration

56. Oxygen as a By-product
Chapter 7

57. Chemiosmosis (2011-skip) DEFINITION:
Chapter 7
DEFINITION:
Because there is a difference in concentration of H+ on either side of the thylakoid membrane (creates a concentration gradient), ions diffuse out of the thylakoid and provide energy for the production of ATP.
Page 228

58. Biology: Life on Earth (Audesirk)
Chemiosmosis 1
Chapter 7
As the electrons pass through the electron transport system, some energy is used to pump H+ into the thy. These H+ are then used…
Chapter 7

59. Biology: Life on Earth (Audesirk)
Chapter 7
…to drive ATP synthesase for the creation of ATP
Chemiosmosis 2
Chapter 7

60. Chemiosmosis animation
Chapter 7

61. LIGHT INDEPENDENT REACTIONS Lecture #5
Chapter 7
LIGHT INDEPENDENT REACTIONS Lecture #5

62. Light Independent Reactions
Chapter 7
OVERVIEW
occurs in stroma (liquid portion of chloroplast)
Involves the Calvin Cycle and carbon fixation
Sometimes referred to as “dark reaction”
Reactants- ATP, NADPH, carbon dioxide
End product- glucose

63. Light-Independent Reactions
Chapter 7
NADPH and ATP from light-dependent reactions used to power glucose synthesis
Light not directly necessary for light-independent reactions if ATP & NADPH available
Light-independent reactions called the Calvin-Benson Cycle or C3 Cycle

64. The C3 Cycle 6 CO2 used to synthesize 1 glucose (C6H12O6)
Chapter 7
6 CO2 used to synthesize 1 glucose (C6H12O6)
Carbon dioxide is captured and linked to ribulose bisphosphate (RuBP)
ATP and NADPH from light dependent reactions used to power C3 reactions

65. Page 229 in your text
Chapter 7
The calvin cycle takes the carbon in carbon dioxide, adds it to one molecule of RuBP and forms sugars through a series of reactions in the stroma of chloroplasts. The NADPH and ATP produced during the earlier light dependent reactions are important molecules for this series of reactions.

66. Question:
Chapter 7
Why is the calvin cycle in plants directly and indirectly important to animals?

67. Preview video
Chapter 7

68. C3 Cycle Has Five Parts pg 229
Chapter 7
1. Carbon fixation (carbon capture)
Carbon atom from carbon dioxide bonds with a five carbon sugar called ribulose biphosphate (RuBP) to form an unstable 6 carbon sugar. (six RuBP plus 6 CO2)
Think of RuBP as carbon dioxide acceptors

69. Formation of three carbon molecules
Chapter 7
Step #2
The six carbon sugar formed in step 1 immediately splits to form two three carbon molecules called PGA

70. Use of ATP and NADPH
Chapter 7
Step #3 A series of NADPH and ATP from the light dependent reactions converts the three carbon molecules into PGAL (phosphoglyceraldehyde) which are 3 carbon sugars with higher energy levels

71. Sugar production
Chapter 7
Step 4 One out of every six molecules of PGAL is transferred to the cytoplasm and used in the synthesis of sugars and other carbohydrates. After THREE rounds of the cycle, (each round fixing one molecule of CO2) six molecules of PGAL are produced.

72. RuBP is replenished
Chapter 7
Step 5 Five molecules of PGAL, each with 3 carbon atoms, produce three molecules of the five carbon RuBP. This requires three more ATP. This replenishes the RuBP that was used up, and the cycle can continue. The 6th molecule of PGAL is available to the organism to make sugar.

73. Chapter 7
The PGAL that leaves the calvin cycle leaves the chloroplast and goes into the cytoplasm
This PGAL can combine with another PGAL to form a 6 carbon sugar molecule
C6H12O6

74. Chapter 7
In summary, the imputs required for the light independent reactions are 6 molecules of CO2, hydrogen from NADPH, and ATP. In the end, the six carbons from the CO2 can be accounted for by the harvest of a six carbon molecule. The remaining PGAL molecules are used to synthesize the RuBP molecules with which more CO2 molecules may combine.

75. Calvin cycle animation
Chapter 7

76. Calvin cycle song
Chapter 7

77. Relationship Between Reactions
Chapter 7
The “photo” part of photosynthesis refers to the capture of light energy (light dependent reactions)
The “synthesis” part of photosynthesis refers to glucose synthesis (light-independent reactions)

78. Relationship Between Reactions
Chapter 7
Light dependent reactions produce ATP and NADPH which is used to drive light-independent reactions
Depleted carriers (ADP and NADP+) return to light-dependent reactions for recharging

79. A Summary of Photosynthesis
Chapter 7
Light-dependent reactions occur in thylakoids
Light- independent reactions (c3 cycle) occur in stroma

80. Chapter 7

81. Lecture #6 C3 and C4 plants and photorespiration
Chapter 7
Lecture #6 C3 and C4 plants and photorespiration

82. Water, CO2, and the C4 Pathway
Chapter 7
The ideal leaf:
has large surface area to intercept sunlight
are porous to allow for CO2 entry from air
Problem: Substantial leaf porosity leads to substantial water evaporation, causing dehydration stress on the plant
Plants evolved waterproof coating and adjustable pores (stomata) for CO2 entry

83. When Stomata Are Closed
Chapter 7
When stomata close, CO2 levels drop and O2 levels rise
Carbon fixing enzyme combines O2 instead of CO2 with RuBP (called photorespiration)
Photorespiration:
O2 is used up as CO2 is generated
No useful cellular energy made
No glucose produced
Photorespiration is unproductive and wasteful

84. When Stomata Are Closed
Chapter 7
Hot, dry weather causes stomata to stay closed
Oxygen levels rise as carbon dioxide levels fall inside leaf
Photorespiration very common under such conditions
Plants may die from lack of glucose synthesis

85. C4 Plants Reduce Photorespiration
Chapter 7
“C4 plants” have chloroplasts in bundle sheath cells as well as mesophyll cells
Bundle sheath cells surround vascular bundles deep within mesophyll
C3 plants lack bundle sheath cell chloroplasts

86. C3 Plants & the Pathway C3 plants use the C3 pathway
Chapter 7
C3 plants use the C3 pathway
In a C3 plant, most chloroplasts are in mesophyll cells.

87. Biology: Life on Earth (Audesirk)
C3 Plants & the Pathway
Chapter 7
When it is hot and dry, stomata are closed to conserve water…wasteful photorespiration occurs (Oxygen combines with RuBP and no useful cellular energy can result…the C3 pathway cannot make glucose.)
Much photorespiration occurs under hot, dry conditions
Chapter 7

88. C4 plants use the C4 pathway
C4 Plants & the C4 Pathway
Chapter 7
C4 plants use the C4 pathway
In a C4 plant, both mesophyll & bundle-sheath cells contain chloroplasts.

89. Biology: Life on Earth (Audesirk)
Mesophyll cell in a C4 plant
Chapter 7
CO2 is captured with a highly specific enzyme.
C4 Plants & the C4 Pathway
PEP reacts with CO2, makes oxaloacetate. this is highly specific and not hindered by the excell O2 caused by closing of pores. Oxalo travels to bundle sheath cells, breaks down to release CO2, regular C3 can take place
C4 plants use more energy to create glucose
C4 thrive in deserts, and midsummer (much light, little water)
Almost no photorespiration occurs under hot, dry conditions.
Much glucose synthesis occurs.
Bundle-sheath cell in a C4 plant
Chapter 7

90. Photosynthesis song http://www.youtube.com/watch?v=Q_1mxZdF2TY
Chapter 7

91. Bozeman Biology Photosynthesis
Chapter 7

92. Chapter 7
The end