1. PHOTOSYNTHESIS

2. Capturing Light Energy
1) White light from the sun is composed of an array of colors called the visible spectrum.
(Red, Orange, Yellow, Green , Blue, Indigo, Violet)
Pigments
2) Chlorophyll is the green pigment (located in the thylakoid) that is responsible for absorbing certain wavelengths of light.

3. Light Spectrum

4. Light Spectrum Not all colors are useable to the same degree for Ps.
Red and Blue light - absorbed and used in Ps.
Green light - reflected or transmitted.

6. Accessory Pigments Absorb light energy and transfer it to chlorophyll.
Carotene (orange)*
Xanthophyll (yellow)*
Anthocyanin (red)**
Phycobilins (blue-purple)***

7. Parts of a Chloroplast
3) Thylakoid- a flattened vesicle lined with chlorophyll and is the site of photosynthesis
4) Granum- a stack of thylakoids.
5) Stroma- the thick fluid found between granum.

8. Overview of Photosynthesis
6-7) Photosynthesis converts light energy from the sun into chemical energy in the form of organic compounds through a series of two reactions.
The first reaction is called the Light Reaction
The second reaction is called the Calvin Cycle or the Light-Independent Reaction

9. Light Reaction 8) Chloroplasts are found in the cells of: plants
some bacteria
algae
9) Light Reaction Formula
H2O + NADP+ + ADP + Pi  NADPH + ATP + O2

10. Converting Light Energy To Chemical Energy
10) The pigments are grouped in clusters of a few hundred molecules in the thylakoid membrane. Each cluster and the proteins that the pigment molecules are embedded in are referred to collectively as a photosystem.
By absorbing light, pigment molecules in photosystem I and photosystem II acquire some of the energy carried by the light.

11. Converting Light Energy To Chemical Energy
Step 1) The acquired energy forces electrons to enter a higher energy level in the two chlorophyll a molecules of photosystem II. These energized electrons are said to be “excited.” The excited electrons have enough energy to leave the chlorophyll a molecules.

12. Converting Light Energy To Chemical Energy
Step 2) The acceptor of these electrons from photosystem II is a molecule called the primary electron acceptor, which donates the electrons to the electron transport chain.
Step 3) As the electrons move from molecule to molecule in this chain, they lose most of the acquired energy. The energy they lose is used to move protons into the thylakoid.

13. Converting Light Energy To Chemical Energy
Step 4) Light is absorbed by photosystem I at the same time it is absorbed by photosystem II. Electrons move from chlorophyll a molecules to another primary electron acceptor.

14. Converting Light Energy To Chemical Energy
Step 5) These electrons are then donated to another electron transport chain, which brings the electrons to the side of the thylakoid membrane that faces the stroma.
In the stroma, the electrons combine with a proton and NADP+. This causes NADP+ to be reduced to NADPH.

15. Replacing Electrons in Light Reactions
11) Electrons from photosystem II replace electrons that leave photosystem I.
Replacement electrons for photosystem II are provided by the splitting of water molecules.
12-13) Oxygen produced when water molecules are split diffuses out of the chloroplast and then leaves the plant.

16. Making ATP in Light Reactions
14) An important part of the light reactions is the synthesis of ATP.
During chemiosmosis, the movement of protons through ATP synthase into the stroma releases energy, which is used to produce ATP.

18. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
1. Which of the following statements is correct?
A) Accessory pigments are not involved in photosynthesis.
B) Accessory pigments add color to plants but do not absorb light energy.
C). Accessory pigments absorb colors of light that chlorophyll a cannot absorb.
D). Accessory pigments receive electrons from the electron transport chain of photosystem I.

19. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
1. Which of the following statements is correct?
A). Accessory pigments are not involved in photosynthesis.
B). Accessory pigments add color to plants but do not absorb light energy.
C). Accessory pigments absorb colors of light that chlorophyll a cannot absorb.
D). Accessory pigments receive electrons from the electron transport chain of photosystem I.

20. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. Oxygen is produced at what point during photosynthesis?
A. when CO2 is fixed
B. when water is split
C. when ATP is converted into ADP
D. when 3-PGA is converted into G3P

21. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. Oxygen is produced at what point during photosynthesis?
A. when CO2 is fixed
B. when water is split
C. when ATP is converted into ADP
D. when 3-PGA is converted into G3P

22. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a portion of a chloroplast. Use the diagram to answer the question that follows.
3. Which of the following correctly identifies the structure marked X and the activities that take place there?
F. stroma—Calvin cycle
G. stroma—light reactions
H. thylakoid—Calvin cycle
J. thylakoid—light reactions

23. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a portion of a chloroplast. Use the diagram to answer the question that follows.
3. Which of the following correctly identifies the structure marked X and the activities that take place there?
F. stroma—Calvin cycle
G. stroma—light reactions
H. thylakoid—Calvin cycle
J. thylakoid—light reactions

24. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a step in the process of chemiosmosis. Use the diagram to answer the question that follows.
4. What is the substance identified as Y in the image?
F. H+
G. NAD+
H. NADPH
J. ADP synthase

25. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a step in the process of chemiosmosis. Use the diagram to answer the question that follows.
4. What is the substance identified as Y in the image?
F. H+
G. NAD+
H. NADPH
J. ADP synthase

26. Calvin Cycle Function - to use ATP and NADPH to build food from CO2
Requirements
6 CO2
18 ATP
12 NADPH
Products
C6H12O6
18 ADP + 18 Pi
12 NADP+

27. Calvin Cycle
15) The Calvin Cycle occurs in the stroma of the chloroplast
16)The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis, the Calvin cycle.
17) In the Calvin cycle, CO2 is incorporated into organic compounds, a process called carbon fixation.
18) Calvin Cycle Formula
ATP + NADPH + CO2  C6H12O6 + ADP + Pi + NADP+

28. Rubisco (enzyme) Long Name: Ribulose Bisphosphate Carboxylase.
Enzyme that adds CO2 to an acceptor molecule.
The acceptor molecule is Ribulose Bisphosphate (RuBP)
Most important enzyme on Earth.

29. Calvin Cycle
The Calvin cycle, which occurs in the stroma of the chloroplast, is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar (C3).

30. Calvin Cycle
20) Most of the three-carbon sugars (G3P) generated in the Calvin cycle are converted to a five-carbon sugar (RuBP) to keep the Calvin cycle operating. But some of the three-carbon sugars leave the Calvin cycle and are used to make organic compounds, in which energy is stored for later use.

31. Standardized Test Prep
Multiple Choice
1. Which of the following is a reactant in the Calvin cycle?
A. O2
B. CO2
C. H2O
D. C6H12O6

32. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
1. Which of the following is a reactant in the Calvin cycle?
A. O2
B. CO2
C. H2O
D. C6H12O6

33. Multiple Choice, continued
Chapter 6
Standardized Test Prep
Multiple Choice, continued
2. light reactions : ATP :: Calvin cycle :
A. H+
B. O2
C. G3P
D. H2O

34. Multiple Choice, continued
Standardized Test Prep
Multiple Choice, continued
2. light reactions : ATP :: Calvin cycle :
A. H+
B. O2
C. G3P
D. H2O

35. Photorespiration
When Rubisco accepts O2 instead of CO2 as the substrate
Generates no ATP
Decreases Ps output by as much as 50%
May reflect a time when O2 was less plentiful and CO2 was more common.

36. Alternative Pathways The C4 Pathway Overview
Some plants that evolved in hot, dry climates fix carbon through the C4 pathway. These plants have their stomata partially closed during the hottest part of the day.
Certain cells in these plants have an enzyme (PEP) that can fix CO2 into four-carbon compounds even when the CO2 level is low and the O2 level is high. These compounds are then transported to other cells, where the Calvin cycle ensues.

37. C4 Ps Found in 19 plant families
Characteristic of hot regions with intense sunlight
Examples - sugarcane, Bermuda grass, crab grass, sorghum, & corn

38. C4 Ps Uses a different enzyme to initially capture CO2
Still uses C3 Ps to make sugar, but only does so in the bundle sheath cells.

39. PEP Carboxylase The enzyme used for CO2 capture in C4 Ps
Can use CO2 down to 0 ppm
Prevents photorespiration

40. PEP Carboxylase
Certain cells in these plants (mesophyll cells) have the enzyme PEP carboxylase that can fix CO2 into four-carbon compounds even when the CO2 level is low and the O2 level is high. These compounds are then transported to other cells (bundle-sheath cells), where the Calvin cycle ensues.

41. C3 Ps vs C4 Ps C3 Ps (normal Calvin Cycle)
Photorespiration
High water use
Cool temperatures
Slow to moderate growth rates
Cool season crops
C4 Ps (occurs before the Calvin Cycle)
No Photorespiration
Moderate water use
Warm temperatures
Very fast growth rates
Warm season crops

42. CAM Ps Crassulacean Acid Metabolism
Found in plants from arid conditions where water stress is a problem
Examples - cacti, pineapples, many orchids

43. Alternative Pathways The CAM Pathway
Some other plants that evolved in hot, dry climates fix carbon through the CAM pathway. These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize water loss.
Night Day

44. CAM Ps Open stomata at night to take in CO2
The CO2 is stored as a C4 acid
During the day, the acid is broken down and CO2 is fixed into sugar

45. CAM Plants Tissues decrease in pH over night, rise in pH during day
Avoid H2O stress by keeping stomates closed during the day
Generally have slow growth

46. C4 vs. CAM

47. C3 vs.C4 vs. CAM

48. Ps:Rs Ratios Reflect a plant’s balance in making food and using food
Ps > Rs, energy available for growth and reproduction.
Ps = Rs, no growth, but don’t die either.
Ps < Rs, death by starvation
Ps = Photosynthesis
Rs = Cell Respiration

49. Comments - Ps:Rs Rs happens 24 hours a day Ps only in light
Plants overwinter on stored food when Ps > Rs
If Ps < Rs, best solution is to increase the amount of light

50. Factors That Affect Ps 1. Light - quantity and quality
2. Temperature - too hot or too cold
3. CO2 - often limits C3 plants
4. Minerals – Like Mg

51. Importances of Ps
1. Food - either directly or indirectly comes from plants
2. Oxygen in the air
3. CO2 balance
4. Plant products
5. Life on Earth

52. Summary Know the main Ps equation Know Light Reaction
Know Calvin Cycle
Know Alternate Ps pathways
Know Ps:Rs ratios

53. Important Vocabulary Words
Autotroph
Heterotroph
Photosynthesis
Chloroplast
Pigment
Spectrum
Photon
Stroma
Thylakoid membrane
Granum
Photoautotroph
Chemoautotroph
Stomata
Chemiosmosis
Electron transport chain
Accessory pigment
Chlorophyll
Fluorescence
Light reactions
Dark reactions
RuBP
Rubisco
Photosystem I
Photosystem II
C4 Plants
C3 Plants
CAM Plants

54. Cycle of Photosynthesis