1. PHOTOSYNTHESIS NOTES
How do cells get energy?

3. How do plants get energy?
Plants get their energy from the sun
Plants absorb sunlight and use it to make oxygen and sugar (organic compounds)
Where do we get this energy?

4. How do animals get their energy?
Animals eat green plants and therefore receive the energy that plants have made.
2 ways animals get energy:
Eat a plant
Eat something that has eaten a plant

5. 2 categories of organisms (based on how they obtain their energy)
We can separate organisms based on how they get their energy
Autotrophs – use energy from sunlight to make food (glucose, which is sugar)
Most autotrophs undergo photosynthesis
2 categories of organisms (based on how they obtain their energy)

6. 2 categories of organisms (based on how they obtain their energy)
Nearly all organisms depend on autotrophs to obtain food
2 categories of organisms (based on how they obtain their energy)
2. Heterotroph – an organism that gets energy from food, not directly from sunlight

7. What would happen if all autotrophs disappeared?
All other organisms would die

8. Photosynthesis Overview
Photosynthesis is a series of complex chemical reactions, where the end result of one reaction is the fuel for another reaction
biochemical pathway – the product of one reaction is the reactant of another reaction

9. Photosynthesis Overview
Photosynthesis – the process of converting sunlight into organic compounds (food) that the cell can use

10. THE BIG PICTURE… So…What’s the point?
Autotrophs convert CO2 and H2O into glucose and O2 in the process of photosynthesis
Cellular respiration uses O2 and glucose to make CO2 and H2O (and ATP)
The products of photosynthesis are the reactants in respiration. How cool is that?!
It’s a cycle

11. 1. 3. 2.

12. Chloroplast – photosynthetic organelle found in plants and algae
The Chloroplast
Surrounded by 2 membranes
Thylakoids – system of membranes arranged as flattened sacs
Granum – a layered stack of connected thylakoids
Stroma – solution surrounding a granum
Chlorophyll – green pigment inside thylakoids
Got the plant, and have the sun. What’s next?
What are some parts of the chloroplast?
chlorophyll

13. Light and pigments
Light appears white, but is actually made of many colors.
When white light strikes an object, it can be
reflected
transmitted
absorbed
You only see the light that is reflected or transmitted
So the chloroplasts absorb light, then what?

14. Light and pigments
For example, if an object is purple, it absorbs all other colors in the spectrum EXCEPT purple.
Purple is reflected.

15. Light and pigments
What colors are being reflected in this chloroplast?
What colors are being absorbed?
Most objects contain pigments – compounds that absorb light
A pigment will absorb some colors and reflect others

16. Why do leaves look green???
Pigments in the leaves absorb all colors except green, and green is reflected.

17. Pigments in thylakoids
Chlorophyll – the most important pigment; why leaves are green
Chlorophyll a – directly involved in light reactions
Chlorophyll b –helps chlorophyll a capture light energy but is not directly involved in the reactions. This is called an accessory pigment.

18. Pigments in thylakoids
2. Carotenoids – other accessory pigments in thylakoids.
Plants also have pigment compounds that reflect red, yellow, and brown light.

19. There is a lot more chlorophyll, which hides the carotenoids
If plants have red, yellow, and brown pigments, then why do leaves look green?
There is a lot more chlorophyll, which hides the carotenoids

20. 1. What colors are chlorophyll a absorbing?
Dark blue, orange/red

21. 2. What colors are chlorophyll b absorbing?
light blue, orange

22. 3. What colors are carotenoids absorbing?
light blue, blue-green

23. 4. What colors will be reflected?
Green, yellow

24. Carotenoids are helping absorb light that neither chlorophyll a nor chlorophyll b can absorb

25. …remember that these pigments are absorbing non-green light to help photosynthesis occur more efficiently

26. 5. Why is it important that carotenoids absorb different wavelengths than a or b?
carotenoids help the chloroplasts capture more energy in light
By absorbing colors than neither a nor b can absorb, the cartenoids help plants capture more energy in light.

27. Why do we see other colors on plants?
What parts will we usually see other colors on?  fruit, flowers
Plant parts with other colors don’t need to do photosynthesis

28. Why do leaves change color in the fall?
They lose their chlorophyll, and carotenoids now become visible.

29. Once the pigments in the chloroplast have captured light energy, the light energy must then be converted to chemical energy.
This chemical energy is temporarily stored in ATP and NADPH.

30. ATP adenosine triphosphate
Within cells, energy is stored in the chemical bonds of molecules. This energy can be used quickly and easily by the cell.
adenosine triphosphate
ATP
This is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it.

31. ATP adenosine triphosphate (ATP) – 3 phosphate groups bond
This is difficult for the phosphates to do because it requires a lot of energy, but binding 3 phosphates stores a lot of energy
AMP – only one P group bonds, so small amt of energy required and small amt. stored
ADP – 2 p groups bond, more energy needed to do this and more energy is stored
ATP – 3 P groups bond (which is tough since charged) – this needs more energy and stores a lot of energy until bonds are broken

32. Adenosine triphosphate (ATP) Adenosine diphosphate (ADP)
The energy of ATP becomes available to a cell when the molecule is broken down.
Adenosine triphosphate (ATP)
Adenosine diphosphate (ADP)
Energy is released when bonds are broken.

33. Remember…Photosynthesis is:
The process of converting sunlight into organic compounds that the cell can use

34. 2 stages of Photosynthesis
Light-dependent reactions
light energy  chemical energy
temporarily stored in the forms of NADPH and ATP
Light-independent reactions (Calvin Cycle)
ATP, and NADPH, CO2  glucose (sugar)

35. Let’s break it down…
Hmmmm…what’s the chemical equation for this amazing process?
6CO2 + 6H2O C6H12O6 + 6O2
“I know you’re all wondering…”
light energy

36. light energy  chemical energy
Photosystem – a cluster of pigment molecules and proteins in the thylakoid membrane
Photosystem II
Photosystem I
The light reactions occur in several steps…

37. 5 steps of light-dependent reaction

38. Step 1 Sunlight strikes the chlorophyll molecules
Light energy is transferred to electrons.
Now there is enough energy to leave chlorophyll a in Photosystem II

39. Step 2
Electrons move on to the primary electron acceptor

40. Step 3
These highly energized electrons are then passed to the electron transport chain (ETC).
ETC is a series of proteins in the thylakoid membrane.

41. Step 3 continued…
The electrons are transferred from one molecule to the next
b) As they move, the electrons are losing energy
c) This “lost” energy is being used to move
H+ protons into the thylakoid

42. ETC video…click the image below to watch…

43. Step 4 Photosystem I also absorbs light
Electrons move to another primary electron acceptor
then on to another electron transport chain

44. Step 4 continued…
Electrons now move to the other side of the thylakoid

45. Also in Step 4… Ph. II is replacing electrons for Ph. I.
Photolysis – Molecules of water are split in photosystem I to replace the lost electrons

46. Step 5
The combination of electrons with H+ protons and NADP+ makes NADPH
H+ protons + electrons (e-) + NADP+  NADPH

47. So we have NADPH…what about ATP???

48. chemiosmosis

49. Chemiosmosis ATP is the main source of energy for all cells
It is made in a process called chemiosmosis:
H+ moves through ATP synthase, down the concentration gradient. This releases energy in the form of ATP

50. Synthesis (“the making”) of ATP by ATP synthase…
ATP synthase uses the generated energy to add 1 phosphate group to ADP, converting it to ATP
NADPH & ATP are the energy molecules necessary for the rest of photosynthesis!!!

51. Light Reaction Summary
What is the purpose of the light reaction?
1. Use light energy to make NADPH
2. H+ ions move through ATP synthase to make ATP

52. Light-dependent reaction video

53. Quick review…

54. Remember where we were…
Inside a leaf
Inside a plant cell
Inside a chloroplast
Now inside the STROMA

55. Review light-dependent reactions

56. Review
2. In the light-dependent reactions oxygen is produced by photolysis, which splits water molecules

57. Remember what we get from the light-dependent reactions…
ATP
NADPH O2

58. Calvin Cycle (AKA Light-Independent Reactions)

59. What’s the point of the light-INDEPENDENT reactions?
Make glucose

60. OVERVIEW of Calvin Cycle
4. What other molecule is needed for the Calvin Cycle???
1. Does it need light???
2. Where does it take place???
 Nope. Also called the “dark reactions”, or “light independent reactions”
 CO2
5. What is the product of the Calvin Cycle???
 stroma
 glucose
3. What energy molecules are used as fuel???
 ATP, NADPH

61. Stomata H2O Stomata – openings on the underside of leaves CO2 enters
O2 exits
What other molecule can enter and exit through stomata?
H2O

62. Carbon Fixation
Carbon fixation - Take CO2, put it into organic compounds (like glucose)

63. Carbon Fixation
Take CO2, put it into organic compounds

64. Calvin Cycle
Calvin Cycle – the most common way that plants take carbon and put it into glucose to be used by the plant
Where do we get the carbon from?
CO2

65. Steps of the Calvin Cycle
CO2 enters through the stomata
CO2 goes into the chloroplast, and into the stroma
When it gets into the stroma it uses energy from ATP and NADPH to make glucose

66. 4 steps of the Calvin Cycle

67. Step 1 *CO2 enters stroma Each CO2 paired with 5-C RuBP
*need 3 CO2 molecules!
Step 1 x3
*CO2 enters stroma
Each CO2 paired with 5-C RuBP
Yields unstable 6-C molecule; immediately splits into two 3-C PGA molecules
There are 3 sets of these 2 (3C) PGA molecules
3-PGA PGA
3-PGA PGA
3-PGA PGA

68. 4 steps of the Calvin Cycle
3 x CO2
4 steps of the Calvin Cycle
3 x RuBP (5C)
6 x 3-PGA (3C)

69. Step 2 Each 3-PGA converted into G3P
This is done using the energy from ATP and NADPH
3-PGA 3-PGA
3-PGA 3-PGA
3-PGA 3-PGA

70. (step 2)
3-PGA
3-PGA (+Pi)
What results:

71. Step 2 3-PGA  G3P Needs energy from ATP and NADPH 3-PGA 3-PGA

72. 4 steps of the Calvin Cycle
3 x CO2
4 steps of the Calvin Cycle
3 x RuBP (5C)
6 x 3-PGA (3C)
6 x G3P (3C)

73. Step 3 Step 4 Then re-enter Calvin Cycle to make more sugars
Let’s go make a carbohydrate!
Step 3
Step 4
Use ATP to convert back into RuBP
Then re-enter Calvin Cycle to make more sugars
Spent ADP returns to light reactions to be again made into ATP
How many times do we need to do the Calvin Cycle to make one molecule of glucose?

74. 4 steps of the Calvin Cycle
3 x CO2
4 steps of the Calvin Cycle
3 x RuBP (5C)
6 x 3-PGA (3C)
5 x G3P (3C)
6 x G3P (3C)
1 x G3P (3C)  leaves Calvin Cycle to make glucose molecules

75. Calvin Cycle Video…click the image below to watch…

76. Calvin Cycle Summary
Most common and efficient way to use carbon to make glucose
Plants that use only the Calvin Cycle for carbon fixation are deemed C3 plants

77. Remember… Stomata – openings on the underside of leaves CO2 enters
O2 exits
a) What might be a problem in hot and dry climates?
Water loss through stomata

78. Stomata
b) Plants can close their stomata to prevent too much water loss
Are there any problems with the stomata being closed???
CO2 enters and O2 leaves through these openings

79. Stomata
c) If stomata are closed, CO2 cannot enter if CO2 levels decrease, the Calvin Cycle will slow down or stop d) If stomata are closed, O2 cannot exit if O2 levels inside increase, the Calvin Cycle will slow down or stop

80. Alternative Pathways
Plants deal with this issue by using alternative pathways
These pathways allow plants to still be able to fix carbon, but in hot and dry conditions

81. “C4 plants” 1. C4 Pathway Stomata are partially closed
Lose ½ the amount of water that C3 plants lose
But they grow slower
Corn Sugar Cane Crabgrass

82. 2. CAM Pathway “Crassulacean acid metabolism”
Open stomata only at night
Go through the Calvin cycle during the day
pro – lose least water
con – slowest growth

83. C3, C4, & CAM Plants Video…

84. Photosynthesis Summary
Light-dependent reactions
light energy  chemical energy
This chemical energy is temporarily stored in the forms of NADPH and ATP
Light-independent reactions (Calvin Cycle)
ATP, NADPH, CO2  glucose (sugar)

85. What affects photosynthesis?

86. What affects photosynthesis?
1. Light intensity: as light increases, rate of photosynthesis increases

87. What affects photosynthesis?
2. Carbon Dioxide: As CO2 increases, rate of photosynthesis increases

88. What affects photosynthesis?
3. Temperature:
Temperature Low = Rate of photosynthesis low
Temperature Increases = Rate of photosynthesis increases
If temperature too hot, rate drops

89. Oxygen and Sugar!

90. Review Questions
The process that uses the sun’s energy to make simple sugars is _____________.
Cellular respiration
Glycolysis
Photosynthesis
Photolysis

91. The function accomplished by the light-dependent reactions is ______________.
Energy storage
Sugar production
Carbon fixation
Conversion of sugar

92. 3. Describe one way plants deal with hot, dry climates.

93. 4. What is the difference between the light-dependent reactions and the light-independent reactions?

94. Video Overview of Photosynthesis…

95. Complete the Photosynthetic rate analysis on the last page of your notes…

96. (a little more review)

97. Autotrophs, heterotrophs
1. There are two categories of organisms based on how they obtain energy. What are they?
Autotrophs, heterotrophs

98. biochemical pathway photosynthesis electron transport chain
2. __________ is the process of converting sunlight into chemical energy that the cell can use
biochemical pathway
photosynthesis
electron transport chain

99. 3. In what plant organelle does photosynthesis occur?
Cell wall
Mitochondria
Chloroplasts

100. 4. What is the green pigment inside chloroplasts called?
Carotene
Chlorophyll
Thylakoid

101. 5. Chemical energy is temporarily stored in a molecule called _____.
ATP
H2O
Na+