1. Photosynthesis

2. Photosynthesis
the process by which plants, some bacteria, and some protists use the energy from sunlight to produce sugar (glucose)
which cellular respiration converts into ATP the "fuel" used by all living things.
A biochemical pathway

3. Autotrophs Organisms that manufacture their own food Algae (protist)
Bacteria (cyanobacteria)
Plants

4. Heterotrophs Cannot manufacture food Take in nutrients
Feed on autotrophs
Primary Consumers
Feed on other consumers
Secondary consumers

5. ATP

6. Adenosine triphosphate
major energy currency of the cell
regulates many biochemical pathways
like batteries for a cell

7. ATP/ADP and Energy ADP + P  ATP ATP  ADP + P + energy
Energy is stored in the covalent bonds between phosphates
the greatest amount of energy is in the bond between the second and third phosphate groups

8. Chlorophyll
The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll

9. Photosynthesis
The photosynthetic process uses water and releases the oxygen that we absolutely must have to stay alive.
Oh yes, we need the food as well!

10. Formula for photosynthesis
6 H2O + 6 CO2 (sunlight) C6H12O6 + 6 O2
six molecules of water plus six molecules of carbon dioxide (in the presence of sunlight) produce one molecule of sugar plus six molecules of oxygen

11. Photosynthesis vs. Respiration
Photosynthesis uses carbon dioxide to make oxygen
Respiration uses oxygen and produces carbon dioxide

12. Leaf cross-section

13. Leaves as food factories
Plants are the only photosynthetic organisms to have leaves (and not all plants have leaves)
A leaf may be viewed as a solar collector crammed full of photosynthetic cells
The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf
The products of photosynthesis, sugar and oxygen, leave the leaf

14. Important leaf structures
Water enters the root and is transported up to the leaves through specialized plant cells known as xylem
Land plants must guard against drying out (dessication) and so have evolved specialized structures known as stomata to allow gas to enter and leave the leaf.
Carbon dioxide cannot pass through the protective waxy layer (cuticle) but it can enter the leaf through an opening (stomata)
Flanked by two guard cells.

15. Stomata

16. The Nature of Light
White light is separated into the different colors (=wavelengths) of light by passing it through a prism.
Wavelength is defined as the distance from peak to peak (or trough to trough).
The energy is inversely proportional to the wavelength

17. The nature of light-wavelength

18. Wavelengths of light
The order of colors is determined by the wavelength of light
Visible light is one small part of the electromagnetic spectrum
The longer the wavelength of visible light, the more red the color
Wavelengths longer than red are referred to as infrared
while those shorter than violet are ultraviolet

19. Characteristics of light
Light behaves both as a wave and a particle.
Wave properties of light include the bending of the wave path when passing from one material into another
The particle properties are demonstrated by the photoelectric effect

20. Electromagnetic spectrum

21. Chlorophyll All photosynthetic organisms have chlorophyll a.
Accessory pigments absorb energy that chlorophyll a does not absorb.
Accessory pigments include chlorophyll b xanthophylls, and carotenoids
Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths.

22. Chlorophyll and Accessory Pigments
A pigment is any substance that absorbs light
The color of the pigment comes from the wavelengths of light reflected
Chlorophyll, absorbs all wavelengths of visible light except green, which it reflects to be detected by our eyes
Pigments have their own characteristic absorption spectra, the absorption pattern of a given pigment.

23. Absorption of chlorophyll

24. Structure of a chloroplast

25. Structure of a chloroplast
The organelle is surrounded by a double membrane
Inside the inner membrane is a complex mix of enzymes and water. This is called stroma and is important as the site of the dark reactions, more properly called the Calvin cycle.
Embedded in the stroma is a complex network of stacked sacs.
Each stack is called a granum and each of the flattened sacs which make up the granum is called a thylakoid.

26. Electron transport
In the light reactions light strikes chlorophyll a in such a way as to excite electrons to a higher energy state
In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH.
Water is split in the process, releasing oxygen as a by-product of the reaction
The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions).

27. Electron transport chain

28. Photosystems
Photosystems are arrangements of chlorophyll and other pigments packed into thylakoids
Many Prokaryotes have only one photosystem, Photosystem II (so numbered because, while it was most likely the first to evolve, it was the second one discovered).
Eukaryotes have Photosystem II plus Photosystem I.

29. Photosystem I

30. Photosystems I & II
Photosystem I uses chlorophyll a, in the form referred to as P700
Photosystem II uses a form of chlorophyll a known as P680
Both "active" forms of chlorophyll a function in photosynthesis due to their association with proteins in the thylakoid membrane

31. Steps to photosystems
1. light forces electrons to enter a higher energy level
Said to be “excited”
2. The excited electrons have enough energy to leave chlorophyll a
LEO – chlorophyll a has been oxidized
Leo says GER

32. Steps to photosystems
If one substance is oxidized (loses electrons) then another must be reduced (gains electrons)
These electrons are gained by the thylakoid membrane
Primary electron receptor
GER- gain of electrons is reduction

33. Primary electron receptor

34. Steps in photosystems
3. Primary electron acceptor donates electrons to a series of molecules in the thylakoid membrane
Known as an electron transport chain
As the electrons are passed from molecule to molecule they lose the energy gained when excited
Energy lost is gained by protons in the thylakoid membrane

35. Electron transport chain

36. Steps of photosystems
4. Light is absorbed by photosystem I at the same time as photosystem II
Electrons move from chlorophyll a to another electron acceptor molecule
Lost electrons are replaced by those gained in photosystem II

37. Electron transport chain

38. Steps to photosystems
5. Primary electron acceptor of photosystem I donates electrons to a different electron transport chain
Chain brings electrons to side of thylakoid membrane
Electrons combine with a proton and NADP+
Causes NADP+ to become NADPH

39. Electron transport chain

40. Photosystem restoration
Electrons from chlorophyll in PS II replace electrons that leave chlorophyll in PS I
If not replaced both electron transport chains stop
Photosynthesis does not occur

41. Net results of PS
For every 2 molecules of water split, four electrons become available to replace electrons lost in PS II
2 H2O  4 H e- + O2
Protons stay inside thylakoid membrane
Oxygen diffuses out- byproduct

42. Chemiosmosis
Relies on a concentration gradient of protons across thylakoid membrane
Build up of protons represents energy
Energy is captured by ATP synthase
Chemiosmosis

43. Chemiosmosis

44. ATP Synthase Acts as a protein carrier Acts as an enzyme
Synthesizes ATP from ADP

45. The Calvin Cycle

46. Carbon fixation
Carbon-Fixing Reactions are also known as the Dark Reactions (or Light Independent Reactions)
The Calvin Cycle occurs in the stroma of chloroplasts
Carbon dioxide is captured by the chemical ribulose biphosphate (RuBP).
RuBP is a 5-C chemical.
Six molecules of carbon dioxide enter the Calvin Cycle, eventually producing one molecule of glucose

47. Melvin Calvin
. The reactions in this process were worked out by Melvin Calvin (shown below).

48. Steps of the Calvin Cycle
1. CO2 diffuses into the stroma
Enzyme combines CO2 with RuBP
Product is a 6 Carbon molecule which splits immediately into 2, 3-Carbon molecules of PGA (phosphoglycerate)

49. Calvin cycle
calvin

50. Calvin Cycle
2. PGA is converted into another 3-C molecule , PGAL (phosphoglyceraldehyde)
A. PGA receives a phosphate from ATP
B. Receives a proton form NADPH and releases a phosphate group
Net result: ADP & NADP+ are created

51. Calvin cycle
calvin

52. Calvin cycle
3. Most PGAL is converted back to RuBP through a series of complex reactions
Requires a phosphate from ATP
By regenerating RuBP to allow Calvin cycle to continue

53. Calvin cycle
calvin

54. Photosynthesis Balance Sheet
Each turn of Calvin cycle fixes one CO2
3 turns to produce each PGAL
Uses 3 ATP and 2 NADPH
In total 3 turns of Calvin cycle uses 9 ATP and 6 NADPH

55. Rate of photosynthesis
Effected by plant’s environment
Light intensity
CO2 concentration
Temperature

56. Photosynthesis