1. Chapter 10 Photosynthesis – Part 1

2. Plan before Thanksgiving Break
Ch. 10 discussion
Quiz on Ch. 9 - Wed., Oct. 28
Quiz on Ch TBD
Cellular Respiration & Photosynthesis Essays due Wed., Nov. 4
Lab 4 (Photosynthesis) and Lab 3 (Mitosis and Meiosis)
Brief discussion of Ch. 11 and 12

3. Assignment Nov
DATES, CHAPTERS TENTATIVE BUT VERY LIKELY TO BE AS STATED
Read/review textbook Ch. 13 – 17 on Cellular and Molecular Basis of Genetics
Take Home Test distributed on Nov. 16
Take Home Test due Nov. 30

4. Assignment Dec. 14 – Jan. 4
Read/review textbook Ch. 50 – 55 on Ecology
Take Home Test distributed week of Dec. 14
Take Home Test due Jan. 4, 2010

5. Photosynthesis in nature
Autotrophs:
biotic producers: photoautotrophs; chemoautotrophs;
obtain organic food without eating other organisms
Heterotrophs: biotic consumers:
obtain organic food by eating other organisms or their by-products (includes decomposers)

6. Principles of Energy Harvest (again!)
Photosynthesis
vs.
Cellular respiration

7. Principles of Energy Harvest - Understand!
Photosynthesis Cellular respiration
Endergonic Exergonic
Products: O2, Products: CO2,
C6H12O6 H2O, ENERGY
Reactants: CO2, Reactants: O2,
H2O, ENERGY C6H12O6
Chloroplasts Mitochondria

8. Principles of Energy Harvest
Cell respiration is catabolic
Breaks down glucose
Photosynthesis is anabolic
Synthesizes glucose

9. ESSAY!

10. ESSAY!
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

11. Powered by light, the green parts of plants produce organic compounds and O2 from CO2 and H2O.
Using glucose as our target product, the equation describing the net process of photosynthesis is:
6CO2 + 6H2O + light energy -> C6H12O6 + 6O2
In reality, photosynthesis adds one CO2 at a time:
CO2 + H2O + light energy -> CH2O + O2
CH2O represents the general formula for a sugar, (CH2O)n.

12. Deciphering the equation
One of the first clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2:
CO2 + 2 H2O -> CH2O + H2O + O2

13. Did you understand? CO2 + 2 H2O -> CH2O + H2O + O2
In the photosynthesis reaction,
CO2 + 2 H2O -> CH2O + H2O + O2
Where do each of these components of the products come from?
Oxygen in glucose?
Oxygen in O2 gas?
Hydrogen in water?
Carbon in glucose?

14. Deciphering the equation – typical AP Biology Exam question
One of the first clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2:
CO2 + 2 H2O -> CH2O + H2O + O2

15. Deciphering the equation – understand this!

16. Photosynthesis: an overview
Redox process
H2O is split, and H (e- and H+) is transferred to CO2, reducing it to sugar
Detect redox reaction with DPIP in Lab 4A

17. Photosynthesis is a redox reaction
Photosynthesis reverses the direction of electron flow in respiration.
Water is split and electrons transferred with H+ from water to CO2, reducing it to sugar.
Chemically: polar covalent bonds (unequal sharing) are converted to nonpolar covalent bonds (equal sharing).
The reaction is strongly endergonic; light boosts the potential energy of electrons as they move from water so they can be used to make sugar.

18. The chloroplast Eukaryotic organelle Site of photosynthesis
Pigment: chlorophylls
Plant cell: mesophyll
Gas exchange: stomata
Double membrane (or is it triple?)
Thylakoids in grana, stroma

19. Chloroplasts are the size of medium to large bacteria
A typical mesophyll cell has chloroplasts, each about 2-4 microns by 4-7 microns long.
Each chloroplast has two membranes around a central aqueous space, the stroma.
In the stroma are membranous sacs, the thylakoids.

20. The chloroplast: 3 membranes?

21. Chloroplasts - the sites of photosynthesis in plants
Any green part of a plant has chloroplasts.
However, the leaves are the major site of photosynthesis for most plants.
There are about half a million chloroplasts per square millimeter of leaf surface.
The color of a leaf comes from chlorophyll, the green pigment in the chloroplasts.
Chlorophyll plays an important role in the absorption of light energy during photosynthesis.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

22. Chlorophyll molecule contains Mg2+
Fig. 10.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

23. Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf.
O2 exits and CO2 enters the leaf through microscopic pores, stomata, in the leaf.
Veins deliver water from the roots and carry off sugar from mesophyll cells to other plant areas.
Fig. 10.2
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

24. Two types of veins
Xylem carries water and minerals from roots to leaves (and all other parts)
Phloem carries sugar water from leaves (to all other parts)
Fig. 10.2

25. Photosynthesis: 2 major steps
Light reactions (“photo”)
NADP+ (electron acceptor nicotinamide adenine dinucleotide phosphate) to NADPH
Photophosphorylation: ADP ---> ATP
Calvin cycle (“synthesis”)
Carbon fixation: carbon into organics

26. 1. Photosystems: first Ps II, then Ps I
Light harvesting units of
the thylakoid membrane
Composed mainly of
protein and pigment
“antenna complexes”
“Antenna pigment”
molecules are struck by photons (light energy)
Energy is passed to reaction centers (redox location)
Excited e- from chlorophyll is trapped by a primary e- acceptor

27. Understand the photosystem scheme

28. Noncyclic electron flow
Photosystem II (P680):
photons excite chlorophyll e- to an acceptor
e- are replaced by splitting
of H2O (release of O2)
e-’s travel to Photosystem I down an electron transport chain
as e- fall, ADP ---> ATP (noncyclic photophosphorylation)

29. Noncyclic electron flow
Photosystem I (P700):
‘fallen’ e- replace excited e- to primary e- acceptor
2nd ETC (Fd~NADP+ reductase) transfers e- to NADP+ ---> NADPH (...to Calvin cycle…)
These photosystems produce equal amounts of ATP and NADPH

30. Light reactions animations
Electron Transport and ATP Synthesis
and Noncyclic Photophosphorylation

31. The Calvin cycle – the “Dark” Reactions
3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3-phosphate (G3P):
Carbon fixation: each CO2 is attached to RuBP (by “rubisco enzyme”)
Reduction: electrons from NADPH reduce to G3P; ATP used up
Regeneration: G3P rearranged to RuBP; ATP used; cycle continues

32. Calvin cycle animations

33. Calvin Cycle, net synthesis
For each G3P (and for 3 CO2)……. Consumption of 9 ATP’s & 6 NADPH (light reactions regenerate these molecules)
G3P can then be used by the plant to make glucose and other organic compounds

34. Cyclic electron flow Alternative cycle when ATP is deficient
Photosystem I used but not II; produces ATP but no NADPH
Why? The Calvin cycle consumes more ATP than NADPH…….
Cyclic photophosphorylation

35. Alternative carbon fixation methods
Avoiding Excessive Photorespiration
Hot/dry days; stomata close; CO2 decreases, O2 increases in leaves; O2 added to rubisco; no ATP or food generated
Two Solutions…..
C4 plants: 2 photosynthetic cells, bundle-sheath & mesophyll; PEP carboxylase (instead of rubisco) fixes CO2 in mesophyll; new 4C molecule releases CO2 (grasses)
ESSAY!

36. Alternative carbon fixation methods
Avoiding Excessive Photorespiration
CAM plants: open stomata during night, close during day (crassulacean acid metabolism); cacti, pineapples, etc.

37. Alternative carbon fixation methods – Another common AP Biology exam question

38. A review of photosynthesis

39. Light and Photosynthesis - 1
Light, like other form of electromagnetic energy, travels in rhythmic waves.
The distance between crests of electromagnetic waves is called the wavelength.
Wavelengths of electromagnetic radiation range from less than a nanometer (gamma rays) to over a kilometer (radio waves).

40. The electromagnetic spectrum.
The most important segment for life is a narrow band between 380 to 750 nm, visible light.

41. Light and Photosynthesis -2
Other light properties are those of a discrete particle, the photon.
The amount of energy packaged in a photon is inversely related to its wavelength.
Photons with shorter wavelengths pack more energy.
While the sun radiates a full electromagnetic spectrum, the atmosphere selectively screens out most wavelengths, permitting only visible light to pass in significant quantities.

42. When light meets matter, it may be reflected, transmitted, or absorbed.
Different pigments absorb photons of different wavelengths.
A leaf looks green because chlorophyll, the dominant pigment, absorbs red and blue light, while transmitting and reflecting green light.

43. A spectrophotometer measures the ability of a pigment to absorb various wavelengths of light.

44. It beams narrow wavelengths of light through a solution containing a pigment and measures the fraction of light transmitted at each wavelength.
An absorption spectrum plots a pigment’s light absorption versus wavelength.

45. Photosynthesis pigments
Chlorophyll a, the dominant pigment, absorbs best in the red and blue wavelengths, and least in the green.
Other pigments with different structures have different absorption spectra.

46. Collectively, these photosynthetic pigments determine an overall action spectrum for photosynthesis.
An action spectrum measures changes in some measure of photosynthetic activity (for example, O2 release) as the wavelength is varied.

47. The action spectrum of photosynthesis was first demonstrated in 1883 through an elegant experiment by Thomas Engelmann.
In this experiment, different segments of a filamentous alga were exposed to different wavelengths of light.
Areas receiving wavelengths favorable to photosynthesis should produce excess O2.
Engelmann used the abundance of aerobic bacteria clustered along the alga as a measure of O2 production.

48. The action spectrum of photosynthesis does not match exactly the absorption spectrum of any one photosynthetic pigment
Only chlorophyll a participates directly in the light reactions but accessory photosynthetic pigments absorb light and transfer energy to chlorophyll a.
Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a.
Carotenoids can funnel the energy from other wavelengths to chlorophyll a and also participate in photoprotection against excessive light.