2. Photosynthesis

3. Photosynthesis in Overview Process by which plants and other autotrophs store the energy of sunlight into sugars. Requires sunlight, water, and carbon dioxide. Overall equation: 6 CO 2 + 6 H 2 0  C 6 H 12 O 6 + 6 O 2 Occurs in the leaves of plants in organelles called chloroplasts.

4. Leaf Structure Most photosynthesis occurs in the palisade layer. Gas exchange of CO 2 and O 2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. Palisade Spongy

5. Chloroplast Structure Inner membrane called the thylakoid membrane. Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana) Stroma is a liquid surrounding the thylakoids.

6. Pigments Chlorophyll A is the most important photosynthetic pigment. Other pigments called antenna or accessory pigments are also present in the leaf. –Chlorophyll B –Carotenoids (orange / red) –Xanthophylls (yellow / brown) These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

7. Pigment Absorption

9. This is an ocean plant. Seaweed

12. Photosynthesis: The Chemical Process Occurs in two main phases. –Light reactions –Dark reactions (aka – the Calvin Cycle) Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.

13. BIG PICTURE

14. Light Reactions Light-dependent reactions occur on the thylakoid membranes. –Light and water are required for this process. –Energy storage molecules are formed. (ATP and NADPH) –Oxygen gas is made as a waste product.

15. Dark Reactions Dark reactions (light-independent) occur in the stroma. –Carbon dioxide is “fixed” into the sugar glucose. – 18ATP and 12NADPH molecules created during the light reactions power the production of this glucose.

16. The Minor Details :P

17. Photosystem I & II

18. Non-cyclic Electron Flow Uses photosystem I (P700) and Photosystem II (P680) Electrons from water replace e- lost from PSII Electrons lost from chlorophyll in PSII replace e- lost in PSI ATP and NADPH are made

19. Cyclic Electron Flow Uses PSI Produces ATP but not NADPH Electron is passed back to the chlorophyll that it left when excited

20. No NADPH Made Only ATP Made Cyclic Electron Flow

21. Light Independent Reactions AKA – Dark Reactions (not really – just don’t need light) Also called Calvin Cycle or C-3 Pathway 1. Occurs in the stroma of the chloroplast 2. Uses ATP and NADPH from the Light Reactions 3. Accepts carbon from carbon dioxide – this is called carbon fixation to make sugar. It reduces CO 2. 4. Produces Glyceraldhyde 3- Phosphate which is a 3-C sugar and is used to make glucose

22. Details 1. Carbon dioxide enters the Calving cycle and become attached to a 5-C sugar – ribulose biphosphate (RuBP). This reaction is catalyzed by Rubisco enzyme. 2. 6-C intermediate breaks apart into two 3-C molecules of 3-phosphoglycerate (3-PGA) 3. Converted to phosphoglyceraldehyde (PGAL) which is used to make glucose. Uses 18 ATP and 12 NADPH. 4. RuBP is regenerated using ATP from Light reactions.

25. At low CO 2 concentration, rate is positively correlated with concentration CO 2 is a substrate in an enyme-catalysed light- dependent reaction.

26. At Low Light Intensity Rate is Proportional to Light Intensity plateau

27. Increased temp. gives increased energy and increased rate of photosynthesis Optimum temperature Above the optimum temp., enzymes are denatured and rate drops steeply. Which enzymes are used in respiration?

29. C4 Photosynthesis AP Biology Unit 4

30. Review: C3 Photosynthesis During “regular” photosynthesis, CO 2 is trapped into a 3-carbon compound by Rubisco  C3 Photosynthesis This 3 carbon compound then goes through the calvin cycle to produce glucose (eventually)

31. C4 Photosynthesis Certain plants go through a slightly modified photosynthesis process (C4 Photosynthesis) C4 Photosynthesis is an adaptation that evolved due to the environment these plants are in.

32. Rubisco ALL plants have it and use it for the Calvin Cycle. Rubisco usually reacts with CO 2, but it can also react with O 2 – 2 competing reactions.

33. Competing Reactions Rubisco can react with CO 2 (Carboxylase Reaction) – good for glucose output

34. Competing Reactions Rubisco can also react with O 2 (Oxygenase Reaction) –not good for glucose output –Even though CO 2 is eventually regenerated, it wastes time and energy (occupies Rubisco)

35. Photorespiration When Rubisco reacts with O 2 instead of CO 2 Occurs under the following conditions: –High O 2 concentrations –High heat Photorespiration is estimated to reduce photosynthetic efficiency by 25%

36. Why high heat? When it is hot, plants close their stomata to conserve water They continue to do photosynthesis  use up CO 2 and produce O 2  creates high O 2 concentrations inside the plant  photorespiration occurs

37. C4 Photosynthesis Certain plants have developed ways to limit the amount of photorespiration –C4 Pathway* –CAM Pathway* * Both convert CO 2 into a 4 carbon intermediate  C4 Photosynthesis

38. Leaf Anatomy In C3 plants (those that do C3 photosynthesis), all photosynthesis processes occur in the mesophyll cells. Image taken without permission from http://bcs.whfreeman.com/thelifewire| Mesophyll cells Bundle sheath cells (no photosynt hesis

39. C4 Pathway In C4 pathway plants photosynthesis occurs in both the mesophyll and the bundle sheath cells. –Light reactions in mesophyll –Calvin Cycle in Bundle sheath Image taken without permission from http://bcs.whfreeman.com/thelifewire|

40. C4 Pathway CO 2 is fixed into a 4- carbon intermediate first Has an extra enzyme– PEP Carboxylase that initially traps CO 2 instead of Rubisco– makes a 4 carbon intermediate

41. C4 Pathway The 4 carbon intermediate “smuggles” CO2 into the bundle sheath cell The bundle sheath cell is not very permeable to CO 2 CO 2 is released from the 4C molecule  goes through the Calvin Cycle C3 Pathway

42. How does the C4 Pathway limit photorespiration? Bundle sheath cells are far from the surface– less O 2 access PEP Carboxylase doesn’t have an affinity for O 2  allows plant to collect a lot of CO 2 and concentrate it in the bundle sheath cells (where Rubisco is)

43. CAM Pathway Fix CO 2 at night and store as a 4 carbon molecule Keep stomates closed during day to prevent water loss Same general process as C4 Pathway Has the same leaf anatomy as C3 plants

44. How does the CAM Pathway limit photorespiration? Collects CO 2 at night so that it can be more concentrated during the day Plant can still do the calvin cycle during the day without losing water

45. Summary of C4 Photosynthesis C4 Pathway –Separates by space (different locations) CAM Pathway –Separates reactions by time (night versus day)

46. Comparison Light intensity is directly related to temperature usually C4 Plants (CAM and C4 Pathway) are able to do more photosynthesis at high temperatures C3 Plants close stomata at high temps