PHOTOSYNTHESIS, RESPIRATION, AND TRANSLOCATION

1. PHOTOSYNTHESIS, RESPIRATION, AND TRANSLOCATION

2. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.htmlhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html

3. PHOTOSYNTHESIS • Green plants convert radiant energy into chemical energy - utilizes chlorophyll of the chloroplasts

4. Molecular model of chlorophyll

5. PHOTOSYNTHESIS • Principal Photosynthetic Process: Hydrogen + Carbon Dioxide → CH2O in presence of: Photosynthetically Active Radiation - PAR

6. Compensation Points • Light: as PAR increases. . . photosynthetic CO2 fixed equals respiration CO2 released no net CO2 movement until more PAR up to the Light Saturation Level

7. Compensation Points • CO2: CO2 fixed by photosynthesis equals CO2 released by respiration no net CO2 movement

8. Note: PAR level required for light saturation rises with increasing CO2 • Also: as PAR level increases, higher concentrations of CO2 are required important differences in C3 and C4 plants

9. Chemical equation for photosynthesis (greatly simplified): 6 CO2 + 6 H2O + radiant energy w/ chlorophyll Yields: 6O2 + C6H12O6 (Glucose)

10. GLUCOSE ENERGY 1 mole Glucose (a 6-carbon sugar (C6)), has energy equal to ~ 686 kcals Written as: 686 kcal/mol

11. Light and Dark Reactions • Two reactions in photosynthesis: Light Reactions - occur only in presence of light Dark Reactions - don’t require light; occur in light or complete darkness

12. Light reactions involve: • photons • electrons of the chlorophyll molecule • water molecule • NADP (nicotinamide adenine dinucleotide phosphate)

13. Visible Light

14. Light Reaction Process: 1) photons (light packets) energize electrons in chlorophyll molecule (z scheme) 2) energized chlorophyll splits water molecule 3) NADP captures H+ ion; holds it as NADP-H 4) ATP (adenosine triphosphate) formed by: a. light energy changed to chemical energy (NADPH) b. electron from H2O; energy released forms ATP Note: free O2 is released in process

15. Structure of ATP

16. Dark Reactions (Calvin Cycle) • Utilize: • NADPH • ATP • CO2 CO2 combines w/ C5 sugar Ribulose Diphosphate (RuDP) (catalyzed by RuDP-carboxylase, an enzyme)

17. Dark Reactions (Calvin Cycle) u n s t a b l e - immediately splits into two PGA molecules (Phosphoglyceric acid) Plants forming these PGA molecules are: C3 Plants

18. Dark Reactions (Calvin Cycle) • H from NADPH transferred to PGA via ATP/NADPH energy • Phosphoglyceraldehyde (PGAL) is formed (a simple sugar) • PGAL combines into Glucose; however most PGAL is used to regenerate RuDP Special enzymes (RuDP-carboxylase) catalyze RuDP to combine with CO2

19. Dark Reactions (Calvin Cycle) Takes: 18 molecules ATP + 12NADPH + 6CO2 = C6H12O6 also yields 6H2O, 18ADP, and 18P

20. Modified photosynthetic equation: 6CO2 + 12H2O + radiant energy w/ chlorophyll → 6O2 + 6H2O + C6H12O6 shows that O2 liberated in light reactions comes from H2Onot CO2 and that there are newly formed H2O molecules

21. C3 and C4 Plants • Photosynthetic pathways are complicated • Simply stated: C3 plants are less efficient at photosynthesis • Reduced efficiency due to an “energy robber”: Photorespiration

22. Photorespiration • Occurs when C3 plants oxygenase instead of carboxylase in the dark reaction; thus refer to enzyme as Rubisco for short • Less efficient - can’t metabolize glycolate (C2) produced; only passes one PGA to be reduced to PGAL • Two carbon atoms are “lost” from cycle

23. C4 Plants C4 plants designed to: • reduce O2 concentrations • increase CO2 concentrations • favor carboxylase reaction

24. C4 Plants C4 advantages: • photosynthesize at lower CO2 concentrations • higher temperature optimums • higher light saturation points • rapid photosynthate movement

25. Rate of Photosynthesis

26. C4 Plants Examples of C4 plants: • Corn* • Sugarcane • Sorghum • Bermudagrass • Sudangrass Note: C4weeds also - crabgrass, johnsongrass, shattercane, pigweed

27. C3 Plants Examples of C3 plants: • Wheat • Rice • Soybeans • Alfalfa • Fescue • Barley

28. CAM Plants CAM Plants - separate light and dark reactions according to: Time of Day CAM (Crassulacean Acid Metabolism) Plants include: Pineapple, Cacti, other succulents

29. CAM Plants Light reactions occur during daytime but • Initial fixation of CO2 occurs at night • Allows stomata to remain closed during the day - conserve H2O

30. CAM Plants Also: • 4-carbon Malic Acid “pool” accumulates overnight (lowers pH) • During day stomata are closed • Malic Acid releases CO2 providing carbon source for dark reaction

31. CAM Plants

32. Environmental Factors Affecting Photosynthesis Light: intensity, quality, duration intensity – (see table 7-1; fig 7-7 p. 127) - etiolated vs. high light intensity - compensation point - saturation point quality - reds and blues; greens are reflected (fig. 7-6) duration - longer days =more photosynthesis

33. Light Spectrum

34. Light Quality - Chlorophyll

35. Light Quality - Photosynthesis

36. Environmental Factors Affecting Photosynthesis CO2: • photosynthetic rate limited by small amounts of CO2 • increase by air movement; also CO2 generators (greenhouse) • Normal CO2 content: 300 - 350 ppm (0.030 - 0.035 %)

37. Environmental Factors Affecting Photosynthesis CO2 (cont) (see fig. 7-8) Recall CO2 compensation point: CO2 evolved in respiration = CO2 consumed in photosynthesis

38. Environmental Factors Affecting Photosynthesis Temperature (Heat) 2xPhotosynthetic Activity for each 10°C (18°F) increase in temperature Excess temp can lower photosynthesis and increase respiration

39. Environmental Factors Affecting Photosynthesis H2O content: • wilted leaves - rate near zero • due to reduced CO2 by closed stomata • water does not directly limit photosynthesis • (only ~ 0.01 % of water absorbed by plants is used as H source)

40. Environmental Factors Affecting Photosynthesis but indirectly: • low turgor - stomatal closing • reduced leaf exposure • enzymes affected • excess soil moisture – anaerobic • Lack of O2 reduces respiration, uptake, etc.

41. RESPIRATION Release of energy stored in foods • Controlled burning or “oxidation” at low temps by enzymes Respiration equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (glucose) (oxygen) (carbon dioxide) (water)

42. RESPIRATION Modified Respiration Equation: • Shows that H2O is an input as well as a product • Specifies total net energy derived from one glucose molecule

43. Modified Respiration Equation: C6H12O6 + 6O2 + 6H2O→6CO2 + 12H2O + 38ATP + heat

44. RESPIRATION Heat energy is of little value to plant (may be detrimental) ATP energy used for: • Chemical reactions (energy req.) • Assimilation (protoplasm) • Maintenance (protoplasm) • Synthesis (misc.) • Accumulation (solutes) • Conduction (foods) • Motion (protoplasm, chromosomes)

45. Gas Exchange in Respiration Gas exchange is the opposite of photosynthesis Respiration takes in O2 and releases CO2 • liberates more O2 than needed for respiration • requires more CO2 than released by respiration

46. Gas Exchange in Respiration @ Compensation point (low light intensity): • O2 released in photosynthesis = CO2 released in respiration

47. COMPARISON OF PHOTOSYNTHESIS AND RESPIRATION Under ideal photosynthetic conditions: Photosynthetic Rate ~ 10x Respiration Rate

48. Photosynthesis Cells w/chlorophyll In light Uses H20 and CO2 Releases O2 Radiant energy to chemical energy Dry weight increases Food and energy produced Energy stored Respiration All living cells Light and dark Uses O2 Forms CO2 and H20 Chemical energy to useful energy Dry weight decreases Food broken down Energy released COMPARISON OF PHOTOSYNTHESIS AND RESPIRATION

49. Factors Affecting Respiration • Temperature - respiration increases as temperature increases • Moisture - respiration increases as moisture decreases (stress) • Injuries - respiration increases with injury • Age of tissue - respiration greater in young tissue • Kind of tissue - respiration greater in meristematic • CO2/O2 - respiration increases with high O2 / low CO2 • Stored carbohydrates - respiration increases with increased stored energy

50. Respiration Problems/Hazards • deterioration (fungi and bacteria) • rot and decay • loss of dry wt. • loss of palatability • high temperatures / high CO2 (diseases; FIRE hazard)