Chapter 10: Photosynthesis

1. Chapter 10: Photosynthesis

2. Essential Knowledge • 2.a.1 – All living systems require constant input of free energy (10.1-10.3). • 2.a.2 – Organisms capture and store free energy for use in biological processes (10.1-10.3).

3. Photosynthesis • Process by which plants use light energy to make food • A reduction process that makes complex organic molecules from simple molecules

4. Ps General Equation 6 CO2 + 6 H2O  C6H12O6 + 6 O2 • Requires: ♦Notice: • Chlorophyll This is VERY • Light similar to the cell resp eq.

5. Ps: a redox process • Hydrogens are added to Carbons-reduces CO2 to sugar • Water is split; becomes source of hydrogens • Complex covalent bonds made • Requires energy

6. Ps • Has two chemical reactions: 1. Light Reaction 2. Dark Reaction • Names are from “light” as a requirement, not where or when they occur

7. Light • A form of electromagnetic radiation/energy • Visible light has the right energy for use in Ps • Travels in waves

8. Too Hot Too Cold JustRight Detected by our eye-hence the term visible

10. Action Spectrum • Not all colors are useable to the same degree for Ps • Red and Blue light - absorbed and used in Ps • Green light - reflected or transmitted

12. Comment • In oceans, red light is lost or filtered out early because it has lower energy • Only blue light which has higher energy can reach the lower depths

13. Result • Many deep ocean fish are bright red in color. • Why? • They can’t be seen because there is no red light to reflect their color

14. Photosynthesis Pigments • Pigment: absorb light • Different pigments absorb different wavelengths • Types: • Chlorophylls (a and b) • Accessory Pigments (carotenoids)

15. Chlorophylls • Have C,H,O,N and Mg • Two major types: a, b • Molecule has a lipophilic tail (allows it to dissolve into membranes) • Contains Mg in a reaction center.

17. Accessory Pigments • Absorb light energy and transfer it to chlorophyll • Various shades of yellow/orange • Function: photoprotection • Ex: Carotene (orange) Xanthophyll (yellow)

18. Fall Leaf Colors • Chlorophyll breaks down • N and Mg salvaged and moved into the stem for next year • Accessory pigments remain behind, giving the various fall leaf colors

19. Parts of Plant: Ps function • Stomata • Roots • Mesophyll • Veins

21. Site of Ps • Chloroplast • Contain chlorophyll pigment • All green parts of plants contain chloroplasts • Most are found in leaves • Why? Larger surface area

22. Chloroplast Structure • Double outer membrane • Inner membrane folded and stacked into grana • Stroma - liquid that surrounds the thylakoidmembranes

24. Photosystems • Collection of pigments that serve as a light trap • Made of chlorophyll and the accessory pigments • Two types known: • PSI & PSII

26. Parts of Photosystem • 1) Rxn center/e- acceptor • Chlorophyll uses light energy to move e- to next energy level • 2) Pigment • Light absorption, photon acceptor • 3) Light-harvesting complex • Proteins, contain pigment

28. Light Reaction • Same thing as NoncyclicPhotophosphorylation • Location - grana of the chloroplast • Function - to split water and produce ATP and NADPH (provide chem energy for next cycle)

30. Requirements: Light Water ADP + Pi NADP+ Products: O2 ATP NADPH Light Reaction

31. Chemiosmosis Model • The chloroplast produces ATP in the same manner as the mitochondria in Rs • Light energy is used to pump H+ across a membrane • When the H+ diffuses back, ATP is generated

32. Chemiosmosis • H+ are pumped into the thylakoidspace • ATP and NADPH are made when the H+ diffuse into the stroma • Both Rs and Ps use ETC to pump H+

33. Light Rxn Tutorial

34. Dark Reactions • How plants actually make food (carbohydrates) • Don't require light directly to run • Also known as the Calvin cycle or C3 Ps

35. Calvin cycle/Dark reaction • Anabolic – builds sugars from smaller molecules • Function - use ATP and NADPH to build food from CO2 • Location - stroma of the chloroplast Calvin Cycle movie

36. Rubisco • RibuloseBisPhosphateCarboxylase • Enzyme that adds CO2 to an acceptor molecule • Most important enzyme on earth • Catalyzes first step of dark rxn

37. C3 plants are plants that DO use Rubisco enzyme “normally” Keep stomata open during day MOST plants are C3 plants When you “think of Ps”, you think of a C3 plant performing Ps Adaptive value: Require less Less enzyme activity, no specialized organs/anatomy C3 Ps

38. Photorespiration • When Rubisco accepts O2 instead of CO2 as the substrate • Generates no ATP • Actually uses ATP • Decreases Ps output by as much as 50%

39. Photorespiration • May reflect a time when O2 was less plentiful and CO2 was more common • Important to evolution of autotrophs • Photo=occurs in light • Respiration=consumes oxygen while producing CO2

40. Alternate Ps Methods 1. C4 Ps 2. CAM Ps

41. Intro to C4 and CAM • Remember: MOST plants are C3 plants that performs Ps “normally” • Both are adaptations to arid conditions • CAM plants “idle” and save energy while C4 plants go through Ps faster

42. C4 Ps • Uses a different enzyme to initially capture CO2 • Separates CO2 capture from carbon fixation into sugar • Still uses C3 Ps to make sugar, but only does so in the bundle sheath cells

43. C4 Ps • Found in 19 plant families • Characteristic of hot regions with intense sunlight • Examples - sugarcane, Bermuda grass, crab grass

44. Can use photorespiration Shade to full sun High water use Cool temperatures Slow to moderate growth rates Cool season crops No Photorespiration Full sun only Moderate water use Warm temperatures Very fast growth rates Warm season crops C3 Ps vs C4 Ps

45. CAM plants • Found in plants from arid conditions (where water stress is a problem) • Avoid H2O stress by keeping stomates closed during the day • Generally have slow growth • Ex: pineapple, cacti, orchids

46. CAM Plants, cont. • Store CO2 as C4 acid • During the day, the acid is broken down and CO2 is made into sugar.

48. Ps:Rs Ratios • Reflect a plant’s balance in making food and using food 1. Ps > Rs, energy available for growth and reproduction 2. Ps = Rs, no growth, but don’t die either 3. Ps < Rs, death by starvation

49. Comments - Ps:Rs • Rs happens 24 hours a day • Ps only in light • Plants overwinter on stored food when Ps > Rs • If Ps < Rs, best solution is to increase the amount of light

50. Factors Affecting Ps 1. Light - quantity and quality 2. Temperature - too hot or too cold 3. CO2 - often limits C3 plants 4. Minerals - especially NPK and Mg