Photosynthesis

2. Photosynthesis

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: Chlorophyll Light

5. Question • Does the Oxygen in sugar come from the CO2 or from the H2O ? • Model: CO2 + 2 H2O ----> CH2O + O2

6. Proof • Used 18O as a tracer. CO2 + 2 H2O ----> CH2O + O2 CO2 + 2 H2O ----> CH2O + O2 Both experiments confirm that water is split. • O2 is a waste product of Ps that altered life on earth.

7. Ps: a redox process • Hydrogens are added to Carbons. • Water is a source for the Hydrogens. • Complex covalent bonds are made.

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

12. Light • A form of electromagnetic radiation. • Visible light has the right energy for use in Ps.

13. Too Hot Too Cold JustRight

15. 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.

18. 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.

19. 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.

20. Photosynthesis Pigments 1. Chlorophylls 2. Accessory Pigments

21. Chlorophylls • Has CHON and Mg. • Several types possible. • Molecule has a lipophilic tail that allows it to dissolve into membranes. • Contains Mg in a reaction center.

24. Accessory Pigments • Absorb light energy and transfer it to chlorophyll. • Ex: Carotene (orange). Xanthophyll (yellow)

25. 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.

26. Chloroplast Structure • Double outer membrane. • Inner membrane folded and stacked into grana. • Stroma - liquid that surrounds the thylakoid membranes.

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

30. The no. and variety of pigment molecules enable PS to harvest light over larger surface and larger portion of the spectrum.

31. After glow is called fluorescence

32. Cyclic Photophosphorylation • Uses PSI only. • Produces ATP. • Requires light.

34. Noncyclic Photophsphorylation • Uses PSI and PSII. • Splits water, releasing H+, a pair of e-, and O2. • Produces ATP and NADPH. (e- carrier similar to NADH)

35. Light Reaction

40. Light Reaction • Same thing as Noncyclic Photophsphorylation. • Location - grana of the chloroplast. • Function - to split water and produce ATP and NADPH.

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

42. 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.

43. Chemiosmosis • H+ are pumped into the thylakoid space. • ATP and NADPH are made when the H+ diffuse into the stroma.

46. Comment • There can be a 3 pH unit difference between the thylakoid space and the stroma.

47. Light independent Reactions • How plants actually makes food (carbohydrates). • Don't require light directly to run. • Also known as the Calvin cycle, Dark reaction or C3 Ps.

48. Dark Reaction • Function - to use ATP and NADPH to build food from CO2 • Location - stroma of the chloroplast.

49. Rubisco • Ribulose BisPhosphate Carboxylase. • Enzyme that adds CO2 to an acceptor molecule. • Most important enzyme on earth.