Photosynthesis

1. Photosynthesis Chapter 7

2. Mader: Biology, 9th Ed. Photosynthetic Organisms Photosynthesis Process that captures solar energy Transforms solar energy into the chemical energy Chemical energy is stored in the form of a carbohydrate All organisms use organic molecules produced by photosynthesizers as a source of chemical energy

3. Mader: Biology, 9th Ed. Photosynthetic Organisms

4. Mader: Biology, 9th Ed. Photosynthesis Photosynthesis occurs in the green portions of plants, particularly leaves Leaf of flowering plant contains mesophyll tissue which contains cells specialized to carry on photosynthesis CO2 enters leaf through stomata Diffuses into chloroplasts in mesophyll cells

5. Mader: Biology, 9th Ed.

6. Mader: Biology, 9th Ed. Flowering Plants CO2 and water diffuse into chloroplasts Double membrane surrounds fluid (stroma) Inner membrane system within stroma form flattened sacs called thylakoids Thylakoids stacked to form grana Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy

7. Mader: Biology, 9th Ed. Photosynthetic Pigments Pigments � molecules that absorb light at different wavelengths Most pigments absorb only some wavelengths of light and reflect or transmit the other wavelengths Absorption Spectra � wavelength of light a pigment can absorb Organic molecules and processes within organisms are chemically adapted to visible light

8. Mader: Biology, 9th Ed. Photosynthetic Pigments

9. Mader: Biology, 9th Ed. Photosynthetic Reaction Net Reaction Solar energy + CO2 + H2O ? (CH2O) + O2

10. Mader: Biology, 9th Ed. Photosynthesis Overview

11. Mader: Biology, 9th Ed. Photosynthetic Reaction Light Reaction - Chlorophyll absorbs solar energy and energizes electrons Electrons move down electron transport chain Pumps H+ into thylakoids Used to make ATP out of ADP and NADPH out of NADP Calvin Cycle Reaction - CO2 is taken up and reduced to a carbohydrate Reduction requires ATP and NADPH

12. Mader: Biology, 9th Ed. Light Reactions Light reactions consist of two electron pathways: Noncyclic electron pathway Cyclic electron pathway Capture light energy with photosystems Pigment complex helps collect solar energy like an antenna Occur in the thylakoid membranes Both pathways produce ATP, but only the noncyclic pathway also produces NADPH

13. Mader: Biology, 9th Ed. Noncyclic Electron Pathway Electrons flow from water to NADPH Uses 2 photosystems, PS I and PS II Photosystem consists of pigment complex and electron acceptor molecules in the thylakoid membrane Pigment complex helps gather solar energy Reaction center � pair of chlorophyll a molecules where electrons are concentrated

14. Mader: Biology, 9th Ed. Noncyclic Electron Pathway PS II captures light energy Causes an electron to be ejected from the reaction center (chlorophyll a) Electron travels down electron transport chain to PS I Replaced with an electron from water Which causes H+ to concentrate in thylakoid chambers Resulting in ATP production

15. Mader: Biology, 9th Ed. Noncyclic Electron Pathway PS I captures light energy and ejects an electron Transferred permanently to a molecule of NADP+ Resulting in NADPH production

16. Mader: Biology, 9th Ed. Cyclic Electron Pathway Cyclic pathway involves PS I PS I pigment complex absorbs solar energy and passes it from one pigment to another until it is concentrated in a reaction center Pathway only results in ATP production

17. Mader: Biology, 9th Ed. Thylakoid Organization PS II Pigment complex and electron-acceptors Adjacent to an enzyme that oxidizes water Oxygen is released as a gas Electron Transport System Consists of cytochrome complexes Carries electrons between PS II and PS I Also pump H+ from the stroma into thylakoid space

18. Mader: Biology, 9th Ed. Thylakoid Organization PS I Pigment complex and electron acceptors Adjacent to enzyme that reduces NADP+ to NADPH ATP Synthase Complex Has a channel for H+ flow Which drives ATP synthase to join ADP and Pi

19. Mader: Biology, 9th Ed. ATP Production Thylakoid space acts as a reservoir for hydrogen ions (H+) Each time water is oxidized, two H+ remain in the thylakoid space Electrons yield energy Used to pump H+ across thylakoid membrane Move from stroma into the thylakoid space Flow of H+ back across thylakoid membrane Energizes ATP synthase Enzymatically produces ATP from ADP + Pi This method of producing ATP is called chemiosmosis

20. Mader: Biology, 9th Ed. Calvin Cycle Reactions Calvin cycle is a series of reactions that produce carbohydrates before returning to the starting point Utilizes atmospheric CO2 to produce carbohydrates Known as C3 photosynthesis Includes the following processes: Carbon dioxide fixation Carbon dioxide reduction RuBP Regeneration

21. Mader: Biology, 9th Ed.

22. Mader: Biology, 9th Ed. Calvin Cycle Reactions Carbon Dioxide Fixation CO2 is attached to RuBP resulting in a 6-carbon molecule which splits into two 3-carbon molecules (3PG) Rubisco (RuBP Carboxylase) is enzyme used

23. Mader: Biology, 9th Ed. Calvin Cycle Reactions Reduction of Carbon Dioxide

24. Mader: Biology, 9th Ed. Calvin Cycle Reactions Regeneration of RuBP

25. Mader: Biology, 9th Ed. Importance of Calvin Cycle PGAL or G3P (glyceraldehyde-3-phosphate) is the product of the Calvin cycle that can be converted to a variety of organic molecules

26. Mader: Biology, 9th Ed. C4 Photosynthesis In hot, dry climates, net photosynthetic rate of C4 plants is about 2-3 times that of C3 plants Stomata must close to avoid wilting CO2 decreases and O2 increases O2 starts combining with RuBP instead of CO2 Photorespiration, avoided in C4 plants In C4 leaf, bundle sheath cells and mesophyll cells contain chloroplasts Mesophyll cells are arranged concentrically around the bundle sheath cells

27. Mader: Biology, 9th Ed. C3 vs C4

28. Mader: Biology, 9th Ed. CO2 Fixation in C3 and C4 Plants

29. Mader: Biology, 9th Ed. CAM Photosynthesis Crassulacean-Acid Metabolism C4 plants partition carbon fixation in space, while CAM partitions by time During the night, CAM plants fix CO2, forming C4 molecules, which are stored in large vacuoles C4 molecules release CO2 to Calvin cycle when NADPH and ATP are available Water Conservation

30. Mader: Biology, 9th Ed. CAM Photosynthesis

31. Mader: Biology, 9th Ed.