1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Light Dependent Reactions Photosystem –clusters of hundreds of pigments and proteins –found in the thylakoid membrane –photosystem I and photosystem II

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem II  Step 1 –Energy absorbed from sunlight by chlorophyll –Energy is transferred to electrons (e - ) –Energized electrons are said to be “excited” –Excited electrons have enough energy to leave the chlorophyll a molecules –e - enter Electron Transport Chain proteins in the thylakoid membrane

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem II  Step 2 –Enzymes break down Water molecules into Oxygen and Hydrogen ions –Oxygen released as waste! –Electrons are released and replace those that left the chlorophyll in Step 1

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem II  Step 3 –Electrons move from protein to protein in the ETC –Energy pumps H+ ions inside the thylakoid –Electrons move to photosystem I

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem I  Step 4 –Light energy is absorbed in the chlorophyll by photosystem I at the same time it is absorbed by photosystem II –Electrons are energized and leave

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem I  Step 5 –Electrons combine with NADP + in the stroma to become NADPH –(similar to ADP becoming ATP)

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem I  Step 6 –Hydrogen ions go through a protein channel in the thylakoid membrane by diffusion

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosystem I  Step 7 –ATP synthase makes ATP by adding phosphate groups to ADP

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calvin Cycle or Light Independent No sunlight is required! Uses energy created during the Light dependent reactions! Occurs in the stroma

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calvin Cycle or Light Independent Step 1 CO 2 is added to 5 carbon molecules, in a process called carbon fixation 6 carbon molecules are made

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calvin Cycle or Light Independent Step 2 Enzymes use ATP and NADPH (from Light Dependent Reactions) to split 6 carbon molecules 3 carbon molecules are made

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calvin Cycle or Light Independent Step 3 3 carbon molecules leave and are bonded together to build glucose (a 6 carbon sugar molecule)

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calvin Cycle Step 4 ATP energy is used to recycle 3 carbon molecules back into 5 carbon molecules 5 carbon molecules stay and are used back at Step 1

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Calvin Cycle

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Factors That Affect Photosynthesis Light Intensity Carbon Dioxide Levels Temperature

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Environmental Influences on Photosynthesis