1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosynthesis Chapter 6 Table of Contents Section 1 The Light Reactions Section 2 The Calvin Cycle

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Obtaining Energy Photosynthesis converts light energy from the sun into chemical energy in the form of organic compounds through a series of reactions known as biochemical pathways.

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Obtaining Energy, continued Autotrophs use energy from sunlight or from chemical bonds in inorganic substances to make organic compounds. Animals and other organisms that must get energy from food instead of directly from sunlight or inorganic substances are called heterotrophs.

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

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chloroplast Structure

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

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 6 Overview of Photosynthesis The oxygen (O 2 ) and some of the organic compounds produced by photosynthesis are used by cells in a process called cellular respiration.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Overview of Photosynthesis, continued Photosynthesis can be divided into two stages: Light Reactions and Calvin Cycle –In the light reactions, light energy is converted to chemical energy, which is temporarily stored in ATP and the energy carrier molecule NADPH. –In the Calvin Cycle, organic compounds are formed using CO 2 and the chemical energy stored in ATP and NADPH.

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Overview of Photosynthesis, continued Equation of Photosynthesis: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 light energy

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Capturing Light Energy The light reactions begin with the absorption of light in chloroplasts, organelles found in the cells of plants, some bacteria, and algae.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Capturing Light Energy, continued Light and Pigments –White light from the sun is composed of an array of colors called the visible spectrum. –Pigments absorb certain colors of light and reflect or transmit the other colors.

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Light Reactions Chapter 6 Capturing Light Energy, continued Chloroplast Pigments –Located in the membrane of the thylakoids of chloroplasts are several pigments, including chlorophylls (such as chlorophyll a and chlorophyll b) and carotenoids.

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

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Photosynthesis Overview Chapter 6

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

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

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

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 6 Calvin cycle The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis called the Calvin Cycle. In the Calvin cycle, CO 2 is incorporated into organic compounds, a process called carbon fixation. Section 2 The Calvin Cycle

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 6 Carbon Fixation, continued The Calvin cycle, which occurs in the stroma of the chloroplast, is a series of enzyme-assisted chemical reactions that produces a three-carbon sugar. Most of the three-carbon sugars (G3P) generated in the Calvin cycle are converted to a five-carbon sugar (RuBP) to keep the Calvin cycle operating. But some of the three-carbon sugars leave the Calvin cycle and are used to make organic compounds, in which energy is stored for later use. Section 2 The Calvin Cycle

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

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 6 Alternative Pathways The C 4 Pathway –Some plants that evolved in hot, dry climates fix carbon through the C 4 pathway. These plants have their stomata partially closed during the hottest part of the day. –Certain cells in these plants have an enzyme that can fix CO 2 into four-carbon compounds even when the CO 2 level is low and the O 2 level is high. These compounds are then transported to other cells, where the Calvin cycle ensues. Section 2 The Calvin Cycle

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 6 Alternative Pathways, continued The CAM Pathway –Some other plants that evolved in hot, dry climates fix carbon through the CAM pathway. These plants carry out carbon fixation at night and the Calvin cycle during the day to minimize water loss. Section 2 The Calvin Cycle

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