1. Ch.8-3
Photosynthesis
Cells

2. POINT > Describe the light-dependent reactions of photosynthesis (light reactions)
POINT > Describe the light-independent reactions of photosynthesis (Calvin cycle)
POINT > Relate fall colors to plant pigments

3. POINT > Describe the light-dependent reactions of photosynthesis
6CO H2O  C6H12O6 + 6O2

4. POINT > Describe the light-dependent reactions of photosynthesis
Photosynthesis includes two sets of reactions: light-dependent reactions and light-independent reactions

5. POINT > Describe the light-dependent reactions of photosynthesis
1. Light-Dependent Reactions Requires direct involvement of light & chlorophyll Occurs in the thylakoids

6. POINT > Describe the light-dependent reactions of photosynthesis
Light-Dependent Reactions produce: 1. ATP: cell’s energy molecule 2. NADPH: carries high energy electrons

7. POINT > Describe the light-dependent reactions of photosynthesis
Requires water (for electrons)
Produces oxygen (as a waste product)

8. WB CHECK: Where in the chloroplast do the light-dependent reactions occur? What is produced during the light-dependent reactions that is a waste product to the plant?

9. WB CHECK: What two things are produced during the light-dependent reactions that are important to the plant? What are two things required for the light-dependent reactions to happen?

10. POINT > Describe the light-dependent reactions

11. 1. Light is absorbed by chlorophyll in Photosystem II

12. 2. The absorbed energy creates high energy electrons and splits water molecules (O2 and H+ produced)

13. 3. The high energy e- are passed through a series of carriers in the thylakoid membrane This is the Electron Transport Chain (ETC)

14. 4. Energy released by the ETC is used to move more H+ into the thylakoid space

15. Place the following in order:
WB CHECK:
Place the following in order:
___ a water molecule is split
___ lots of H+ accumulate in the thylakoid space
___ light energy is absorbed by Photosystem II
___ high energy electrons move through the ETC

16. Place the following in order:
WB CHECK:
Place the following in order:
_2__ a water molecule is split
_4__ lots of H+ accumulate in the thylakoid space
_1__ light energy is absorbed by Photosystem II
_3__ high energy electrons move through the ETC

17. 5. Light absorbed by chlorophyll in Photosystem I is used to further energize the e- in the ETC

18. A H+ gradient is now established across the thylakoid membrane
A H+ gradient is now established across the thylakoid membrane. High H+ in thylakoid space, low H+ in stroma

19. 6. The H+ gradient is used by ATP Synthase in the thylakoid membrane to make ATP from ADP

20. 7. The high energy electrons are transferred to NADP+ to form NADPH

21. Place the following in order:
WB CHECK:
Place the following in order:
___ NADP+ accepts a high energy electron
___ light energy is absorbed by Photosystem I
___ ATP synthase uses H+ gradient to make ATP
___ light energy is absorbed by Photosystem II

22. Place the following in order:
WB CHECK:
Place the following in order:
_4__ NADP+ accepts a high energy electron
_2__ light energy is absorbed by Photosystem I
_3__ ATP synthase uses H+ gradient to make ATP
_1__ light energy is absorbed by Photosystem II

23. Recap: Light energy drives the ETC in the thylakoid membrane, producing ATP and NADPH ATP and NADPH will be used in the light-independent reactions to make sugars (in the stroma)

24. Recap: Light energy drives the ETC in the thylakoid membrane, producing ATP and NADPH Question: So, if the plant made lots of ATP in the light reactions, why make sugar? Answer: ATP and NADPH have lots of energy but are unstable (break down after a few minutes) The plant makes glucose (and other carbohydrates) because those are stable molecules for energy storage

25. POINT > Describe the light-independent reactions of photosynthesis (Calvin cycle)
Light-Independent Reactions: No direct involvement from light Occurs in the chloroplast stroma Uses ATP & NADPH to produce sugars Requires carbon dioxide

26. POINT > Describe the light-independent reactions of photosynthesis (Calvin cycle)

27. WB CHECK:
Where in the chloroplast does the Calvin cycle take place?
What are two products of the light reactions that are used in the Calvin cycle?
What else is required in the Calvin cycle?

28. In the Calvin cycle, CO2 is combined with a 5-carbon compound called ribulose bisphosphate

29. The enzyme that catalyzes the reaction of CO2 is called Rubisco (ribulose bisphosphate carboxylase)

30. There is more Rubisco on earth than any other protein

31. ATP and NADPH from the light reactions power all of the reactions in the Calvin cycle!

32. For every six CO2 that enter the Calvin cycle, two 3-carbon sugars are produced
The 3-C sugars are then made into glucose, cellulose, starch, etc, depending on the needs of the plant

33. WB CHECK:
What is produced in the Calvin cycle?
What is the enzyme that combines CO2 with ribulose bisphosphate?
What powers the Calvin cycle?

34. (Light-Independent Rxns)
H2O O2
Light-Dependent Rxns
ATP
NADP+
NADPH
ADP + Pi
CO2
Calvin Cycle
(Light-Independent Rxns)
Sugar

35. Light Reactions of Photosynthesis
sun
sun e e H+ O
to Calvin Cycle
Two places where light comes in.
Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy.
Need to look at that in more detail on next slide
split H2O
ATP

37. POINT > Relate fall colors to plant pigments
Chlorophyll Breaks Down First
Other pigments remain in leaves longer
Temp, Light, Water Supply affect color

38. Homework:
Read pages (Figs and 8-11)
Assess #1-3 page 241
Workbook pages