1. Chapter 5 Photosynthesis
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2. All life ultimately depends on photosynthesis.

3. Learning Outcomes
Explain how plants convert light into chemical energy
Draw and describe the net reaction in photosynthesis
Explain how photosynthesis has influenced the evolution of life
Explain how light interacts with pigments
Describe the structures in a leaf that are involved in photosynthesis

4. Learning Outcomes
Compare and contrast the light and carbon reactions of photosynthesis
Describe how light energy is converted to ATP and NADPH in the light reaction.
Identify the products and reactants in the carbon reaction
Explain how the products and reactants of the light and carbon reactions are linked
Compare and contrast C3, C4, and CAM plants

5. 5.1 Life Depends on Photosynthesis
Solar energy harnessed
Converted into chemical energy
All life ultimately depends on photosynthesis

6. 5.1 Life Depends on Photosynthesis
A. Photosynthesis Builds Carbohydrates Out of Carbon Dioxide and Water
Pigment molecules capture the sun’s energy
Energy to build glucose (C6H12O6) from carbon dioxide (CO2)
Uses water and releases oxygen gas (O2)
Light energy
6CO2 + 6H2O → C6H12O6 + 6O2

7. 5.1 Life Depends on Photosynthesis
Oxidation- reduction (redox) process
Electrons moved from H2O to CO2
Energy from sunlight
Uses for glucose
Half for plant’s own fuel
Manufacture other compounds
Cellulose for cell walls
Store as starch or sucrose

8. 5.1 Life Depends on Photosynthesis
Feeds plants
Provides energy and raw materials for other organisms
Waste product oxygen essential to life

9. Figure 5.1 Cycle of Life.

10. 5.1 Life Depends on Photosynthesis
B. The Evolution of Photosynthesis Changed Planet Earth
Most organisms rely directly or indirectly on photosynthesis
First organisms all heterotrophs
Autotrophs evolved later
Photosynthesis release oxygen gas
Aerobic organisms outcompeted anaerobic organisms

11. Figure 5.2 Oxygen Gas Changed the World.

12. Why is photosynthesis essential to life on Earth?
5.1 Mastering Concepts
Why is photosynthesis essential to life on Earth?

13. 5.2 Sunlight Is the Energy Source for Photosynthesis
A. What is Light?
Visible light part of electromagnetic spectrum
Photons
Shorter wavelength = more energy
Sunlight
Ultraviolet radiation, visible light, infrared radiation

14. Figure 5.3 The Electromagnetic Spectrum.

15. Clicker question Which below has the MOST energy? Visible violet light
Visible red light
Ultraviolet radiation
Infrared radiation

16. 5.2 Sunlight Is the Energy Source for Photosynthesis
B. Photosynthetic Pigments Capture Light Energy
Pigments capture light energy
Chlorophyll a
Accessory pigments
Absorb only some wavelengths
Transmit or reflect others

17. Figure 5.4 Everything but Green.
If you could expose plants to just one wavelength of light at a time,
would a wavelength of 300 nm, 450 nm, or 600 nm produce the highest
photosynthetic rate?

18. 5.2 Sunlight Is the Energy Source for Photosynthesis
C. Chloroplasts Are the Sites of Photosynthesis
Leaves are the main organ of photosynthesis
CO2 and O2 enter/exit through stomata
Leaf mesophyll contains chloroplasts

19. Clicker question Oxygen is a _____ of photosynthesis. waste product
substrate

20. Figure 5.5 Leaf and Chloroplast Anatomy.

21. 5.2 Sunlight Is the Energy Source for Photosynthesis
Chloroplast structure
2 membranes enclose stroma
Grana composed of stack of thylakoids
Thylakoid membrane studded with photosynthetic pigments
Thylakoid membrane encloses thylakoid space

22. Figure 5.5 Leaf and Chloroplast Anatomy.

23. 5.2 Sunlight Is the Energy Source for Photosynthesis
Chloroplast structure
Photosystem
Chlorophyll a aggregated with other pigment molecules
Proteins anchor complex in membrane
Reaction center
Antenna pigments – funnel energy to reaction center

24. Figure 5.6 Thylakoid membrane.

25. 5.2 Mastering Concepts
How does it benefit a photosynthetic organism to have more than one type of pigment?

26. 5.3 Photosynthesis Occurs in Two Stages
Light reactions
Convert solar energy to chemical energy
Produce ATP and NADPH
Carbon Reactions
Reduce CO2 to glucose
CO2 from atmosphere

27. Figure 5.7 Overview of Photosynthesis.

28. Clicker Question
The high energy molecule is?
ADP
AMP
ATP
APP

29. 5.4 The Light Reactions Begin Photosynthesis
2 types of photosystems
Photosystem I
Reaction center P700 – 700nm
Photosystem II
Reaction center P680 – 680nm
Connected by electron transport chain

30. 5.4 The Light Reactions Begin Photosynthesis
A. Photosystem II Produces ATP
Light energy transferred to reaction center
Boosts 2 electrons from chlorophyll a
Passed down electron transport system
Chlorophyll a replaces electrons
Split water
Oxygen waste product

31. 5.4 The Light Reactions Begin Photosynthesis
A. Photosystem II Produces ATP
Electron transport chain
Energy drives proton active transport
From stroma into thylakoid space
ATP synthase uses potential energy
ATP produced
Chemiosmotic phosphorylation

32. 5.4 The Light Reactions Begin Photosynthesis
B. Photosystem I Produces NADPH
Energy passed to reaction center
2nd electron transport chain
Electrons replaced from 1st electron transport chain
Electrons reduce NADP+ to NADPH

33. Clicker Question Photosystem II replaces its electrons from water.
oxygen.
the electron transport system.
NADPH.

34. 5.5 The Carbon Reactions Produce Carbohydrates
Also called Calvin cycle
Occur in stroma
Uses NADPH and ATP to reduce CO2

35. 5.5 The Carbon Reactions Produce Carbohydrates
Carbon fixation
Ribulose bisphosphate (RuBP)
RUBP carboxylase/oxygenase (rubisco)
PGAL synthesis
PGAL combined to form glucose
RuBP regeneration
ATP and NADPH from light reactions

36. Clicker Question Which below does NOT come out of the light reactions?
Glucose
Water
NADPH
ATP

37. 5.6 C3 Plants Use Only the Calvin Cycle to Fix Carbon
C3 pathway
3-carbon PGA is first stable molecule
95% of plants are C3
Photorespiration reduces efficiency
Rubisco uses O2 instead of CO2
Open stomata minimizes problem
Water loss problem

38. 5.7 The C4 and CAM Pathways Save Carbon and Water
C4 pathway
Physically separate light reactions and carbon reactions
Light reactions in mesophyll cells
Calvin cycle in bundle-sheath cells
Unique arrangement of cells in leaves

39. 5.7 The C4 and CAM Pathways Save Carbon and Water
Crassulacean acid metabolism
Open their stomata to fix CO2 only at night
Fix it again in the Calvin cycle during the day
Both fixation reactions occur in the same cell

40. Describe how a C4 plant minimizes photorespiration.
5.7 Mastering Concepts
Describe how a C4 plant minimizes photorespiration.

41. 5.8 Investigating Life: Solar-Powered Sea Slugs
Sea slug Elysia chlorotica
Acquire the chloroplasts by eating algae
Cells lining the slug’s gut absorb the chloroplasts
2 hypotheses
Chloroplasts autonomous – no
Slug’s cells support chloroplasts
psbO gene

42. 5.8 Mastering Concepts
The researchers also looked for the psbO gene in pufferfish (a vertebrate animal) and slime molds (a nonphotosynthetic protist). The gene was absent in both species. How was this finding important to the interpretation of the results of this study?