1. Chapter 8: Photosynthesis

2. 8-1
ATP
Adenosine triphosphate (ATP) is the directly usable form of energy for cellular processes

3. 8-1
ATP
Energy in ATP is released when the bond between the second and third phosphate group is broken

4. 8-1
ATP
ADP can be “recharged” to ATP with the addition of energy and a phosphate group
Energy
Energy
Adenosine diphosphate (ADP) + Phosphate
Adenosine triphosphate (ATP)
Partially
charged
battery
Fully
charged
battery

5. Autotrophs vs. Heterotrophs
8-1
Autotrophs vs. Heterotrophs
Heterotrophs obtain food by consuming other organisms
Hetero = other or different
Trophic = nutrition
Autotrophs can produce their own food
Most often via photosynthesis
Auto = self

6. Photosynthesis Overview
8-2
Photosynthesis Overview
Method of using light energy to convert CO2 and water into sugar (glucose) and oxygen
This is how carbon and energy enters the food chain

7. Light
“White” light is actually a mixture of many different wavelengths (colors) of light
Visible light is only a small section of the electromagnetic spectrum (ROYGBIV)

8. 8-2

9. 8-2
Pigments
Plants gather the energy with light-absorbing molecules called pigments
Pigments absorb specific wavelengths of light
Chlorophyll is the primary photosynthetic pigment
2 types: chlorophyll a and b
Absorbs red and blue light but reflects green
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a

10. 8-2
Pigments
Absorption of Light by
Chlorophyll a and Chlorophyll b

11. Pigments Carotenoids are accessory pigments Absorb more blue light
8-2
Pigments
Carotenoids are accessory pigments
Absorb more blue light
Reflect yellow, orange, and red light

12. 8-2
Chloroplasts

13. Chloroplasts Photosynthetic organelle Thylakoids are saclike membranes
8-2
Chloroplasts
Photosynthetic organelle
Thylakoids are saclike membranes
Organized into stacks called grana
(singular: granum)
The stroma is the space outside the thylakoid membranes

14. 8-2

15. Light-dependent Reactions
Requires light to charge electrons
Energy from electrons used to produce ATP and NADPH
This chemical energy then powers the second part of photosynthesis, The Calvin Cycle

16. Electron Carrier Molecules
8-2
Electron Carrier Molecules
Light-charged, high-energy electrons are highly reactive and require a special “carrier” molecule
NADP+ is accepts 2 electrons and a hydrogen ion to become NADPH
NADPH can be thought of as a charged battery similar to ATP

17. Light-dependent Reactions
8-3
Light-dependent Reactions

18. Light-dependent Reactions
8-3
Light-dependent Reactions
Primary electron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for synthesis of
by chemiosmosis
Light + 2H2O  ATP + 2NADPH + O2

19. Light-dependent Reactions
8-3
Light-dependent Reactions
Take place within the thylakoid membrane
Hydrogen
Ion Movement
Photosystem II
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
ATP Formation

20. Light-dependent Reactions
8-3
Light-dependent Reactions
Photosystem: light capturing unit
contains chlorophyll
Electron transport chain: sequence of electron carrier molecules that shuttle electrons
Use their energy to pump H+ ions into the inner thylakoid space
Electrons must be replaced so that cycle may continue
these electrons come from splitting of water molecules
ATP and NADPH produced
used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

21. Calvin Cycle (light independent or “dark” reactions)
Powered by ATP and NADPH generated in light reactions
Occurs in the stroma

22. The Calvin Cycle (light independent or “dark” reactions)
CO2 is carbon source for glucose (sugar)
Carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (eventually glucose)

23. 8-3

24. 8-3 CO2 Enters the Cycle Energy Input 5-Carbon Molecules Regenerated
6-Carbon Sugar Produced

25. 8-3

26. 8-3

27. Using Chemical Energy
Plants and animals both use products of photosynthesis (glucose) for metabolic fuel
Remember:
Autotrophs: can make this energy themselves (e.g. plants)
Heterotrophs: must take in energy from outside sources/cannot make their own (e.g. animals)
Glucose is not directly usable
Must be converted into ATP first