1. Photosynthesis
Textbook pages 97 – 103

2. Photosynthesis
process used by plants using light energy to create sugar (glucose, C6H12O6) from carbon dioxide (CO2) and water (H2O)
oxygen gas (O2) is produced as a waste product and the light energy used is stored as chemical energy

3. Investigating Photosynthesis
Jan Van Helmont (1643)
Carefully massed soil, and tree seedling and watered over 5 years.
Determined most of the mass of the tree came from water.

4. Investigating Photosynthesis
Joseph Priestley (1771)
Lit a candle and placed a bell jar over it, watching the flame go out.
Reasoned that there was something in the air necessary to keep the flame going.
When a plant was placed under the bell jar, discovered that the candle could be relit after several days.
Reasoned that the plant released something into the air necessary for the flame.

5. Investigating Photosynthesis
Jan Ingenhousz (1779)
Showed the effect observed by Priestley only occurred when plants were exposed to light.

6. Investigating Photosynthesis
Julius Robert Mayer (1845)
Proposed that plants convert light energy into chemical energy

7. Photosynthesis Equation
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2

9. Stages of Photosynthesis
Capture energy from sunlight
Convert light energy into chemical energy
Use stored chemical energy to produce organic compounds (food) from carbon dioxide

10. 1. Capture energy from sunlight

11. 1. Capture energy from sunlight
Pigments (chlorophyll) in the membranes of the thylakoids absorb light energy
Gets transferred to electrons
Electrons are replaced from water
H+ ions are left
Remaining O from into O2 gas as waste product

12. 2. Converting light energy to chemical energy

13. 2. Converting light energy to chemical energy
Light dependent reactions
Occurs in thylakoid membranes
Use high-energy electrons to produce two high-energy products
Convert ADP into ATP
Convert NADP+ into NADPH

14. 2. Converting light energy to chemical energy

15. 2. Converting light energy to chemical energy
Electron transport chains (ETC)
A series of molecules through which excited electrons are passed
Energy from the electrons is used to pump H+ ions across the thylakoid membrane
A second ETC provides energy to make NADPH, a high energy electron carrier

16. 2. Converting light energy to chemical energy

17. 2. Converting light energy to chemical energy
Production of ATP
A concentration gradient is present now for H+ ions
Passing of ions back out of the thylakoid provides energy to make ATP

18. 2. Converting light energy to chemical energy

19. 2. Converting light energy to chemical energy
Both ATP and NADPH are used in the next step
ATP carries necessary energy
NADPH carries high-energy electrons

20. 3. Use stored chemical energy to make food

21. 3. Use stored chemical energy to make food
Light independent reactions
Calvin Cycle is one example
Occur in stroma inside chloroplasts, but outside of thylakoids
Using energy from ATP and electrons from NADPH, CO2 is fixed into sugars

22. Investigating Photosynthesis
Melvin Calvin (1948)
received the Nobel prize in chemistry (1961) for discovering pathways that carbon follows to make glucose in photosynthesis

23. Factors that affect Photosynthesis
light intensity
CO2 concentration
water levels
temperature