1. PHOTOSYNTHESIS

2. Converts sunlight energy into chemical energy
Photosynthesis
Converts sunlight energy into chemical energy
Photosynthesis is an anabolic pathway that converts sunlight energy into chemical energy.
Anabolic – building larger molecules from smaller ones.
Cellular Respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cell.
Catabolic – pathway in which organic molecules are broken down to release energy for use by the cell.

3. Chemical Equation 6CO2 + 6H2 O +light energy C6 H 12 O 6 + 6O2
Carbon dioxide and water are the reactants and glucose and oxygen are the products.
Chlorophyll is the pigment necessary to run the reaction.
There are different types of chlorophyll pigments which differ in their ability to absorb different wavelengths of light.

4. Requirements Light Energy (Sun)
Chlorophyll a,b and accessory pigments (these absorb wavelengths of light)
Raw materials (CO2 and H2O )
Enzyme: NADP (taxi cab)

5. Cross Section of a Leaf Leaf has many layers of specialized cells.
Notice the location of the chloroplasts.

6. Stomata guard cells create the stomata
Stomata (leaf mouth) allows gas exchange (O2 and CO2)
guard cells create the stomata

7. Inside the Chloroplast
Saclike membranes called thylakoids contain chlorophyll and accessory pigments.
Stacks of Thylakoids
are called Grana.
Stroma is the fluid
filled space.

8. are stacks of thylakoids
Chloroplast Again
Chloroplast
Below
Notice the grana
are stacks of thylakoids
Granum = one stack of thylakoids
Grana = plural form of granum

9. The Two Phases of Photosynthesis
Phase I - Light Dependent Reaction (occurs in thylakoids)
Light energy is absorbed and converted to chemical energy in the form of ATP and NADPH.
Phase II - Dark Reaction (Calvin Cycle) (occurs in stroma)
NADPH and ATP that were formed during light dependent reactions are used to make glucose.

10. Light Reactions Overview:
1. Light energy is absorbed in the THYLAKOID.
2. Water is split or pulled apart: 2H and ½ O2
3. CO2 is NOT involved yet.
4. ATP is formed.
5. Reactants: chlorophyll, light energy, water, and NADP.

11. 3. An electron is released into the electron transport system.
Light Reactions
Steps:
Light energy is absorbed by chlorophyll.
Electrons in chlorophyll become “excited” (high energy) and split H2O apart.
H2O: 2H + ½ O2
* 6 molecules of water total are split apart:
12 H+ , 6, ½ O2 (released into air as a byproduct).
3. An electron is released into the electron transport system.

12. Light Reactions
4. NADP picks up the H + and electrons and transports them across the thylakoid membrane into the stroma.
NADP + H +  NADPH
* 6 H2O are split: 12 NADPH are formed by the Light Reaction.

13. 5. Hydrogen protons (H+) move across the thylakoid into the stroma to create ATPs from ADPs.
Light energy is absorbed by PSII and is used to split a molecule of water. When water splits, 02 is released from the cell.
H+ ions (protons) stay in the thylakoid space and an electron enters the electron transport chain.
As electrons move through the membrane, protons are pumped into the thylakoid space.
At PSI, electrons are reenergized by light and NADPH is formed. Ferrodoxin is the final electron acceptor.
CHEMIOSMOSIS: H+ accumulate in the thylakoid space, creating a concentration gradient.
Protons get pumped out of thylakoid space into stroma. When this occurs, ADP is converted to ATP.

14. Products of Light Reactions
6, ½ O2 are released into the air via stomata.
NADPH and ATP go to the stroma for Phase II (The Calvin Cycle).

15. Calvin Cycle or Dark Reaction
Reactants:
ATP and NADPH from Light Reactions
6 CO2
6 RuBP (ribulose bisphosphates)
Products: Glucose (C6H12O6) and 6 RuBP
Takes place in the stroma.

16. Steps of the Calvin Cycle (Dark Reaction)
CO2 Fixation:
CO2 combines with RuBP 6CO2 + 6RuBP 12 PGA
PGA is a 3-Carbon molecule and is
UNSTABLE!
Total: 6 CO RuBP  12 PGA

17. Calvin Cycle 12 PGA + 12 ATP + 12 NADPH 12 G3P + 12 ADP + 12 NADP
* What happens to NADP? ADP?
* PGA and PGAL are 3 Carbon molecules.
Answer: NADP and ADP go to the light reactions where they are used outside the thylakoid membrane. NADP picks up H+ (protons),ADP gets phosphorylated to become ATP.

18. Calvin Cycle Con’t. Formation of glucose: 2G3P 2Glucose
C3H6O3 + C3H6O3  C6H12O6
* Recall: G3P is a 3- Carbon molecule.

19. Calvin Cycle

20. Importance of Photosynthesis
Forms glucose which is necessary for cellular respiration.
Forms the source of oxygen we breathe.

21. Factors that Affect Photosynthesis
1. Amount of water
2. Temperatures
3. Light Intensity
4. Amount of CO2

22. Summary of Photosynthesis