1. Bellwork: What happens during the light independent reactions of photosynthesis

2. The process of photosynthesis
Section 8.3

3. Photosynthesis Two parts of photosynthesis Light Dependent
Occurs in thylakoid membrane
Light independent
Occurs in Stroma

4. Light dependent reactions
Energy from the sun is used to produce oxygen and convert ADP to ATP and NADP+ to NADPH
Occurs in thylakoid membranes
Clusters of chlorophyll and proteins called photosystems
Surrounded by accessory pigments
Absorb sunlight
Generate high energy electrons

5. Photosystem II Pigments in photosystem II absorb light
Light energy absorbed by electrons in pigments
Passed to the electron transport chain
More light – more electrons
Water molecule - source of electrons in chlorophyll
Split into 2 H+ ion, 1 O atom and 2 electrons by enzymes on inner thylakoid surface
Oxygen released
H+ ions are released into thylakoid

6. Electron Transport Chain
Energy from electrons used to pump H+ ions from stroma into thylakoid space
Example of active transport
Electrons end up at a second photosystem – Photosystem I

7. Photosystem I
Electrons do not contain as much energy when they reach photosystem I
It has been used up by pumping H+ ions into the thylakoid
Light energy re-energizes the electrons
Passed onto second electron transport chain before NADP+ molecules pick up electrons and H+ to form NADPH

8. Hydrogen Ion movement and ATP Formation
Buildup of Hydrogen ions within thylakoid makes the Stroma negatively charged in comparison to stroma
This gradient provides the energy to make ATP
H+ ion can not cross the membrane directly
ATP synthase – protein that spans the membrane
Flow of H+ ions causes it to spin
Acts like a turbine
Binds phosphate and ADP to form ATP
Causes Chemiosmosis

9. Summary

10. Light independent reactions
NADPH and ATP formed during light dependent reactions contain lots of energy
Not effective long term store
In the Calvin Cycle this energy is used to create sugars

11. Carbon enters the cell
Carbon dioxide enters the Calvin cycle from the atmosphere
Enzyme in chlorophyll binds CO2 with 5 carbon compounds already in chloroplast
6CO2 molecules lead to carbon molecules
These 3 carbon molecules are converted to higher energy forms
Comes from ATP and NADPH

12. Sugar production
Halfway through the cycle 2 of the 3-C molecules are removed
Used as building blocks to produce sugars or other compounds
Can be used by the plant or passed on to organisms when plant is eaten
Remaining carbon molecules are re-arranged into 6 5-C molecules ready to go around the cycle again

13. Factors affecting photosynthesis
Temperature
Enzymes function best between 0 and 35 degrees Celsius
At very low temperatures photosynthesis can stop entirely
Light Intensity
More light = more photosynthesis until a point
There is a maximum rate
Water
Raw material for photosynthesis
No water, no photosynthesis
Explain waxy coatings on plants in arid environments

14. Photosynthesis under extreme conditions
Under bright hot conditions many plants will close small openings in their leaves that allows CO2 to enter
Stops water leaving, but also stops CO2 from entering
CO2 level drops, photosynthesis can stop
Specific types of plants have adapated C4
CAM plants
Water loss is minimized
Photosynthesis can still take place

15. C4 photosynthesis and CAM plants
C4 plants
Specialized chemical pathway
Low levels of COR can be captured and passed to the Calvin cycle
Requires extra energy to function
4 carbon atoms in first compound formed
Example – Corn, sugar cane
CAM plants
Carbon dioxide is incorporated into organic acids in cool darkness
Carbon is trapped within the leaves
Leaves are sealed during day time, but carbon has already been stockpiled
Example – pineapple, cactus