2. Overview All organisms need a constant supply of energy to survive.
For most life on earth, the ultimate source of energy is the sun.
Converting that energy source into something usable is accomplished by photosynthesis.

3. Overview
Photosynthesis: the overall process by which sunlight (solar/light energy) chemically converts water and carbon dioxide into chemical energy stored in glucose (a sugar/carbohydrate.)
Water is absorbed in roots
CO2 is absorbed through stomata
It can be represented by the following chemical equation:
6CO2 + 6H2O C6H12O6 + 6O2
Image Credits: © Zappys Technology Solutions’s
Solar energy

4. Overview 6CO2 + 6H2O C6H12O6 + 6O2 Reactants = ingredients
Solar energy
6CO2 + 6H2O C6H12O6 + 6O2
Reactants = ingredients
CO2 (carbon dioxide) and H2O (water)
Products = results
C6H12O6 (glucose) and O2 (oxygen)
Note: Solar energy from the sun is necessary for photosynthesis to happen (as well as some enzymes) but isn’t considered a reactant or product.

5. Structure of Chloroplast
Photosynthesis takes place in the chloroplast which has 2 main parts:
Grana: pancake-like stacks of thylakoid membrane
Stroma: fluid-like substance that fills the space between the grana
grana
thylakoid membrane

6. Why are plants green? The presence of the pigment chlorophyll
Chlorophyll a, chlorophyll b, and other pigments called carotenoids absorb every color of light in sunlight except green
Therefore, green is leftover and is reflected and is what we see

7. Two Stages of Photosynthesis
Photosynthesis can be divided into two sets of reactions:
1. Light-dependent (“photo”) Reaction
Requires solar energy.
AKA the Electron Transport Chain (or light rxn)
2. Light-independent (“synthesis”) Reaction
Does not require any solar energy.
AKA the Calvin Cycle (or dark rxn)

8. Light-Dependent Reaction
Purpose = Capture energy from the sun and store energy in “energy-carrying molecules” (ATP and NADPH)
Location = occurs in the grana (specifically the thylakoid membrane) where the chlorophyll is stored.

9. Light-Dependent Reaction
Summary:
Water molecules are split into hydrogen and oxygen.
Oxygen is released as a waste product.
ATP and NADPH are charged up by the sun.

10. Light-Dependent Reaction
Details:
Energy from sun is passed down the Electron Transport Chain and is stored in the bonds of ATP and NADPH
Light energy excites e- (electrons)
e- move down ETC
At end they combine with “final electron acceptors/carriers” of NADP+ and ADP, making NADPH and ATP
Chemiosmotic process b/c H+ ions move down the gradient to make ATP
ATP, NADPH, and H+ leave the grana and go into the stroma for the next stage!

11. How is light absorbed? Photosystems absorb light
They are clusters of chlorophyll and proteins that trap energy from the sun
Chlorophyll is a pigment that can absorb sunlight
Energy is transferred to electrons  makes “excited” electrons

12. What are electron carriers?
Molecules that carry electrons in order to pass on their energy
Ex. Compound (NADP+) that can accept a pair of high-energy electrons and transfer them to another molecule
NADP+ grabs/carries 2 electrons and a H+  becomes NADPH
ATP and NADPH carry energy from the light-dependent rxn to the light-independent rxn.

13. Light-Dependent Reaction
Image Credits: © BlueRidgeKitties
I like to show them this picture so they can appreciate the complexity of the process and understand that I am not making them memorize every detail but want them to have a solid foundation in the process in case they are to ever take AP bio.

14. Light-Independent Reaction
Purpose = use the energy from the “energy-carrying molecules” from the light-dependent reaction to make sugar (glucose)
Location = occurs in the stroma

15. Light-Independent Reaction
Summary = Calvin Cycle
Series of enzyme-assisted chemical reactions powered by ATP and NADPH that produce three-carbon (3-C) sugars from CO2 and the H+ from water.
The cycle happens twice and then these 3-C sugars combine to make glucose = C6H12O6

16. Light-Independent Reaction
Details
Grab
CO2 diffuses into stroma
Enzyme attaches CO2 to 5-C RuBP
Produce unstable 6-C molecules
Split
Energy from ATP and NADPH and an enzyme break the 6-C molecule into 2 3-C molecules (PGA)
RuBP = 5-carbon ribulose bisphosphate
PGA = phosphoglycerate
G3P = glyceraldehyde 3-phosphate

17. Light-Independent Reaction
Details
Leave
Each 3-C molecule (PGA) is converted to a different 3-C molecule (G3P)
One G3P leaves the cycle to become glucose
The other G3P moves on to next step
Switch
Remaining G3P converts back to 5-C RuBP by using a phosphate from ATP and the cycle starts again!
RuBP = 5-carbon ribulose bisphosphate
PGA = phosphoglycerate
G3P = glyceraldehyde 3-phosphate

18. Light-Independent Reaction
Image Credits: © Allen Gathman
I like to show them this picture so they can appreciate the complexity of the process and understand that I am not making them memorize every detail but want them to have a solid foundation in the process in case they are to ever take AP bio.

19. Rate of Photosynthesis
Speed is affected by 3 factors:
Light intensity
Excites more e- causing light reactions to happen faster
Amount of CO2
More ingredients to work with and process through cycle
Temperature
Increased temperature accelerates chemical reactions to a degree

20. Why do root cells in a plant not need chloroplasts?
Chloroplasts catch sunlight! Since roots are underground, they are not exposed to the sun!
So they can’t do photosynthesis.

21. Alternate Pathways Stomata = pores on underside of leaf. Where…
Plants lose water
CO2 enters
O2 exits
If it is too hot or dry out, the plant will close its stomata so that it doesn’t lose too much water and become dehydrated
However this eliminates the gas exchange!!
SO  the levels of CO2 drop and the levels of O2 increase
This results in…. PHOTORESPIRATION
Photorespiration adds oxygen to the Calvin Cycle instead of carbon dioxide
- This makes NO sugar or ATP 
- This wastes all of the plants resources!
Two types of alternative pathways in plants to avoid this:
1. CAM
2. C4

22. Alternate Pathways CAM Done by cacti and pineapples
Open stomata at night and close during day
Opposite of normal plants
Causes them to grow slowly

23. Alternate Pathways C4 Done by corn and sugarcane
Partially close stomata during hottest part of day
Allows them to only need ½ as much water as normal plants!