1. Trapping Light Energy to Build Carbohydrates
Photosynthesis
Trapping Light Energy to Build Carbohydrates

2. Which organisms are photosynthetic?
Photoautotrophs
Means “light feeders”
Plants
Algae
Some bacteria

3. What is photosynthesis?
Process by which plants use light energy to build carbohydrates (food).
Chemical equation:
light + chlorophyll
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water yields carbohydrate + oxygen gas
in the presence of light & chlorophyll

4. Why are plants mostly green?
Chlorophyll
Green pigment
Located in chloroplasts
Are they always green?
No!
Think about the leaves in the fall – what happens to them?
Chlorophyll is the most dominant pigment so we see it most, but when it dies out the other pigments show through

5. Chloroplast Structure
Chloroplast Membranes
Two of them
Inner and outer
Both composed of a
lipid bilayer
Thylakoids
Disks of membranes
Contain chlorophyll
Grana
Stacks of thylakoids
Stroma
Fluid inside the chloroplast

6. Photosynthesis Reactions
Light Reactions (aka light dependent reactions)
Needs light
Takes place in the thylakoids
Calvin Cycle (aka light independent reactions)
Does not need light
Takes place in the stroma

7. Light Reactions Trap Light Energy
GOAL: To make NADPH & ATP for the Calvin Cycle
BY - PRODUCT: Oxygen gas

8. 1: Energy is Captured from Sunlight
Chlorophyll, located in the thylakoid membranes, absorbs light
Light energy excites chlorophyll electrons
These electrons are released when a water molecule is split
Releases Oxygen gas a by-product (waste product)
Excited electrons enter the electron transport chain (ETC)

9. Stage 2: Electron Transport Chain
Excited electrons from chlorophyll and H+ from split water travel through the thylakoid membranes and move to NADP+
Nicotinamide dinucleotide phosphate (you do not need to know this name)
Forming NADPH
An electron carrier that moves electrons between the reactions of photosynthesis
e- + H+ + NADP+  NADPH
Travels to the Calvin Cycle (Stage 3)
ATP is also formed and travels to the Calvin Cycle (stage 3) to provide energy for the final reactions

10. Light reaction recap Takes place in the thylakoid membrane
Chlorophyll absorbs light
Water is split
Gives off oxygen as by product
NADPH and ATP are produced and sent to the Calvin Cycle

11. The light independent Reactions – do not have to take place in light
Stage 3: Calvin Cycle
The light independent Reactions – do not have to take place in light
GOAL: To make simple sugars

12. This is the Calvin Cycle….but you don’t have to know all of this

13. Calvin Cycle consists of carbon fixation
CO2 from the air is converted into a form that is usable by living things
“fixed” into 6 carbon sugars as more carbon and hydrogens are added
That’s why it needs NADPH
Eventually becomes glucose
and other sugars
Requires ATP to create the
sugars

14. ELECTRON CARRIERS