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

2. Which organisms are photosynthetic?
Photoautotrophs
Plants
Algae
Some bacteria

3. What is photosynthesis?

4. 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

5. 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

6. 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

7. A closer look at where it all takes place…

9. Photosynthesis Reactions
Light Reactions
Need light
Take place in the thylakoids
Dark Reactions/Calvin Cycle
Do not need light
Take place in the stroma

10. Light Reactions Trap Energy
GOAL: To make NADPH & ATP for the Calvin Cycle
BYPRODUCT: Oxygen gas

11. Stage 1: Energy is Captured from Sunlight
Chlorophyll absorbs light
Light energy excites chlorophyll electrons
Excited electrons enter the electron transport chain (stage 2B)

12. Stage 2A: Photolysis Photolysis: An enzyme splits water molecules
2H2O  O2 + 4H+ + 4e-
Oxygen is released by chloroplasts as a waste product!
Oxygen gas supplies nearly all the oxygen in the atmosphere
Electrons replace excited electrons in chlorophyll of the thylakoids

13. Stage 2B: Electron Transport Chain
Excited electrons from chlorophyll and H+ from split water travel through the thylakoids and move to NADP+
Nicotinamide dinucleotide phosphate (you do not need to know this name)
Coenzyme: act as carriers in many biological processes (“the shuttle bus”)
NADPH is formed
e- + H+ + NADP+  NADPH
NADPH travels to the Calvin Cycle (Stage 3)
ATP is formed and travels to the Calvin Cycle (stage 3) to provide energy

14. The Light Reactions of Photosynthesis
NADPH H+ e
The Products of the Light Reactions
ATP

15. Stage 3: Calvin Cycle
The Dark Reactions
GOAL: To make simple sugars

16. Carbon Fixation 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
Eventually become glucose and other sugars

17. Calvin Cycle Reaction Basics
Reactants
5-carbon molecule
CO2
H from NADPH
from Light Reaction’s splitting of H2O
Products
Simple sugars
Used to make other carbohydrates
ATP from Light Reactions powers the Calvin Cycle

18. The Overall Net Result of Photosynthesis
The overall result of photosynthesis is that for every 6 carbon dioxide molecules (plus 6 water) that a plant uses, 1 glucose molecule (plus 6 oxygen) is created.

19. ELECTRON CARRIERS

20. Discussion Questions Where do the light reactions take place?
What are the products of the light reactions?
Where do the chlorophyll replacement electrons come from?
Where do the dark reactions take place?
Where does the NADPH in the Calvin Cycle come from?
Where does the ATP in the Calvin Cycle come from?
What are the products of the Calvin Cycle?
What are chemoautotrophs?