1. Photosynthesis
Food from light and air

2. What organisms use photosynthesis?
Autotrophs (“self-nutrition”) produce their own food (sugars) from small molecules
Plants
Algae
Photosynthetic bacteria
Have chloroplasts
No chloroplasts

3. Where does photosynthesis take place?
Thylakoid
Stroma
Granum

4. Pigments in the chloroplast
Chlorophyll a
Absorbs violet and red light
Chlorophyll b
Absorbs blue and orange light
Carotenoids
Absorb blue light
What color is not absorbed? What color do we see?

5. How does it work? There are two stages:
The light-dependent (“light”) reactions
The light-independent reactions or Calvin Cycle

6. The light-dependent reactions
Light Reaction Animation
Reactions take place in the thylakoid membrane
Water is split into oxygen (waste product) and hydrogen ions
Sunlight excites chlorophyll and sends electrons through the electron transport chain (ETC)
The ETC produces NADPH (an electron acceptor) and pumps hydrogen ions into the lumen
The gradient of hydrogen ions powers ATP synthase, an enzyme that makes ATP
Called chemiosmosis

7. Light reactions summary
From environment
Power for Calvin cycle
Waste
Water (H2O)
ATP
Light energy O2 + + +
Occurs in the thylakoid membrane
NADP+ + H+
ADP + P
From Calvin cycle

8. The light-independent reactions (Calvin cycle)
Uses carbon dioxide from the air
Occurs in the stroma
ATP and NADPH give energy
Each “turn” produces PGAL (or G3P)
TWO PGAL are needed to make glucose
Summary Video

9. Return to light reactions to “recharge”
Calvin cycle summary
From environment
From light reactions
Product
ATP
CO2 + +
Glucose
NADP+ + H+
ADP + P
Occurs in the stroma
Return to light reactions to “recharge”

10. Overall photosynthesis reaction
Water (H2O)
Light energy
CO2 O2 + +
Glucose +

11. Where do the reactants come from?
Exposure to sunlight
Water taken up by roots
Carbon dioxide enters through leaf stomata
Small holes on bottom of leaf
Can open and close according to weather
Oxygen and water also leave through stomata

12. Photosynthesis rap :)