Photosynthesis Food from light and air

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

Where does photosynthesis take place? Thylakoid Stroma Granum

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?

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

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

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

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

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”

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

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

Photosynthesis rap :)