Chloroplasts 1. plants (leaves) 2. algae

ADP + Pi + energy*  ATP* Energy captured from sunlight This energy used to drive ATP synthesis - light reactions ADP + Pi + energy*  ATP* *Light energy from the sun

Energy in ATP used to drive the synthesis of organized molecules - light independent reactions 6CO2 + 12 H2O + *energy  glucose* *Energy comes from the hydrolysis (breakdown) of ATP.

Photosynthesis 6CO2 + 12 H2O + light  C6H12O6 + 6H2O + 6O2

Structure 1. thylakoids - chlorophyll pigments in membrane (photosystem) 2. grana 3. stroma

Photosystem 1. pigments “capture” photons 2. excites an electron

3. energy of the electron is passed through the system 4. energy transferred to membrane-bound proteins on the thylakoid membrane

Electromagnetic spectrum

Plants absorb mainly red and blue. Pigments only absorb photons of particular wavelengths.

Pigments are molecules developed for absorbing photons Retinal found in the human retina absorbs light in the “visible spectrum” Some organismal pigments absorb outside the visible spectrum

Chlorophyll a and b forms absorb red and blue and reflect green

Chlorophyll is extremely efficient at capturing a narrow range of photons. It excites an electron whose energy is passed through the pigment.

Carotenoids - absorb light at different wavelengths than chlorophyll - absorb blue and green and reflect orange and yellow

Making Glucose: C6H12O6 Need H 1. there’s no H in CO2 2. reducing power - source of attachable H - from H2O

There is a different chlorophyll which absorbs another photon (Photosystem I). excited electron on H atom transferred to NADP

NADPH carries H to growing carbon chain of glucose. Energy from that electron used to “stick on” H

Calvin Cycle C3 photosynthesis