Chloroplasts 1. plants (leaves) 2. algae

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

Energy in ATP used to drive the synthesis of organized molecules 6CO H 2 O + *energy  glucose* *Energy comes from the hydrolysis (breakdown) of ATP. - light independent reactions

Photosynthesis 6CO H 2 O + light  C 6 H 12 O 6 + 6H 2 O + 6O 2

Chloroplast 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

Photons: 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: C 6 H 12 O 6 Need H 1. there’s no H in CO 2 2. reducing power - source of attachable H - from H 2 O

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 C 3 photosynthesis