Photosynthesis Photosynthesis Photoautotrophs have lightabsorbing substances pigments that

Photosynthesis

Photosynthesis • Photoautotrophs have lightabsorbing substances (pigments) that absorb visible light.

Chlorophyll • Stored in chloroplasts • Absorb light in the violet/blue and orange/red regions • Reflect light in the green region

What’s a photon? • When pigments absorb photons (light energy) their atoms’ electrons (e-) get excited

I’m so excited & I just can’t hide it… • An excited e- moves further away from the nucleus • The e- quickly go back to their original location emitting energy. – eventually the energy hits the reaction center exciting the e- there

I’m so excited & I just can’t hide it… • These e- do not go back to their original position, instead they are passed down an electron transport chain via proteins in the thylakoid membrane. • Ultimately e- will be captured by an electron carrier, NADP+ reducing it to NADPH. • e- are replaced by H 2 O • This excitement of e- occurs in the photosystems found in the thylakoid membranes

Stomata CO 2 Chloroplast Mesophyll cell

Chloroplast Outer and inner membranes Thylakoid Stroma Granum Thylakoid space Intermembrane space

Photosynthesis • Photosynthesis can be summarized as the following equation: 6 CO 2 + 12 H 2 O + Light energy C 6 H 12 O 6 + 6 O 2 + 6 H 2 O • H 2 O is split into H (+ & -) and O, incorporating the e- of hydrogen into sugar molecules • Redox process in which H 2 O is oxidized and CO 2 is reduced

Products: 12 H 2 O 6 CO 2 Reactants: C 6 H 12 O 6 6 H 2 O 6 O 2

The 2 Stages of Photosynthesis • Light reactions (the photo part) and light independent reactions/Calvin cycle (the synthesis part) – The light reactions (in the thylakoids) split water, release O 2, produce ATP, and form NADPH – The light independent reactions/Calvin cycle (in the stroma) forms sugar from CO 2, using ATP and NADPH – carbon fixation

H 2 O CO 2 Light NADP+ ADP + Pi LIGHT REACTIONS LIGHT INDEPENDENT REACTIONS/ CALVIN CYCLE ATP NADPH Chloroplast O 2 [CH 2 O] (sugar)

H 2 O Light LIGHT REACTIONS Chloroplast

H 2 O Light LIGHT REACTIONS ATP NADPH Chloroplast O 2

Photosystem • 2 types of photosystems in the thylakoid membrane • Photosystem II functions first & is best at absorbing a wavelength of 680 nm (P 680) • Photosystem I functions second & is best at absorbing a wavelength of 700 nm (P 700) • Both work together to use light energy to make ATP & NADPH

Energy of electrons Primary acceptor 2 H+ + 1/2 O 2 Light H 2 O e– e– e– P 680 Photosystem II (PS II)

Energy of electrons Primary acceptor 2 H+ + 1/2 O 2 Light H 2 O Ele ctro n tr ans e– e– e– P 680 ATP Photosystem II (PS II) por t ch ain

Energy of electrons Primary acceptor 2 H+ + 1/2 O 2 Light H 2 O Ele ctro n tr Primary acceptor e– e– e– ans por t ch ain e– P 700 P 680 ATP Photosystem II (PS II) Photosystem I (PS I) Light

Primary acceptor H+ 2 + 1/2 O 2 Light H 2 O Ele ctro n tr Primary acceptor e– ans por t ch ai e– n e– e– E Tr lec an tro ch sp n ai ort n e– – e NADP+ reductase P 700 P 680 Light ATP Photosystem II (PS II) Photosystem I (PS I) NADP+ + 2 H+ NADPH + H+

LE 10 -14 e– ATP e– e– NADPH Mill makes ATP n e– e– Photon e– Photosystem II Photosystem I

H+ and Generating ATP • H+ from the splitting of H 2 O are inside of the thylakoid space • More H+ are PUMPED into the thylakoid space as emove down the electron transport chain (using active transport) • The diffusion of H+ from the thylakoid space back to the stroma (chemiosmosis) through ATP synthase makes ATP (photophosphorylation – using light to drive the synthesis of ATP) • ATP and NADPH are produced in the stroma, where the Calvin cycle takes place

O 2 STROMA (Low H+ conc. ) Photosystem II NADP+ reductase 2 H+ NADP+ + 2 H+ NADPH + H+ H 2 O THYLAKOID SPACE (High H+ conc. ) STROMA (Low H+ conc. 1/2 O 2 +2 H+ To Calvin cycle Thylakoid membrane ATP synthase ADP + Pi H+ ATP

Animation: ETC and ATP Synthesis • http: //glencoe. mcgrawhill. com/sites/9834092339/student_view 0/ chapter 39/photosynthetic_electron_transp ort_and_atp_synthesis. html

Photosynthesis • What are the final results of the light dependent reactions? -ATP, NADPH, O 2, + Protons(H ) • Why is photosynthesis not complete? -No new organic carbon molecules have been formed