Solar Power Photosynthesis

Photoautotrophs Photosynthetic organisms (plants, algae and some bacteria) make their own food from light and CO2 Mostly occurs in chloroplasts of the leaf cells (spongy mesophyll)

Chloroplasts Found in all green parts Most abundant in mesophyll cells Chlorophyll is a green pigment which give plants their color

Chloroplast Structure Thylakoids are membrane-bound discs in the chloroplast Outside fluid is called the stroma Contained in a double membrane

Chloroplast x5,755

Basic Chemical Equation 6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O Or CO2 + H2O → CH2O + O2 Carbon Dioxide + Water + Light  Carbohydrates + Oxygen

Water is Split and Reformed Page 171 of your book describes the discovery process (interesting read) The water in the products is not the same water! 6 C O2 + 12 H2 O ↓ C6H12O6 + 6 H2O + 6 O2

Oxidation/Reduction An oxidation reaction removes electrons from an atom H | HO-C-OH → O=C=O A reduction reaction adds electrons to an atom H | O=C=O → HO-C-OH (20 electrons) (16 electrons)

OIL RIG Oxidation is Loss (of electrons) Reduction is Gain (of electrons) (reducing the charge)

Reduction Process Splitting of water releases electrons and hydrogen ions These bond to the carbon, reducing it to a sugar Electrons increase the potential energy of the molecule ∆G is + (endergonic) Light provides the extra free energy

Steps of Photosynthesis Light Reactions Sunlight harvested to create ATP and NADPH Calvin Cycle ATP and NADPH turn CO2 into sugar

The Basics of Light Light = electromagnetic energy Shorter the wavelength, the higher the energy Chlorophyll absorbs the energy contained in light

Part 1: The Light Reactions

Phase 1: Excitation of Electrons

How Chlorophyll Absorbs Light The electron in chlorophyll gets excited and jumps to a higher orbital When it falls back into its normal orbital, it releases light energy This can then energize the molecule next to it Light light Step 1

Light and heat! High free energy = unstable Energy is spontaneously given off as heat and light

These electrons can be excited by energy from the sun

Photosystems Chlorophyll is arranged in photosystems Hundreds of chlorophyll molecules and proteins All molecules “pass their energy” to one particular chlorophyll Called the reaction center Step 1

The Primary Electron Acceptor When the reaction center chlorophyll molecule's electron is excited it passes to the primary electron acceptor Does not fall back down Step 1

Photsystem e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- To Primary Electron Acceptor Photsystem Energy! e- e- e- e- e- Energy! e- e- e- e- e- Energy! e- e- e- e- e- Energy! e- e- e- e- e- e- e- e- e- e-

Located in the thylakoid membrane Photosystem I and II Have slightly different reaction centers and absorb slightly different wavelengths of light Located in the thylakoid membrane Chlorophyll is the same! Protein arrangement around the chlorophyll is different

Phase 2: Electron Flow generates ATP and NADPH 2A Noncyclic Electron Flow 2B Cyclic Electron Flow

2A Non-cyclic electron flow The predominate route Electron from photosystem II transferred to photosystem I ATP is made during this process Electron ends up on NADP+ molecule, forming NADPH Water is split, replacing the electron of the Reaction center

Step 1 Photosystem II absorbs light Energy passed to reaction center Electron is excited Electron is passed to primary electron receptor Reaction center has an electron hole

Step 2 Enzyme splits water 2H2O → 4H+ + O2 + 4e- Electrons replace the reaction center electron Forms O2

Splitting of Water H H e e e e e e e e O O H H e e e e e e H H e e H

Step 3 Each electron is passed down an Electron Transport Chain to Photosystem I ATP made via chemiosmosis!

Step 4 Electrons “falling” down the chain allow proteins to pump H+ ions into thylakoid space Buildup of H+ in thylakoid space H+ ions diffuse through ATP synthase

Chemiosmosis Electrons falling down the chain is coupled with pumping H+ into the thylakoid space (innermost part of thylakoids) This causes the concentration of H+ in the thylakoid to be much higher than in the stroma H+ ions cannot simply pass through the membrane Instead they diffuse through ATP Synthase which uses the energy of the concentration gradient to produce ATP

Step 5 Electron ends up in the reaction center of Photosystem I Replaces an electron that is passed to the primary electron acceptor

Step 6 The primary electron acceptor of photosystem I passes electrons to NADP+ forming NADPH No ATP is made

Note this diagram uses a different set of numbers

H+ H+ H+ Light Light H+ NADPH e- H+ H2O O2 e-

Noncyclic Electron Flow Review http://trc.ucdavis.edu/biosci10v/bis10v/media/ch05/noncyclic_v2.html http://www.youtube.com/watch?v=eY1ReqiYwYs Sunlight energizes electrons, which drive the synthesis of ATP as they are passed from photosystem II to photosystem I They are again excited in photosystem I and transferred to NADP+ to form NADPH NADPH and ATP are used in the Calvin cycle to make sugar

Review of Light Reactions http://www.youtube.com/watch?v=Q_1mxZdF 2TY&feature=video_response

2B Cyclic Electron Flow Non-cyclic electron flow creates equal amounts of ATP and NADPH but the Calvin cycle requires more ATP than NADPH So electrons are sometimes rerouted back to the ETC from photosystem I to produce more ATP No NADPH is produced, nor is water split

No water split! e- No O2 made No NADPH made

Review of Light Reactions Light is harnessed by chlorophyll pigments in chloroplast's thylakoid membranes This energy is used to create NADPH and ATP via Non Cyclic Electron Flow Water is split and O2 is released as a byproduct Extra ATP is made via Cyclic Electron Flow The ATP and NADPH is used in the Calvin Cycle

DNA Make a list of everything needed in the light reactions of photosynthesis

Light Reaction Requirements Chloroplast/ thylakoid membrane Chlorophyll / photosystems H2O – provides electrons Light – provides energy ETC / NADP+ reductase NADP+ / ADP + Pi ATP Synthase H+

The Two Steps

Part II: The Calvin Cycle

Overview Takes place in stroma of chloroplast Uses CO2 and energy from NADPH and ATP to make sugar Actual product is glyceraldehyde 3- phosphate (G3P) G3P can then form glucose and other sugars 3CO2 + 9ATP + 6NADPH → 1 G3P + 9 ADP + 9Pi + 6NADP+

Review of Calvin Cycle http://www.science.smith.edu/departments/Bio logy/Bio231/calvin.html http://www.youtube.com/watch?v=OYSD1jOD 1dQ