Photosynthesis Light Absorption Sun gives off visible light

Photosynthesis

Light Absorption • Sun gives off visible light (ROYGBIV) • Unabsorbed light reflects to our eyes – Most green light not absorbed by leaves • Chlorophyll absorbs sunlight – Absorb mostly reds and blues

The Chloroplast • Site of photosynthesis • Thylakoid membranes: light dependent reactions • Stroma (fluid interior): light independent reactions

Stomata: pore underneath leaves through which gases enter/exit

Photosynthesis Overview • Two Stages • 1) Light Dependent Reactions – Photosystems: groups of molecules that capture/transfer energy – Creates: O 2, ATP, NADPH • 2) Light Independent Reactions – Creates: Glucose

Light Dependent Reactions: Photosystem II Step 1: Chlorophyll absorbs sunlight – Chlorophyll e- become excited & transfer to thylakoid membrane › Thylakoid membrane becomes negatively charged – Starts an electron transport chain

Step 2 & 3: H 2 O broken into H+, e-, and O › e- replace those lost by chlorophyll › O waste › H+ pumped inside thylakoids and accumulate

Thylakoid membrane becomes negatively charged e e chlorophyll Electrons replace those which left chlorophyll e H e e e H O e H chlorophyll e H O Oxygen waste is released

Light Dependent Reactions: Photosystem I eee- • Chlorophyll absorbs sunlight – Chlorophyll ebecome excited & transfer to thylakoid membrane › Accumulate with those from photosystem II

H+ H+ • NADPH produced (H taxi) › e- causes H+ to bond with NADP H+ ATP • ATP produced › H+ ions diffuse and bond ADP with Pi

Light Dependent Summary • O 2, ATP, NADPH created • NO GLUCOSE CREATED!

Light Independent Reactions (Calvin Cycle) • Step 1: CO 2 bonds with Ru. BP (5 C) molecule to make a 6 C molecule

6 C Ru. BP molecule CO 2

• Step 2: 6 C molecule splits into two PGAL molecules (3 C) » ATP & NADPH provide the energy

6 C molecule ADP

• Some PGAL (3 C) bonds to make glucose (6 C) • Some PGAL recycled to start the cycle over

glucose!

Light Independent Summary • CO 2, ATP, & NADPH create glucose

Your essay question on the next test! Trace the flow of energy, including ATP, from the sun to your muscles, after eating a green leaf salad.