Bio: Announcements Take out coloring WS to be checked from last class if you did not get it stamped Work on chloroplast do now Note: I will be out of the country Wed-Fri. You will be working on your photosynthesis project those days. Unit 4A Test WED 12/16, THURS 12/17

6

Photosynthesis Reactants Products

5) Why do plants appear green? Chloroplasts absorb and use red & blue light and reflect green back out This is why plants appear green Everything can be explained at a molecular level!!

Light Dependent Reaction Occurs in the thylakoid part of the chloroplast Within the thylakoid membrane, the green pigment chlorophyll and other molecules are arranged in clusters called photosystems that absorb solar energy Two photosystems we care about: Photosystem I (PSI) or P700 (absorbs light at wavelength of 700 nm) Photosystem II (PSII) or P680 (absorbs light at wavelength of 680 nm)

The Light Reaction Photosystem II Absorbs sunlight energy, which excites electrons Electrons are passed through an electron transport system to photosystem I Electrons lost from PSII are replaced by the splitting of water (2 H2O  2 H+ + O2 + 2 e-), which produces O2. Hydrogen ions (from splitting of water) flowing out of the thylakoid via a protein channel provide the free energy needed to convert ADP to ATP

The Light Reaction Photosystem I Electrons passed through electron transport system from PSII get here Absorbs sunlight energy, which re-excites these electrons Electrons are passed through a carrier to NADP, forming NADPH. Electrons lost from PSI are replaced by the electrons that are transported from photosystem II

Why not just use the light reaction? Energy is NOT Stored in ATP and NADPH because they are unstable The products of the light cycle, ATP and NADPH, are then used in the Calvin Cycle which allow plants to store the energy as a carbohydrate (glucose)

Why is the Calvin Cycle sometimes called the dark reaction? Calvin cycle is known as the dark or light independent reaction it can’t use the light directly because there is no chlorophyll present in the stroma Occurs in the stroma (liquid part of chloroplast)

Calvin Cycle Rubisco is the enzyme that attaches carbon dioxide to a compound present in the stroma called RuBP. This causes the formation of a molecule known as PGA Energy from ATP and NADPH is used to convert PGA to an intermediate sugar called PGAL Some of the PGAL is used to make Glucose and other useful molecules for the plant Some PGAL is used to regenerate RuBP to keep the cycle going

Photosynthesis Project Due Date: FRI 12/18