Light and Pigments n Photosynthesis also requires light

Light and Pigments n Photosynthesis also requires light catching pigments n These photosynthetic pigments are designed to capture the energy from light that is in a specific range of wavelengths

Most common pigment is chlorophyll n Other pigments exist in most plants to capture energy in other wavelengths

Other pigments… n xanthophyll is yellow in color, but is hidden by the green in chlorophyll n beta carotene is orange n chlorophyll gets broken down when the temperature goes down, so other pigments can be seen in the autumn leaf colors

The Reactions of Photosynthesis Inside a chloroplast n Thylakoids – membrane sacs that contain clusters of pigment molecules called photosystems n Grana – stack of thylakoids n Stroma – area outside thylakoids

Light dependent reactions happen inside thylakoids; makes sense, that’s where the photosynthetic pigments are n Light independent reactions happen in the stroma; they are not in the way of the light-dependent reactions n

NADPH n n The process of capturing sunlight results in the formation of high energy electrons (electrons that have jumped to another level; they will give off lots of energy on their way back towards the nucleus of the atom) These high energy electrons require special carrier molecules

NADP+ is a carrier molecule n nicotinamide adenine dinucleotide phosphate accepts a pair of high energy electrons along with a hydrogen ion: H+ creates NADPH – carries the high energy electrons elsewhere in the cell, so there energy can be used to drive other reactions

Light-dependent reactions n require light + n turn ADP and NADP into high energy carriers ATP and NADPH

How does it work? n Light is absorbed by pigments in Photosystem II (discovered after Photosystem I) n Absorbed light increases energy in electrons which are passed on to the electron transport chain n New electrons (to replace the ones the chlorophyll passed on) come from water

High-energy electrons travel from Photosystem II to Photosystem I on the e- transport chain; drives the transport of H+ across the membrane of the thylakoid n Photo. I reenergizes high energy electrons & transfers them to + NADP which becomes NADPH + after picking up H n

n Process creates a charge difference across the thylakoid membranes; restoring the charge balance drives ATP creation n ATP synthase helps with facilitated diffusion of hydrogen ions, but uses their passage to create ATP

The Calvin Cycle n ATP & NADPH are not stable enough to store energy for a long time n The Calvin Cycle converts less stable, high energy molecules into high energy sugars n Calvin cycle is light-independent

How does it work? a. six carbon dioxides enter cycle b. combine with six 5 -carbon molecules which split creating twelve 3 carbon molecules c. 3 carbon molecules are then converted to high energy form using the energy from ATP and NADPH

How does it work? (cont. ) d. 2 of the twelve 3 -carbon compounds are converted to similar molecules and combined to form a 6 -carbon sugar e. The remaining ten 3 -carbon compounds are recombined into 5 carbon compounds and re-enter the cycle

n Plants use 6 -carbon sugars for energy for growth and repair, and to construct complex carbohydrates like cellulose