Chapter 7PhotosynthesisA. Light Visible light makes up only a small portion of the electromagnetic spectrum. Characteristics of Visible Light: 380 – 750 nanometersis a spectrum of colors ranging from violet to redconsists of packets of energy called photons photons travel in waves, having a measurable wavelength (8)photon’s energy is inversely related to its wavelength....the shorter the wavelength, the greater the energy it possesses.Which of the following photons possess the greatest amount of energy?Green photons 8 = 530nmRed photons 8 = 660nmBlue photons 8 = 450nmWhat happens to light when it strikes an object?reflected (bounces off)transmitted (passes through) absorbedThe absorption of th cholorophyll shows the strongest light absorption in the 450-500 narometer (blue color) and in the 625-675 (red color) region.B. Photosynthetic PigmentsMolecules that capture photon energy by absorbing certain wavelengths oflight.1. Primary pigmentsBacteriochlorophyll - green pigment found in certain bacteria.Chlorophylls a & b - bluish green pigments found in plants, green algae & cyanobacteria. Cholorophyll a found in all photosynthetic plants, cholorophyll b is found in all higher plants.Cholorophyll contains a Magnisium atom held at the center of the ring-shaped structure.2. Accessory PigmentsCarotenoids - red, orange, yellow pigments found in plants, algae, bacteria & archaea.Phycoerythrin - red pigment found in red algae.Phycocyanin - blue pigment found in red algae & cyanobacteria.Each pigment absorbs a particular range of wavelengths.C. ChloroplastsSites of photosynthesis in plants & algae.Concentrated in mesophyll cells of most plants.Stroma - gelatinous matrix; contains ribosomes, DNA & various enzymes.Thylakoid - flattened membranous sac; embedded with photosynthetic pigments.Granum – consist of a stack of thylakoidsD. Photosynthesis6CO2 + 6H2O ® C6H12O6 + 6O2 reduce CO2 to carbohydrate.Occurs in two stages:Light reactions - harvest photon energy to synthesize ATP & NADPH. Carbon reactions (Calvin cycle) - use energy from light reactions to reduce CO2 to carbohydrate.1. light actionoccur in thylakoids of chloroplastsinvolve photosystems I & II (light harvesting systems).a. Photosystems contain antenna complex that captures photon energy &passes it to a special pair of cholorophyll a II680 and I700- reaction center.Only this pair cholorophyll is capable of transferring electrons to an electrons receptors.All the other molecules funnel the light energy to this special cholorophyll , which is called reaction center.b. Photosynthesis II P680, receive light energy then eject 2 electrons to electron carriers in electron transport chain, active transport of H+ from the the stroma to thylakoid space creates gradient energy is captured by membrane bound protein -ATP synthase to form ATP – Chemiosmotic phosphorylation Use light energy to split H2O ½ O2 + 2 H+ + 2 e-, use the 2 e- from the water to replace the 2 electrons ejected.c. Photosynthesis I P700, received light energy then ejected 2 electrons pass to (ETC), combine with NADP+ to form NADPH.Two electrons passed down from the first ETC (photosynthesis II) replaced the 2 electrons ejected from photosynthesis IATP and NADPH formed in the light reaction are the important products passed on to the light independent reaction.2. Carbon Reactions (Calvin cycle; C3 cycle) do NOT require light (occur in both darkness & light as long as ATP & NADPH are available)occur in stroma of chloroplastsrequire ATP & NADPH (from light reactions), and CO2CO2 + Ribulose biphosphate + ATP + NADPH  Glucose + ADP + NADPRubisco enzyme is involved.Photolysis: PII get electron replacement by H2O, ½ O2 + 2 e- + 2H+Chemiosmotic phosphoration:H+ ions move down the concentration gradient, ffrom inside the thylakoid disc to the stroma of the choloroplast, ATP is formed from ADP + P.Plants store starch in amyloplasts.C3 plant: fix carbon dioxide in 3 carbon compound. (PGAL)C4 plant: fix carbon dioxide in 4 carbon compound,separating photosynthesis in mesophyll cells and Calvin cycle(fixes the carbon) in the bundle -sheath cells (surround the vein).Pumping CO2 into bundle- sheath cells keeps the internal concentration of CO2 much higher than normal. This decreases photorespiration, make C4 plant more efficient in the hot dry weather.CAM plant: take in carbon dioxide at night then fix in Calvin cycle during the day. Plants in the