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This 9 page Class Notes was uploaded by Kezia Notetaker on Tuesday September 27, 2016. The Class Notes belongs to bio1134 at Mississippi State University taught by Martha Barton in Fall 2016. Since its upload, it has received 3 views. For similar materials see General Biology I in Biology at Mississippi State University.
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Date Created: 09/27/16
CAHPTER 8: PHOTOSYNTHESIS Photo synthesis is the process of using light energy to make glucose from CO a2d water. Reaction : 6CO2 + 6H2O C6H12O6 + 6O2 ΔG = +686 kcal/mol (shows that the reaction needs energy) The benefits of photosynthesis Photosynthesis ultimately provides organic food for both heterotroph and autotroph for cellular respiration. Provides oxygen for organism to do cellular respiration. Place where the photosynthesis happens Photosynthesis occurs in the chloroplast which are mostly found in leaves. Leaf structure Chloroplast structure o Chloroplast contains the pigment called chlorophyll o Thylakoid: the place where chlorophyll are found o Granum: stack of thylakoid o Stroma: the fluid filled region between thylakoid membrane and inner membrane. Pigments Pigments: Molecules that absorb light energy. Pigments absorb certain light energy and reflect others Wavelength of light that a pigment absorbs depends on the amount of energy needed to boost an electron to a higher orbital. Having different pigments allows plants to absorb many kinds of light energy. Kinds of pigments: o Chlorophyll The pigment that absorb the red and violet light and reflected the green light (that’s why leaves are green in color). o Carotenoid An accessory pigment that aid photosynthesis by transferring their excited electron—the electron which becomes unstable after absorbing energy—to the chlorophyll. Carotenoid absorbs green and blue light and reflected yellow, red, or orange. It’s the pigments that gives color to the flowers and fruit. 2 stages of photosynthesis Light reaction Produce: ATP, NADPH, oxygen Occurs in thylakoid membrane Called “light reaction” because it needs the presence of light as an energy source for the reaction to occur. Steps: Photosystem II 1. Pigment molecules in photosystem II absorb energy from sunlight 2. The energy from light excites an electron to a higher energy level. 3. Water is split to oxygen and hydrogen (H = 2H+ + 2e-) The electrons from H are used to replace the electron lost from PSII The H+ ions contribute to the formation of a proton gradient 4. The electron is passed down an electron transport chain to PSI Energy is released as it moves down the chain Energy released from electron transfer is used to pump H+ across the thylakoid to form an H+ gradient. Energy stored in the gradient will be used by ATP synthase to produce ATP. Photosystem I 5. Pigments in PSI absorbs energy from sunlight The energy from sunlight excites an electron to a higher energy level. 6. The electron is transferred down a second electron transfer chain & the energy released is used by NADPH reductase to reduce NADP+ into NADPH. Calvin cycle Uses NADPH, ATP, carbon dioxide to make sugars. Occurs in stroma The reaction can occur with or without light. Calvin cycle doesn’t directly produce sugar (glucose), in fact it produces G3P (Glyceraldehyde-3-phosphate) which is then made into glucose. The production of ATP by ATP synthase o ATP synthase provides a passage for the facilitated diffusion of hydrogen ions (H+) down their gradient. It uses energy that was stored in the gradient to make ATP o ATP synthase uses the same mechanism to produce ATP in aerobic cellular respiration and photosynthesis Variation of photosynthesis C3 plants o 3 carbon molecule is the first product of carbon fixation o Example: wheat plant o Photorespiration: Rubisco adds an oxygen molecule to RuBP when O2 levels are high and CO2 levels are low Photorespiration is inefficient; reduces photosynthetic output (Releases CO2, uses ATP and NAPDH, does not produce sugar). C4 plants o It has an additional carbon fixation step before Calvin cycle o Rubisco is supplied with CO2 from the C4 molecule and is shielded from O2 o CO2 is initially incorporated into a 4 carbon molecule o Mesophyll cells fix CO2 and provide bundle sheath cells with steady CO2 supply o Rubisco in the bundle sheath cells is shielded from high O2 o Example: sugar cane, corn CAM plants o Temporally separates the carbon fixation and Calvin cycle o CAM plants fix carbon dioxide into a 4C molecule at night and release CO2 into the Calvin cycle during the day o Example: cactus
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