Ch 8 Photosynthesis PDF

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Calvin Cycle: Reactions depend on the products of the light reactions.  Energy from ATP and NADPH (products from light reactions) drive reactions to combine CO2 and water into organic molecules.  Also know as Light Independent Reactions Location Uses CO2 and water to make sugars which can drive more complex reactions. Once a chloroplasts runs low of ATP and NADPH it cannot do the Calvin cycle. (at night) Three Major Phases  Can be used to restart the activity 1. Phase 1: Carbon Fixation Phase (implies carbon that is in a form that cells cannot control, takes CO2 and makes it a controlled carbon form) a. 1 CO2 is available. b. Rubisco(RuBP) 5 carbon sugar. c. RuBP is given a CO2 molecule. d. Transforms to a 6 carbon molecule - not stable and it breaks into 2-3 carbon materials. 2. Phase 2: Reduction and Carbohydrate production a. Hydrolyzed and ATP is created b. NADPH gives up electrons and gives them to the carbon containing materials. (Reduced State) c. High energy 3-Carbon materials are made. 2. Phase 3: Regeneration of RuBP a. Regeneration of RuBP **Calvin Cycle Will be on Next Test** Chapter 8: Photosynthesis 8.1 Overview of Photosynthesis  Biosphere: describes the regions on the surface of the Earth and in the atmosphere where living organisms exists.  Heterotrophs: must consume food to sustain life  Photoautotrophs: autotrophs that use light as a source of energy to make organic molecules o Green plants, algae and some bacteria species. o Make a large portion of the Earths organic molecules via photosynthesis using light and CO2  Chloroplasts: organelles found in plant and algal cells that carry out photosynthesis. o All plants contain chloroplasts and can perform photosynthesis. o A majority of it is done in the leaves o Contains an outer and an inner membrane with a intermembrane space in between o Third membrane called thylakoid membrane  Contains pigment.  Take place in the thylakoid membrane  Produce 3 chemical products: ATP, NADPH and O2  NADPH: Nicotinamide adenine dinucleotide phosphate- electron carrier that can accept 2 electrons  Starts with light energy and ending with chemical energy o Calvin cycle  photo refers to light reactions that capture energy from sunlight and synthesis of carbohydrates that occurs in Calvin cycle. 8.2 Reactions That Harness Light Energy

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Light is a type of electromagnetic radiationForms flattened, fluid-filled tubes called thylakoids which enclose a single, convoluted compartment known as the thylakoid lumen. Stroma is the fluid filled region of the chloroplasts between thylakoid membrane and inner membrane Stack on top of each other to for a structure called a granum. Chlorophyll: pigment that gives plants their green color. Photosynthesis occurs in 2 stages Light reactions Wavelength: distance between peaks in a wave pattern Electromagnetic spectrum: encompasses all possible wavelengths of electromagnetic radiation from short to long waves. Photons: massless particles traveling in a wavelike pattern and moving at the speed of light (about 300 million m/sec) When light strikes an object one of three things can happen. o First the light may simply pass through. o Second the light may change the path of light to a different direction o Third is an object may absorb the light. Pigment: describes a molecule that can absorb light energy. o When light hits pigment some wavelengths are absorbed o In the visible spectrum light energy may be absorbed by boosting electrons to a higher energy level o In order for electrons to be boosted it must overcome the difference in energy between orbital its in and orbital to which its going into. Electrons may release energy in different ways o First: when an excited electron drops back down to a lower energy level it may release heat. o Second: in the form of light. Phenomenon called fluorescence. o In the case of photosynthetic pigments an excited electron is removed from that molecule and transferred to another molecule where its more stable. When it happens it is said the energy is "captured" because the electron does not readily drop down to a lower energy level. Two types of Chlorophyll pigments o Chlorophyll a o Chlorophyll b o Both bound to integral membrane proteins in the thylakoid membrane. o Contain a porphyrin ring and phytol tail. Carotenoids: another type of pigment found in chloroplasts. o Color ranges from yellow to orange to red. o Often major pigments in flowers and fruit. Absorption spectrum: a graph that plots a pigments light absorption as a function of wavelength. Action spectrum: plots the rate of photosynthesis as a function of wavelength. Thylakoid membranes contain two distinct complexes of proteins and pigments called photosystem I (PSI) and photosystem II (PSII) o PSII is the first step. o Key difference between the two is the source of the electrons received by their respective pigment molecules.

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Linear electron flow: combined action of photosystem II and photosystem I because electrons move linearly from one to the other.  Photophosphosphorylation: synthesis of ATP in chloroplasts is achieved by this chemiosmosis mechanism.  A H+ electrochemical gradient is generated by 3 events o The splitting of water which places H+ in the thylakoid lumen. o The movement of high energy electrons through the ETC from photosystem II to photosystem I o The formation of NADPH which consumes H+ I the stroma.  Products of photosynthesis o O2  Produced in thylakoid lumen by oxidation of water by PSII. o NADPH  Produced in stroma using high energy electrons that start PSII and are boosted a second time in PSI. o ATP  Produced in stroma via ATP synthase that uses a H+ gradient.  Cyclic photophosphorylation: a pattern of electron flow that is cyclic and generates only ATP because 1) the path of electrons is cyclic, 2) light energizes the electrons and 3) ATP is made via phosphorylation.  Cyclic electron flow: due to the path of electrons, the mechanism is also called this. 8.3 Molecular Features of Photosystems  PSI and PSII play roles in 2 aspects of photosynthesis o First both absorb light energy and capture the energy in the form of excited electrons. o PSII oxidizes water  PSI and PSII have 2 main components: o A light harvesting complex  Thylakoid membrane  Composed of several dozen pigment molecules that are anchored to transmembrane proteins  Role is to absorb photons of light when an electron is boosted to a higher energy level  The energy is transferred to adjacent pigment molecules by a process called resonance energy transfer  Energy may be transferred until its transferred to a special pigment molecule designated P680  Located in reaction center o A reaction center  Role is to quickly remove the high energy electron from P680* and transfer it to another molecule where the electron is mores stable.  Primary electron acceptor: what the molecule is called.  Another role is to replace the electron so that P680+ can revert back to P680* and is usually replaced with a love energy electron from water  In turn creates O2  Z scheme: an electron proceeds through a series of energy changes during photosynthesis. o Z refers to the zigzag shape of the energy curve  Events that increase/decrease energy in electrons

o an electron with a non-excited pigment molecule in PSII has the lowest energy o In PSII light boots electrons to a much higher energy level o As the electron transfers to PSII to PSI some energy is is released o Input of light in PSI boots electron to an even higher energy level that in PSII o Electron releases a little energy before its eventually transferred to NAD+ 8.4 Synthesizing Carbohydrates via the Calvin Cycle  Consists of a series of steps that occur in a metabolic cycle. o In plants and algae it occurs in stroma. o In cyanobacteria it occurs in the cytoplasm of the bacteria cells.  Takes CO2 from the atmosphere and incorporates the carbon into organic molecules - mainly carbohydrates o Carbohydrates are important for 2 reasons.  First because they provide the precursors to make organic molecules and macromolecules  Secondly because the storage of energy.  Calvin Cycle creates carbohydrates so that when a plant is in the dark it can still use energy.  Also called the Calvin-Bensen cycle  For every 6 carbon dioxide molecules incorporated 18 ATP molecules are hydrolyzed and 12 NADPH molecules are oxidized  Calvin Cycles 3 Phases o Carbon Fixation Phase:  CO2is incorporated into a RuBP, a five carbon sugar.  Fixation means carbon has been removed from atmosphere and fixed into an organic molecule that is not a gas.  Rubisco: RuBP- the enzyme that catalyzes the splitting to form 2 molecules of 3phosphoglycerate (3PG)  Most abundant protein in chloroplasts o Reduction and Carbohydrate Production Phase:  ATP is used to convert 3PG to 1,3-bisphosphoglycerate (1,3BPG)  Electrons from NADPH reduce 1,3BPG to glyceraldehyde-3-phsphate (G3P)  G3P is a carbohydrate with three carbon atoms.  12 G3P molecules are made and only 2 are used in carbohydrate production the other 10 are used to keep the Calvin Cycle turning. o Regeneration of RuBP Phase:  A series of enzymatic steps covert the 10 G3P into 6 RuBP molecules using 6 molecules of ATP 8.5 Variations in Photosynthesis  C3 Plants: a plant that uses C02 to make RuBP molecules o 90% of plants are these  Photorespiration: uses O2 and liberates CO2 o Considered wasteful since it releases CO2 and limits plant growth. o Likely to occur when plants are expose to hot and dry environments.  C4 Plants: 4 carbon molecule. o Sugarcane o Unique leaf anatomy that allows them to avoid photorespiration o An interior later in leaves composed of mesophyll and bundle-sheath cells.

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C4 have an advantage in warm, dry environments because they can keep their stomata partiall closed to conserve water and minimize photorespiration. CAM plants o Crassulacean acid metabolism o To avoid water loss plants keep their stromata closed during the day and open at night when its cooler and humidity is higher....