Presentation on theme: "Where It Starts - Photosynthesis"— Presentation transcript:
1Where It Starts - Photosynthesis Chapter 7Where It Starts - Photosynthesis
2Photosynthesis - Intro Photosynthesis – makes food (sugar and other compounds) byusing sunlight as an energy sourcecarbon dioxide as the carbon sourceReleasing water and oxygen
37.0 Sunlight and SurvivalPlants are autotrophs, or self-nourishing organisms; they get Carbon and energy from the environment and make their own food.The first autotrophs filled Earth’s atmosphere with oxygen, creating an ozone (O3) layerThe ozone layer became a shield against deadly UV rays from the sun, allowing life to move out of the ocean and diversify.
4Other types of organisms Heterotrophs – Cannot obtain energy and C from the environment. They feed on autotrophs, one another, and organic wastes.Plants are photoautotrophs. They make sugars and other compounds using sunlight as the energy source and CO2 and release great amounts of oxygen.Plants around the world produce 220 billions tons of sugar each year
5ProkaryotesThe first prokaryotes were chemoautotrophs, they did not have the enzymes needed. (So they extracted energy and carbon from methane and hydrogen sulfide, there was little free oxygen.)Some prokaryotes evolved to neutralize toxic oxygen radicals and flourished. Those that did not perished.
67.1 Sunlight as an Energy Source Plants (Photoautotrophs) utilize the energy from the sun, in the form of photons , particles of wavelengths of visible light.Organisms use only a small range of wavelengths for photosynthesis(380 – 750nm)Light energy is packed as photons.
7Electromagnetic Spectrum Shortest Gamma rays*wavelength X-rays*UV radiation*Visible lightInfrared radiationMicrowavesLongest Radio waveswavelength * alters or breaks bonds in DNA and Proteins. Threat to all organisms.
8Photons Packets of light energy Each type of photon has fixed amount of energyPhotons having most energy travel as shortest wavelength (blue-violet light)Photons having least energy travel in longer wavelengths. (red Light, pg. 108)
9Visible Light Wavelengths humans perceive as different colors Violet (380 nm) to red (750 nm)Longer wavelengths, lower energyFigure 7-2 Page 108
10PigmentsPigments are a class of molecules that absorb photons in certain wavelengths only.The color you see is the wavelength not absorbedLight-catching part of molecule often has alternating single and double bondsThese bonds contain electrons that are capable of being moved to higher energy levels by absorbing light
11Pigment MoleculesPigment molecules on the thylakoid membranes absorb photons.Chlorophyll a (major) pigments absorb violet and red, but reflect green & yellow (leaves)Chlorophyll b (accessory) pigments reflects green & blue.Carotenoid pigments absorb blue-violet and blue-green but reflect yellow, orange, and redThe light-catching portion is the flattened ring structure (see page 109)
12Pigment MoleculesXanthophylls reflect yellow, brown, purple, or blue lightAnthocyanins – reflect red and purple light in fruit and flowersPhycobilins – reflect red or blue-green light and are accessory pigments found in red algae and cyanobacteria
13Pigments in Photosynthesis BacteriaPigments in plasma membranesPlantsPigments and proteins organized into photosystems that are embedded in thylakoid membrane system
147.2 Harvesting the Rainbow Wilhelm Theodor Engelmann, a botanist, knew that plants use sunlight, water and something in the air.What he wanted to know what which parts of sunlight do plants favor?He designed an experiment using photosynthetic alga, Cladophora and aerobic bacterial cells.
15Englemann’s Experiment He knew that certain bacterial cells will move toward places where oxygen concentration is highHe also understood that Photosynthesis produces oxygenHe identified violet and red light are best at driving photosynthesis, as most of the bacterial cells gathered at this point.
167.3 Overview of Photosynthesis Reactions Photosynthesis proceeds in two reaction stages. See page 111.Light-dependent reactions -thylakoid membraneSunlight energy is converted to chemical bond energy of ATPWater molecules are split, and typically the coenzyme NADP+ accepts the released hydrogen and electrons, thus becoming NADPH, oxygen is released
17Photosynthesis – Second Stage Light Independent reactions - stromaRuns on energy delivered by ATP.This energy drives the synthesis of glucose and other carbohydrates.The building blocks are the hydrogen atoms and electron from NADPH, as well as carbon and oxygen atoms stripped from carbon dioxide and water.
18light-dependant reactions light-independant reactions Two stages of PhotosynthesisSUNLIGHTH2OO2CO2NADPH, ATPlight-dependant reactionslight-independant reactionsNADP+, ADPsugarsCHLOROPLASTFig. 7-6c, p.111
197.4 Light-Dependent Reactions Occurs in the thylakoid membrane of the chloroplastHundreds of Pigments absorb light energy, give up e-, which is transferred to a photosystem.Two molecules of chlorophyll a are at the center of a photosystem.Chloroplasts have two kinds of photosystems, type I and type II. (Focus on type II)
20Light Dependent continued The freed e- enter an electron transfer chain, an orderly array of enzymes and co- enzymes.This is the first step in the conversion of light to chemical energy.Water molecules split, ATP and NADH form, and oxygen is released.
21Light Dependent continued Pigments (PS II)that gave up electrons get replacement electrons (from water molecules –through the process of photolysis)H+ moves from the stroma into the thylakoid compartment.The e- now enter photosystem 1This is also known as the noncyclic pathway of ATP formation.
22cross-section through a disk-shaped fold in the thylakoid membrane LIGHT-HARVESTINGCOMPLEXPHOTOSYSTEM IIP 680sunlightPHOTOSYSTEM IP 700H+NADPHe-e-e-e-e-e-NADP + + H+e-H2OH+H+H+H+thylakoidcompartmentH+H+H+H+H+H+O2H+thylakoidmembranestromaADP + PiATPcross-section through a disk-shaped fold in the thylakoid membraneH+Fig. 7-8, p.113
23Noncyclic pathway of ATP This pathway of photosynthesis photon energy forces electrons out of photosystem II to an electron transfer chain, which sets up H+ gradient that drive ATP formation, and ultimately end up in NADPH.The electrons are not cycled back into photosystem II.
24Cyclic Pathway of ATPPhotosystem I may run independently so that cells can continue to make ATP.It is a cyclic because the electrons that leave photosystem I get cycled back to it.These electrons pass through an ETC that moves H+ into the thylakoid compartments. This drives ATP formation, but no NADPH forms.
257.5 Energy Flow in Photosynthesis Most pigments in photosystem are harvester pigmentsWhen excited by light energy, these pigments transfer energy to adjacent pigment moleculesEach transfer involves energy loss
26Photosystem Function: Reaction Center Energy is reduced to a level that can be captured by molecule of chlorophyll aThis molecule P700 (I) or P680 (II) is the reaction center of a photosystemReaction center accepts energy and donates electron to acceptor molecule
27Cyclic Electron Flow Electrons are donated by P700 in photosystem I to acceptor moleculeflow through electron transfer chain and back to P700 to be reusedElectron flow drives ATP formationThis is the process of the first anaerobic photoautotrophs. See page 114
28Noncyclic Electron Flow Two-step pathway for light absorption and electron excitationUses two photosystems: type I and type IIe_ that leave PS II are not returned to it.Produces ATP and NADPHInvolves photolysis - splitting of waterSee page 114
29Chemiosmotic Model of ATP Formation Electrical and H+ concentration gradients are created between thylakoid compartment and stromaH+ flows down gradients into stroma through ATP synthesis ( ATP synthase)Flow of ions drives formation of ATP
307.6 Light-Independent Reactions Synthesis part of photosynthesis – make sugarTakes place in the stroma and can proceed in the darkSteps – carbon fixation, Rubisco mediatedCalvin-Benson cycle – a series of enzyme mediated reactions
31Carbon FixationA Carbon atom from CO2 becomes attached to an organic compound.Plants get the carbon dioxide from the air, and algae get it from carbon dioxide dissolved in water.Rubisco (ribulose bisphosphate carboylase/oxygenase meditates this step in most plants.
32Calvin-Benson Cycle This is known as the sugar factory It is a series of enzyme mediated reactions that take place in the stroma.Reactants – carbon dioxide attaches to rubisco, and splits into phosphoglycerate. ATP, and NADPHProducts – Glucose, ADP, and NADP+This is cyclic and RuBP is regenerated
33phosphorylated glucose Calvin- Benson CycleSix turns to make one glucose molecule6CO2ATP6 RuBP12 PGA126 ADP12 ADP +Calvin-Bensoncycle12 PiATP12NADPH4 Pi12 NADP+10 PGAL12 PGAL1 Pi1phosphorylated glucoseFig. 7-10b, p.115
347.7 The C3 Pathway Gases diffuse in/out of a plant through stomata. In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGABecause the first intermediate has three carbons, the pathway is called the C3 pathway
35Photorespiration in C3 Plants On hot, dry days stomata closeInside leafOxygen levels riseCarbon dioxide levels dropRubisco attaches RuBP to oxygen instead of carbon dioxide (photorespiration)Only one PGAL forms instead of twoSee page 117
36C4 Plants Carbon dioxide is fixed twice In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetateOxaloacetate is transferred to bundle-sheath cellsCarbon dioxide is released and fixed again in Calvin-Benson cycle. See page 117.
37CAM Plants Crassulacean Acid Metabolism Carbon is fixed twice (in same cells)Never uses oxygen, no matter the concentrationNight – stomata openCarbon dioxide is fixed to form organic acidsDayCarbon dioxide is released and fixed in Calvin-Benson cycle. See page 117.
387.8 Autotrophs and the Biosphere PhotoautotrophsCarbon source is carbon dioxideEnergy source is sunlightHeterotrophsGet carbon and energy by eating autotrophs or one another