Photosynthesis Life Is Solar Powered! What Would Plants Look Like On Alien Planets? 1
Why Would They Look Different? Different Stars Give off Different types of light or Electromagnetic Waves The color of plants depends on the spectrum of the star s light, which astronomers can easily observe. (Our Sun is a type G star.) 2
Anatomy of a Wave Wavelength Is the distance between the crests of waves Determines the type of electromagnetic energy 3
Electromagnetic Spectrum Is the entire range of electromagnetic energy, or radiation The longer the wavelength the lower the energy associated with the wave. 4
Visible Light Light is a form of electromagnetic energy, which travels in waves When white light passes through a prism the individual wavelengths are separated out. Visible Light Spectrum Light travels in waves Light is a form of radiant energy Radiant energy is made of tiny packets of energy called photons The red end of the spectrum has the lowest energy (longer wavelength) while the blue end is the highest energy (shorter wavelength). The order of visible light is ROY-G-BIV This is the same order you will see in a rainbow b/c water droplets in the air act as tiny prisms 5
Light Options When It Strikes A Leaf Reflect a small amount of light is reflected off of the leaf. Most leaves reflect the color green, which means that it absorbs all of the other colors or wavelengths. Absorbed most of the light is absorbed by plants providing the energy needed for the production of Glucose (photosynthesis) Transmitted some light passes through the leaf 6
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Photosynthesis Overview oncept Map Photosynthesis includes uses Light dependent reactions occur in occurs in Light independent reactions uses Light Energy Thylakoid membranes Stroma ATP NADPH to produce of to produce ATP NADPH O 2 hloroplasts Glucose Anatomy of a Leaf Leaf cross section Vein Mesophyll Stomata O 2 O 2 Figure 10.3 8
hloroplast 9
hloroplast Are located within the palisade layer of the leaf Stacks of membrane sacs called Thylakoids ontain pigments on the surface Pigments absorb certain wavelenghts of light A Stack of Thylakoids is called a Granum Mesophyll hloroplast 5 µm Thylakoid Thylakoid Stroma Granum space Outer membrane Intermembrane space Inner membrane 1 µm Pigments Are molecules that absorb light hlorophyll, a green pigment, is the primary absorber for photosynthesis There are two types of cholorophyll hlorophyll a hlorophyll b arotenoids, yellow & orange pigments, are those that produce fall colors. Lots of Vitamin A for your eyes! hlorophyll is so abundant that the other pigments are not visible so the plant is green Then why do leaves change color in the fall? 10
Absorption of light by chloroplast pigments 3/21/2012 olor hange In the fall when the temperature drops plants stop making hrlorophyll and the arotenoids and other pigments are left over (that s why leaves change color in the fall). The absorption spectra of three types of pigments in chloroplasts EXPERIMENT Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. RESULTS hlorophyll a hlorophyll b arotenoids Wavelength of light (nm) (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Figure 10.9 11
Rate of photosynthesis (measured by O 2 release) 3/21/2012 The action spectrum of a pigment Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids. The action spectrum for photosynthesis Was first demonstrated by Theodor W. Engelmann Aerobic bacteria Filament of alga 400 500 600 700 (c) Engelmann s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O 2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b. ONLUSION photosynthesis. Light in the violet-blue and red portions of the spectrum are most effective in driving 12
hlorophyll hlorophyll a Is the main photosynthetic pigment hlorophyll b Is an accessory pigment H 3 H H 3 H H 2 H H 2 H 3 H 2 H 2 N N H H H H 3 Mg N N O O H H 3 H 3 HO in chlorophyll a in chlorophyll b Porphyrin ring: Light-absorbing head of molecule note magnesium atom at center O O O H 3 H 2 Figure 10.10 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown PHOTOSYNTHESIS omes from Greek Word photo meaning Light and syntithenai meaning to put together Photosynthesis puts together sugar molecules using water, carbon dioxide, & energy from light. 13
Happens in two phases Light-Dependent Reaction onverts light energy into chemical energy Light-Independent Reaction Produces simple sugars (glucose) General Equation 6 O 2 + 6 H 2 O 6 H 12 O 6 + 6 O 2 First Phase Requires Light = Light Dependent Reaction Sun s energy energizes an electron in chlorophyll molecule Electron is passed to nearby protein molecules in the thylakoid membrane of the chloroplast 14
Excitation of hlorophyll by Light When a pigment absorbs light It goes from a ground state to an excited state, which is unstable Excited state Heat Photon hlorophyll molecule Photon (fluorescence) Ground state Figure 10.11 A If an isolated solution of chlorophyll is illuminated It will fluoresce, giving off light and heat Figure 10.11 B 15
ET Electron from hlorophyll is passed from protein to protein along an electron transport chain Electrons lose energy (energy changes form) Finally bonded with electron carrier called NADP+ to form NADPH or ATP Energy is stored for later use Two Photosystems Photosystem II: lusters of pigments boost e- by absorbing light w/ wavelength of ~680 nm Photosystem I: lusters boost e- by absorbing light w/ wavelength of ~760 nm. Reaction enter: Both PS have it. Energy is passed to a special hlorophyll a molecule which boosts an e- 16
Thylakoid membrane 3/21/2012 A mechanical analogy for the light reactions ATP NADPH Mill makes ATP Figure 10.14 Photosystem II Photosystem I Photosystem A photosystem Is composed of a reaction center surrounded by a number of light-harvesting complexes Thylakoid Photon Photosystem Light-harvesting complexes Reaction center STROMA Primary election acceptor Figure 10.12 Transfer of energy Special Pigment chlorophyll a molecules molecules THYLAKOID SPAE (INTERIOR OF THYLAKOID) 17
Where those electrons come from Water Electrons from the splitting of water (photolysis) supply the chlorophyll molecules with the electrons they need The left over oxygen is given off as gas The Splitting of Water hloroplasts split water into Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules Reactants: 6 O 2 12 H 2 O Products: 6 H 12 O 6 6 H 2 O 6 O 2 Figure 10.4 18
High Quality H2O Photolysis Splitting of water with light energy Hydrogen ions (H + ) from water are used to power ATP formation with the electrons Hydrogen ions (charged particle) actually move from one side of the thylakoid membrane to the other hemiosmosis oupling the movement of Hydrogen Ions to ATP production Animation takes a min. to load be patient Animation II Does not take as long to load but it is not as good 19
The light reactions and chemiosmosis: the organization of the thylakoid membrane LIGHT H 2O O 2 NADP + ADP ALVIN LIGHT YLE REATOR ATP NADPH STROMA (Low H + concentration) O 2 [H 2O] (sugar) ytochrome Photosystem II complex Light 2 H + Photosystem I Fd NADP + reductase 3 NADP + + 2H + Pq Pc NADPH + H + H 2O THYLAKOID SPAE 1 (High H + concentration) 1 2 O 2 +2 H + 2 2 H + To alvin cycle Figure 10.17 STROMA (Low H + concentration) Thylakoid membrane ATP synthase ADP P H + ATP Vocabulary Review Light-Dependent Pigment hlorophyll Electron Transport hain ATP NADPH Photolysis hemiosmosis 20
Light-Dependent onverts light into chemical energy (ATP & NADPH are the chemical products). Oxygen is a by-product ATP NADPH Mill makes ATP Figure 10.14 Photosystem II Photosystem I Pigment Molecules that absorb specific wavelengths of light hlorophyll absorbs reds & blues and reflects green Xanthophyll absorbs red, blues, greens & reflects yellow arotenoids reflect orange 21
hlorophyll Green pigment in plants Traps sun s energy Sunlight energizes electron in chlorophyll Electron Transport hain Series of Proteins embedded in a membrane that transports electrons to an electron carrier 22
ATP Adenosine Triphosphate Stores energy in high energy bonds between phosphates NADPH Made from NADP+; electrons and hydrogen ions Made during light reaction Stores high energy electrons for use during light-independent reaction (alvin ycle) 23
hemiosmosis The combination of moving hydrogen ions across a membrane to make ATP H 2 O O 2 Light NADP LIGHT REATIONS ADP + P ALVIN YLE ATP NADPH Figure 10.5 hloroplast O 2 [H 2 O] (sugar) 24
PART II LIGHT INDEPENDENT REATION Also called the alvin ycle No Light Required Takes place in the stroma of the chloroplast Takes carbon dioxide & converts into sugar It is a cycle because it ends with a chemical used in the first step Begins & Ends The alvin ycle begins and ends with RuBP O2 is added to RuBP; fixing the O2 in a compound One compound made along the way is PGAL PGAL can be made into sugars or RuBP alvin ycle uses ATP & NADPH 25
The alvin cycle Light H 2O O 2 NADP + ADP LIGHT REATION ATP NADPH ALVIN YLE Input 3 (Entering one O at a time) 2 Phase 1: arbon fixation O 2 [H 2O] (sugar) 3 P P Ribulose bisphosphate (RuBP) (G3P) Rubisco 3 ADP ALVIN YLE 3 ATP Phase 3: Regeneration of the O 2 acceptor (RuBP) 5 P 3 P P Short-lived intermediate 6 3-Phosphoglycerate 6 P P 1,3-Bisphoglycerate 6 P Glyceraldehyde-3-phosphate (G3P) P 6 NADPH 6 NADPH + 6 P 6 ATP 6 ADP Phase 2: Reduction Figure 10.18 1 P G3P (a sugar) Output Glucose and other organic compounds hloroplast Where the Magic Happens! + H 2 O O 2 Energy Which splits water ATP and NADPH 2 Light is Adsorbed By hlorophyll hloroplast ADP NADP Used Energy and is recycled. alvin ycle O 2 6 H 12 O 6 Light Reaction Dark Reaction 6 O2 + 12 H2O + Light energy 6H12O6 + 6 O2 + 6 H2 O + 26