Photosynthesis
Englemann Experiment In 1883, Thomas Engelmann of Germany used a combination of aerobic bacteria and a filamentous alga to study the effect of various colors of the visible light spectrum on the rate of photosynthesis. He passed white light through a prism in order to separate the light into different colors of the spectrum; then he exposed different segments of the alga to the various colors. He observed in which areas of the spectrum the greatest number of bacteria appeared.
Light form the sun is composed of a range of wavelengths (colors). The visible spectrum to the left illustrates the wavelengths and associated color of light. Combined together these wavelengths give the 'white' light we associate with full sunlight. The shortest wavelengths are the 'blues' which have more energy. The longer wavelengths are the 'reds' which have less energy.
Action spectrum and absorption spectrum
Photosynthesis SUN 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 photons An anabolic, endergonic, carbon dioxide (CO 2 ) requiring process that uses light energy (photons) and water (H 2 O) to produce organic macromolecules (glucose). Carbon dioxide and water are taken in by plants Plants absorb light energy and convert it to a usable form (ATP) Energy is used to fix carbon dioxide into sugar molecules (i.e. Chemical energy) Sugar is converted to starch (and other carbs) and stored for use by the plant, and for use by animals when they eat plants.
Where does photosynthesis take place?
General Breakdown of Photosynthesis Two main parts (reactions) 1. Light Dependent Reaction (occurs within thylakoid) - During the light reaction, there are two possible routes for electron flow and Two Photosystems involved. A. Cyclic Electron Flow generates ATP B. Noncyclic Electron Flow - generates ATP & NADPH 2. Light Independent Reaction (occurs within stroma) - Calvin Cycle or Light Independent Reaction or Carbon Fixation or C 3 Fixation - Uses energy (ATP and NADPH) from light dependent rxn to make sugar (GALP glucose).
An overview of photosynthesis
LDR
Non-Cyclic Electron Flow Occurs in the thylakoid membrane and uses PS II and PS I PS II is photooxidized releasing an 'excited' electron. Uses Electron Transport Chain (ETC) reduced membrane proteins pumps H+ from the stroma into the space inside the thylakoids generates ATP. Electrons enter PS I which is photooxidized releasing an 'excited' electron. Electrons move thru a short ETC which culminates in the reduction of NADP+ to NADPH Water is split (photolysis) in order to replace the lost electrons from PSII (generates oxygen as a waste product) Generates O 2, ATP (thru chemiosmosis) and NADPH
Hill Z Scheme for Noncyclic Electron Flow Primary Electron Acceptor 2e - 2e - ETC Primary Electron Acceptor 2e - Enzyme Reaction SUN Photon H 2 O 2e - ATP P680 1/2O Photosystem II 2 + 2H + Photon 2e - P700 NADPH Photosystem I
Cyclic Electron Flow Occurs in the thylakoid membrane and uses PS II and PS I PS II is photooxidized releasing an 'excited' electron. Uses Electron Transport Chain (ETC) reduced membrane proteins pumps H+ from the stroma into the space inside the thylakoids generates ATP. Electrons enter PS I which is photooxidized releasing an 'excited' electron. Electrons move thru a short ETC which culminates in the reduction of NADP+ to NADPH Water is split (photolysis) in order to replace the lost electrons from PSII (generates oxygen as a waste product) Generates O 2, ATP (thru chemiosmosis) and NADPH
Cyclic Electron Flow SUN Primary Electron Acceptor e - Photons e - P700 e - e - ATP produced by ETC Accessory Pigments Photosystem I
How noncyclic electron flow during the light reactions generates ATP and NADPH
Light Dependent Reactions SG
Overview of the Light Independent Cycle Occurs in the stroma, uses the products of the light dependent reactions (ATP and NADPH) and controlled by enzymes. Carbon Fixation - Ribulose Bisphosphate Carboxylase (Rubisco) allows carbon (carbon dioxide) to be fixed into an initial organic molecule - Rubisco therefore can be seen as a link between inorganic (non-living) and the organic (living) e.g. Primary productivity To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH. Plants have this remarkable ability to manufacture all their own organic molecules and by definition all the basic organic molecules required by all life forms. C, H, O are enough to form lipids and carbohydrates. With a Nitrogen source, amino acids and (therefore) proteins can be made.
The Calvin cycle
Light Independent Reactions SG
Photorespiration On hot, dry, bright days the stomates close. Rubisco is promiscuous and fixes oxygen instead of carbon dioxide (fixation of O 2 instead of CO 2 ) Produces 2-C molecules instead of 3-C sugar molecules. Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants
Types of photosynthesis C3 The majority of plants they transpire rapidly in hot dry environments because they fix carbon dioxide inefficiently at hot temps (about 30 C) Examples are Trees, Wheat, Potatoes, Rice, etc
C4 photosynthesis Hot, moist environments Divides photosynthesis spatially. Light rxn - mesophyll cells. Calvin cycle - bundle sheath cells. CO 2 temporarily stored as 4-C organic acids resulting in more efficient C exchange rate Advantage in high light, high temperature, low CO 2 they can open their stomata less wide and so transpire less because they can fix carbon dioxide at low concentrations they can fix carbon dioxide above 30 C Examples: Corn, Sugar Cane, Crabgrass
Fig. 10.21
CAM photosynthesis Hot, dry environments. Stomates closed during day. Stomates open during the night (cooler and less transpiration). Light rxn - occurs during the day. Calvin Cycle - occurs when CO 2 is present. Many succulents (e.g., cacti, euphorbs, bromeliades)
CAM Pathway
Cell Respiration Vs. Photosynthesis C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + 36 ATP Cellular Respiration 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Photosynthesis
Creative Diagraming Describe the journey of a single hydrogen atom (i.e. the 2 electrons and protons) from water in photosynthesis as it passes through non cyclic and cyclic flow. Describe the journey of a single oxygen atom from water in photosynthesis. Describe the journey of a carbon dioxide molecule in photosynthesis.