Lecture7BIO115Winter11d2l - BIO115 Photosynthesis Dr....

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Unformatted text preview: BIO115 Photosynthesis Dr. Jessica Pamment Overview Overview • Significance of photosynthesis • Site of photosynthesis, the chloroplast • 1. 2. Two stages of photosynthesis: Light reactions Calvin Cycle Significance of Photosynthesis Significance of Photosynthesis • It produces ~ 160 billion metric tons of organic material each year • All of the food consumed by humans can be traced to photosynthetic plants Significance of Photosynthesis Significance of Photosynthesis • Photosynthesis provides materials used for clothing, housing, pharmaceuticals and cooking • The chemistry of photosynthesis affects our global environment Green Energy Green Energy • • • • Wood burning was used by humans to produce heat and light before industrialization Use of fossil fuels took over Renewed interest in alternative sources, such as biomass Wood burning is renewable, few sulfur compounds, tree crops remove CO2 Energy Plantation Energy Plantation http://www.esf.edu/pubprog/brochure/willow/willow.html Photosynthesis Photosynthesis • The conversion of light energy into chemical energy in the form of sugars and other organic molecules Types of Photosynthesizers Plants (mostly on land) Photosynthetic Protists (aquatic) Photosynthetic Bacteria (aquatic) Forest plants Kelp, large algae Micrograph of cyanobacteria LM Leaf cross section Vein CO2 O2 Chloroplast cell Chloroplasts: Site of photosynthesis 5 µm Chloroplast Outer membrane Thylakoid Stroma Granum Thylakoid space Intermembrane space Inner membrane 1 µm Equation for Photosynthesis Equation for Photosynthesis Photosynthesis • During cellular respiration there is a ‘fall’ of electrons from food molecules to O2 to produce water and energy • During photosynthesis electrons are boosted ‘uphill’ and added to CO2 to produce sugar Photosynthesis Photosynthesis • • 6CO2 + 12H2O Light energy C6H12O6+6O2+ 6H2O Two processes: 1. The light reaction converts solar energy to ATP energy 1. Calvin Cycle converts ATP to chemical H2O Light NADP+ ADP + Pi Light Reactions Chloroplast H2O Light NADP+ ADP + Pi Light Reactions ATP NADPH Chloroplast O2 H2O CO2 Light NADP+ ADP + Pi Light Reactions ATP NADPH Calvin Cycle Chloroplast O2 H2O CO2 Light NADP+ ADP + Pi Light Reactions ATP NADPH Calvin Cycle Chloroplast O2 [CH2O] (sugar) Light Energy Light Energy • Leaves absorb a portion of light that falls on them • Sun’s energy is transferred to Earth by electromagnetic waves light spectrum • Photosynthesis is driven by part of the visible The Electromagnetic Spectrum Light Reflected light Chloroplast Absorbed light Transmitted light Granum The Process of Science The Process of Science • Observation: Certain bacteria cluster in areas of high O2 concentration • Question: Which wavelengths of light are best for promoting photosynthesis? • Hypothesis: O2­seeking bacteria will congregate near regions of algae undergoing most photosynthesis The Process of Science The Process of Science • Experiment: algae on slide with bacteria Shine spectrum of light on slide • Results: most bacteria congregate around algae exposed to red­orange and blue­ violet light. Least in area of green light. Investigation: Investigation What wavelengths drive photosynthesis The Process of Science The Process of Science • Conclusion: Light in the violet­blue and red ends of the spectrum are the most effective in driving photosynthesis Chloroplast Pigments • Chlorophyll a, absorbs mainly blue­violet and red light. It is the primary pigment • Chlorophyll b, absorbs mainly blue and orange light • Carotenoids, absorb mainly blue­green light Carotenoid Pigments in Autumn Carotenoid Stage 1: Light Reaction Stage 1: Light Reaction • The power of sunlight will: 1. Strip water of electrons 1. Boost these electrons to a higher energy level Chlorophyll • Chlorophyll molecule is excited by light energy= electrons pushed to outer shell • Excited molecule is unstable. Electron will return to its original, unexcited state • Energy is released Chlorophyll Chlorophyll 1. Extra energy converted to heat or combination of heat and light (fluorescence) 1. Extra energy transferred, but not the electron, to neighboring chlorophyll electron acceptor 1. High­energy electron transferred to an Excited state – Light Heat Light (fluorescence) Photon Pigment molecule Ground state (a) Absorption of a photon, results in excited electrons Photosystems Photosystems • Multiprotein complexes that transfer absorbed light energy in the form of electrons Two components: Reaction centre Antenna complex • i. ii. Photon Photosystem Antenna complexes STROMA Primary electron acceptor Reaction-center complex Thylakoid membrane e– Special pair of chlorophyll a molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) A Photosystem A Photosystem The Light Reaction of Photosynthesis The Analogy for Light Reactions Reactions Roles of Photosystems • PSII: water is split and electrons from water pushed uphill. O2 released • ETC: electrons passed from PSII to PSI releasing energy/ATP as a result of REDOX • PSI: electrons accepted by electron carrier Light Reactions Light Reactions • • Light reactions use solar energy to generate ATP and NADPH ATP and NADPH required for the Calvin Cycle Thylakoid membrane: site of conversion from light to chemical energy light Summary of Light Reactions Summary of Light Reactions • Take place in the thylakoid membrane • Light energy is captured by photosystems and used to transfer electrons from water to the top of the transport chain and ATP • The end result of the light reaction is NADPH The Calvin Cycle The Calvin Cycle • Similar to the Citric Acid cycle in that it is a cycle • Different in that it makes organic compounds, instead of breaking them down leaves in the form of sugar • Carbon enters in the form of CO2 and The Calvin Cycle INPUT OUTPUT 9 ATP 9 ADP 6 NADPH 3CO 6 NADP+ Glucose Summary of The Calvin Cycle Summary of The Calvin Cycle • Doesn’t require light • Uses electrons from NADPH and energy from ATP • Takes place in the stroma • Carbon from CO2 molecules fixed into organic compounds Environmental Impact of Environmental Impact of Photosynthesis The products of photosynthesis ultimately supports all life Photosynthesis removes CO2 and provides O2 to the atmosphere Deforestation contributes to increases in CO2 in atmosphere­ Effect on global warming Orchids growing in a Greenhouse Orchids Atmosphere, CO2 and Global Warming Atmosphere, Summary Summary • Photosynthesis takes place in the thylakoids within chloroplasts • Two stages, the light reaction and the Calvin Cycle • Light reactions capture solar energy and use it to make ATP and make NADPH Summary • Calvin Cycle uses NADPH and ATP to make sugar from CO2 • The sugar made supplies the entire plant with chemical energy and carbon skeletons for synthesis of organic compounds respiration by mitochondria • 50% organic material is used for Review Review The Process of Science • Why is it beneficial for plants to have two types of chlorophyll instead of just one? • What would you expect concerning the rate of photosynthesis for a plant that had only one typeof chlorophyll? • Predict what will happen in the following experiment based on what you know about photosynthesis and cellular respiration: in the presence of sunlight. Assume a watering system is provided. What will happen to the plant (live/die) and why? container with food and a source of water. What will happen to the mouse and why? airtight container with food, water, and sunlight. What will happen to the plant and the mouse and why? • 1. You place a plant alone in a covered airtight container • 2. You place a mouse alone in a covered airtight • 3. You place the plant and mouse together in a covered ...
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This note was uploaded on 04/26/2011 for the course BIO 115 taught by Professor Pamment during the Winter '11 term at DePaul.

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