Chapter note 5.pdf

9/17/20 Chapter 5 Photosynthesis and Global Warming Where does energy eventually come from? Carbohydrate Respiration Energy stored Carbohydrate Store energy ??? CO2 + H2O Energy released CO2 + H2O Convert energy 1 9/17/20 Where does our energy come from? Our energy is directly or indire...

9/17/20 Chapter 5 Photosynthesis and Global Warming Where does energy eventually come from? Carbohydrate Respiration Energy stored Carbohydrate Store energy ??? CO2 + H2O Energy released CO2 + H2O Convert energy 1 9/17/20 Where does our energy come from? Our energy is directly or indirectly from plants! Cereals, vegetables, fruits Meat from animals How doe plant produce energy? CO2 O2 Water Carbohydrate 2 9/17/20 Three major events in photosynthesis - Light absorption Convert sunlight energy into chemical energy Release the oxygen Light Absorption • Fate of light radiated on plant canopy A) Absorbed B) Transmitted C) Reflected • Light is absorbed by pigment molecules contained in the leaf * Why does the leaf look green? 3 9/17/20 Radiation Emitted by the Sun The absorbed part of the spectrum is called Photosynthetically Active Radiation 4 9/17/20 Primary Pigments – Chlorophylls • Two parts in a chlorophyll molecule: - Porphyrin head (contain - Long lipid-soluble hydro-carbon tail • Absorb all colors of visible light except green 4 N atoms and one Mg atom) Other Pigments – Carotenoids • Predominant when chlorophyll is degraded in the fall, present in leaves, roots and fruits • Absorb blue and some green light – reflect orange and yellow 5 9/17/20 Where does photosynthesis take place? • Leaf – solar collector, full of photosynthetic cells • Location of photosynthesis – chloroplasts 20-60 /cell, 3-10 mm in diameter Structure and Function of Chloroplast 1) Envelop – double layer membrane 2) Thylakoid – highly-structured membrane system - Stacked thylakoids – grana Pigments on surface 3) Lumen – the intra-thylakoid space - Site of water oxidation Oxygen as a “waste” product 4) Stroma – matrix around the grana within chloroplast - Contain all enzymes 6 9/17/20 Light-dependent reaction Light-independent reaction Light Reaction – Collection and conversion of light energy • Central components – two multi-molecular chlorophyll-protein complexes – Photosystem I (PSI) – Photosystem II (PSII) The reaction center chlorophyll molecule receives electron from its neighbor. That electron is excited to a higher energy level using the light energy harvested by antenna chlorophyll molecules, then passed away. 7 9/17/20 Products of the Light Reaction • ATP and NADPH - Temporary energy carrier - Required later in the dark reaction – release energy stored in their high-energy bonds ATP – adenosine triphosphate NADPH – nicotinamide adenine dinucleotide phosphate Dark Reaction – Carbon fixation and carbohydrate production • Absorb CO2 • Utilize the light energy harvested in the light reaction – carried by ATP and NADPH • Produce carbohydrates (glucose) 8 9/17/20 How does CO2 get into the plant? - Leaf Stoma • Structure: Subsidiary cells - Guard cells (one pair) - Subsidiary cells • Functions: - CO2 entry: photosynthesis - Release of O2 - H2O loss: transpiration Chloroplast How is CO2 converted to carbohydrates? • Three carbon assimilation pathways: 1. C-3 metabolism / Calvin cycle (C3) - For mostly cool-season plants, e.g. winter wheat 2. C-4 metabolism (C4) - For mostly warm-season plants, e.g. corn 2. Crassulacean acid metabolism (CAM) - For mostly desert plants, e.g. cactus 9 9/17/20 The Carbon Cycle The Atmosphere Photosynthesis Plants Consumption Animals Respiration Death The Grounds (Fossil fuels) Burning Burning of Fossil Fuels • Fossil fuels: formed by natural decomposition of buried dead organisms – Include coal, petroleum, and natural gas 10 9/17/20 Global Warming • The progressive increase of Earth’s average temperature Video - Due to increased concentrations of greenhouse gases: water vapor (H2O), methane (CH4), carbon dioxide (CO2) - Greenhouse effect: The trapping of the sun’s warmth in the lower atmosphere of the earth by greenhouse gases “Natural” vs. “Man-made” Greenhouse Effect • “Natural” effect: Keep the Earth’s climate warm and habitable • “Man-made” effect: Enhance the natural effect by adding greenhouse gases from fuel burning 11 9/17/20 Impacts of Global Warming Video Maintenance of Carbon and Energy Balance Photosynthesis - Absorb CO2 - Fix solar energy Respiration & Burning of fuel - Produce CO2 - Release energy 12 9/17/20 CO2 concentration (parts per million) Photosynthesis and Global Warming Average concentration of CO2 is steadily increasing. CO2 fluctuates yearly because photosynthesis is suppressed in the winter. Year Figure 4.5 What can we do to decrease the effects of global warming? Each of us can work to reduce our own contribution (“carbon footprint”) to the worldwide emissions 10 Ways to Reduce Your Carbon Footprint Ethanol – From farm to fuel 13