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CHAPTERS 6 & 7 Cellular Respiration & Photosynthesis Photosynthesis and Cellular Respiration provide energy for life All Living Organisms Must Take in Energy and Use It: Life Processes Require Energy: – These include growth, transport, manufacture, movement, reproduction, and others – Energy that supports life on Earth is captured from sun rays reaching Earth through plant, algae, protist, and bacterial photosynthesis Copyright © 2009 Pearson Education, Inc. Photosynthesis and cellular respiration provide energy for life • Energy in sunlight is used in photosynthesis to make glucose from CO2 and H2O with release of O2 • Other organisms use the O2 and energy in sugar and release CO2 and H2O through cellular respiration • Together, these two processes are responsible for the majority of life on Earth Copyright © 2009 Pearson Education, Inc. Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose + + H2O O2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy Breathing supplies oxygen to our cells for use in cellular respiration and removes carbon dioxide • Breathing and cellular respiration are closely related – Breathing is necessary for exchange of CO2 produced during cellular respiration for atmospheric O2 – Cellular respiration uses O2 to help harvest energy from glucose and produces CO2 in the process Copyright © 2009 Pearson Education, Inc. O2 Breathing CO2 Lungs CO2 Bloodstream Muscle cells carrying out Cellular Respiration Glucose + O2 CO2 + H2O + ATP O2 Cellular respiration banks energy in ATP molecules • Cellular respiration is an exergonic/degradative process that transfers chemical energy from glucose to ATP – Cellular respiration produces 38 ATP molecules from each glucose molecule – Other foods (organic molecules) can be used as a source of energy as well Copyright © 2009 Pearson Education, Inc. C6H12O6 Glucose + 6 O2 Oxygen 6 CO2 Carbon dioxide + 6 H2O Water + ATPs Energy The human body uses energy from ATP for all its activities • The average adult human needs about 2,200 kcal (nutritional calories) of energy per day – A kilocalorie (kcal) is the quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1oC – This energy is used for body maintenance and for voluntary activities Copyright © 2009 Pearson Education, Inc. Cells tap energy from electrons “falling” from organic fuels to oxygen • Energy can be released from glucose by simply burning it • The energy is dissipated as heat and light and is not available to living organisms Copyright © 2009 Pearson Education, Inc. Cells tap energy from electrons “falling” from organic fuels to oxygen • On the other hand, cellular respiration is the controlled breakdown of organic molecules – Energy is released in small amounts that can be captured by a biological system and stored in ATP Copyright © 2009 Pearson Education, Inc. Cells tap energy from electrons “falling” from organic fuels to oxygen • There are electron “carrier” molecules that carry the electrons released from the breakdown of the glucose molecule in cellular respiration – They form a staircase where the electrons pass from one to the next down the staircase – These electron carriers collectively are called the electron transport chain, and as electrons are transported down the chain, ATP is generated – The final acceptor of the electrons is OXYGEN Copyright © 2009 Pearson Education, Inc. NADH NAD+ + ATP 2e– Controlled release of energy for synthesis of ATP H+ 2e– H+ H 2O 1 2 O2 STAGES OF CELLULAR RESPIRATION AND FERMENTATION Copyright © 2009 Pearson Education, Inc. Overview: Cellular respiration occurs in three main stages • Stage 1: Glycolysis – Glycolysis begins respiration by breaking glucose, a six-carbon molecule, into two molecules of a three-carbon compound called pyruvate – This stage occurs in the cytoplasm – Only 2 ATPs are produced (NO oxygen is involved) Copyright © 2009 Pearson Education, Inc. Overview: Cellular respiration occurs in three main stages • Stage 2: The Citric Acid Cycle – The citric acid cycle breaks down pyruvate into carbon dioxide and supplies the third stage with electrons – This stage occurs in the mitochondria Copyright © 2009 Pearson Education, Inc. Overview: Cellular respiration occurs in three main stages • Stage 3: Oxidative Phosphorylation (electron transport system) – During this stage, electrons are shuttled through the electron transport chain – As a result, ATP is generated through oxidative phosphorylation (OXYGEN is REQUIRED = AEROBIC) – This stage occurs in the mitochondria – Another 36 ATPs are produced in stages 2 and 3 Copyright © 2009 Pearson Education, Inc. NADH Mitochondrion High-energy electrons carried by NADH NADH FADH2 and OXIDATIVE GLYCOLYSIS Glucose PHOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE Pyruvate Cytoplasm Inner mitochondrial membrane CO2 CO2 ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation ATP Oxidative phosphorylation Fermentation enables cells to produce ATP without oxygen • Fermentation is an anaerobic (without oxygen) energy-generating process – It takes advantage of Glycolysis, producing 2 ATP molecules for every glucose molecule – Why can’t humans survive by fermentation alone??? Copyright © 2009 Pearson Education, Inc. Fermentation enables cells to produce ATP without oxygen • Human muscle cells and certain bacteria perform lactic acid fermentation • Lactic Acid produces some of the burning sensation in your muscles after you’ve exercised Copyright © 2009 Pearson Education, Inc. Fermentation enables cells to produce ATP without oxygen • The baking and winemaking industry have used alcohol fermentation for thousands of years – Yeasts are single-celled fungi that not only can use respiration for energy but can ferment under anaerobic (NO OXYGEN) conditions – They convert pyruvate to CO2 (gas) and ethanol Copyright © 2009 Pearson Education, Inc. Fermentation enables cells to produce ATP without oxygen • Some bacteria perform acetic acid fermentation – They convert pyruvate to acetic acid (VINEGAR) Copyright © 2009 Pearson Education, Inc. EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth • Glycolysis is the universal energy-harvesting process of living organisms – So, all cells can use glycolysis for the energy necessary for viability – The fact that glycolysis has such a widespread distribution is good evidence for evolution Copyright © 2009 Pearson Education, Inc. Cells use many kinds of organic molecules as fuel for cellular respiration • Although glucose is considered to be the primary source of sugar for cellular respiration and fermentation, there are actually three sources of molecules for generation of ATP – Carbohydrates (disaccharides) – Proteins (after conversion to amino acids) – Ammonia (a TOXIN) is generated by the use of amino acids for energy – Fats Copyright © 2009 Pearson Education, Inc. Food, such as peanuts Carbohydrates Fats Glycerol Sugars Proteins Fatty acids Amino acids Amino groups Glucose G3P GLYCOLYSIS Pyruvate Acetyl CoA ATP CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) CHAPTER 6 & 7 (continued) PHOTOSYNTHESIS Light energy 6 CO2 +6 Carbon dioxide H2 O Water C6H12O6 Photosynthesis Glucose + 6 O2 Oxygen gas PLANT POWER • “Plant Power” would be an excellent energy solution, because air pollution, acid precipitation, and greenhouse gases could be significantly reduced (plant power is also RENEWABLE) • Fossil Fuels contain contaminants that lead to the production of other greenhouse gases and pollutants that cause acid rain: – Sulfur Dioxide + Water Sulfuric Acid – Nitrogen Oxide + Water Nitric Acid Why is acid rain harmful to life??? Autotrophs are the producers of the biosphere • Autotrophs (PRODUCERS) are living things that are able to make their own food without using organic molecules derived from any other living thing – Autotrophs that use the energy of light to produce organic molecules are called photoautotrophs – Most plants, algae and other protists, and some prokaryotes are photoautotrophs Copyright © 2009 Pearson Education, Inc. Photosynthesis occurs in chloroplasts in plant cells • Chloroplasts are the major sites of photosynthesis in green plants – Chlorophyll, an important light absorbing pigment in chloroplasts, is responsible for the green color of plants – Chlorophyll plays a central role in converting solar energy to chemical energy Copyright © 2009 Pearson Education, Inc. Leaf Cross Section Leaf Mesophyll Vein CO2 O2 Stoma Mesophyll Cell Chloroplast Outer and inner membranes Thylakoid Stroma Granum Thylakoid space Intermembrane space Photosynthesis is a biosynthetic & endergonic process; cellular respiration is the opposite (degradative & exergonic) • Photosynthesis is a biosynthetic & endergonic process – Water molecules are split apart; they lose electrons and produce hydrogen ions (H+) – Then 6 CO2 molecules are built into a sugar (GLUCOSE) molecule as electrons and hydrogen ions are added to them Copyright © 2009 Pearson Education, Inc. Photosynthesis is a biosynthetic & endergonic process; cellular respiration is the opposite (degradative & exergonic) • Photosynthesis is a biosynthetic & endergonic process – Water molecules are split apart; they lose electrons and produce hydrogen ions (H+) – Then 6 CO2 molecules are built into a sugar (GLUCOSE) molecule as electrons and hydrogen ions are added to them Copyright © 2009 Pearson Education, Inc. The two stages of photosynthesis are linked by ATP • Actually, photosynthesis occurs in two metabolic stages – One stage involves the light reactions (REQUIRES LIGHT) – In the light reactions, light energy is converted to chemical energy (ATP) – Water is split to provide the O2 as well as electrons – Water Hydrogen ions + Oxygen + electrons Copyright © 2009 Pearson Education, Inc. Overview: The two stages of photosynthesis are linked by ATP • The second stage is the Calvin cycle – It is a cyclic series of reactions that builds sugar molecules (GLUCOSE) from CO2 and the products of the light reactions – During the Calvin cycle, CO2 is incorporated into organic compounds, a process called carbon fixation – This is the endergonic/biosynthetic part of the reaction that uses the ATP (energy) produced during the Light Dependent Stage – This is the Light Independent Stage Copyright © 2009 Pearson Education, Inc. CO2 H2O Chloroplast Light NADP+ ADP P LIGHT REACTIONS CALVIN CYCLE (in stroma) (in thylakoids) ATP NADPH O2 Sugar : GLUCOSE THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Copyright © 2009 Pearson Education, Inc. Visible radiation drives the light reactions • Sunlight contains energy called electromagnetic energy or radiation – Visible light is only a small part of the electromagnetic spectrum, the full range of electromagnetic wavelengths – Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves Copyright © 2009 Pearson Education, Inc. Increasing energy 10–5 nm 10–3 nm Gamma rays X-rays 103 nm 1 nm UV 106 nm Infrared 103 m 1m Microwaves Radio waves Visible light 380 400 600 500 Wavelength (nm) 700 650 nm 750 Light Reflected light Chloroplast Absorbed light Thylakoid Transmitted light Visible radiation drives the light reactions • Chloroplasts contain several different pigments and all absorb light of different wavelengths – Chlorophyll a absorbs blue violet and red light and reflects green – Chlorophyll b absorbs blue and orange and reflects yellow-green – The carotenoids absorb mainly blue-green light and reflect yellow and orange – SO: Most leaves look GREEN Copyright © 2009 Pearson Education, Inc. LIGHT ENERGY Photosystem II Electron transport chain Provides energy for synthesis of ATP NADP+ + H+ LIGHT ENERGY Photosystem I Stroma 1 Primary acceptor Primary acceptor 2 e– Thylakoid membrane e– 4 P700 P680 Thylakoid space 3 H2O 1 2 5 O2 + 2 H+ 6 NADPH THE CALVIN CYCLE: CONVERTING CO2 TO GLUCOSE Copyright © 2009 Pearson Education, Inc. ATP powers sugar (GLUCOSE) synthesis in the Calvin cycle • The Calvin cycle makes sugar (glucose) within a chloroplast – To produce sugar, the necessary ingredients are atmospheric CO2, and ATP & Hydrogen ions which were generated in the light reactions Copyright © 2009 Pearson Education, Inc. Step 1 Carbon fixation Input: 3 CO2 Rubisco 1 Step 2 Reduction P 3 P P 6 RuBP 3-PGA 6 3 ADP ATP 6 ADP + P Step 3 Release of one molecule of G3P 3 ATP CALVIN 4 2 CYCLE 6 NADPH 6 NADP+ Step 4 Regeneration of RuBP P 5 P 6 G3P G3P 3 Output: 1 P G3P Glucose and other compounds PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE Copyright © 2009 Pearson Education, Inc. Photosynthesis moderates global warming • The greenhouse effect results from solar energy warming our planet – Gases in the atmosphere (often called greenhouse gases), including CO2, reflect heat back to Earth, keeping the planet warm and supporting life – However, as we increase the level of greenhouse gases, Earth’s temperature rises above normal, initiating problems Copyright © 2009 Pearson Education, Inc. Photosynthesis moderates global warming • Increasing concentrations of greenhouse gases lead to global warming, a slow but steady rise in Earth’s surface temperature – The extraordinary rise in CO2 is mostly due to the combustion of carbon-based fossil fuels – The consequences of continued rise will be melting of polar ice, changing weather patterns, and spread of tropical disease Copyright © 2009 Pearson Education, Inc. Some heat energy escapes into space Sunlight Atmosphere Radiant heat trapped by CO2 and other gases Photosynthesis moderates global warming • Perhaps photosynthesis can mitigate the increase in atmospheric CO2 (Photosynthesis uses up Carbon Dioxide) – However, there is increasing widespread deforestation, which aggravates the global warming problem Copyright © 2009 Pearson Education, Inc.