03 Respiration General - Copy - PLS 172 Lecture 3 1 of 10...

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PLS 172 Lecture 3 1 of 10 RESPIRATION Mikal E. Saltveit, Department of Plant Sciences, UC Davis TABLE OF CONTENTS Topic page Introduction 1 Respiration – Basic Mechanism 1 Respiration 2 Overall reactions of respiration 3 Measurement of respiration 4 Measurement of gas exchange 5 Instruments and techniques 9 Measurement of heat production 9 References 9 INTRODUCTION Metabolism is comprised of two opposite sets of reac- tions: anabolism and catabolism. Anabolic reactions synthesize molecules such as sugars, carbohydrates, amino acids, proteins, nucleic acids, DNA, RNA, lip- ids, membranes, pigments, etc. Catabolic reactions breakdown these complex compounds to regenerate and transform, and release energy. The two process work in concert during plant growth and development Photosynthesis (anabolic) and respiration (cata- bolic) are the two processes by which carbon and en- ergy are cycled through the biosphere. Photosynthesis utilizes energy from light to reduce carbon dioxide from the air and water from the soil to carbohydrates. In this process water is split into its components of hy- drogen and oxygen. The hydrogen combines with car- bon dioxide to form carbohydrates, while the oxygen, which is a by-product of the reaction, diffuses away. Carbohydrates are formed by photosynthesis in the green, chlorophyll containing tissues of plants (usu- ally leaves) and are translocated to other cells in the plant where they are either stored or oxidized. In the process of oxidation, carbohydrates are combined with oxygen from the air to produce energy, carbon dioxide and water. As glucose is broken down, many of the resulting fragments are used in the synthesis of larger molecules that constitute the living cell. Some of the energy released during respiration is captured in the high-energy bonds of ATP, which is used in many cel- lular reactions. The remainder of the energy that is not captured is lost and appears as heat. Carbon dioxide produced by respiration is dissolved in the liquid por- tion of the cell and slowly diffuses into the gas phase within and surrounding the tissue. Energy (light) CO 2 H 2 O O 2 Sugars Energy (ATP + heat) Carbon fragments Interrelationship between photosynthesis and respira- tion in aerobic organisms. RESPIRATION - BASIC MECHANISMS In the common usage, the term respiration is applied to "...the physical and chemical processes by which an organism supplies its cells tissues with the oxygen needed for metabolism and relieves them of the carbon dioxide produced in energy-producing reactions" (Webster). To biochemists, and particularly those of us concerned with plant physiology, the term has a more specific meaning. To us it means "...any of various energy-yielding oxidative reactions in living matter" (Webster, again). It is readily apparent that respiration is a vital process to humans and other animals (just try holding your breath for a few minutes!), and we will see that it is equally important to plants.
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