2.3_Cell_biology_III - Hello, lets continue with the topic...

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Hello, let’s continue with the topic of cell biology by examining energy transfer in organisms. 1
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The presentation will cover two coupled processes called cellular respiration and photosynthesis. We will mostly focus on cellular respiration. 2
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3 The ecological basics of energy on earth is summarized here in this illustration. Nearly all energy is sourced from the sun which is captured by photosynthetic organisms and converted to chemical energy associated with carbohydrates such as glucose. Oxygen is produced as a byproduct. All cells need energy and utilize the energy associated with molecules such as glucose through a process called cellular respiration. This energy is used to impart energy to a commonly used molecule called adenosine triphosphate or ATP. This molecule is like a rechargeable battery: when charged up and ready to use for energy needs by the cell, it has a third phosphate group attached to it and is called adenosine triphosphate. When the energy is drawn down on an ATP molecule, it loses its third phosphate becoming adenosine diphosphate or ADP. The charging center is primarily the mitochondria in eukaryotic cells. The byproducts of utilizing energy from glucose to charge up ATP molecules is carbon dioxide and water. These are just some of the molecules needed by plants and algae to form more carbohydrates. Notice that matter such as carbon is recycled continuously; whereas, energy flows from sun energy through chemical energy and finally as heat energy that ultimately is dissipated as heat.
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We often use the term respiration to mean breathing. They are related; however, they are not the same in scientific use. Respiration refers to the cellular process of harvesting energy from molecules such as glucose and this requires the organism to exchange oxygen and carbon dioxide with the atmosphere. This is accomplished by breathing or some form of breathing such as aquatic organisms using gills to exchange these gases with the water. 4
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5 This is the chemical model of respiration and involves the rearrangement of hydrogen atoms (with their electrons) in a series of redox reactions. Recall that reduction- oxidation reactions are those that involve the exchange of electrons. Redox reactions are always coupled with a molecule gaining electrons or being reduced and a molecule losing electrons or being oxidized. In this case the loss or gain of electrons is associated with hydrogen atoms. These atoms contain one proton and one electron each. The reverse of this model characterizes photosynthesis with the sun being the source of the energy. We will deal with photosynthesis later in the presentation.
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6 This schematic provides an overview of cellular respiration. The basics to remember
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This note was uploaded on 01/29/2012 for the course BIOL 212 taught by Professor Rockhill during the Spring '08 term at Seattle Central Community College.

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2.3_Cell_biology_III - Hello, lets continue with the topic...

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