Foundations of respiration and metabolism
Bioenergetics • Respiration
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Key concepts
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Cellular respiration: basic definition and equation
Respiration is a series of controlled chemical reactions that release energy from glucose. The overall word equation is: glucose + oxygen → carbon dioxide + water + energy, and the balanced symbol equation is C6H12O6 + 6O2 → 6CO2 + 6H2O. The process occurs continuously in mitochondria so that cells maintain their life processes .
Exothermic nature of respiration
Respiration releases energy to the surroundings and is therefore exothermic; energy released appears as thermal energy and as a chemical store available for other reactions and processes. Because cells require constant energy, respiration runs continuously; if a cell stops respiring, cell function fails and the cell dies .
Metabolism: overall definition and control
Metabolism is the sum of all chemical reactions that occur in a cell or the whole organism, including digestion, respiration and synthesis of macromolecules. Enzymes catalyse metabolic reactions and hormones (such as those from the thyroid) influence the overall metabolic rate .
Energy needs of organisms
Energy from respiration provides chemical energy for biosynthetic reactions that build larger molecules, mechanical energy for movement, and thermal energy to keep warm. Active cells have many mitochondria to meet higher energy demands. Photosynthesis in producers stores energy in glucose, which consumers and the producers themselves later release by respiration .
Roles of sugars, amino acids, fatty acids and glycerol
Sugars act as immediate energy sources and as building blocks for carbohydrates. Amino acids provide the monomers for protein synthesis and are formed using glucose and nitrate ions. Fatty acids and glycerol combine to form lipids, which serve as membrane components and long-term energy stores. These small molecules interconvert in metabolic pathways under enzymatic control .
Key metabolic synthesis reactions
Glucose converts to insoluble starch for storage, to cellulose for cell walls, and to glycogen for storage in animals; glycerol plus three fatty acids form lipids; glucose plus nitrate ions form amino acids which are linked to form proteins. These synthesis reactions require energy supplied by respiration .
Key metabolic breakdown reactions
Breakdown reactions release smaller molecules and often require little external energy. Respiration breaks down glucose to release energy. Excess proteins are broken down into amino acids and then converted in the liver to form urea, which is excreted in urine. Fermentation in some microorganisms breaks down glucose anaerobically to ethanol and carbon dioxide .
Key notes
Important points to keep in mind