Zoo 2

Aerobic respiration energy production using oxygen: the breakdown of foodstuffs to create energy in the presence of oxygen. Cellular respiration is critical for the survival of most organisms because the energy in glucose cannot be used by cells until it is stored in ATP. Cells use ATP to power virtually all of their activities—to grow, divide, replace worn out cell parts, and execute many other tasks. Cellular respiration occurs within a cell constantly, day and night, and if it ceases, the cell—and ultimately the organism—dies. Two critical ingredients required for cellular respiration are glucose and oxygen. The glucose used in cellular respiration enters cells in a variety of ways. Regardless of how they obtain it, cells must have a steady supply of glucose so that ATP production is continuous. Oxygen is present in the air, and also is found dissolved in water. It either diffuses into cells—as in bacteria, fungi, plants, and many aquatic animals, such as sponges and fish—or it is inhaled—as in more complex animals, including humans. Cellular respiration transfers about 40 percent of the energy of glucose to ATP. The rest of the energy from glucose is released as heat, which warm-blooded organisms use to maintain body temperature, and cold-blooded organisms release to the atmosphere.

Anaerobic respiration production of energy without oxygen: the production of energy without the presence of oxygen. Fermentation is a type of anaerobic pathway used by certain species of bacteria that live in anaerobic environments, such as stagnant ponds or decaying vegetation. Some cells produce ATP using both anaerobic and aerobic pathways. For example, muscle cells typically carry out cellular respiration, but if they do not receive enough oxygen, as can occur during strenuous exercise, muscles switch to fermentation. Yeast cells also carry out both pathways, depending on whether they are in an aerobic environment, such as soil, or an anaerobic one, such as inside a wet lump of dough. Cellular metabolism With the help of an enzyme, six molecules of carbon dioxide bond to six molecules of RuBP to create six new molecules. Several intermediate steps, which require ATP, NADPH, and additional enzymes, rearrange the position of the carbon, hydrogen, and oxygen atoms in these six molecules, and when the reactions are complete, one new molecule of glucose has been constructed and five molecules of RuBP have been reconstructed. This process occurs repeatedly in each chloroplast as long as carbon dioxide, ATP, and NADPH are available. The thousands of glucose molecules produced in this reaction are processed by the plant to produce energy in the process known as aerobic respiration, used as structural materials, or stored. The regenerated RuBP is used to start the Calvin cycle all over again. Metabolism (chemistry), inclusive term for the chemical reactions by which the cells of an organism transform energy, maintain their identity, and reproduce. All life forms—from single-celled algae to mammals—are dependent on many hundreds of simultaneous and precisely regulated metabolic

reactions to support them from conception through growth and maturity to the final stages of death. Each of these reactions is triggered, controlled, and terminated by specific cell enzymes or catalysts, and each reaction is coordinated with the numerous other reactions throughout the organism.