3.7: Cell Respiration
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Define cell respiration.
Cell respiration is the controlled release of energy for use in the cell from organic compounds. The energy is in the form of ATP.
Outline the importance of respiration.
Cell respiration is vitally important and is one of the indicators of life. All living things use respiration as a means to release stored energy.
Identify some sources of stored energy used by organisms in cellular respiration.
Most plants and animals use glucose as the source of stored energy for respiration. Other organic compounds used include amino acids and fatty acids. Bacteria and archaea can use inorganic compounds for respiration, e.g. methane, sulfur compounds.
What is glycolysis?
Glycolysis is a series of anaerobic reactions that convert one molecule of glucose into two molecules of pyruvate. Glycolysis occurs in the cytoplasm and is the first part of cellular respiration.
What are ATP and ADP?
ATp is adenosine triphosphate and ADP is adenosine diphosphate. ATP contains stored energy in high energy bonds. ATP releases energy when the terminal phosphate group is cut from the molecule to form ADP.
Outline what happens after glycolysis.
After glycolysis the pyruvate is converted to acetyl Coa (acetyl coenzyme A). The acetyl CoA is inovlved in the formation of citrate which is a part of the citric acid cycle. The citric acid cycle or Krebs cycle is a series of reactions with different enzymes at each step and in eukaryotic cells occurs in the mitochondria. The reactions yield energy in the form of ATP and other compounds and form carbon dioxide.
Outline the main steps of respiration in animals.
In the first step of respiration, called glycolysis, glucose is split into pyruvate and a net formation of 2 ATP. If aerobic respiration occurs in the mitochondrion, carbon dioxide and an additional 36 ATP are formed. If anaerobic respiration occurs in the cytoplasm, lactic acid and 2 ATP are formed.
Distinguish between alcohol fermentation and lactic acid fermentation.
If condition are anaerobic, fermentation occurs. Fermentation is glycolysis followed by other reactions. In alcohol fermentation, the pyruvate is converted to ethanol (ethyl alcohol) in two steps, while in lacic acid fermentation the pyruvate is reduced directly to form lactate (ionised form of lactic acid). The two steps in alcohol fermemntation involve: 1. Release of carbon dioxide from the pyruvate to form acetaldehyde and then 2. The reduction of acetaldehyde to ethanol. Thus alcohol fermentation has no release of carbon dioxide (e.g. cheese and yogurt making). there is no further yield of ATP.
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