Answer:
A) The production of energy without the presence of oxygen - Anaerobic respiration
B) The chemical breakdown of a substance - Fermentation
C) The breakdown of food to create energy in the presence of oxygen - Aerobic respiration
D) An organic molecule that occurs as an intermediate in many metabolic processes - Pyruvate
Explanation:
A) Anaerobic respiration is a type of cellular energy production that occurs in the absence of oxygen. it is much less efficient than aerobic respiration (see question C). In cellular respiration, cells produce ATP, which is the "currency" of energy in the cell, by breaking down glucose. ATP is required to carry out the normal functions of a cell.
As it is much less efficient than aerobic respiration, it produces much less ATP. However, when there is no oxygen, it is the only choice. An example is when muscle cells are working very hard and use up all the oxygen in the tissue. To keep producing some energy, they undergo anaerobic respiration, which only produces 2 molecules of ATP for every molecule of glucose.
B) In respiration, Fermentation is a pathway of breaking down glucose into chemical energy that occurs in the absence of oxygen. Anaerobic respiration can lead to two types of fermentation, lactic acid fermentation (described above) and ethanol fermentation which is another type of anaerobic respiration in which fungi (such as yeast) break down glucose into ethanol, producing 2 molecules of ATP carbon dioxide as a by-product. This is how we make bread and beer!
C) Aerobic respiration is cellular respiration in the presence of oxygen. It creates a net gain of 36 molecules of ATP, compared to the 2 ATPs created without oxygen. This is because in aerobic respiration, the oxygen acts as a final electron acceptor for the electron transport chain. In its absence the electron transport chain cannot proceed. The electron transport chain is how cells generate most of their chemical energy.
D) Pyruvate is an important molecule in the process of respiration. Both aerobic and anaerobic respiration begin with the same process, glycolysis. Glycolysis is the process by which 1 molecule of glucose is broken down into two molecules of pyruvate - a metabolic intermediate. This releases 2 molecules of ATP. In the presence of oxygen, pyruvate is oxidised and enters the Krebs cycle, which makes a series of compounds that donate electrons to the electron transport chain, which produces extra ATPs through oxidative phosphorylation.
In the absence of oxygen, pyruvate is converted either to lactic acid or ethanol by fermentation
