Question

What is the difference between aerobic and anaerobic respiration? How does anaerobic respiration relate to fermentation? And what is the role of bacteria in bread making?

Answer 1

Ans.

Aerobic processes in cellular respiration can only occur if oxygen is present. When a cell needs to release energy, the cytoplasm (a substance between a cell's nucleus and its membrane) and mitochondria (organelles in cytoplasm that help with metabolic processes) initiate chemical exchanges that launch the breakdown of glucose. This sugar is carried through the blood and stored in the body as a fast source of energy. The breakdown of glucose into adenosine triphosphate (ATP) releases carbon dioxide (CO2), a byproduct that needs to be removed from the body. In plants, the energy-releasing process of photosynthesis uses CO2 and releases oxygen as its byproduct.

In fermentation, no electron transport chain is used, and oxidative phosphorylation does not take place. Instead, the sole energy extraction pathway is glycolysis, with one or two extra reactions tacked on at the end.

These extra reactions, which we’ll examine in more detail below, regenerate NAD⁺⁺ from the NADH produced during glycolysis. To accomplish this, electrons are transferred from NADH to pyruvate, the end product of glycolysis, or to one of its derivatives. This step is necessary because each cell has a limited pool of NAD⁺⁺ ​​ which cycles back and forth between its oxidized and reduced forms. Without a regeneration mechanism, all of the NAD⁺⁺ would get stuck in its NADH form, and glycolysis would stop because NAD⁺⁺ would be unavailable to participate in reactions.Anaerobic processes do not use oxygen, so the pyruvate product — ATP is one kind of pyruvate — remains in place to be broken down or catalyzed by other reactions, such as what occurs in muscle tissue or in fermentation. Lactic acid, which builds up in muscles' cells as aerobic processes fail to keep up with energy demands, is a byproduct of an anaerobic process. Such anaerobic breakdowns provide additional energy, but lactic acid build-up reduces a cell's capacity to further process waste; on a large scale in, say, a human body, this leads to fatigue and muscle soreness. Cells recover by breathing in more oxygen and through the circulation of blood, processes that help carry away lactic acid.

Bacteria alsoplays a major role in bread making which is either by positively or by negatively.. In sourdough bread, bacterial cultures are categorized under the rather poorly defined "wild yeast" category. This is in reference to ambient yeast and bacterial microorganisms already present in the flour, water, air, on your hands and anything else that comes into contact with the dough. Bacterial growth, like yeast, is affected by moisture, ph, temperature, food supply, salt, sugar, oxygen supply and light. Most bacteria grow well in moist environments with temperatures ranging between 25-40C. However, some like it colder (just over freezing) and some like it hot (60-80C). Bacteria thrive at a pH around neutrality (6.5- 8.0). Most chemicals will kill bacteria. Since bacteria will not grow in mediums with large amounts of salt, salt plays a contributing factor to the leavening of sourdough bread. It is important to note that not all bacteria is beneficial to bread. Some cause infections that have negative effects on the finished product. High hydration doughs are more susceptible to bacterial infections like "Ropy Bread" and the particularly interesting "Bleeding Bread" .