Anaerobic respiration in organisms - class-XI

• The yeast changes the sugar in the dough into carbon dioxide gas and ethanol (alcohol).
•  The gas, trapped in the dough, makes it rise; the alcohol produced during fermentation evaporates during baking. Hence, When you add yeast to the dough, it rises because the rapidly reproducing yeast cells release carbon dioxide due to anaerobic respiration.

Yeast are the organism that executes the process of fermentation in which they break down the sugar into its simpler forms for obtaining energy. In this process carbon dioxide and alcohol are also forms and CO$ _2$ helps the dough to rise. The process is favorable in humid and warm conditions in colder environment it slows down.

Fermentation is a form of anaerobic respiration in which alcohol is formed by the breakdown of glucose in the absence of oxygen. It usually done by the yeast. In alcoholic fermentation, pyruvic acid is converted into ethanol with the liberation of carbon dioxide. The alcoholic fermentation equation is as follows: 
C$ _6$H$ _{12}$O$ _6$ + 2 ADP + P --> 2 C$ _2$H$ _5$OH + 2 CO$ _2$ + 2 ATP

Anaerobic respiration refers to the type of respiration that takes place without oxygen. In plants, the glucose is anaerobically converted to ethyl alcohol, ATP and carbon dioxide.

Intracellular acidosis occurs due to lactic acid accumulation, it has been regarded as the most important cause of skeletal muscle fatigue. Lactic acid is formed and accumulated in the muscle under conditions of high energy demand, rapid fluctuations of the energy requirement and insufficient supply of oxygen. Subsequently, the pyruvate synthesised during glycolysis is converted to lactic acid in anaerobic condition. Thus, the correct answer is option D.

Fermentation is an anaerobic process which takes place in the absence of oxygen that converts sugar to acids or alcohol. It occurs in yeast, bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. 

Facultative anaerobes are organisms which can switch over to the anaerobic mode of respiration when needed they can also grow in absence of oxygen. 

• Anaerobic respiration is done by the organisms which live in a condition with very little oxygen or no oxygen at all such as some of the bacteria and prokaryotic organisms. 
• Also the cells in the body of a multicellular organism when they are used for extreme physical active where the body may not be able to provide oxygen to each and every cells. For example muscles of arms and legs while excriseing. 
• In anaerobic condition the glucose molecule will undergo glycolysis where it is broken down to 2 molecules of pyruvate wilt the net gain of 2 ATP after which dur to unavailability of oxygen the pyruvate will under go lactic acid fermentation or alcoholic fermentation where the pyruvate molecule is converted to lactic acid or ethanol & carbon dioxide respectively with the regeneration of NAD for the continuation of glycolysis. 
• Prokaryotic organisms perform this type of respiration as they do not have membrane bound organelles like mitochondria which is required for the competion of the aerobic cellular respiration. 
• Also some of the aerobic respiring cells can survive in no oxygen condition for sometime by respiring this way. But they are usually under a stressful condition where they cells will not grow or divide as they whole energy will be focused on conserving energy and surviving. 
• And prokaryotic organisms which mostly have cellular level of organisation or a single celled they are provided with immediate burst of ATP by breaking down glucose by glycolysis. 
• Therefore the correct answer for this option B and C

• In anaerobic respiration, glucose breaks down without oxygen.
•  The chemical reaction transfers energy from glucose to the cell.
•  Anaerobic respiration produces lactic acid, rather than carbon dioxide and water. Hence, The respiration carried in the absence of oxygen is called anaerobic respiration.

Anaerobic respiration is a type of respiration that does not use oxygen. It is used when there is not enough oxygen for aerobic respiration. 
Anaerobic respiration in some microorganisms (such as yeast) produces ethanol and carbon dioxide, as opposed to lactic acid.

• Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom.
•  Yeast is a microorganism that can undergo aerobic as well as anaerobic respiration. 
• Yeast requires oxygen for growth. In addition to oxygen, they require a basic substrate such as sugar. 

During strenuous exercise, the demand for oxygen in muscles exceeds the supply, leading to anaerobic respiration where glucose is converted into lactic acid.

Glycolysis is the initial stage of glucose breakdown, occurring in the cytoplasm. It yields a small amount of energy compared to the complete oxidation of glucose in the Krebs cycle and electron transport chain, accounting for approximately 5% of the total energy.

One glucose molecule produces 2 PGAL (G3P) during glycolysis. Therefore, 3 glucose molecules produce 6 PGAL. The complete respiration of 6 PGAL (via Krebs cycle and ETC) yields 120 ATP (since 1 glucose yields 38 or 36 ATP, and 3 glucose yields roughly 114-120 ATP).

Obligate means restricted to the particular environment so the anaerobes that grow and multiply in the absence of molecular oxygen and are not able to survive in the presence of oxygen.