شرح التنفس من دون الأكسجين | مادة الأحياء | الصف الثاني عشر (فصل دراسي ثاني)

This video explains Lesson 4 of Unit 6 in the Grade 12 Biology curriculum, which covers "Anaerobic Respiration" (respiration without oxygen) in the absence of oxygen or when its levels are severely reduced. The video explains that the absence of oxygen leads to the cessation of the electron transport chain and the Krebs cycle due to the lack of a final electron acceptor. This forces the cell to resort to glycolysis in the cytoplasm to produce a small amount of energy (2 ATP). To ensure the continuation of this process, cells undergo fermentation to re-oxidize the reducing agent (NADH) to the oxidizing agent (NAD+). Content Timeline: [00:17] - The Concept of Respiration in the Absence of Oxygen: Explaining that respiration is a process of energy production (ATP), not merely gas exchange. [00:28] - The Effect of Oxygen Absence on Mitochondria: Explaining the cessation of the electron transport chain, oxidative phosphorylation, and the Krebs cycle. [03:14] - Anaerobic Respiration and Glycolysis: Focusing on glycolysis in the cytoplasm as an alternative pathway for energy production. [05:06] - Ethanol Fermentation: An explanation of the process that occurs in yeast and some plants, involving decarboxylation and the production of ethanol and carbon dioxide. [08:34] - Lactate Fermentation: An explanation of the process that occurs in mammalian muscles and some microorganisms, where pyruvate is converted to lactate. [12:05] - Comparison between Lactate and Ethanol Fermentation: A comparison table showing the locations of occurrence, products, and end result. [14:15] - Practical Application: Rice Cultivation: An explanation of how rice plants adapt to waterlogging (airnchyma, rapid growth, and the breakdown of toxic ethanol by the enzyme ethanol dehydrogenase). [20:11] - Practical Skills 6-2: Measuring the respiratory rate using redox reagents (such as methylene blue and DCPIP) that change from blue to colorless upon reaction.