CBSE Class 10 Answered

• The energy required for all cellular activities is obtained by the oxidation of glucose.
• The first step towards obtaining energy is six-carbon glucose is broken down into two molecules of three-carbon pyruvate. This process takes place in the cytoplasm.

Respiration in the presence of oxygen in mitochondria:

• The breakdown of glucose in the presence of oxygen is called aerobic respiration. This process takes place in the mitochondria.
• The process of aerobic respiration releases carbon dioxide, water, and energy.
• The energy released in aerobic respiration is 38 ATP.

Respiration in the absence of oxygen in muscle cells:

• The breakdown of glucose in the absence of oxygen is called anaerobic respiration. 
• During heavy physical exercise such as cycling, running or lifting heavy weights, the body is often deprived of oxygen.  
• The demand for energy is high, while the supply of oxygen to the body is limited.
• Therefore, muscle cells perform anaerobic respiration to fulfill the increasing energy demands of the body. In this case, glucose gets converted to lactic acid.

Respiration in the absence of oxygen in yeast:

• Organisms which do not require the presence of oxygen for the process of respiration are called anaerobes. 
• Unicellular organisms such as yeast and some bacteria are examples of anaerobes.
• The process of anaerobic respiration in yeast results in the formation of ethanol along with the release of carbon dioxide and energy. Water is not released in this process. 2 ATP energy is released during anaerobic respiration.