The method by which glycogen is broken down into glucose, also known as 'sugar', and is converted into energy is called _______.

• A. Glycogen
• B. Sweating
• C. Glycolysis
• D. Lactic acid

Answer: (C)

Glycolysis is the process that turns glucose into usable cellular energy. When energy is needed, glycogen stored in muscle or liver is first broken down into glucose through glycogenolysis, and that glucose then enters glycolysis in the cytoplasm. In glycolysis, glucose is split into two three-carbon molecules, yielding a net two ATP and two NADH molecules. This pathway can proceed with or without oxygen: with oxygen, pyruvate from glycolysis can enter the mitochondria for further energy production; without oxygen, it can be converted to lactate. The important point is that glycolysis is the energy-producing step that uses glucose, while glycogenolysis merely supplies the glucose. The other options don’t describe the energy-producing pathway from glucose: glycogen is the storage form, sweating is a cooling process, and lactic acid is a byproduct, not the energy pathway itself.