Question

What are the different ways in which glucose is oxidised to provide energy in various organisms? Give one example of each.

What are the different ways in which glucose is oxidised to provide energy in various organisms?

Answer 1

Glucose is oxidised to provide energy through three distinct pathways depending on the availability of oxygen. In all organisms, the process begins in the cytoplasm, where glucose (a 6-carbon molecule) is first broken down into a 3-carbon molecule called pyruvate.

From pyruvate, the three different pathways and their examples are:

1. Anaerobic Respiration: This process takes place in the absence of oxygen, e.g., in yeast during fermentation. In this case, pyruvate is converted into ethanol and carbon dioxide. For example, yeast cells use this pathway to live and grow, which is heavily utilised in baking and brewing.
2. Aerobic Respiration: In aerobic respiration, the breakdown of pyruvate occurs in the presence of oxygen, producing 3 molecules of carbon dioxide and water. The energy released in aerobic respiration is much greater than that released in anaerobic respiration. For example, humans (and most animals and plants) during normal, everyday activities.
3. Lack of Oxygen: Sometimes, when there is a lack of oxygen, especially during vigorous activity, in our muscles, pyruvate is converted into lactic acid (3-carbon molecule compounds). Formation of lactic acid in muscles causes cramps. For example, human muscle cells switch to this pathway during vigorous physical exercise, such as sprinting, which can lead to temporary muscle cramps.