GCSE Biology - Respiration #21

Cellular respiration is an exothermic reaction essential for releasing energy stored in glucose molecules, which are primarily produced by plants during photosynthesis. This process continuously occurs in living cells and involves breaking down glucose to transfer its trapped energy. Importantly, this does not create new energy but redistributes the existing one from glucose.

Organisms use energy for building larger molecules, muscular contraction, and maintaining body temperature. Energy is essential for numerous cellular reactions catalyzed by enzymes; collectively, these processes are termed metabolism. Metabolism encompasses all chemical activities necessary to sustain life. Aerobic respiration occurs when oxygen is available and efficiently transfers energy from glucose in plants and animals within mitochondria. Its equation—glucose plus oxygen forming carbon dioxide plus water—is the reverse of photosynthesis.

Anaerobic respiration occurs without oxygen, typically during intense activities like sprinting when the body cannot supply enough oxygen for aerobic respiration. The process converts glucose into lactic acid but is less efficient due to incomplete glucose breakdown, as no oxygen is available to fully oxidize it. This inefficiency means not all energy from glucose is utilized. Additionally, lactic acid accumulation poses a problem since it must be removed later.

In anaerobic respiration within yeast, glucose is converted into ethanol and carbon dioxide instead of lactic acid. This process, known as fermentation, has significant industrial uses. In bread-making, the carbon dioxide produced by yeast creates air pockets that make bread light and fluffy. Additionally, fermentation's production of ethanol enables its use in creating alcoholic beverages like beer and wine.