OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is the word equation for anaerobic respiration in animals?

1. Glucose + Ethanol --> Carbon Dioxide

2. Glucose --> Oxygen + Lactic Acid

3. Glucose --> Lactic Acid

4. Glucose + Oxygen --> Carbon Dioxide + Water

The correct answer is: Glucose --> Lactic Acid

In anaerobic respiration in animals, the process primarily takes place in muscle cells during intense exercise when oxygen levels are insufficient for aerobic respiration. The correct word equation captures the breakdown of glucose in the absence of oxygen, resulting in the production of lactic acid. This process can be summarized as glucose being converted into lactic acid, which is a vital point because it explains how energy can be generated quickly under anaerobic conditions, albeit less efficiently than aerobic respiration. This is crucial for sustaining muscle activity during short bursts of intense effort when the oxygen supply is limited. The accumulation of lactic acid is also linked to muscle fatigue during excessive physical exertion. Other provided equations reflect different biological processes. Options involving ethanol and carbon dioxide pertain to anaerobic respiration in yeast (fermentation), while one option describes aerobic respiration, which requires oxygen. Understanding the specific context of anaerobic respiration in animals helps clarify why the equation representing glucose converting to lactic acid is the correct one.