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

Which of the following is a useful product of microbe respiration?

1. Chlorophyll

2. Biogas

3. Oxygen

4. Glucose

The correct answer is: Biogas

Microbial respiration involves the breakdown of organic matter by microorganisms, leading to the production of several byproducts. Among these, biogas is a significant and practical product, particularly known for its components such as methane. Microorganisms, particularly anaerobic bacteria, decompose organic materials in environments devoid of oxygen to produce biogas, which can be harnessed as a renewable energy source. This makes biogas a major output of microbial respiration, showcasing its utility in energy generation and waste management. Chlorophyll, oxygen, and glucose all play critical roles in various biological processes but are not direct products of microbial respiration. For instance, chlorophyll is the pigment necessary for photosynthesis in plants, oxygen is a byproduct of photosynthesis rather than respiration, and glucose is a primary energy source that can be used by microbes but is not a product of their respiration. Thus, biogas stands out as the useful product emerging directly from the respiration of microbes, particularly in anaerobic conditions.