🔍 Key Concepts

• Microbial growth in fuels – what bacteria and fungi actually need to live and multiply (water, oxygen, nutrients) • Differences between heavy fuel oils and lighter distillate fuels like marine diesel oil in terms of composition and complexity • Where in a ship’s fuel system microbial contamination typically develops (e.g., at water–fuel interfaces, in storage tanks)

💭 Think About

• Think about what makes an environment suitable for bacteria and fungi: what specific things must be present in a simple, accessible form? • Compare the structure and complexity of heavy fuel molecules with lighter fuels: which would be easier for microorganisms to break down for food? • Ask yourself whether refinery quality, added chemicals, or effects on humans are the main reason, or whether it’s more about the availability of nutrients in the fuel itself.

✅ Before You Answer

• Check which option correctly focuses on nutrient availability and complexity rather than refinery quality or additives. • Verify that none of the choices incorrectly state that fuel isn’t affected, when in reality microbial growth can and does affect fuels. • Confirm that the option you choose explains why organisms cannot easily use heavy fuel as food, instead of just stating that heavy fuel is “better processed” or “treated with chemicals” without mechanism.