microorganism

Everyday

A living thing so tiny that you can only see it with a microscope, such as a bacterium, a virus (usually counted with them), some fungi like yeast, or algae. tree →

In the lessons

In science, microorganisms (microbes) can be helpful — making bread rise, yogurt, cheese and compost, and living in your gut — or harmful, causing illness and making food go off. Hygiene lessons explain washing hands to remove harmful microorganisms. Phrases: «harmful microorganisms», «useful microorganisms», «under a microscope», «germs».

Examples

• Yeast is a microorganism that makes bread dough rise. tree →
• Some microorganisms cause food to go mouldy. tree →
• Washing your hands with soap removes many harmful microorganisms. tree →
• We looked at pond water and saw microorganisms swimming under the microscope. tree →
• Bacteria in yogurt are helpful microorganisms. tree →
• Microorganisms in the compost heap break down leaves and peel. tree →
• Fridges slow down the growth of microorganisms. tree →

Note

Countable: a microorganism, microorganisms. Also spelled «micro-organism» (common in the UK). Everyday words: «microbe», «germ» (germ usually means a harmful one). Myth: not all microorganisms are bad — most are harmless or helpful. Viruses are often grouped with microorganisms although scientists argue whether they are truly alive.