Tiny living things that help and harm us
Microorganisms, or microbes, are living things too small to see without a microscope. They include bacteria, fungi, protozoa and algae. Viruses are also microscopic but can reproduce only inside the cells of other living things. Microbes live almost everywhere: in soil, water, air and inside our bodies.
Many microbes are useful. Lactobacillus bacteria turn milk into curd, and yeast, a fungus, makes bread dough rise and is used to produce alcohol through fermentation. Some bacteria and fungi make antibiotics, like penicillin, which Alexander Fleming discovered from a mould. Rhizobium bacteria in the roots of pea and bean plants fix nitrogen from the air into the soil, and decomposers turn dead matter into manure. Other microbes cause diseases: bacteria cause cholera and typhoid, viruses cause flu and measles, and protozoa cause malaria. Food is protected from spoiling microbes by salting, adding sugar or oil, refrigerating and pasteurising milk.
Why it matters
Microbes help make foods such as curd, idli and bread, keep soils fertile and clean up waste. Knowing how harmful microbes spread helps prevent disease through vaccines, clean water and good hygiene. Using antibiotics only when prescribed slows the spread of antibiotic resistance. This topic links to health, disease and biotechnology.
Key terms
- Microorganism
- A living thing too small to be seen without a microscope.
- Fermentation
- The process by which yeast or bacteria convert sugar into alcohol or acids.
- Antibiotic
- A medicine made from microbes that kills or stops the growth of disease-causing bacteria.
- Nitrogen fixation
- Converting nitrogen gas from the air into compounds plants can use.