Microorganisms: friends and foes

There is a living world that we cannot see. A spoonful of garden soil holds more living things than there are people on earth. These tiny beings, visible only under a microscope, are called microorganisms or microbes. They live everywhere: in air, water, soil, inside our bodies, in hot springs and under ice.

The main groups

• Bacteria: single-celled organisms of many shapes: rods, spheres, spirals.
• Fungi: yeast, moulds and mushrooms. They cannot make their own food.
• Protozoa: single-celled, animal-like organisms such as Amoeba and Paramecium.
• Algae: simple plant-like organisms that make their own food, such as Spirogyra.
• Viruses: even smaller than bacteria. They are different from the rest: they can multiply only inside the living cells of another organism.

Microbes as friends

• Curd: a bacterium called Lactobacillus turns milk into curd.
• Bread, idli and dosa: yeast feeds on sugar and gives out carbon dioxide. The bubbles of gas make dough and batter rise. This process is called fermentation.
• Medicines: antibiotics such as penicillin are obtained from fungi and bacteria. They kill or stop the growth of disease-causing bacteria. Antibiotics should be taken only on a doctor's advice and the full course completed. They do not work against viruses such as the common cold.
• Vaccines: a vaccine contains weakened or dead microbes. It teaches the body to recognise the germ and fight it later. Vaccination has wiped out smallpox and protects children against polio, measles and many other diseases.
• Soil fertility: bacteria such as Rhizobium, which live in the roots of pulses and beans, change nitrogen from the air into a form that plants can use.
• Cleaning the environment: microbes decompose dead plants, animals and waste into simple substances and return them to the soil. This is how compost is made.

Microbes as foes

Microbes that cause disease are called pathogens. Diseases that spread from a sick person to a healthy one through air, water, food or contact are called communicable diseases.

Microbes also spoil food. Bread left in a damp place grows mould, and spoiled food can cause food poisoning.

Keeping food safe

Food is preserved by stopping microbes from growing: drying, salting (pickles), adding sugar (jams), oil and vinegar, boiling, and keeping food in the refrigerator. Milk is pasteurised: heated to about 70°C for a short time and then cooled quickly, a method developed by Louis Pasteur.

Staying safe

• Wash hands with soap before eating and after using the toilet.
• Drink boiled or filtered water and eat freshly cooked, covered food.
• Cover your mouth and nose while coughing or sneezing.
• Do not let water collect around the house; mosquitoes breed in it.
• Get all vaccinations on time.