Single-celled wonders in ponds, soil and bread

Some living things are made of just one cell. That one cell has to do everything: find food, move, get rid of waste and make more of itself. Living things too small to see without a microscope are called microorganisms, or microbes. Most are single-celled, like bacteria, yeast and the protists that live in ponds.

Pond life

Put a drop of pond water under a microscope and you might see a crowded city.

When fertiliser or animal waste washes into a pond, green algae can multiply so fast the water turns bright green. This is called an algal bloom, and some blooms are poisonous to dogs and people.

Soil life

Scientists say one teaspoon of healthy soil holds more living things than there are people on Earth. Billions of bacteria and metres of fine fungal threads break down dead leaves and turn them into nutrients plants can use. Many fungi join onto plant roots. The fungus reaches water and nutrients the roots cannot, and the plant pays it back with sugar it made in its leaves. Soil without this life can hold nutrients but struggles to hand them over to plants.

Yeast in the kitchen

Yeast is a single-celled fungus. Give it warm water and sugar and it breaks the sugar down for energy, giving off carbon dioxide gas. In bread dough the gas gets trapped in bubbles and the dough rises. Rēwena, a Māori bread, rises using a bubbling potato starter, a living culture that bakers feed and keep going.