Microalgae, and why the cell is the basic unit

Microalgae are tiny plant-like living things found in water, soil, air and even on trees. They make their own food using sunlight, and give off oxygen while they do it. Together they make more than half of the Earth's oxygen.

They are full of nutrients and are food for many water animals. People use some of them, such as Spirulina, Chlorella and diatoms, as health supplements and medicines. Microalgae also help clean water and are used to make biofuel.

Spirulina is called a superfood: it is more than 60 per cent protein by weight, a good source of vitamin B12, and has only a little fat and sugar.

Pollution, climate change and the loss of their habitats now threaten microalgae. Protecting them matters, for the environment and for the oxygen balance of the Earth.

Back to cells. The body of every living thing is made of cells:

Algae and fungi can be either: yeast is a unicellular fungus, while mould is a multicellular one.

All these cells have a cell membrane. Fungal cells also have a cell wall, but no chloroplasts, so they cannot make their own food by photosynthesis.

Bacteria are different from all the rest. They have no proper nucleus and no nuclear membrane. Their genetic material sits loose in a region called the nucleoid. That one feature sets them apart from the cells of yeast, protozoa, algae, fungi, plants and animals.

To see the very small parts inside a cell, we need far more magnification: an electron microscope magnifies about 10,00,000 times.