Cells: the building blocks of life

In 1665 an English scientist called Robert Hooke looked at a thin slice of cork through a microscope he had built. He saw rows of tiny empty boxes and called them cells, after the small rooms monks lived in. We now know that every living thing, from a kauri tree to a kererū to you, is made of cells. They are the smallest units that are alive.

Parts with jobs

Inside a cell are smaller structures called organelles. Each has a job, a bit like rooms in a house.

What plants have extra

Plant cells also have a stiff cell wall outside the membrane, which gives them shape and lets a plant stand up without bones. Many plant cells also have chloroplasts, green organelles that capture sunlight to make sugar. That is why a leaf cell is green and an onion skin cell, grown underground, is not. Animal cells have no wall and no chloroplasts, so they come in many more shapes.

Cells with special jobs

In a big living thing, cells specialise. A nerve cell is long and thin to carry messages. A red blood cell is a squashed disc that carries oxygen. A root hair cell has a long finger to soak up water, and guard cells open and close tiny holes in a leaf. Cells of the same kind work together as a tissue, tissues make organs like a leaf or a heart, and organs work together as systems. Your body has around 30 trillion cells, all working as a team.