Cells: the basic units of life — Science, 11–13 years
Living things may look very different, but they are all built from cells. This topic shows how scientists use microscopes to see these tiny living units and how plant and animal cells share a basic plan.
Idea
A cell is a tiny living unit that carries out the jobs needed for life. Animal and plant cells both have a cell membrane, cytoplasm and genetic material; plant cells also have a cell wall, a large vacuole and chloroplasts. A microscope lets us see structures too small for our eyes.
Why cells matter
Before microscopes, people could not explain how a leaf, a muscle or a drop of pond water was organised. The cell idea solved this problem: life is not one smooth substance, but many tiny working units. It also explains growth, because an organism can grow when cells get larger or, more often, when cells divide.
Worked example
A cell image is 4 millimetres wide, but the real cell is 0.02 millimetres wide. Step 1: divide image size by real size: 4 ÷ 0.02 = 200. Step 2: write the result as 200× magnification. The picture is therefore two hundred times wider than the actual cell.
A common trap
It is tempting to call every part seen through a microscope a cell. That is reasonable because a whole cell can look like one small box in a diagram. But a cell may contain several structures, such as a nucleus or chloroplast, and a microscope image can show many cells touching each other.
Outside school
Doctors examine cells in blood tests and tissue samples to look for infection or disease. Farmers and gardeners use knowledge of plant cells when choosing light, water and fertiliser. Cell science also helps create medicines, but researchers must test them carefully because a treatment can affect healthy cells as well as harmful ones.
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