Tiny Builders: Cells and Tissues

Pinch the skin on your arm gently. What do you think it is made of? It looks like one solid thing, but it is actually built from millions of tiny pieces called cells. Every living thing — you, a flower, a mushroom — is built from cells. They are so small you cannot see them without a microscope.

A cell is the smallest unit of life. It is like a tiny room with different parts, each doing a special job. The cell membrane is a thin, flexible layer that wraps around the whole cell. It acts like a skin, controlling what goes in and what comes out. Inside the cell is a jelly-like liquid called cytoplasm. It fills the cell and holds all the other parts in place. Floating in the cytoplasm is the nucleus. The nucleus is the control centre of the cell. It carries instructions that tell the cell what to do and how to grow. Plant cells have two extra parts that animal cells do not have. A stiff cell wall surrounds the outside of the membrane — it gives the plant cell a strong, box-like shape. Plant cells also contain chloroplasts, which are green structures that capture sunlight to make food for the plant. Now, one cell on its own cannot do very much. But when many cells of the same type group together and work as a team, they form a tissue. For example, the muscle tissue in your arm is made from millions of muscle cells all packed together. Each muscle cell is weak alone, but together they are strong enough to lift a bag or throw a ball. In the same way, the leaves of a plant contain leaf tissue made from many plant cells working together to capture sunlight.