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Every living thing is built from cells, and a cell is not a simple bag. Inside it, separate parts handle instructions, energy, building, demolition and what crosses the boundary. Match six parts to their jobs in an interactive playground.

Plant and animal cells share almost everything. Only three structures are found in a plant cell and never in an animal one, and the shared parts settle nothing. Sort six structures in an interactive playground.

A cell membrane is a double layer of fat molecules with proteins set into it. Small uncharged molecules cross it freely, charged or larger ones need a protein doorway, and big ones never get through. Sort six molecules in an interactive playground.

The nucleus holds DNA, but chromosome, chromatin and gene all describe that same material at different levels. Follow the zoom from a cell down to a single gene in an interactive playground.

A bacterium has no nucleus and no membrane-bound organelles, yet it does everything a cell must do. Follow the two ways of organising a cell in an interactive playground.

Diffusion is the net movement of particles from where they are crowded to where they are not, caused by nothing but random motion. Follow the five stages in an interactive playground, including the one most people get wrong.

Osmosis is the diffusion of water across a membrane that the dissolved substance cannot cross. Water moves towards the more concentrated side. Label the classic demonstration in an interactive playground.

Put a cell in pure water and water moves in; put it in a strong solution and water moves out. What happens next depends entirely on whether there is a cell wall. Sort four outcomes in an interactive playground.

Diffusion and osmosis move substances down a gradient for nothing. Moving something the other way needs a carrier protein and energy from respiration. Compare the two routes in an interactive playground.

A single cell does every job itself. In a large organism the jobs are split between groups of specialised cells — tissues — which build organs and then systems. Sort six examples by level in an interactive playground.

A plant grows only at its tips and from a ring inside its stem. Everywhere else is permanent tissue that has specialised and stopped dividing. Find the growth regions in an interactive playground.

A plant has two transport tissues. Xylem carries water upward through dead hollow cells; phloem carries dissolved sugar in either direction through living ones. Follow both in an interactive playground.

Epithelial tissue covers every surface of an animal, inside and out. Connective tissue fills the space between and holds the rest together — including bone and blood. Sort six examples in an interactive playground.

Muscle tissue is cells that shorten; nervous tissue is cells drawn out into fibres that carry signals. Neither can do the other job, and most responses need both. Compare them in an interactive playground.

Classification is not filing. A grouping based on shared ancestry lets you predict things about an organism you have never examined, while one based on appearance tells you nothing. Sort six criteria in an interactive playground.

Classification is a set of nested groups running from kingdom down to species, each rung smaller and more closely related than the last. Follow all seven for a human in an interactive playground.

Every species has a two-word scientific name: the genus first, then the species. It is the same in every country and it carries the organism's group with it. Compare the two naming systems in an interactive playground.

All life was long divided into five kingdoms, separated by whether cells have a nucleus, whether the organism is one cell or many, and how it obtains food. Place five organisms in an interactive playground.

A virus is genetic material in a protein coat with no cell, no ribosomes and no chemistry of its own. It fits none of the five kingdoms, and whether it is alive depends on where you draw the line. Compare it with a cell in an interactive playground.

A microorganism is anything too small to see without a microscope, which turns out to span four kingdoms plus viruses. Sort four familiar microbes into the groups they really belong to in an interactive playground.