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A bacterium does not grow a family — it splits in two, and both halves split again. Follow that doubling step by step in an interactive playground and see why warm food spoils so suddenly.

Bread mould has no mouth and never moves, yet it feeds on the loaf and reaches the next one. Label each part by the job it does in an interactive playground.

Disease-causing microbes are a tiny minority. Sort four essential ones by the job each does — rotting, fixing nitrogen, fermenting food and living in your gut — in an interactive playground.

Every method of preserving food either destroys microbes or makes conditions too poor for them to multiply, and the two are not the same. Sort four methods in an interactive playground.

Not every disease is caught. Some are caused by a pathogen that arrived from somewhere else, and some by a missing nutrient or an inherited gene. Sort four of them in an interactive playground.

A pathogen has to leave one host, travel, arrive at another, get past its defences and multiply. Follow the whole chain in an interactive playground and see why every control measure targets one link.

A cut lets bacteria past the skin, and the body does several things at once — sealing the gap, widening vessels and bringing white cells in. Trace the whole web of consequences in an interactive playground.

White blood cells are not one thing. Phagocytes swallow pathogens whole; lymphocytes never touch them and make antibodies instead. Follow both routes from one starting point in an interactive playground.

The first infection takes days to clear and the second never happens at all. Follow the reasoning step by step in an interactive playground, and see what a vaccine actually does.

A leaf is not a green sheet but a stack of layers, each solving one problem. Cut one across and label the cuticle, palisade, air spaces, vein and stoma by the job each does, in an interactive playground.

A stoma is not a fixed hole — two guard cells open and close it by taking in water and bending. Trace the chain from light to an open pore, and the cost that comes with it, in an interactive playground.

Adding more light speeds photosynthesis up — until it suddenly does not. Reason your way from that one observation to the limiting factor rule in an interactive playground.

Photosynthesis makes sugar, which a leaf stores as starch — and iodine turns blue-black on starch. Follow the classic test in order in an interactive playground, and see why each step is there.

Photosynthesis produces glucose, which contains only carbon, hydrogen and oxygen. Proteins and chlorophyll need elements it cannot supply. Sort what a plant builds in an interactive playground.

Breathing moves air into a body. Respiration releases energy inside every living cell, including a plant's. Sort four statements into the right one in an interactive playground.

Glucose holds energy but a cell cannot spend it directly — it is the wrong form and there is too much of it at once. Reason step by step to why respiration never stops, in an interactive playground.

A mitochondrion has two membranes, and the inner one folds deep inside. Label the outer membrane, the matrix, a crista and its own loop of DNA in an interactive playground, and see why the folding matters.

With oxygen, glucose is broken down completely for a large yield of ATP. Without it, the breakdown stops early and leaves lactic acid or ethanol behind. Follow both routes in an interactive playground.

Plants respire every hour of their lives, including in full sunshine. Close the loop between photosynthesis and respiration in an interactive playground and see why a plant is not the reverse of an animal.

One parent gives copies, quickly. Two parents give offspring that all differ, slowly. Follow both routes from the same starting point in an interactive playground and see what each one buys.