The five kingdoms: Monera, Protista and Fungi

Fig. 12.5 in your book is a concept map of the five kingdoms. Below, the same logic runs as a key you can walk: four questions, each one either naming a kingdom or sending you further down. In Explore, tap any kingdom to light its route and read its features. In Identify, take eight mystery organisms down the key yourself. Watch out for the yeast.

Compare the questions in the key with the criteria the system uses. There are four: cell type, prokaryote or eukaryote; cell structure, cell wall present or absent; level of organisation, unicellular or multicellular; and mode of nutrition, autotrophic or heterotrophic.

If your lab has permanent slides of bacteria and cyanobacteria, look at both under the microscope. No lab handy? Flip between the two views below and compare.

Both are single cells with no true nucleus, so both belong to Monera. You will find bacteria in soil, water and air, in scalding hot springs where little else survives, and inside your own body. In the gut of cud-chewing animals such as cows they help make biogas from dung.

Some bacteria are pathogens and cause disease. Many more are helpful: Lactobacillus sets milk into curd, and Rhizobium lives in the roots of pea family plants. Cyanobacteria make their own food, and bacteria as a group recycle nutrients, and some even break down pollutants such as oil, pesticides and sewage.

Protists are single cells with a true nucleus. Some have no cell wall; others have one made of cellulose. They are microscopic and astonishingly varied, and you can grow your own to look at, using a hay infusion.

Protists live in water or damp places. Some make their own food, others eat. In ponds and seas they are a key link in food chains: some release oxygen, others are eaten by tiny animals, and some act as decomposers that keep nutrients cycling.

Fungi are mostly multicellular eukaryotes whose cell walls are made of chitin. They cannot make their own food. Watch one go to work on a fallen leaf.

Their threads, together called a mycelium, soak up food from whatever they grow on. For most fungi that is something dead: a leaf, a twig, a carcass. Such fungi are saprophytes, and as decomposers they turn complex dead matter into simple minerals the soil can hold. Take them away and the forest floor would pile up with undecayed remains while the soil grew poorer. Not every fungus lives this way: some team up with other organisms for mutual benefit (symbiosis), and some are parasites that make plants and animals ill. Leave bread in a warm, damp kitchen and you will see how fast they grow; they breed both with and without a partner, usually by releasing spores.

Three fungi worth knowing: yeast, a single cell, filed under Fungi because its wall is chitin; the mushroom, a fungus big enough to pick, which spreads by spores; and moulds such as Aspergillus and Penicillium, put to work making enzymes and antibiotics.