World of living things

Living things grow, make more of their own kind and all respond to some sort of stimulus. They need and use energy. Nearly all living things respire using oxygen to gain this energy from complex nutrients.

The living things of the world are collectively called organisms. In an ecosystem, you will find five different groups or 'kingdoms' of living things:

• Animals
• Plants
• Fungi
• Bacteria
• Protista.

Bacteria are very small, single-celled living things. Their cell walls differ from those of other living things — they are made from a different material and the nuclei and organelles are not enclosed in membranes. Bacteria are very successfully adapted to an immense range of habitats. While most need oxygen for respiration, others use sulphate and nitrates instead of oxygen.

Protista are small, single-celled creatures. They are mostly aquatic and need oxygen to respire.

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